CLAM

CL 12

BRALEY, R.D.
Reproduction in the giant clams Tridacna gigas and T. derasa in situ on the north-central Great Barrier Reef, Australia, and Papua New Guinea.
1984 7 pp
Coral Reefs, 3, 221–227

Small groups of T. gigas and a single individual of T. derasa have been observed to spawn in nature during the austral summer on the Great Barrier Reef. In T. gigas dial periodicity to the spawning generally coincided with incoming tides near second (full), third and fourth (new) quarters of the moon phase. Intense spawning ranged from 30 min to 2.5 h, with spawning contractions occurring every 2–3 min. Eggs were never observed being spawned in nature. A new technique, an egg catching device, was used for sampling eggs of T. gigas which were observed spawning sperm. Results indicated that the egg phase of spawning did not follow spawning of sperm. Some clams which do not respond to a spawning neighbor may be reproductively inactive. In 70% of observations of nearest spawning neighbors the clams were within 9 m of one another. A hypodermic extraction technique was used for clam gonadal material. Examination of tissue suggested a potential early to mid-austral summer spawning for T. gigas and to a lesser degree for T. derasa.

CL 13

BROWN, J.H. and M.R. MUSKANOFOLA
An investigation of stocks of giant clams (family Tridacnidae) in Java and of their utilization and potential.
1985 15 pp
Aquaculture and Fisheries Management, 1, 25–39

A survey was carried out in Karimun Jawa, a group of islands off the north coast of Central Java, in order (1) to investigate the environmental effect of the collection of giant clam shells used for floor tile manufacture, (2) to investigate the distribution and abundance of living populations of Tridacna spp. and to determine whether the larger species of giant clams are still to be found in the area and (3) to determine the suitability of this area for reseeding of giant clam species for mariculture and/or fishery development. Results showed that the collection of T. gigas shells for the manufacture of floor tiles did not have the same damaging effect on the coral environment as reported elsewhere. They also showed that populations of T. crocea, T. maxima and T. squamosa were still thriving while T. gigas, H. hippopus and T. derasa were extermely rare if not actually extinct, one individual alone of T. derasa being found. The potential for reintroduction of these latter species and for the encouragement of mariculture or fishery development into these islands seems great and is strongly advocated.

CL 14

BRYAN, P.G. and D.B. MCCONNELL
Status of giant clam stocks (Tridacnidae) on Helen Reef, Palau, western Caroline Islands, April 1975.
1976 4 pp
Marine Fisheries Review, vol. 38, no. 4, 15–18

A total of 24.800 m2 were covered in transects made on Helen Reef to assess population levels of Tridacnidae. Standing stock estimates were: Tridacna gigas 8.6 × 10-3; T. derasa, 12.9 × 10-3; T. maxima, 1.4 × 10-6; and Hippopus hippopus, 47.4 × 10-3. Tridacna crocea was omnipresent. Tridacna squamosa was difficult to identify and only three were seen. A similar study conducted in 1972 gave the following estimates: Tridacna gigas, 49.8 × 10-3; T. derasa, 32.8 × 10-3; T. maxima, 1.7 × 10-6 and H. hippopus, 44.6 × 10-3. A large percentage of three species were dead (empty shells): Tridacna gigas - 4 live, 206 dead; T. derasa - 6 live. 168 dead; and H. hippopus - 22 live, 458 dead. The reduction in population numbers of these three species is attributed to human exploitation. Tridacna maxima and T. crocea did not appear to have been exploited.

CL 15

HESLINGA, G.A. and T.C. WATSON
Recent advances in Giant Clam mariculture.
1985 6 pp
Proceedings of the fifth International Coral Reef Congress, Tahiti, 5, 531–537

Giant tridacnid clams were once an important food resource on Indo-West Pacific coral reefs, but in many areas they are becoming increasingly rare or extinct as a result of harvesting for subsistence and commercial purposes. The laboratory culture of giant clams, initiated a decade ago, has now advanced to a scale where it can play a meaningful role in population enhancement and food production. Because tridacnids derive their nutrition from autotrophic symbionts, their domestication is uniquely appropriate for oligotrophic seas. This article review state-of-the-art technology for the mass production of tridacnid clam seed and ocean-based growout to maturity as developed by the staff of the MMDC laboratory at Palau. In 1984 the MMDC produced over 100,000 juvenile giant clams, 80,000 of which were second generation offspring. A multi-year program of tridacnid hatchery production, applied research, resource assessment, local and international field planting and mariculture training is in progress at Palau, with funding from the Pacific Fisheries Development Foundation. Tridacnid mariculture research programs are also underway in Australia, Papua New Guinea, Fiji and the Philippines. One commercial giant clam hatchery has opened near Cairns on Australia's Great Barrier Reef.

CL 16

JAMESON, S.C.
Early life history of the giant clams Tridacna crocea Lamarck, Tridacna maxima (Roding), and Hippopus hippopus (Linnaeus).
1976 5 pp
Pacific Science, vol. 30, no. 3, 219–233

Giant clams may be stimulated to spawn by the addition of macerated gonads to the water. Individuals of Tridacna maxima collected at Anae Island, Guam, spawned from November to March. On Palau, Hippopus hippopus spawned in June and Tridacna crocea, in July. Tridacna crocea, T. maxima, and H. hippopus displayed a stereotyped development pattern in morphogenesis and rate of development. Fertilized eggs of T. crocea, T. maxima, and H. hippopus had mean diameters of 93.1, 104.5, and 130.0 um, respectively. The day-2 straight-hinge veligers of T. crocea, T. maxima, and H. hippopus had mean shell lengths of 155.0, 168.0, and 174.4 um, respectively. Settlement occurred 12, 11, and 9 days after fertilization at a mean shell length of 168.0, 195.0, and 202.0 um for T. crocea, T. maxima, and H. hippopus, respectively. Metamorphosis was basically complete about 1 day after settlement. Juveniles of T. crocea, T. maxima, and H. hippopus first acquire zooxanthellae after 19, 21 and 25 days, respectively. Growth rates increase sharply after the acquisition of zooxanthellae. Juvenile shells show first signs of becoming opaque after 47 days for T. maxima and after 50 days for H. hippopus.

CL 17

LABARBERA, M.
Larval and post-larval development of the giant clams Tridacna maxima and Tridacna squamosa (Bivalvia: Tridacnidae).
1975 11 pp
Malacologia, 15 (1): 69–79

The larval development of Tridacna maxima and T. squamosa and the early post-larval development of T. squamosa are described. In both species the prodissoconch I is very large (length greater than 128 um) and metamorphosis occurs at a relatively small size (length about 200 um). Zooxanthellae do not appear until after metamorphosis. Each generation of giant clams is independently infected with the algal symbionts; the possible modes of infection are discussed. Shell deposition in juvenile T. squamosa is 1.5–2 times as great on the posterior and postero-ventral margins as on the anterior margin. This supports the concept that the form of tridacnids is, as in other monomyarian bivalves, best explained by different growth.

CL 18

MUNRO, J.L. and J. GWYTHER
Growth rates and maricultural potential of Tridacnid clams.
1981 4 pp
Proceedings of the fourth International Coral Reef Symposium, Manila, Vol.2, 633–636

A four-year study of the growth rates of Tridacna gigas, T. squamosa, T. maxima and Hippopus hippopus at Motupore Island on the south coast of Papua New Guinea has shown that T. gigas has a relatively rapid growth rate. If suitable hatchery and rearing techniques for juveniles can be developed, the growth rates of T. gigas combined with their very high degree of autotrophy, their hardiness and marketability all suggest a relatively good potential for mariculture. Some suggestions are made as to how a mariculture operation might be undertaken.

CL 19

YAMAGUCHI, M.
Conservation and cultivation of giant clams in the tropical Pacific.
1977 8 pp
Biol. Conserv., 11: 13–20

Giant clams (Tridacnidae) are slow-growing and long-lived animals on the coral reefs of the Indo-West Pacific faunal region. There is a peak period, either summer or winter, in breeding activity of four giant clam species studied. Fertilized eggs develop into planktotrophic veliger larvae which settle and metamorphose into benthic juveniles about ten days after spawning. Although short pelagic larval life favours cultivation of the clams, spat handling is difficult because of the small size in post-metamorphosis juveniles of about 0.2 mm shell length. Colonizing and maintenance strategies of giant clam populations resemble those of forest trees, indicating that giant clam resource management might parallel that of forestry.

CL 20

SOLIS, E.P. and G.A.HESLINGA
Effect of dessication on Tridacna derasa seed: Pure oxygen improves survival during transport.
1989 4 pp
Aquaculture, 76: 169–172

A simple and inexpensive method is described for shipping Tridacna derasa seed in a pure oxygen environment. Under experimental conditions, survival of seed in pure oxygen was higher than that in ambient atmosphere at exposure times ranging from 16 to 48 h. The low cost of the treatment justifies its routine use for commercial shipments of T. derasa seed.

CL 21

BROUSSEAU, D.J.
A comparative study of the reproductive cycle of the soft-shell clam, Mya arenaria in Long Island Sound.
1987 9 pp
Journal of Shellfish Research, Vol. 6. No. 1, 7–15

Three populations of Mya arenaria in Long Island Sound were studied during a 2.5 yr period to determine the sequence of gametogenic development of gonadal tissue and the frequency and duration of spawning under natural conditions. Some individuals in the population at Stonington, CT spawned twice annually, while the two populations in Westport, CT exhibited a single spawning cycle. There was no evidence of hermaphroditism or protandry in any of the populations studied. Sex ratios of M. arenaria in each of the three populations did not differ significantly from 1:1. Photomicrographs of the gametogenic cycles of both male and female clams are included.

CL 22

COPLAND,J.W.AND J.S.LUCAS (Eds.)
Giant clams in Asia and the Pacific.
1988 274 pp
Australian Centre of International Agriculture Research (ACIAR).
Monograph No. 9, 274 pp

Farming giant clams could become a significant new industry in Australia and in countries of Southeast Asia and the South Pacific. Results presented at a workshop at James Cook University in April 1988 indicate that the culture of giant tridacnid clams is both technically and economically viable, with markets for both clam meat, particularly in Taiwan and Japan, and for the shells. The latter are used in variety of ways, and can be marketed through the well-established shell trade. This publication brings together the literature and results of most of the world's research on the giant clams, most of which was presented at the workshop, and is likely to be a benchmark on the knowledge and potential of giant clams for the restocking of tropical reefs, and farming clams both extensively and intensively, in the Indo-Pacific region. There are many problems to be overcome before the farming of giant clams become an established new industry. The research so far strongly indicate that clam mariculture has considerable potential even at this early stage of development.