PART II (continued)

TRADITIONAL OYSTER CULTURE IN FRANCE

By Mr. Maurice HERAL

1- INTRODUCTION

The indigenous oyster of mainland France, the flat oyster, Ostrea edulis has been part of the human diet for centuries. The Romans collected them and exported them to Rome. Although tanks for holding oysters after harvesting were in use at that time (Grelon 1978) it seems that true culture was not developed along the coast contrary to the records of Pliny the Older. It appears that oysters were already being captured on boards off the Italian coast. The exploitation of natural stocks continued through the Middle Ages and the Renaissance. However, it was not until the 17th century that oyster culture began, first in the pools of the salt marshes of the Atlantic coast and then in specially managed ponds. Papy (1941) repeats a good description given in 1688 of the oyster beds of the Marennes-Oléron which showed that stocks of flat oysters were by then being managed and improved. A decree by the Council of State in 1762 ordered the destruction of any beds which prevented the circulation of water in the channels in the marshes. There is an article in the Encyclopedia published in 1765 on the techniques of rearing in salt marshes which describes methods of culturing flat oyster from seed collected from rocks or dragged from natural beds. After two years the flat oyster were separated from each other and grown for four or five years' rearing in beds or «claires». Later, although other uses of the salt marshes declined for technical and economic reasons, oyster culture flourished (Lemonnier 1980). However, in the early days, the juvenile oysters all came from natural stocks.

From the 18th century natural beds on the Atlantic coast were overexploited, and from to time decrees had to be issued forbidding the harvesting of flat oysters during the breeding season around the French coast (1750). Sometimes, as in the Arcachon Basin, interdicts totally forbidding the removal of oysters for several years were issued by the Admiralty. In 1755, the Parliament of Brittany issued an interdict forbidding fishing for 6 years in the Treguier beds. During the 19th century, in spite of increasingly strict regulations, stock provided more and more variable returns Fishing effort increased, stimulated by the beginnings of oyster culture with its high demand for seed brought in from the wild and by the increase in trade possible by the improvements in communications (railways, postal systems, etc…). Fishing effort on the Cancale oyster beds increased by 13 rimes from 1857 to 1872. Added to the effect of overfishing were the effect of variable recruitment in some years, as a result of extremely cold winters and the appearance of predators and competitors. Coste, in 1861, thought that the stocks from Cancale to Granville and those at Arcachon had been reduced, and those at La Rochelle, Charente, Oléron, and Marennes had disappeared. If modern oyster culture can be defined as the culture of oyster from captured spat it can be said to have began in 1850. The development s of the techniques of spat capture were made by several different individuals. Since 1852, in the La Rochelle region, the spat of flat oyster has been captured on posts. From 1853–1859, De Bon and de Coste pioneered the use of wooden collectors similar to those in use in Italy. It was not until 1865 that Michel developed the technique of liming tiles in the Arcachon Basin and the «caisse ostreophile» which allowed the rearing of the young stage. From 1870, spat rearing-units were installed alongside oyster beds. From 1852, regulation of exploitation's in the Domain Public Maritime began, allowing coordinated development to take place in estuarine regions.

From 1860, because of the shortage of flat oysters, cup oysters were imported the month of the Tagus in Portugal to the Arcachon Basin. During one delivery, a boat, the Morlaisien, had to take refuge in the estuary of the Gironde. The cargo was ejected, and thus began the settlement of cup, or Portuguese, oysters (Crassostrea angulata) around the coast of France. This hardy species spread rapidly. In 1873 it covered the banks of the estuary of the Gironde (Verdon & Talmont). By 1874 it had reached the old flat oyster beds of the Marennes and Oléron regions and the Charentes estuary; by 1878, La Rochelle and the Ilc de Ré and then the South coast of the Vendee. In 1923, a decree was issued forbidding the culture North of Vilaine because of problems caused when the new species, which had established itself throughout the South West, was grown together with the flat oyster particularly around Arcachon. However, the Portuguese oyster could still be cultured in the Penerc and Etel rivers as well as in the Bay of Cancale. In the Marennes-Oléron area, settlement of cup oysters developed; the first samples in 1883 showed ⅔ of the spat to be Portuguese and ⅓ to be flat oyster. From 1923, capture became common in the mouth of the Charente and the Seudre on collectors made from strings of oysters, faggots, and stakes of hazel and chestnut. In 1910, the Portuguese oyster did not spawn in the Arcachon Basin, but in 1927, LLinard & Lambert stated that C. angulata had replaced Ostrea edulis on the collectors.

These development in oyster culture were halted suddenly by massive mortalities which occurred among the flat oyster between 1920 and 1922 for reason which were never fully understood but were probably caused by a disease brought on through unusual temperature conditions which either killed the adult oysters directly or upset their physiology because their diet was insufficient (Hinar & Lambert - 1928-. At this time the oyster farmers feared that the native oyster would disappear completely.LLowever, settlement of Ostrea edulis began fairly soon, in the summer of 1925 and then 1928. New resistant populations appeared in South Brittany, particularly in the Auray, Crache, Po., and Plouharnel rivers. However, to the South of Vilaine Portuguese oysters have almost completely replace the flat oysters.

First attempts at culture in the Mediterranean were carried out in floating parks off Sète. in 1900, suspended-culture methods began to be used in the étang de Than; the oysters were attached to steel ropes with cement. At the same time, at Seyne and at Marseille, rearing operations began on the sea bed in shallow waters (3–4m) with several million flat oysters being produced in the étang de Thau, In 1932, the only oyster culture present in the étang de Thau was in one concession between Bouzigues and Mèze. From that time, oysters purchased in Brittany were stuck into posts individually with cement. These were suspended from a framework in the mussel parks.Mediterranean, oyster culture has development only recently. The flat oyster was cultivated in suspension in the Mediterranean up to 1950–51, years during which the stock was severely reduced. Stock were then replaced with Portuguese oyster.

On the Atlantic coast, intensive culture developed up to 1960 (85.000 tones of C. angulata, 28.000 tones of O. edulis) (Fig. 1). During the development of production, rearing became concentrated in favored sites, more or class enclosed by bays where they are protected from the worst of the weather. In the largest rearing basins (Marennes-Olcron, Arcachon, etc…) the growth of oysters decreased and mortalities increased. An increasingly large percentage appeared to «stagnate»; oyster farmers described them as being «sulky». From 1966 to 1969, in different French oyster-producing regions. Portuguese oysters suffered from gill disease. Massive mortalities between 1970 and 1973 caused the disappearance of the Portuguese oyster from the French coast.

The import of the Pacific oyster, C. gigas, began a new pbase of oyster production from 1972 onwards. However, in 1975, a drop in yield from the stock occurred again, at the same time as numbers were being increased. This happened particularly in the Marcnnes-Oléron region, Arcachon, and the Bay of Bourgneuf. During this same period, the flat oyster, Ostrea edulis, was attacked successively by two parasites diseases: Marteila refringens from 1974 and Bonamia ostreae from 1979. The parasites occurred in almost all the centers of flat oyster culture (Fig.1)

In 1984, the production of oysters in France (100.000 tones) was made up of 98% Pacific oyster, cultivated over an area of 20.000 ha.

This brief history demonstrates, how, over a century, several features have recurred in the French oyster industry. There have been successive phases of over exploitation of natural stock of the flat oyster diseases, the importation of a foreign species (Crassostrea angulata), high density culture, and diseases again (of flat and cup oysters) leading to the needs for new imports (C. gigas) This points to the need to manage the culture beds towards an ecological and physiological equilibrium for the species so that the oyster stocks are better able to withstand attacks from pathogens.

2- ASPECTS OF THE BIOLOGY

2.1. Classification and geographical distribution

Using the criteria given by Grasse (1960), oysters belong to the mollusc, Class bivalves or lamellibranch. Order Filibranchs and the Family Ostreidae, with two genera cultivated in France (Fig. 2):

Genus Crassostrea Sacco 1897
Represented by two species of cup oysters; Crassostrea angulata (I) the Portuguese oyster and Crassostrea gigas Thunberg, the Pacific oyster: In the adult oyster the shell is elongated and ridged, the left shell is done domed allowing the visceral mass to develop, while the right shell is flat and, for the Pacific oyster, market by a series of «curls». These oviparous oysters, which have a high fecundity, live in the intertidal zone. They have a high tolerance of low salinities and can thus spread into estuaries.

Traditional oyster culture in France

Figure 1 - Changes in oyster in oyster production in France from 1865 to 1983
(statistics from Marchande; after Heral 1986)

Figure 2 - Anatomy of the two species of oyster cultivated in France
(a) Crassostrea gigas (cup or cupped oyster);
(b) Ostrea edulis (flat oyster).

C. gigas is native of the Pacific ocean, being found in the Sea of Okhotsk (Vladivostok), Sakhalin (USSR). in Japan where there are two local races in the Iwate and Hiroshima prefectures. in Korea, and along the Pacific coast of North America from Alaska through British Columbia and then through the Unites States to California. It was brought to France in 1966 when there was a largescale import of seed from japan (Sendai and Hiroshima). In 1972 there were imports from British Columbia to build up the naturally reproducing stocks.

Some experts believe that C. gigas and C. angulata are the same species. Ranson (19851, 1967) found identical larval characteristics. Menzel (1974) obtained viable hybrids by crossing the two types of oyster. Buroker et al. (1979) studied the genetic variation of proteins and enzymes and found a similarity of 99% between the two forms for 24 Ioci studied. They put forward the hypothesis that Japanese oysters my have been transported to Portugal on boats which were making frequent voyages in the 16th and 17th centuries. However, the oysters do show some different characteristies: respiration rate filtration rate, growth, type of reproduction, and different susceptibility to diseases, suggesting two races with distinctly different physiology's

Genus Ostrea Linnacus 1758
Represented by Ostrea edulis. The adult oyster has a roughly circular shell. This species is viviparous and has a lower fecundity. It is more of an oceanic mollusc than the cupped oyster, preferring water of relatively high salinity and low turbidity. Natural and cultured beds are found below the low tide mark or in areas always covered by water, It is a native of Northern Europe, from Norway to France, through Denmark, Germany, the Netherlands, Belgium, Great Britain and Ireland. To the South it is found on the Atlantic coast through Sapin to as far as the South of Morocco. In the Mediterranean it is found in France, Italy, Sicily, and also Morocco and Tunisia its Distribution extends to the Adriatic and Black Seas.

2.2. Physiology

Lucas (1976) reviewed the literature published since the start of the 20th century on reproduction, the detection of larvae, ecology of the cultured-bed ecosystems, and population dynamics of the molluscs, showing that these had been well understood, as had the control of disease and the health of the oysters. This had allowed the development of modern aquaculture and the planning of its day-to-day operations.

Specialist works covering the life cycle of the oyster include the Traité de Zoology (Grassé 1960) and the Lanuel de la conchyliculture (Vols 1,2,3 - 1974, 1976, 1979). In this section, the most recent biological information necessary to understand the rearing procedures is detailed.

2.2.1. Nutrition

The oyster has two ways of absorbing food : either directly absorbing dissolved substances present in the sea water or through the ingestion of particles in suspension (Fig.3)

Direct absorption of dissolved organic matter (DOM)
Experiments carried out by Ehrnard & Heinemann (1975), Fevrier (1976), and Frankboner & De Burgh (1978) indicated that lipids in solution is sea water can be absorbed rapidly by the molluscs. Sorokin & Wyshkwarzev (1973), Amouroux (1982) and Jorgensen (1982–1983) established the kinetics of the absorption of amino acids and glucose in the gills and the mantle where digestive activity is extremely intense. Recent work, using high-resolution chromatography with whole animals, has demonstrated the active absorption of amino acids. These results can be added to those on nutrition on artificial diets based on sugars and oils carried out by Castel & Trider (1974).
Empirical observations made by oyster farmers have shown that the inflow of fresh water from the rivers leads to increase growth in oysters, which cannot be related entirely to the fact that salinities are low. The direct absorption of organic matter may involve the intake of substances which act as growth factors. Collier et al. (1953) demonstrated the extremely beneficial effects of carbohydrate present in the marine environment to the filtration rate and internal activity of molluscs. Recently, Heral et al. (1984) put forward evidence to show that the concentration of dissolved organic carbon and nitrogen compounds in the Marennes-Oléron region was highly correlated with the production of flesh in oysters of between 1 and 2 years of age. This absorption was equivalent to 5 % of the particulate energy actually absorbed (Heral et al. 1987).

Figure 3 - Ecosystem of an oyster bed in the Marennes-Oléron Basin (after Heral 1977)

Ingestion of suspended particles
Mineral and organic particles are filtered and retained on the surface of the gills and surrounded by mucus. They are then directed towards the labial palps by rows of cilia on the gills, It is likely that these cilia and the labial palps carry out effective qualitative grading of the food, thus effectively enriching the diet at the beginning of the digestive process. The food is then ingested and partly digested in the stomach which contains the crystalline style and digestive enzymes (amylase, glycogenase, cellulase). Digestive diverticulae also have an intracellular digestive function (Wilson & La Touche 1978) in Ostrea edulis. The remainder passes through the intestine and is evacuated through the anus as faeces. When particulate matter is too abundant or too large it is ejected by the gills and labial palps or bound together by mucus, dropped into the mantle, and ejected in the form of pseudofaeces.

The rate of particle retention of the filtration rate is defined as the quantity of water thoroughly ‘purifies’ by the molluscs and is expressed per hour per gram dry weight of mollusc flesh (gdw). Most authorities calculate this by using and indirect method in closed containers where the consumption of phytoplanktonic algae can be monitored for a fixed period. It varies principally with temperature, quantity and quality of food, current, and the size of the mollusc (Widdows 1978).
It appears that, at the same temperature, the Pacific oyster filters at five tima the rate of the flat oyster (Table 1). C. gigas seems to possess a mechanism whereby filtration is regulated in relation to the number of phytoplanktonic cells. With natural food (organic/mineral mixture), filtration efficiency is optimal between 6 and 10 mm particle size, When the density of particles is greater, filtration efficiency is higher with the small sized particles (Fig.4). Elsewhere it was found that at 5°C, retention reached 10 l/h/gdw while at the same temperature the flat oyster is almost inactive (Table 1). The difference in activity between the flat oyster and the Pacific oyster results in a different pattern of food consumption which has consequence for both the growth and the fattening of the two species.

Table 1 - Rate of retention of particles for the cupped oyster and for the flat oyster

Figure 4 - Annual cycle in the efficiency of retention of the oyster (Crassostrea gigas) in relation to the size of the particle characteristic of the estuarine environment (after Deslous-Paoli et al. 1987)-.

2.2.2. Reproduction

Adult oyster reproduce sexually. Spanners produce male or female gametes. The species Ostrea edulis changes sex. producing male or female gametes successively but not at the same time. Marteil (1976) showed that the flat oyster is male in the autumn following settlement. The spermatogonia break down and the ovaries develop in the following season when the oyster will be a female. C. gigas differs from this; the oyster can function as a male or as a female during one season before changing sex during the following year. Some hermaphrodite individuals persist. The environment (temperature and nutrition) and also internal hormonal factors apparently control the determination of the change of sex.

Effect of temperature on gametogenesis
For C. gigas, correlation's between the date of spawning and the cumulative monthly temperatures measured from 1972 to 1985 in the Marennes-Oléron Basin provide evidence of significant inverse correlation between the temperature in the autumn preceding spawning and the date of spawning (Heral et al. 1986). Lubet (1980) showed the importance of autumn temperatures on the early stages of gametogenesis. However, there appears to be no connection with winter temperatures and, finally, the effect on the speed of gametogenesis. The degree-day sum from September to June gave a provisional equation for the date of spawning (Y) but when temperature (T) falls below 15°C the gametogenesis of C. gigas is significantly retarded, speeding up again when temperatures increase (Mann 1979).

y= 282–2.87 (T.September to February) + 1.078 (T. March to June)
.R=0.9227

The comparative study of reproduction in two years (1979 and 1981) gives evidence of the supplementary indirect effect of temperature, through the food chain, on gametogenesis. There appears to have been a significant deficit in assimilable particulate organic matter, both phytoplanktonic and detritic, for all of the beginning of 1981 compared with 1979. The food deficit, linked with lower temperatures, caused a significant depletion in glycogen and lipids in males and females (Fig.5), resulting in a low, or even absent recruitment in 1981, while in 1979, a single massive spawning in August resulted in strong recruitment (Deslous-Paoli 1981).
Marteil (1976) found that the minimum temperature for the start of gametogenesis for Ostrea edulis was 10°C, and that for spawning between 14 and 16°C. Unlike Crassostrea gigas. Ostrea edulis, when kept in a hatchery, has a period of sexual dormancy (Lubet 1980) which is likely to occur in December. Other workers have demonstrated the importance of the nutrition of the spawners. Helm et al. (1973) showed experimentally that giving supplementary nutrition during gametogenesis leads to more rapid larval growth.

Number of broodstock required
There are two possibilities : either the stock is very large, sometimes too large, and the relationship between stock and recruitment will be through the food web, or the stock is very low and reproduction becomes chancy. In this latter case it is necessary to determine the minimum stock level necessary to maintain recruitment. In Marennes-Oléron, at the time of disappearance of Crassostrea angulata and its replacement by C. gigas in 1972. While the stock of C. angulata dropped to 15.000 tones and while there were no more than 8.000 tones of C. gigas no further recruitment took place. However, the same numbers of larvae as in the preceding and succeeding years were found in the water, but these larvae did not develop and settle. It appears that, in spite of the critical state of the stock at this time (viral disease and gill disease, Comps (1970), Comps et al. (1976)) it was not the level of the stocks but other factors acting on the larvae which prevented recruitment. However, the problem became more crucial for Ostrea edulis when the stock seriously depleted by different parasites.

Ch. 3]                 Traditional oyster culture in France

Figure 5 - Change in glucide and lipid composition for standard 50 g male and female oysters during 1979 (•) and 1981 (▲) (after Deslous-Paole et al. 1982).

Age structure of the population
The cultivation of stocks by man has entailed the regular removed of the oldest animal. These removals free part of the biotic capacity of the environment and allow a more rapid rotation of stock with a consequent increase in production and rejuvenation of the cultivated population. While this «rejuvenation» appears to increase the quality of the gametes and therefore the larvae, it brings a decrease in the mean fecundity of the population.
While a three years old cupped oyster produces around 80 % of its body weight gametes, a two years old oyster produces no more than 60 %, and a one year old only 7 (Deslous-Paoli & Heral unpublished). For C. gigas where the mean individual fecundity is several tens of millions of oocytes. the lowering of the population age may be compensated for by the sheer volume of the stock in culture. However, for Ostrea edulis, Where them mean fecundity is between 500.000 and I million eggs and where stocks have decreased drastically, a significant lowering of average age can have consequences for recruitment.

Spawning and larval life
When the gonads are mature, the spawners expel the gametes. In the flat oyster, fertilization takes place in the pallial cavity with spermatozoa brought in on the water current. The larvae are incubated there for 8–10 days before being liberated into the external environment. They are slate-grey in color.
For the cupped oyster, fertilization takes place in the sea at the mercy of the currents and by chance meeting of the sperm ova. Trochophore larvae develop and rapidly produce a two-valued shell. The D-shaped veliger larva, at 24 h measure 70 mm for C. gigas and 160–200 mm for O. edulis. The shaped of the larva changes as it grows. After around 10 days (150 mm for C. gigas and 200 mm for O. edulis) a sort of hook, the umbo, develops. Several days later, at a size 0f 200 mm, a foot develops which allows the «pediveliger» to move round by using its velum and to seek out a suitable substrate for attachment with the byssus. The byssogenic gland rapidly secretes cement which sticks the oyster to the substrate. Metamorphosis occurs next; the foot and the velum disappear and the resulting larva is termed the spat. For C. gigas, larval survival appears to relate more to temperature than to salinity. Analysis of the temperature-salinity chart over the period of larval development in the Marennes-Oléron Basin, in 1980–1986, shows that at a temperature below 17°C there is a deficiency of recruitment, as happened in 1981 and 1986 (Fig. 6).

The length of the larval stage depends mainly on temperature. For C. gigas it varies between 15 and 28 hours. The survival rate in situ may reach 10 % in the years when larval development takes place satisfactorily (Fig. 7). For Ostrea edulis, the planktonic phase is 8–14 days, depending on temperature (Marteil 1976) and the survival rate may reach 10 % at 22°C. However, not all emissions result in settlement, and it is essential that temperatures should be above 15–16°C.
The action of salinity seen less important. In Japan, C. gigas survives and reproduces over a range of salinities; but there seems to be a correlation between the temperature and salinity for successful reproduction. However, even though C. angulata does not reproduce in the Mediterranean and the same appeared to be true for C. gigas after its introduction, it now appears to reproduce in Yugoslavia and occasionally in the étang de Thau even though the salinity has not varied.

The optimum salinity was determined to be 25‰ by Helm & Millican (1977), and was verified experimentally at Arcachon. Nevertheless, it appears that the tolerance of C. gigas allows good recruitment even at 20‰, as in the Gironde. This species appears to be relatively independant of salinity, as is shown by studies on the influence of salinity in the Charente estuary on the settlement in the Marennes-Oléron Basin for C. gigas.

Although the problem of larval nutrition can be dealt in a hatchery, they are not well understood in the wild (Lucas 0982). Experimentally, growth of C. gigas larvae is better when mixtures of algae are used rather then monospecies cultures (Millican & Helm 1983). Despite this, the size of the particles used by wild oysters remains to be determined, as does their composition, Although it has been show that bacteria are used as food by larval bivalves (Martin & Mengus 1977, Prieur 1980), the part they plan in nutrition has been ignored. It has been shown that larvae can use dissolved organic substances (Stephens & Manahan 1983), but it has not yet been determined whether these are a source of energy or whether they have a role a growth factors. On the one hand, in the Arcachon region it appears that the disappearance for the nanoplankton (His et al. 1983) brought on by human-related factors was largely responsible for the absence of recruitment from 1977 to 1981. Conversely, the work of Miller and Scott (1967) showed that O. edulis larvae can fast for 3–4 days. and then resume normal nutrition when food is again available.

Traditional oyster culture in France

Figure 6 - Temperature and salinity during the period of larval development for the oyster (Crassostrea gigas) in the Marennes-Oléron Basin (after Prou & Heral, unpublished)

To make short-term predictions of the date to install collectors and to inform oyster farmers, the different IFREMER laboratories (La Trinité, La Tremblade, Arcachon, La Rochelle) carry out bi-weekly surveys of the abundance of larval oysters present in sea water. After the spawning of oysters has been detected, the veliger larvae of C. angulata in the past, and C. gigas and O. edulis now, are monitored up tot the attachment stage.

A chronological sequence of the abundance of larvae ready to attach shows up years where there is an absence of settlement, and this can be checked again information in the public archives (Figure 8).

In the Marennes-Oléron, the series of the abundance of larval oysters from 1925 to 1972 for C. angulata and from C. gigas shows an absence of recruitment for C. angulata in 4 years out of the 47 where data are available, and for C. gigas an absence of recruitment in 3 of the 11 years available; In the Marennes-Oléron Basin the capture of C. gigas is more uncertain than that of C .angulata; this appears to be due to the higher temperature requirement for the pacific oyster for the maturation of spawners and the survival of larvae.

By contrast, in the Arcachon region during those man-made disturbances which have a profound influence on the mechanism of the development of the larval oyster.

The culture of molluscs and echinoderms

Figure 7 - Change in the number of small (S) and developing (D) medium-sized (M) and Large (L) larvae for Crassostrea gigas at Arcachon (after His)

Action of man-made influences
There was no recruitment of oysters in the Arcachon Basin between 1977 and 1981. This was caused by perturbations in the progress of development of the pelagic larvae of C. gigas during the first days of their lives. Pigmentation of the veligers was reduced and growth ceased. so that the larvae did not reach the stage where the food begins to develop. The veligers do not show any abnormalities in their developing shells, and there appears to be nor relationship between failure and temperature. Three hypotheses have been put forward to explain this phenomenon; defective gametogenesis in the spawners in the Arcachon Basin, mortality of the larvae caused by the direct action of pollutants in the water in that area, or a change in the food supply to the veligers. Observations and experiments have been carried out on the veligers obtained from controlled environments or veligers collected from the wild and put into a controlled environment, an on the algal food supplied to the veligers in the controlled environment. Results showed that the quality of the spawners and the «biological quality» of the water in the Arcachon Basin were sufficient to allow the development of the veligers (Robert 1983). This suggests that the failures on organometallic compounds has been shown Amongst others the use of anti-fouling paints based on organometallic compounds has been shown to affect not just embryogenesis and larval development in C. gigas (His & Robert 1980 - Robert & His 1981) but also the growth and cell division of Chaetoceros calcitrans and Isochrysis galbana (His & Robert 1981). Measures forbidding the use of organo-tin anti-fouling paints have been effected, and they coincided with a return of spat settlement from the summer of 1982 (His et al. 1983).

Traditional oyster culture in France

Figure 8 - Years of Zero spat capture (I) for Crassostrea angulata and Crassostrea gigas in the Marennes-Oléron Basin

2.3. Energetics

In species cultivated at high density controlled or semi-enclosed environments, it appears that factors such as the limited quantity of available food and the ability of the organism to use this food have a strong influence on production. Thus for sessile molluscs cultivated at a high density in a confined environment it is necessary, at the same times as determining models of overall production, to determine the different forms of nutrient available and also the dietary requirements not only of the cultivated molluscs but also of non-cultivated species in the locality.

This energetic concept holds the key to the analysis as it encompasses a wide range of mechanisms under a single unifying concept, as described by Odum (1971).

Many laboratory studies (Walne 1970 - Thompson & Bayne 1974 - Winddows 1978) have shown that growth in bivalves is directly related to the amount of food supplied to them. Few of the studies have covered both the food present in the environment and the feeding behavior of the molluscs living there. Bernard (1974) for C. gigas, Widdows at el. (1979) for Mytilus edulis and Vahl (1981) for Chlamys islandica have shown, at various levels, that organic matter is the main source of food, and have thus been able to establish the energy budgets and nutrition of these species in relation to particular environmental conditions. Other studies, using small-scale laboratory experiments (Winter 1976 - Winddows et al. 1979 - Griffiths 1980 and Kiorboe et al. 1981) have shown different between cultures in water containing phytoplankton alone and the those with a mixture of algae and minerals. These mixtures resemble conditions found in estuaries, and they demonstrate that the influence of minerals and detritus in suspension on the assimilation of molluscs is, in effect, to dilute the food.

Little information on the abundance of potential food in areas where molluscs are reared intensively is available in the literature. In practice, the complete range of nutrients of different origin is not taken into account, although some excellent studies have concentrated on one small aspect, ignoring the others. It is thus difficult to review the whole system (Heral 1987).

Looking at the relationship between oyster in situ and the environment, Deslous-Paoli et al. (1981)-showed that there was a light relationship between the biochemical constituents of C. gigas and the richness of the organic content of the water, principally the phytoplankton. The same workers (Deslous-Paoli et al. 1982) put forward the theory that, when there is a shortfall in the quantity of nutrients available, the products of the gonads fail to develop and mature satisfactorily.

Energy equations and indices of conversion differ between authors. The definitions used here are those given by Lucas (1982). The general equation for the energy budget of a population of oysters can be written as :

A=P+R=C-(F+U)

Production is composed of :

P=Pg+Pr+Ps

Assimilation efficiency (A/C) and crude production (P/C) are calculated by the method given by Mac Fadyen (1966).

Production, Pg is the quantity of energy accumulated in the tissues during growth; Fig. 9 shows the increase in dry weight of a population of C. gigas over 3 years. Pg cam be determine form microbomb-calorimetry as can the quantity of energy necessary for the production of the shell (Fig.10).

Pr, production of gametes, is estimated indirectly by finding the difference in the energy content of the oyster at the stage of maximum gonad development and after completion of spawning.

Respiration, R, is the active metabolism of the mollusc, i.e. the energy necessary for all the chemical reactions which keep the animal alive. Bernard (1974) studied respiration in relation to water temperature in C. gigas. Results were low compared with those of Boukabous (1983), Copello (1982), Gerdes (1983) and Heral et al. (1987).

Faeces and pseudofaeces (F) is the quantity of biological wastes excreted by the molluscs determined in situ, using traps arranged around the culture beds. The technique used in the intertidal beds is given by Sornin (1981). Estimates of their energy content are made by the same methods as those used to estimate the energy content or organic matter in water.

Figure 9 - Change in dry weight of flesh of Crassostrea gigas caught in 1978. Vertical bars : variance, females, males (after Deslous-Paoli & Heral 1987).

The culture of molluscs and echinoderms

Figure 10 - Monthly variations in the mean energy value of dry flesh (Pg)
of one year old oysters (1), and two years old (2), shell of three years old oysters (3) and four years old (4)
(after Heral et al. 1983 - Deslous-Paoli & Heral 1984)

Urine excretion (U), is generally not measured; they only figures are nitrogen excreted by C. gigas (Mann 1979 - Griffiths 1980). However, excretion of organic forms of nitrogen by C. gigas is far from negligible. Results, although incomplete (Robert et al. 1981), show that in the summer months 77 – 93 % of nitrogenous waste is in the organic form. Heral et al. (1987) measured urea excretion in C. gigas which was found to be low (0.25 mmole/j/g dry weight), while excretion of amino acids can reach 2 mmole/h/g dry weight in summer.

A study of the energy budget, carried out in the Merennes-Oléron Basin, the foremost European oyster culture region, showed that production for young oysters is highest in June and July and negative in the autumn; In older oysters, the two periods of negative production, one in winter and one in summer after reproduction, give gross and net yields which are largely negative. Shafee & Lucs (1982) found two periods of negative production for the scallop Chlamys variae. For C. gigas cultured in the Marennes-Oléron Basin it appears that there is a particularly long period of negative production (around 6 months) which causes a progressive wasting of the oyster as reserves are consumed.

The other characteristic of this estuarine region is the high rate of deposition of organic matter throughout the year, nut particularly in the winter. This is linked to the high levels of seston in the water (Sornin et al. 1983). The energy from this accounts for 73,8 % of the energy consumed by the young oysters. This gives mean annual assimilation rates of 26,2 % for juveniles and only 7,9 % for adults. The yields are much lower than those given in the literature for other species. Bernard (1974) showed that large quantities of organic matter were not assimilated, but rejected either directly by the labial palps as pseudofaeces or remain undigested during their passage through the gut, suggesting that C. gigas is either inefficient of highly selective qualitatively in its digestive capacity or not adapted to life in the extremely turbid water which clogs the gills and has a negative effect on assimilation.

In practice, the high turbidity in winter linked with a low level of organic matter induces a high production of pseudofaeces and, correspondingly, an expenditure of energy in sorting the particles, mucus secretion, and brachial cleansing. This explains the poor performance of adulty oysters in the arennes-Oléron Basin. However, after reproduction which is an important part of the energy balance (84 % of production of adult oysters), the negative yields in September and October may come from a lack of food, particularly phytoplankton; the mollusc may not have sufficient usable energy available. This autumnal deficit varies from year to year; it depends on the quantity of phytoplankton as well as the density of consumers which include other molluscs in culture and wild competitors.

Transfer of energy between the water column and the mollusc population
At the same time the quantity of energy from the particulate food has been studied every month in relation to time and the tidal coefficient. Taking the currents into account, this allows the establishment of the mean monthly quantities of energy available (Heral et al. 1983 - Deslous-Paoli & Heral 1984).

Thus it can be seen that in the same region (Marennes-Oléron) the quality of the food available is controlled by the huge input of detritus. The potential food available for the mollusc was given by Widdows et al.(1974) in terms of the sum of protein, lipids, and glycogen, and represented only 2,6 % of the total seston and 24,385 of the organic matter, on average. However, phytoplankton appear to play major role with the periods of development corresponding to high production of the oyster. The heterotrophic bacteria appear to be only a nutritional complement as they represent a mean of only 0,6 % of the total energy.

Examination of the quantity of food which passes through the 10 cm of water around the banks of oyster shows that the transfer of energy with the surface water appears to be very low, around 1 % (Figs. 11, 12). This does not take into account factors such as the density of molluscs in the surroundings and the cumulative effect of the progressive exhaustion of the water column. No account is taken of the length of time for which the water mass remains above the areas of intensive rearing and thus the new cumulative effect linked with the time taken for wastes to be removed from the system. This time may be relatively long, particularly in semi-enclosed areas.

Elsewhere, for year old oysters, % of the energy is used for production of flesh? % for the shells, while for adults, the energy is distributes as 3,6 %, 78,4 %, and 17,8% for the flesh, gametes and the shell. This shows that 1 year old C. gigas oysters concentrate on flesh production while hose in their second year direct energy towards reproductive products.

Figure 11 - (1) Annual energy flux (1979) between the water column (0,1 m) deep in a current of 0,3 m/s and a population of two-year-old oysters reared an a density of 200 individuals/m2 (calculated per m2) ( from Deslous-Paoli & Heral 1984)

(2) Percentage of the total energy consumed calculated from levels of proteins, lipids, glucides

Construction of energy budgets gives information on the amount of food needed by a population of oyster, and it serves as a base for the development of models of food consumption in oyster culture basins.

Similar studies are under way for the principal species which compete with the oysters for food. These include mussels, Japanese clams, cockles, and slipper limpets. Deslous-Paoli & Heral (1984) Produced such a budget (Fig. 13) for the slipper limpet (Crepidula fornicata). They showed that 4,1 kg of slipper limpets consumed energy equivalent to that consumed by 1 kg of oysters. By studying the action of animals competing for food it should be possible to develop methods of managing and controlling their development (e.g. destruction of 2.100 tones of slipper limpets in the Marennes-Oléron bassin in 1982, 1983 and 1984).

Traditional oyster culture in France

Figure 12 - (1) Annual energy flux (1980) between the water column (0,1 m) deep in a current of 0,3 m/s and a population of two years old oysters reared at a density of 200 individuals/m2 (calculated from Heral et am. 1983)

(2) Percentage of the total energy consumed calculated from proteins, lipids and glucides

3 - STUDIES CARRIED OUT ON CULTURES STOCKS

The amount of oysters produced from culture operations can be determined from statistics available from the marine fisheries service (Fig.1). This generally corresponds to the quantity of oysters sold with a health certificate by each producing area (hasin). However, these figures give no information on the numbers of oysters in culture, which must be available to biologists designing methods of managing the oyster beds. Growth and fattening of oysters depends not only on the quantity of food available but also on the abundance of competitors for food and particularly on the size of the stock in culture which fluctuates from one year to another according to the size of the spat settlement in the preceding year.

The culture of molluscs and echinoderms

Figure 13 - Annual energy balance for an individual of mean energy content 1,8 KJ, representative of the population of Crepidula in the Marennes-Oléron Basin B : biomass; C : energy R : energy expended in metabolism; P : energy fixed for flesh production (g), gametes (r), and the shell (s) (after Delous-Paoli 1984)

The study of stock in culture needs the implementation of a carefully designed sampling system, The most simple technique is to make a plan of the oyster beds which shows the layout of concessions, and then to take a certain number of points (2 % of the area) either by random sampling, simple sampling, or stratified sampling.

Two parameters must be estimated : the rate of exploitation and the biomass. Five geographical strata and two types of culture (flat and raised) were, for example, chosen for the Marennes-Oléron Basin (Bacher 1984). In 1984, the amount of oysters in culture was 30.235 in flat culture with 59 % of the total area exploited, and 38.594 tones in raised culture with 30 % of the parks exploited. The error in this method of sampling is around 25 %. To improve the of estimation, aerial photography on the scale 1:10,000 allows the drawing of an improved plan, excluding unexploited areas. Aerial photographs can be used to count small culture areas and the number of culture units, and used together with actual sampling to obtain figures for biomass. On the West Contentin coast, the stock of oysters in culture in 1983 was 18,000 tones (Deschamps, in press), and in the Bay of Bourgneuf, in 1982, 36.400 tones (St Felix et al. 1982) with an error of 3 %. For the largest areas it is possible, either by counting only randomly chosen stocks or by systematic sampling, using a 3 mm grid, to estimate exploited areas to an accuracy of 3 % (Bacher 1984, Bacher et al. 1986). These estimates of the stocks of oysters in cultivation have been made annually since 1985 in the Marennes-Oléron Basin, in Arcachon, and in the Bay of Bourgneuf. Accuracy of estimation is to within 6 % through stratifying into types of culture and breaking down into age classes, which reduces the variance.

Actual measurements with computer-assisted analysis allows rapid treatment with optimum precision, using the image obtained from a high-resolution video. At the same time, attempts to use satellite remote sensing (simulation of SPOT) have shown that the obtainable resolution (20 mm) allows only the outlines of the cultivated areas to be determined. The absence of any unique spectral character for the oyster culture areas and the interference caused by algae which covers part of the rearing structure complicate the use of this method.

In the Mediterranean, estimation of stock size has been carried out in the étang de Thau (Hamon & Tournier 1981) by boat. The number or ropes per table is counted in each rearing zone, and then 3–4 % of the cultivated area is sampled at random by divers fir different depths (5m, 5–7m, deeper than 7m). The different type of culture and the ages are thus determined, and the biomass on each rope weighed on land. 18.923 tones of cupped oysters and 611 tones of flat oysters were grown in the étang de Thau in 1984. This figure was estimated to have a possible error of 7 % (Hamon pers comm.)

The methodology at present being developed to monotor stocks in culture is allowing the development of models for the management of culture beds which take into account the growth and maturity of the stock to be made.

4- OVERALL MODEL

It is only in the medium term, when the period of acquisition of precise information on stocks and their performance in culture has been sufficient and a knowledge of the extent of variation has been gained, that a dynamic overall model can be constructed. At present, in some culture areas (Marennes-Oléron, By of Bourgneuf) there are obvious signs of changing yields. An approach to the understanding of this problem can be made through the reconstruction of a historical treatment has the advantage of supplying, for the present time, overall laws covering the exploitation of the ecosystem through the culture of molluscs and supplying a basis for control. The Marennes-Oléron Basin was chosen for this method as it has almost half of the production of cupped oyster.

This model is based on the hypothesis that for the given period, environmental factors have a constant mean, although there is a certain variation around this mean. The development of production of cupped oyster in the Marennes-Oléron Basin is estimated from 1885–1984 from three different sources, as shown in Fig. 14. The time series shows that the growth rate has decreased for both Portuguese and Pacific oysters at the same time as the chronic mortality rate has increased (Fig. 15). The stocks in culture have been calculated from annual production, taking into account growth and mortality (Fig. 16). These calculations give results comparable with the estimates of stock size obtained by sampling.

The establishment of a relationship between the stock and production shows that, overall, for a given biomass in culture, production tends to platform out at a maximum level of 40.000 tones. This level corresponds to the maximum production capacity of the ecosystem which is limited by the trophic capacity of the bay (Fig. 17). Maximum production of the ecosystem can be determined by modeling the development of the production curve, using an equation similar to that used in modeling population growth. Thus the von Bertalanffy equation takes the form P=Pmax (1-e-kb) where P is the maximum production in the Arennes-Oléron and B is the stock under culture. For C. angulata. K=0.026 and Pmax =41.873 tones; for C. gigas, K=0.0288 and Pmax =42.450 tones. At the same time the relationship between production and stock (P/B) as a function of the total stock in culture follows a negative exponential. Leading to a decline in yields from culture.

The culture of molluscs and echinoderms

Figure 14 - Annual production of oysters in the Marennes - Oléron Basin (after Heral et al. 1986)

The maximum production of 40.000 tones can be obtained from a stock of 130.000 tones of C. angulata and 80.000 tones of C. gigas. This difference between the two species can be ascribed to differences in the energetic requirements of each oyster. At an equal biomass, the assimilation of food by the Pacific oyster is 1.7 times greater than the Portuguese oyster (Heral et al. 1986). If a comparison of the effect of the two oyster species on the ecosystem is made, this conversion coefficient must be taken into account. This work demonstrates that, without management of the stock, the numbers cultivated by the oyster growers tend to exceed the minimum biomass necessary to reach the potential maximum production, and that control of the quantity of oysters in culture would bring about a decrease in the duration of the rearing cycle, in mortalities during growth, and also the probability of the occurrence of epizootics.

5 ANALYTICAL MODEL

After having shown the energy requirements of one population of oysters as well as the transfer of energy between the population and the water column and the relationship between the number of individuals in culture and production in the ecosystem, the possibility opens up of constructing a model describing the division of food and the energy requirements of the stock of molluscs to predict the growth performance of oysters in culture. The model must contain physical factors (transport and biological factors - energetic models of growth). This approach has been used in the Marennes-Oléron Basin (Bacher 1987). The transport of food (on the currents) was estimated by using a numerical model which gives the patterns of the currents and the depth of water. The growth of molluscs was simulated (Fig. 18), taking into account assimilation, consumption and respiration which are related to weight, temperature, to the total available seston and the particulate energy available in the water column (Bacher 1987).

To calculate the supplies of food a compartmentalized structure is applied to the grid of the physical numerical model. The retention time is around 1 day, the Lagrangian residual currents are calculated from current tables, and dispersal is calculated by using a transport time proportional to the difference in concentrations between adjacent compartments and the tidal path estimated by using Eularian residuals at the boundary (Bacher 1987). The food supply is a forcing variable and is put into the model differently in three areas : the Northern oceanic sector, the Charente estuary in the South, and in the pertuis de Maumusson.

Traditional oyster culture in France

Figure 15 - Change in growth rate needed for an oyster to reach market size.
(A) Portuguese oysters, (B) Pacific oysters and survival rates after the first year of culture,
(C) Portuguese oysters, (D) Pacific oysters (after Heral et al. 1986)

Figure 16 - Calculated change if biomass of oysters cultured in the Marennes-Oléron Basin (after Heral et al. 1986)

The culture of molluscs and echinoderms

Figure 17 - Change in production relative to biomass under culture for Crossostrea angulata (ù), Crassostrea gigas(?), and Crassostrea gigas transformed to the equivalent Crassostrea angulata (*) (after Heral et al. 1986)

Traditional oyster culture in France

Figure 18 - Simulation of the growth of individual oysters in KJ in relation to observed growth (after Bacher 987)

The transport model is calculated by using a chronological series of salinities at the limits of the model. This allows the calculation of salinity at all points. Thus, in spite of a time lag in some of the salinity peaks, the amplitude of fluctuations and seasonal patterns are simulated correctly (Fig. 19).

Figure 19 - Salinities observed and calculated in a control station in the Marennes-Oréron Basis (after Bacher 1987)

The culture of molluscs and echinoderms

Figure 20 - Impact of the fluctuation (-60% -+ 60%) of stock on individual growth for Crassostrea gigas (after Bacher 1987)

For the calculations, the stocks of oysters in each compartment are divided into two classes, and the growth model allows growth to be simulated as a function of the food distributed in each compartment. Stock levels of competitors and their assimilation of food are introduced (Fig. 20) as a forcing variable. This approach allows the stock levels to be varied and then predictions to be made of variations of growth in the different compartment.

This model still uses too many simplifications to be of predictive value. It could be improved by constructing :

• a predictive energetic model where the different coefficients calculated experimentally should be independent of those measured in situ;
• a model of the phytoplankton which allows the simulation of variations in the supplies of nutrients and which gives an indication of the impact of different methods of management of the Charente estuary.

However, this novel analytical approach, which needs a multidisciplinary approach between biologists, physicists and sedimentologists is the only one which will allow prediction of the development of the mollusc culture ecosystems in the long term in relation to changes in densities, species cultured, food supply, run-of from the land and man-made perturbations.

6- DISEASES

In this section, diseases which have occurred as epidemics, seriously reducing French oyster stocks since 1965, are described.

Crassostrea angulata
Marteil (1976) described how from 1966–1969 the Portuguese oysters showed an exceptionally high mortality rate which was apparently cased by severe lesions on the gills and labial palps. This disease is referred to in France as «maladie des branches» or gill disease. The necrosis observed was first attributed to an new species of protozoa, Thanatastrea polymorpha, by Franc & Arvy (1970). However, Comps & Duthoit (1976) found viral particles and lesions in the necrotic gills, the virus appearing to cause a cellular hypertrophy. Viruses have only recently been shown to affect marine invertebrates. The first description of a viral disease affecting the oyster Crassostrea virginica was made only in 1972. The gill disease caused a decrease in respiration (His 1969) adversely affected gametogenesis (Marteil 1969) and caused a mortality of 40 % of the stock of cupped oysters from Marennes-Oléron to Arcachon.

In relation to the disease of 1970–72, Comps et al. (1976) presented evidence of the existence of viral particles in oysters dying in an epidemic which completely destroyed the stocks of the Portuguese oyster under culture (Plate 1). The description of the virus, with mature particle having an iso < > structure of 350 mm, suggested that it could be classified as an Iridovirus. During this epidemic, around 90 % of the stock of cupped oysters were killed.

Crassostrea gigas
This species, introduced into France in 1966, resisted both of the above viral attacks, demonstrating the host-specificity of the pathogens. However, during limited summer mortalities in the Arcachon Basin in 1977, viral lesions identical to those in C. angulata in 1970 found in c. gigas by Comps & Bonami (1977) which cased a reconsideration of the Pacific oyster with respect to the Iridovirus. This work showed the precarious nature of the French cupped-oyster rearing industry and encouraged growers to manage the shellfish basins better to avoid the losses consequent on periods of poor growth and physiological weakness in the oysters, which make them more susceptible to pathogenic diseases. At the same time, all imports of molluscs from other countries must be strictly forbidden to avoid the introduction of new parasites which, in certain environmental conditions, form the basis of epizootics.

Plate 1 - Massive mortality of Portuguese oyster (1970–1973) intracytoplasmic viral lesions observed in blood cells under electronmicroscopy (× 6.500) (Photo M. Comps)

The infection of C. gigas by Myticola orientalis is a recent phenomenon. This crustacean is a small, reddish-orange copepod which lives in the oyster's digestive tract. His (1977) found an infestation rate of between 10 and 40% in the Arcachon region. Up to 40 individuals develop in the intestine of the oyster where they can form a partial blockage. His et al. (1978) found evidence of damaged to the wall of the digestive tract caused by the copepod, while Deslous-Paoli (1981) showed that in the Marennes-Oléron Basin, 64% of the cultured oysters are parasitized but 93,5 % of the infected oysters have fewer than six female parasites. This appears to have little effect on the condition factor in spring and winter. However, a mean infection rate of 3 or more females gives a significant reduction in the total levels of glucides and of glycogen.

Ostrea edulis
The first mortalities began in 1968 on the North coast of Brittany and then spread rapidly to the clears of Marennes-Oléron. Little by little the parasitosis extended into almost all the centers of culture of the flat oyster, reaching the beds of South Brittany in 1975. The parasite has not yet developed in bays which are largely open to oceanic water (Quiberon, Binic, Cancale) (Grizel 1983). Comps (1970) and Herback (1971) isolated the parasite Martelia refringens which is responsible for malfunction of the digestive gland.

The life cycle of the parasite and the anatomy of the different stages in its development have been studied by electron microscopy (Bonami et al. 1971 - Grizel et al. 1974). The characteristics of the parasite (Fig. 21) Marteilia refringens have led to its classification in a new protozoan genus. Its pathogenic action is probably due to a modification of cellular metabolism through the mechanical action of the closure of the digestive canal and finally through secretion of a toxin by the parasite. The disease declined after 1979, but a second disease then hit the flat oyster.

Traditional oyster culture in France

Figure 21 - Life cycle of Martelia refringens for Ostrea edulis (after Grizel et al. 1974)

This protozoan disease was first noticed in the Ile Tudy in France, in 1979 (Comps et al. 1980). The parasite Bonamia ostreae spread rapidly through all the Breton culture centers. It induces ulceration's in the gills with perforations and indentations as well as lesions in the connective tissue. This parasite affects the older oysters particularly and causes the mortality of 50–80% of the stock. The percentage infection is lower in young oysters.

As the seed oysters show a low rate of infection with Bonamia ostreae and infection levels correlate with age, the plan to re-introduce the flat oyster after massive eradication of the adults entails low-density culture in deep, open water (Cancale). This technique allows the culture of several hundred tones of flat oysters on a three years cycle.

To improve the control of the parasites and to develop methods to prevent their spread, immunodiagnostics have been developed (Mialhe et al. 1987). Use of monoclonal antibodies specific for the purifies parasite Bonamia ostreae allows rapid determination with a reliability which relates to the level of infection of the flat oysters (Fig. 22).

7 - TECHNIQUES USED IN REARING

7.1 Spat production

Seed oysters for culture can be supplied in one of three ways : regulated fishing of juveniles from natural classified beds; natural capture of juveniles produced by spawners in culture; and supply from a hatchery or nursery (See Part 2 Chapter 1). The production of spat in hatcheries is of secondary importance in the French mollusc culture industry, except to make up for deficiencies in natural settlement. In this context, the development of hatcheries will go ahead only if the seed produced has benefits which make its extra cost worthwhile. If disease-resistant strains of flat oysters could be selected, or if research on the genetics of cupped oysters made triploid stocks with better growth characteristics available, the future pattern of the oyster culture industry in France would be different. The settlement of spat on a collector provides major supply of oysters for rearing. It has already been noted that the development of oyster culture has gone hand-in-hand with the development of the technique of settlement on collectors.

The culture of molluscs and echinoderms

Figure 22 - Principle of the immunodiagnostic test developed for the parasite of the flat oyster (after Mialhe et al. 1987)

Types of collectors
C. gigas appears to be indifferent to the type of substrate on which it settles, which explains the great diversity of types of collectors used for spat. However, while the larvae are searching for a substrate on which to attach, fouling matter, particularly algae and silt, should be excluded. O. edulis is more particular in its choice of substrate for attachment.

For the cupped oyster the farmers keep to the traditional calcareous stones in the Charentes region. In the Arcachon Basin tiles coated with lime are used. These make it possible to remove the very young oysters by scraping. The tiles are arranged in cages or stacks in the parks. Stakes and wooden planks are no longer used. In all the rearing areas, on the culture tables (Fig. 23) various types of support can be used; slate posts or rods, iron bars, oyster shells, scallop shells, and slates strung out or arranged in special bags. Plastic collectors came into use at least 10 years ago; these are light, resistant, and practical from the point of view of removal of the oysters. They are either plastic tubes of various size or moulded plastic cells with oblique lamellae (Pleno).

Limed tiles are the most frequently used collector for the flat oyster. They are placed in groups at the appropriate time. The type of lime differs according to the culture region and the collector (Marteil 1979). A new type of collector consists of «sausages» of mussel shells suspended form metal frames (Grizel et al. 1979) and is used in the parks in the deepest water. The mussel shells covered in spat are then separated; this removes the need for scraping.

Many studies have been carried out with the aim of determining the numbers of collectors which need to be installed as a function of the abundance of spat. Thus, in Arcachon, it has been estimated that the potential for recruitment is around 5 thousand million spat (20 million collectors with 250 spat/collector). Berthomé et al. (1984) measured the length of collectors by aerial photography, and, after having determined the abundance of spat on each type of collector by sampling, calculated theoretical production from settlement in 1978, 1980 and 1982 in the Seudre and Bonne Anse regions, taking into account growth and cumulative mortalities in the rearing beds. These studies clearly demonstrate the significant differences in settlement from one year to another; 1982 hat a production four times greater than that in 1981. Martin et al. (1980) estimated the quantity of tiles positioned in the Auray region as well as using a sampling technique to estimate the settlement on each tile. They showed, from 1983 to 1986, a fall-off in the number of spat settling on each collector.

7.2. Rearing

After a period varying from 6 to 18 months, according to growth and the techniques used in culture in each Basin or even sector, the seed oysters are detached from the collectors. This operation is generally carried out by hand, although mechanization is beginning to be introduced. Mortality occurring during this operation approaches 25%.

During the second year of culture the oysters may remain on the collectors which can be spaced out on the sea bed or attached to culture tables; they may be separated and place individually on the sea bed or raised above the sea bed. They are usually reared until they are 3 years old.

Flat culture
Flat culture is carried out ont he uncovered sea bed. Concessions, leased to the oyster growers by the state, are protected around the perimeter by plastic mesh nets so that the oysters are retained in the parks during storms. In the Gulf of Morbihan, parks for young oysters are protected from predation by crabs by mesh fences which are 30–50 cm high and are supported by wooden posts onto which horizontal planks are fixed. In the Arcachon Basin, the areas of flat culture are surrounded by hedges of twigs or stones which provide extremely effective protection. Densities of oyster vary between sectors. In the Marennes-Oléron region the mean figure is 500 kg/100 m2 for oysters in the middle of the culture cycle, and 700 kg/100 m2 for adult oysters (Bacher1984). In the Arcachon region densities are of the same order of magnitude. However, according to Marteil (1979), for flat oysters it is 50–60 Kg/100 m2 in the second year, 100–120 kh/100 m2 in the third year, and from 300 to 450 kg/m2 in the fourth year. These densities applied before the epidemics of parasitic diseases. During their growth the oysters are regularly harrowed or forked over to avoid the beds becoming silted up.

Rearing on the sea bed in deep water
This is a rearing technique which has been developed in the South of Brittany, mainly in the Bay of Quiberon, but is also used in the Bay of Cancale in Northern Brittany. The densities at planting out are 50kg/100 m2 for seed and 70–90 kg/100 m2 for 2 years old oysters. Since the epizootics, a plan to safeguard the flat oyster has been implemented. The first stage was the destruction of 1.367 tones in the parks of South Brittany and in Cancale in North Brittany. This plan was based on results from experiments which showed that densities 5 times lower than previously (100 kg/100 m2) allowed growth over 2 to 3 years and avoided the parasitic outbreaks. All maintenance operations arc carried out by dredging.

Raised culture
The oysters are either still attached to the collector or enclosed in baskets which were originally made from wood but are now usually made from plastic. The most frequently used method uses net bags whose mesh increases with the size of the oysters. The standard bags which measure 1 m × 0,5 m are arranged in a line on metal tables which are 50 cm high and 4 m in length. The bag are turned over regularly to prevent the development of algae, and the numbers in the bags are halved when the biomass becomes excessive. The biomass allowed in each bag is very variable, from 5 to 15 kg depending on the age of the oyster; the mean varies from 9 to 11 kg. There are several advantages to this form of culture : better growth and quality, ease of maintenance, and low mortality from storm damage. However, they are some disadvantages : the danger of putting too many oysters in the culture system which causes poor growth and silting up (Sornin 1981) and the growth of fouling organisms on the installations which may prevent the use of this type of apparatus at certain times of year. Theses disadvantages have led professional operators and administrators to regulate this method of culture very strictly. For example, in the Marennes-Oléron only 1/3 of the area of the concession may be cultivated in this way, and the tables must be removed in the winter to improve the transport of silt?. They are installed again when the settlement of mussel spat is over.

Suspended culture
This technique is used in the Mediterranean, particularly in the étang de Thau where fixed tables are constructed from old railway lines measuring 50 m in length and 10–12 m across. Each one has 5l wooden bars to which around 1.000 supports can be attached (Hamon é Tournier 1981). The C. gigas collectors which are brought from the Atlantic are strung on lines and can be put directly onto the culture tables. Part of the stock is sold after 18 months in culture; the remainder is attached singly, with cement, by the «heel» onto rods made from foreign hardwood. After this second year of culture, the oyster is of superior quality (Raimbault 1984). The advantage of this culture method is that the entire water column is available to the molluscs. However, the constant immersion in water leads to the development of competitors (Ascidians) and seaweed (Sargassum) on the rearing structures.

In Corsica (étang de Diane and d'Urbino) rafts are formed by floats made in the same way as the structure used in the rearing of mussels in Galicia. Oysters and mussels are reared together in suspended culture.

Recently, on the coast of Brittany and around the Golfe du Lion, cultures using suspended ropes have given promising results (See Part 2, Chapter 54).

7.3. The use of «claires» to «finish» oysters

The use of «claires» was developed in the ancient salt marshes. They now cover an area of 3.500 ha in the Marennes-Oléron Basin (Grelon 1978) and are also found on the Ile de Ré, the Bay of Bourgneuf, and in the Ile de Noirmoutier. There ponds are used for «greening» and fattening the oysters which are stocked at a density of 25–30/m2 for «fines de claires» and from 4–5/m2 for special oysters (huîtres spéciales). The fine de claires remain in these ponds for several weeks while the huîtres spéciales remain there for several months. These ponds have a high biomass of phytoplankton (Rindé 1979), particularly of a diatom Navicula ostrearia which is responsible for the greening of the oysters. The oysters absorb the green pigment liberated by the breakdown of the diatoms through their gills. Many studies have been carried out on the biology of this diatom in culture (Neuville & Daste 1970), while Moreau (1970) and Robert (1983) have examined the ecosystem of the claires, particularly in relation to Navicula ostrearia. Robert (1983) showed that nitrogen was the major limiting factor in the production of unicellular algae, and the Navicula ostrearia is a species which, to develop, uses organic matter excreted by the oysters. The research carried out on the development of the greening and the factors which control the development of Navicula ostrearia have been aimed at making the process less uncertain in the oyster claires of the Atlantic marshes.

8 - ECONOMIC ASPECTS AND PERSPECTIVES

The production of cupped oysters oscillates around 100.000 tones (130.000 tones in 1986), which puts French oyster culture in 4th place in worldwide terms, behind the USA, Japan and Korea. In 1982, France produced 12% of the worldwide production (FAO, 1980).

The financial return from oysters is the highest of any species under the French maritime fisheries control, reaching 1.1 thousand million francs in 1984 or 20 % of the total for marine fish and shellfish, 98 % of the turnover comes from cupped oysters (Fig. 24).

Activities connected with the culture of oysters occupy a large part of the littoral zone. There are 20.000 ha of concessions : 14.000 in estuaries and 6.000 in deeper waters.

According to Bonnet et al. (1983) the oyster culture industry employs 23.000 fulltime staff and 31.000 seasonally. No estimate was made of land-based jobs, but these represent a far from negligible contribution to employment : there are plastics factories making equipment for culture and packaging, boat builders, manufacturers of specific tools (graders, calibrators, etc…). The market for oysters is largely internal; there are few imports and exports. This implies that production is almost entirely dependent on the national market. According to the SECODIP panel (1983), direct sales represent 20 % on average. Dumont (1983) found that between 1978 and 1982 there had been an increase form 7,9 to 178 % in the proportion of the oysters going through the hypermarkets and supermarkets. 50 % of sales take place in December, which requires well-organized marketing. The price received by the farmer is determined by syndicates in relation to the quantity and quality available. However, individual markets find their own level by mutual agreement, and prices fluctuate in relation to the product offered by the producer and the demand from the market.

The culture of molluscs and echinoderms
	CAPTURE INSTALLATIONS
	On the left seen from above, on the right oblique view. These are made from wooden posts linked by iron bars. Their height above the sea bed varies between 0.5 m to 1 m.
	Slates threaded on a spindle arrangement	CHARACTERISTICS Mean number of slates per spindle = 12 Maximum number of spindles per metre of installation - 50
		Maximum area for spat collection = 22m2/m True capture area = 15.4 m2/m Relative capture index - Standard collector
	String of scallops/shells	CHARACTERISTICS Number of shells per spindle = 12 Maximum number of spindles per meter of installation = 100 Maximum area of spat collection = 30 m2/m True captive area = 21 m2/m Relative captive index = 1.05
	String of oyster shells	CHARACTERISTICS Mean number of shells per spindle = 60 Maximum number of spindles per metre installation 90
		Maximum area for spat collection = 60 m2/m True capture area = 42 m2/m Relative capture index = 2.45
	Plastic tube	CHARACTERISTICS Number of tubes per bundle = 7 Maximum number of bundles per metre of installation = 50
		Maximum capture area = 31 m2 m/m True capture area 2.7 m2/m Relative capture index = 1.43
	Slate bars	CHARACTERISTICS Size of bar (in cm)= 70 × 10 × 2 Number of bars per metre of installation - 20 Maximum capture area = true capture area = 3.44m2/m Relative capture index not calculated
	Bags of oyster shells	CHARACTERISTICS Size of bag (in cm)=100 × 50 Number of oyster shells per bag around 650 Maximum number of bags per metre installation=10 Maximum capture area : 55 m2/m Remark: Never used alone but covers in a single layer other types of collerctors Relative capture index = 1.17

Figure 23 - Different type of collector used in the Marennes-Olérin Basin (after Berthomé et al. 1984)

Figure 24 - Distribution of cupped oysters sold with health tickets in the principal French producer departments in 1985 and 1986

The mechanism for fixing the price is far from straightforward (Fig. 25). It depends on the quantity of oysters available both locally and nationally; there is a great deal of trade between the different culture basins. The market for the cupped oyster has had to absorb an increase in production caused by improvements in techniques (raised culture) and the development of new areas (Normandy), changing over from the production of flat oysters. 90% of the increase in the production of cupped oysters comes from the new regions, while the ancient basins of Marennes-Oléron and Arcachon, for example, have seen no increase in production and even a decline, linked to the biotic capacity of these over-exploited areas; Production techniques and equipment differ from one region to the next; this gives rise to differences in the sale price. Small family businesses in the old growing areas which have been divide up into small parcels have high operating costs in comparison with those in the new «industrial» oyster culture in the developing areas.

With this competition between regions and the increase in the production of C. gigas, the problem of overproduction must be addressed, particularly as the price of oysters is increasing at a rate below the rate of inflation, reducing returns and causing dumping when the sale price is lower than the rearing costs. Dumont (1983) demonstrated the elasticity of the demand of for cupped oysters in relation to price and income, and concluded that the difficulties faced by the oyster farmer in years of high production result from a surplus of production in relation to the marketing and distribution mechanisms. According to this author, the term «overproduction», a surplus of production in relation to demand at a price acceptable to producers, cannot strictly be applied to cupped oysters. The problem is to determine the cost price of each oyster in the different rearing procedures and to assess whether the sale price is acceptable to the farmer. The future of the small family units in the old rearing centers will depend on reaching a relationship between rearing costs and sale price.

Two studies on the economic effects of disease in the oysters in Brittany have been carried out recently (Grizel 1983 - Meuriot & Grizel in press). These authors have shown that the two epizootics have cause modifications to be made to the culture practice : developments towards the sea, where parasites have less effect, collection of flat oyster spat from deeper water, and an increase in the culture of C.gigas since 1974 with production increasing from 3.000 to 16.000 tones. In economic terms, the accumulated losses are high : 1.6 thousand million francs in turnover and 1.3 thousand million francs n added value. Comparing this with estimates of the economic consequences of the wreck of the Amoco-Cadiz (Bonnieus et al. 1980) where losses were estimated to be 114 million francs to the mollusc culture industry, it can be seen that the losses are not of the same order of magnitude. However, more care has been taken to prevent further grounding of tankers than to avoid further epizootics.

The culture of molluscs and echinoderms

Figure 25 - Change in the price of farmed oysters in francs (1985 prices) (•),
in relation to national production (®) and production in the Marennes-Oléron Basin (‡)

While the first disease (Bonamia) had only a slight effect on the numbers employed it caused the changeover to the rearing of cupped oysters. As the culture of the cupped oyster is less lucrative than that of the flat oyster, growers experienced a mean reduction in revenue, and the second epizootic in 1980 appeared to have a more direct effect on employment (drop of 20 %) in salaries between 1980 and 1982).

As has been seen from the biology, to put forward models for the management of the mollusc culture basins, which define optimum densities, it is necessary to know what stocks are being cultured. At the same time the economic approach can give reliable statistics on production and on the revenue to producers. All the politics of buying and selling should be based on a better understanding of the level of national production because the increase in the size of all the culture centers for cupped oysters increases the complexity of the market. Accurate statistics are also important for use in defending aquaculture in the competition for management of the space around the coasts.

The future development of oyster culture must take into account :

• spat settlement and the maintenance of environmental quality to give good larval survival and also the regulation of settlement with the eventual determination of a quota of collectors in order to avoid the production of surplus juveniles in relation to the food supply in the culture basins and in relation to the market;

• the distribution of cultured oysters within the basins. For good growth and fattening it is essential that the oysters should be in equilibrium with the biotic capacity of the basin;

• outbreaks of parasitic disease and, particularly, the conditions for their appearance, should be controlled by strict prohibition of the import of all molluscs and also by ensuring that the cultured stock is kept in conditions under which it can defend itself against disease. Basins must not be overstocked;

• genetic research on new stocks, aimed at directing energy ingested by C.gigas to the production of flesh rather than to gametogenesis. Juveniles from these new improved strains are already being produced in hatcheries;

• the development of more diverse culture. Monoculture techniques are more prone to epizootics than culture of complementary species in the ecosystem;

• marketing, particularly a study of the financial returns to each type of rearing system, allows the development of several standards of financial profitability for the development of the cupped oyster in France.

REFERENCES

Historical introduction

COSTE, M. - 1867 - Voyage d'exploration sur le littoral de la France et de l'Italic. Paris - Imp. Impériale

GRELON, M. - 1978 - Saintonge, pays des huîtres vertes. La Rochelle, Ed. Rupella - 364 p.

HINARD, G. - 1927 - Le contrôle sanitaire des établissements coquilliers pendent l'annêe 1927. Rev. Trav. Off. Pêches Maritimes - 1 (1) : pp. 89–97

HINARD, G. & LAMBERT, L. - 1927 - Tableau de l'ostréiculture française (première partie). Rev. Trav. off. Pêches Maritimes - 1 (3) : pp. 37–89

HINARD, G. & LAMBERT, L. - 1928 - Tableau de l'ostréiculture française (deuxième partie). Rev. Trav. off. Pêches Maritimes - 1 (4) : pp. 61–127

LEMONNIER, P. - 1980 - Les salines de l'Ouest, logique technique, logique sociale. Presse universitaire de Lille - Ed. Maison des sciences de l'Homme : 222 p.

PAPY, L. - 1941 - La côte atlantique de la Loire à la Gironde, Tome 1 : Les aspects naturels - Introduction à une étude de géographie humaine, Tome 2 : L'homme et la mer - Étude de géographie humaine. Bordeaux, - Ed. Delmas : 302 p.

PIZETTA, J. & DE BON, M. - 1880 - La pisciculture fluviale en France, l'ostréiculture en France. paris - Ed. J. Rothchild

ROCHE, G. - 1897 - La culture des mers. Tours - Ed. Bibliothèque scientifique Internationale : pp. 162–312

Archives de la revue Ostréiculture, culture marines : de 1932 à 1947

Archives de la revue Cultures marines : de 1947 à 1983

Statistiques des pêches maritimes - Marine Marchande : de 1867 à 1981

Classification and geographical breakdown

BUROKER, N.E. - HERSHBERGEN, W.K. & CHEW, K.K. (1979), Population genetics of the Family ostreidae, I : Intraspecific Studies of Crassostrea gigas and Saccostrea commercialis, Il : Interspecific Studies of the general Crassostrea and Saccostrea. Mar. Biol. - 54 : pp. 157–169 and 54 : pp. 171 – 184

GRASSE, P. - 1960 - Taité de zoologie - Mollusques Lamellibranches. Tome V (2) - Paris - Ed. Masson et Cie MARTEIL, L. - 1976 - La conchyliculture française - 2ème partie - Biologie d'huître et de la moule Rev. Trav. Inst. Pêches Marit. - 40 (20) : pp. 149–346

MENZEL, R.N. - 1974 - Portuguese and Japanese oysters are the same species. J. Fish. Res. Bd. Canada - 31 (4) : pp. 45, -456

RANSOM, G. - 1951 - Les huîtres, giologie, culture - Savoir en Histoire naturelle. Vol. 23 - Paris-Ed. Lechevalier : 260 P.

RANSON, G. - 1967 - Les espèces d'huîtres vivant actuellement dans le monde, définies par leurs coquilles larvaires ou prodissoconques - Etude des collections des grands musées d'Historie naturelle.Rev. Trav.Onst. Pêches Marit. 31 (2) et (3) :pp. 128–199 et 205–274

Physiology, absorbtion of dissolved organic matter

AMOUROUX, J.M. - 1982 - Ethologie, filtration, nutrition, bilan énergétique de Venus Verrucosa. Thèse de doctorat d'Etat - Université Pierre et Marie Curie - Paris VI : pp. 1–99

BAMFORD, D.R. & GINGLES, R. - 1974 - Absorption of sugars in the gill of the Japanese oyster Crassostrea gigas. Comparative biochemistry Physiology - 47 A : pp. 637–649

CASTELL, J.D. & TRIDER, D.J. - 1974 - Preliminary feeding trials using artificial diets to studs the nutritional requirements of oysters (Crassostrea virginica). Journal Fisheries Research Board of Canada - 21 (1): pp. 95–99

COLLIER, R., MAGNITZKY, O. & BELL - 1953 - Effect of dissolved organic substances on oysters. Fishery Bulletin - 84 (54) : pp. 67–183

EHRHARDT, M.& HEINEMANN, J. - 1975 - Hydrocarbons is blue mussels from the Kiel Bight. Environnemental Pollution - 3 : pp. 257–271

ELLIOT, A.J. - 1979 - Laboratory investigation into the absorption of dissolved free amino acids by the gill of the mussel Mitylus edulis L. Irish Fisheries Investigation - B - 22 : pp. 1–15

FANKBONER, P.V. & DE BURGH, M.E. - 1978 - Comparative rates of dissolved organis carbon accumulation by juvenile and pediveligers of the Hapanese oyster Crassostrea gigas Thunberg. Aquaculture - 13: pp. 205–212

FEVRIER, A. - 1976 - Evolution des matières organiques en solution dans l'eau de mer : relations avec l'activité métabolique des organismes marins. These 3ème cycle - Université Pierre et Marie Curie - Paris VI : pp. 1–52

HERAL, M. - 1977 - Etudes préliminaires des potentialités nutritives dans le bassin de Marennes-Oléron. Océanexpo Bordeau : 14 p.

HERAL, M., DELSOUS-PALOI, J.M., RAZET, D. & PROU, J. - 1984 - Essais de mise en evidence in situ de paramètres biotiques et abiotiques de l'eau et de l'interface eau-sediment intervenant dans la production de l'huître de l'huître C. gigas. Océanis - 10 (4) : pp. 465–475

JORGENSEN, C.B.- 1982 - Uptake of dissovled amino acids from natural sea water in the mussel Mitylus edulis. Ophelia - 21 (2) : pp. 215–221

JORGENSEN, C.B. - 1983 - Patterns of uptake of dissolves amino acids in mussels (Mitylus edulis). Mar. Biol. - 73 : pp. 177–182

LUCAS, A - 1976 - La culture des mollusques ou conchiliculture - L'exploitation de la vie marine, Océanographie biologique appliquée. Paris - Ed. Masson : pp. 229–258

PEQUINAT - 1973 - A kinetic and autoradiographic study of the direct assimilation of Amino acids and glucose by organs of the mussels Mitylus edulis Mar. Biol. - 19 : PP. 227–244

SOROKIN & WYSHK WARZEV - 1973 - Feeding on dissolved organic matter by some marine animals. Aquaculture - 2 : pp. 141–142

WRIGHT, S.M. & STEPHENS, G.C. - 1978 - Removal of amino acid during a single passage of water across the gill of marine mussels. The journal of Experimental zoology - 205 (3) : PP. 337–352

Ingestion of particles in suspension

FIALA.A - MEDIONI, A. & COPELLO, M. - 1984 - Relations trophiques entre huître et milieu : influence de la concentration et de la taille des particules. Colloque sur les bases biologiques de l'aquaculture - Actes et colloques CNEXO - Sous presse: 16 p.

GERDES, D. - 1983 - The pacific oyster Crassostrea gigas - Partie II : Oxygen consumption of larvae and adults. Aquaculture - 31 : pp. 221–231

RODHOUSE, P.G. - 1978 - The energy transformation by the oyster Ostrea edulis L. in a temperature estuary.J. Exp. mar Ecol. - 34 : pp. 1–22

WIDDOWS, J., FIETIL, P. & WORRALL, C.M. - 1979 - Relationship between seston, availagle food and feeding activity in the common mussel Mitylus edulis. Mars. Biol. - 50 : pp. 195207

WILSON, J.M. & LA TOUCHE, R.W. - 1978 - Intracellular digestion in two sublitooral populations of Ostrea edulis. Mars. Biol. - 47 : pp. 71–77

Reproduction

DESLOUS-PAOLI, J.M., HERAL, M., BERTHOME, J.P., RAZET, D. & GARNIER, J. - 1981 / 1982, Reproduction naturelle de Crassostrea gigas Thunberg dans le bassin de Marennes-Oléron en 1979 et 1981 : aspects biochimiques et énergétiques. Rev. Trav. Inst. Pêches Marti. -45 (4) : pp. 319–327

HELM, M.N., HOLLOAND, D.L. & STEPHENSON, R.R. - 1973 - The effect of supplementary algal feeding of a hatchery breeding stock of Ostrea edulis on larval vigour. J. Mar. Biol. Ass - U.K. -53 : pp. 673–684

HELM, M.N. & MILLICAN, P.F. - 1977 - Experiments in the hatchery of Pacific oyster larvae (Crassostrea gigas Thunberg). Aquaculture - 11 : pp. l–12

HIS, E. & ROBERT, R. - 1980 - Action d'un sel organo-métallique, l'acétate de tributyl-étain sur les oeufs et les larves D de Crassostrea gigas(Thunberg). Note an C.I.E.M., C.M. - 1980 - F. :27 p.

HIS, E. & ROBERT R. - 1981 - LES Causes de mortalité larvaire de Crassostrea gigas dans le bassin d'Arcachon. Rapport I.S.T.p.M. - 7septembre 1981 : 31 p.+ annexes

HIS, E., MAURIER, D. & ROBERT, R. - 1983 - Estimation de la teneur en acétate de tributyl-étain dans l'eau de mer, par une méthode biologique. Proc. 2nd. Franco-British Symp - London - 6–9 September 1982 - J.Moll. Stud. - Suppt . 12 A : pp. 60–68

LUBET, P.E. - 1980 - Influence des facteurs externes sur la reproduction des lamilli-branches. Océanis - 6 (5) : pp. 469–489

LUCAS, A. - 1982 - La nutrition des larves de bivalves. Océanis - 8 (5) : pp. 363–388

MANN, R. - 1979 - Some biochemical and physiological aspects of growth and gametogenesis in Crassostrea gigas and Ostrea edulis at sustained elevated temperature. J. Mar. Biol. Ass. - U.K. - 59 : pp. 95–110

MARTEIL - 1976 - La conchyliculture française - 2ème partie : Biologie de l'huître et de la moule. Rev. Trav. Inst. Pêches Marit. - 40 (2) : pp. 149–346

MARTIN, Y.P. & MENGUS, B.M. - 1977 - Utilisation de souches bactériennes sélectionnées dans l'alimentation des larves de Mytilus galloprovincialis Lmk (Mollusque bivalve) en élevages expérimentaux. Aquaculture - 10 : pp. 253–262

MILLICAN, P.F. & HELM, M.M. - 1973 - Preliminary observations on the culture of the larvae of Pacific oyster, Crassostrea gigas Thunberg. ICES, C.M. - 1973/K - 33 : 10 P.

MILLAR, R.H. & SCOTT, J.M. - 1967 - The larval of oyster Ostrea edulis during starvation. J. Mar. Biol. Ass. - U.K.- 47 : pp. 475–484

PRIEUR, D. - 1980 - Les relations entre mollusques bivalves et bactéries hétérothrophes en milieu marin. Etude analytique et expérimentale. Thèse d'Etat - Université de Bretagne Occidentale : 266p.

ROBERT, R. - 1983 - Etudes sur les causes de la perturbation de la reproduction et du développement larvaire de Crassostrea gigas dans le bassin d'Arcachon. Thèse 3éme cycle - Université de Bretagne Occidentale : 169 p.

ROBERT, R. & HIS, E. - 1981 - Action de l'acétate de tributyl-étan sur lesoeufs et larves D de deus mollusques d'intérêt commercial : Crassostra gigas (Thungerg) et Mytilus galloprovincialis (Lmk). Note au C.I.E.M. C.M. - 1980/E : 42 P.

Energy budget

ANONYME - 1987 - Bilan énergétique ches les mollusques bivalves : terminologie et méthodologie. Vie Marine - Hors série № 7 : 68 p.

BAYNE, B.L., THOMPSON, R.J.& WIDDOWS, J.- 1976 - Physiology l., In : Bayne B.L., Ed. Marine mussels, their ecology and physiology. Cambridge University Press - I.B.P. - 10 : pp. 121–206

Bernard, F.R. - 1974 - Annual biodeposition and gross energy budget of mature pacific oyster Crassostrea gigas. J. Fish. Res. Board. Can. - 31 (2) : pp. 185–190

BOUKABOUS, r. - 1983 - Etude préliminaire des adaptations écophysiologiques de l'huître Crassostrea gigas(Thunberg) dans la lagune de Oualidia. Mémoire 3ème cycle Agonomie-Institut Agronomique et Vétérinaire Hassan II - Maroc : 51 p.

COPELLO, M. - 1982 - Données écophysiologiques sur un organisme filtreur benthique des étangs littoraux méditerranéens : Crassostrea gigas. Rapport de DEA - Université Paris VI

DESLOUS-PAOLI, J.M., HERAL M. & ZANETTE, Y. - 1982 - Problèmes posés par l'analyse des relations trophiques huître-milieu. In : Indices biochimiques en milieux marins - Journée du GABIM - Bres 18–20 november 1981. Pub. CNEXO (Actes de colloques) - 14 : pp. 335–340

DESLOUS-PAOLI, J.M. & HERAL, M. - 1984 - Transferts énergétiques entre l'huître Crassostrea gigas de l'an et la nourriture potentielle disponible dans l'eau d'un bassin ostréicole. Haliotis - 14 : 79–90

DESLOUS-PAOLI, J.M., HERAL M. & MASSE, H. - 1985 - Bilan énergétique d'une population naturelle de Crepidula fornitica dans le bassin de Marcnnes-Oléron. Bases biologiques de l'Aquacuture - Montpellier 1983 - IFREMER - Actes de Colloques - 1 : pp. 109, 124

DESLOUS-PAOLI, j.M. - 1985 - Assessment of energetic requirements of reared molluscs and of their main competitors. In : Aquaculture : Shellfish culture development and management - La Rochelle - March 1985 - Ed. IFREMER : pp. 31 – 346

DESLOUS-PAOLI, J.M., HERAL M., GOULLETQUER, P., BORONTHANARAT, W., RAZET, D., GARNIER, J., PROU, J. & BARILLET, L. - 1986, Evolution saisonnière de la filtration de bivalves intertidaux dans des conditions naturelles. GABIM - La Rochelle - Océanis - Sous presse.

DESLOUS-PAOLI, J.M., HERAL M., GOULLETQUER, P., BORONTHANARAT, M. - PROU, J., RAZET, D. & GARNIER, J. - 1987 - Efficiency of particle retention and filtration rate in intertidal bivalve molluscs ; seasonal variations under natural conditions. Posters EMBS Barcelona - Septembre 1987

GRIFFINS, R.J. - 1980 - Natural food availability and assimilation in the bivalves Choromytilus meridionalis. Mar. Ecol. - 3 : pp. 151–156

HERAL, M. & DESLOUS-PAOLI, J.M. - 1983 - Valeur énergétique de la chair de l'huître Crassostrea gigas estimée par mesures microcalorimétriques de la chair de l'huître Océanol. Acta. - 6 (2) : pp. 193–199

HERAL, M. - DESLOUS-PAOLI, J.M., & SORNIN, J.M. - 1983 - Trransferts énergétiques entre l'huître Crassostrea gigas et la nourriture potentielle disponible dans un bassin ostréicole : premières approches. Océanis - 9 (3) : pp. 169–194

HERAL, M. - 1985 - Evaluation of the carrying capacity of molluscan shellfish ecosystems In Aquaculture : Shellfish culture development and management. La Roche - March 1985 - Ed. IFREMER : PP. 297–318

HERAL, M. - DESLOUS-PAOLI, J.M. & PROU J. - 1986 - Influence de climat sur le recrutement et sur la production d'huîtres cultivées (Crassostrea angulata et Crassstrea gigas) dans le bassin de Marennes-Oléron (France). Note au CIEM - Comité de la Mariculture F/40 : 20 p.

HERAL, M. - DESLOUS-PAOLI, J.M., BOULLETQUER, P., RAZET, D., PROU, J., RAVAIL, B. & VINCENDEAU, M.L. - 1987 - VARIATIONS SAISONNIÈRES DE L'EXCRÉTION AZOTÉE ET RESPIRATION DE 5 MOLLUSQUES INTERTIDAUX : L'HUÎTRE (Crassostrea gigas), la moule (Mitylus edulis), la coque (Cerastoderma edule), la palourde japonaise (Ruditapes philippinarus) et la crépidule (Crepidula fornicata). Haliotis, sous presse

KIØRBOE, T., M∅HLENBERG, F. & NØHR, O. - 1981 - Effect of suspended bottom material on growth and energetics in Mitylus edulis. Mar. Biol. - 61 : pp. 288

LUCAS, A. - 1982 - Remarques sur les rendements de production chez les bivalves marins. Haliotis - 12 : pp. 47–60

MAC FAYDEN, A. - 1966 - Les méthodes d'étude de la productivité des invertébrés dans les écosystèmes terrestres. La terre et la vie - 4 : pp. 361–392

SHAFEE, M.S. & LUCAS, A. - 1982 - Variations saisonnières du bilan énergétique chez les individus d'une population de Chlamys varia (L) (Bivalvia, Pectinidae). Oceanol. Acta. - 5 (3) ; pp. 331–338

ODUM, E.D. - 1971 - Fundamentals of Ecology. Philadelphia 3rs - Ed. Sounders ; 254 p.

SORNIN, J.M., FEUILLET, M., HERAI, M. & DESLOUS-PAOLI, J.M. - 1983, Effet des biodépôts de l'huître Crassostrea gigas(Thunberg) sur l'accumulation des marières organiques dans les pares du bassins de Marennes-Oléron. J. Moll. Study - Supplt. 12 A : 12 p.

THOMPSON, R.J. & BAYNE, B.L. - 1974 - Some relationship between growth, metabolism and food in the mussel Mitylus edulis. Mar. Biol. - 27 : pp. 317–326

VAHL, D . - 1981 - Energy transformation gy the Iceland scallop Chlamys islandica (D.F.Muller) from 70°N - I : The age specific energy budget and net growth efficiency. J. Exp. Mar. Biol. Ecol - 53 : pp. 281–296

WALNE, P.R. - 1970 - The seasonal variations of meat and glycogen content of seven populations of oysters Ostrea edulis L. and a revie of the literatuure. Fish. Invest. - 2 : 35 p.

WINTER, J.E. - 1976 - Feeding experiments with Mitylus edulis L. at small laboratory scale - The influence of suspended silt in addition of algal suspensions on growth. Proc. 10th Eur. Symp. Mar. Biol. - Ostende - Belgium : pp. 583–600

WINTER, J.E. - 1978 - A critical review on some aspects of filter-feeding lamellibranchiate bivalves. Haliotis - 7 : pp. 71–87

WIDDOWS, J. - 1978 - Combined effects of body size - Food in the mussel Mitylus edulis. J. Mar. Biol. Ass. - U.K. - 58 : pp. 109–124

Models

BACHER, C. - 1985 - Development of shellfish production models, In : Aquaculture : Shellfish culture development and management. La Rochelle - March 1985 - Ed. IFREMER : PP. 347–362

BACHER, C. - 1987 - Modélisation de la croissance des huîtres dans le bassin de Maren, nes-Olzéron. Rapport IFREMER-CNRS - Octobre 1987 : 12 p.

HERAL, DESLOUS-PAOLI, J.M. & PROU, J. - 1985 - Analyse historique de la production conchylicole du bassin de Marcnnes-Oléron (France). Coll. Fr. Japon Oceanogr. - Marseille - 6–21 septembre 1985 – 7 : pp. 55–65

HERAL, M., DESLOUS-PAOLI, J.M & PROU, J. - 1986 - Dynamique des productions et des biomasses des huîtres creuses cultivées (Crassostrea angulata et Crassostrea gigas) dans le bassin de Marennes-Oléron depuis un siècle. Note au CIEM - Comité de la Maricultrue - F/41 : 22 p.

Stocks in culture

BACHER, C. - 1984 - Echantillonnage du stock d'huîtres du bassins de Marennes-Oléron. Rapport de DEA - Université de Paris : 38 p.

HAMON. P.Y. & TOURNIER, IL - 1981 - Estimation de la biomasse en culture dans l'étang de Thau. Sciences et Pêches - Bull. Inst. Pêches Marit. № 313 : 38 p.

SAINT-FELIX, C., BAUD, J.P. & HOMEBON, P. - 1982 - Estimation de la biomasse ostréicole de la Baie de Bourgneuf. Science et Pêche - Bull. Inst. Pêches Marit : pp. 3–9

Disease

BONAMI, J.R., GRIZEL, H., VAGO, C. & DUTHOIT, J.L. - 1971 - Recherche sur une maladie èpizootique de l'huître plate Ostrea edulis Linné. Rev. Trav. Inst. Pêches Marit. - 35 (4) : pp. 415–418

COMPS, M. - 1970 - Observation sur les causes d'une mortalité anormale des huîtres plates dans le bassin de Marennes. Cons. Int. Explor. Mer - K4 : 7 p.

COMPS, M., BONAMI, J.R., VAGO, C. & CAMPILLO, A. - 1976 - Une virose de l'huître portugaise Crassostrea angulata C.R. Acd. Sci. - Paris - 282 série D : pp. 1991–1993

COMPS, M. & DUTHOIT, J.L; - 1976 - Infections virale associée à la «maladie des branchies» de l'huître portugaise Crassostrea angulata C.R. Acad. Sci. - Paris - 283 série D : pp. 1595–1597

COMPS M. & BONAMI, J.R. - 1977 - Infection virale associée à des mortalités chez l'huître Crassostrea gigas Thunberg. C.R. Acad. Sci. - Paris - 285 série D : pp. 383–385

DESLOUS-PAOLI, J.M. - 1981 - Mytilicola orientalis Mori, Crassostrea gigas Thunberg's biochemical composition of oysters during rearing. Cons. Int. Explor. Mer. - K 29 : 16 p.

FRANCE, A. & ARVY, L. - 1970 - Données sur lévolution de la «maladie des branchies» chez les huîres et sur son agent causal : Thanatrostrea polymofpha. France et Arvy - 1969 - Bull. Biol. - 104 (1)

GRIZEL, H., COMPS, M., BONAMI, R., COSSERANTS, F. & DUTHOIT, J.L. - 1974, Recherche sur l'agent de la maladie de la glande digestive Ostrea edulis Linné. Science et Pêche - Bull. Inst. Pêches Marit. - 240 : pp. 7–30

GRIZEL, H; - 1983 - Impact de Marteilia refringens et bonamia ostreae sur l'ostréiculture bretonne. Cons. Int. Explor. Mer. - G 9 : 30 p.

HERBACH, B. - 1971 - Sur une affection parasitaire de la glande digestive de l'huître plate Ostrea edulis Linné. Rev . Trav. Inst. Pêches Marit. - 35 (2) : pp. 79–87

HIS, E. - 1969 - Recherches d'un test permettant de comparer l'activité respiratoire des huîtres au cours de l'évolution de la maladie des branchies. Rev. Trav. Pêches Marit. - 33 (2) : 171–175

HIS, E. - 1977 - Observations relatives à l'infestation de Crassostea gigas Thunberg par le copépode parasite Mytilicola orientalis Mori dans le bassin d'Arcachon. Cons. Int. Explor. Mer. - k 33 : 10p.

HIS, E., TIGE, G. & RABOUIN, M.A. - 10978 - Mytilicola orientali Mori : son action sur les huîtres de bassin d'Arcachon au cours de l'été et de l'automne 1977. Cons. Int. Explor. Mer. - K 14 : 12 p.

MARTEIL, L - 1969 - Données générales sur la maladie des branchies. Rev. Trav. Inst. Pêches Marit. - 33 (2) : 145–150

MIALHE, E., PAOLUCCI, F., ROGIER, H. & GRIZEL, H. - 1987, Monoclonal antibodies : a new tool in mollusc pathology, In : Disease Process In Marine Bivalve Molluscs publié par : American Fisheries Society, Special Publication Series - In Press

Culture technique

BERTHOME, J.P, - PROU, J., RAZET, D. & GARNIER, J. - 1984 - Première approche d'une méthode d'estimation prévisionnelle de la production potentielle d'uître creuse C. gigas d'élevage. Haliotis - 14 : pp. 39–48

GRIZE, H., K LANGLADE, A. & PERODU, J.B. - 1979 - Premiers essais d'une nouvelle technique de captage d'huître plate en Baie de Quiberon. Cons. Int. Explor. Mer - K 24 : 14 p.

MARTELI, L. - 1979 - La conchyliculture française - 3ème partie. Rev. Trav. Inst. Pêches Marit. - 43 (1) : 5–130

MARTIN, A.G., GRIZEL, H. & LANGLADE, A. - 1980 - Evaluation du recrutement d'huîtres plates (Ostrea edulis) collectées sur tuile dans le quartier d'Auray (Bretagne) en 1979. Cons. Int. Explor. Mer - K 31

MOREAU, J. - 1970 - Contribution aux recherches écologiques sur les claires à huîtres du bassins de Marennes-Oléron. Rev. Trav. Inst. Pêches Marit. - 34 : 380–462

NEVILLE, D. & DASTE, Pg. - 1970 - Premières observations concernant la culture uni algale de souches de Diatomées provenant de claires ostréicoles de l'ILe d'Oléron. C.R. Acad. Sci. - Paris - 270 série D : pp. 2486–2488

NEUVILLE, D - 1978 - Les diatomées des claires ostréicoles - Contribution des techniques de culture in vitro à l'étude de leur biologie. thèse Doct. Etat - Université Poitier : 279 p.

RAIMBAULT, R. - 1984 - La conchyliculture en Méditerranée Française. Haliotis - 14 : pp. 1–22

RINCE, Y. - 1979 - Cycle saisonnier des peuplements phytoplanctoniques et microphytobenthiques des claires ostréicoles de la baie de Bourgneuf. Rev. Algal. - 14 : 297–313

ROBERT, J.M., MAESTRINI, S.Y., HERAL, & ZANET TTE, Y. - 1982 - Production des microalgues des claires ostréicoles en relation avec l'azote organique dissous, excrété par les huîtres. Silco - Bordeaux - September 81 - Oceanol. Acta. № sp. : pp. 389–395

ROBERT, J.M. - 1983 - Fertilité des eaux des claires ostréicoles et verdissement - Utilisation de l'azote par les diatomées dominantes. Thèse doct. Etat - Université de Nantes : 281 p.

SORNIN, J.M. - 1981 - Processus Sédimentaires et biodéposition liés à différentes modes de conchyuliculture. Thèse 3ème cycle : 188 p.

Economics

BONNET, M., DARDIGNAC-CORBEL, M.J. & DUCLERC, J. - 1983 - L'aquaculture marine française, bilan et perspectives. Note A.P.P. : 17 p.

BONNIEUX, F., DAUCE, P. & RAINELLI, P. - 1980 - Impact soio-économique de la marée noire provenant de l'Amoco-Cadiz. Rapport INRA-UVLOE : 100 P

DUMONT, P. - 1983 - Le marché de L'huître creuse - Essai de modélisation économique. Rapport ENGREF: 58 P. + annexes

MEURIOT, E. & GRIZEL, H. - Note sur l'impact économique de maladies de l'huître plate en Bretagne (in press).