Molluscs of economic importance and highly potential for seafarming development in Indonesia coastal waters are cockle (Anadara granosa), mussel (Perna viridis), oyster (Saccostrea lugubris, S. cucullata., Crassostrea rivularis, and C. iredalei) and pearl oyster (Pinctada martensii, P. maxima, P. margitifera and Pteria penguin).
In 1984, 50 124 ton of molluscs were produced from natural beds. The production can be increased at least 20 times of the present production through the proper management and with introduction of new technologies of seafarming.
In site selection for molluscs culture, risk factors that may impact on subsequent culture operation and need to consider are more or less the same as those of the finfish culture and already discussed in section 2.1.1. Only ecological factors required by species for its optimum growth will be discussed below:
The cockle culture was practiced by native at Mauk from 1950 to 1969 with estimated production of 5 ton/ha/yr (Unar et at., 1982). The activity was halted in 1975 due to lack of seed. The production of cockle rose from 32 183 mt in 1979 to 48 926 mt in 1985, and declined to 30 959 mt in 1985 (Table 3). Cockle is found abundance in coastal zones in West Sumatra, South Java, Malacca Strait, East Java, North Java, Bali, East Nusatenggara, South Kalimantan, West Kalimantan, East Kalimantan, South Sulawesi, North Sulawesi, Maluku and Irian jaya.
3.1.1 Criteria for assessment of site
The ecological criteria used for evaluation of suitability of culture site for cockle are following:
3.1.1.1 Sheltered area
The site should locate in protected areas where winds and wave actions does not seriously prevail over the area. Otherwise deposition of mud and sand sediments will bury the cockle population. The regular strong wave action can also either wash the cockle up on beach or into the mangrove.
3.1.1.2 Substrate
The potential area for culture cockle should be clay. The upper layer between 6 to 10 inches depth of the stratum should be grey color without fragmented shells containing particles size less than 0.53 mm about 80–90%. The water content of the substrate should about 47–50 per cent organic detritus should present between 6–11 per cent after ignition at 475 degree Celsius for 7 hr.
3.1.1.3 Water depth
For convenience in culture operation and to avoid long exposure during the extreme low water spring tides (ELWS), the area with a water depth of about 1–2 m mean tide level (MTL) is considered as a good site.
3.1.1.4 Land elevation
The site should have a slop seaward between 5–15 degree. If the gradient of slop is too small, the culture area will expose too long between the tides, and where is too great, the cockle does not grow well, and working conditions will be difficult.
3.1.1.5. Water movement
The site should not be in the vicinity of strong current. A current speed between 0.02–0.1 m/sec is justify for cockle culture operation, and strong enough to transport natural food for the cockle.
3.1.1.6 Salinity
The cockle, A. granosa is able to function efficiently at salinities above 23 ppt. Young cockle seems to be able to continue normal feeding activity at a lower salinity than older specimens. Very young individuals remain active at salinity down to at least 18 ppt. Feeding efficiency and activity decrease substantially at salinities less than 20 ppt. For the potential culture site, it should have a salinity within the range of 25–30 ppt which allow to be subjected to long and short-term fluctuations.
3.1.1.7 Source of seeds
The potential site should have the natural seed. If it has to be transported elsewhere, it should be brought in within a reasonable cost.
3.1.2 Potential site
The potential areas suitable for culture of cockle are around 22 950 ha. The main areas are in Tanjung Balai, North Sumatra; Bintan bay, Riau; Kuala Tungkal, Jumbi; Kuala Penet, Lampung; Mauk Tangerang Pancakencan, Gebang, Banten bay, Ketapang bay, Gagara Menyan and Tarumajaya in West Java ; Demak, Jepara, Tayu Pati, and Rembang in Central Java; Kenjeran, Pasuruan, and Probolinggo in East Java; Bunyuwedang bay and Pegametan bay, Bali; Bima bay Sumbawa in West Nusatenggara; and Sinjai, Ujung Pandang in South Sulawesi (Table 4).
The culture green mussel in Indonesia are still in trial stage. The culture trials were carried out by the Marine Fisheries Research Institute Ketapang by and Banten by in west Java with the technical assistance of the Japan International Cooperation Agency. The production at Ancol with Bamboo stake method is about 200 ton/ha/yr. About 400 ton/ha/yr and 1 156 ton/ha/yr were obtained at Mauk Tangerang and Banten by respectively with the hanging method (Unar et al., 1983).
The commercial trial was also carried out at Kuala Penet, Maringgai, Lampung by the Seafarming Project Development project FAO/UNDP INS/81/008. The production was 160 ton/ha/yr with suspension from fixed horizontal frame method.
3.2.1 Criteria for assessment of site
The ecological criteria used for assessment the suitability of the potential site for mussel culture are following:
3.2.1.1 Salinity
Optimal salinity values for the good growth of mussel is ranging from 15–30 parts-per-thousand. The site with salinity below or above the range can be regarded as not worth for the investment.
3.2.1.2 Water depth
Suitable depth for mussel culture operation depends on culture method. For stakes method the water depth should be within a range between 3–8 m (MTL). This is mainly for ease in operation and installation of culture facilities. For raft and hanging method, water depth does not be a limiting factor. To avoid high turbidity of water near the seabed during the low tide, the culture rope should be above the sea bed at least 1 m during the extreme low water spring tide (ELWS).
3.2.1.3 Current
The current speed of the potential site should be within a range of 10–30 cm/sec. Slow water movement results in poor growth of mussels due to the poor replenishment of food. Furthermore slow currents also promote the settling of organic and inorganic particulate materials on the mussels. On contrary, too strong current endangers stakes or culture facilities
3.2.1.4 Turbidity
High water turbidity causes ill effect to the mussels and parasites infection resulting in high mortality at the end. A site with water turbidity containing high suspended load of more than 400 mg/l is considered to have lethal effect on the grow-out mussels.
3.2.1.5 Substratum
Soft mud substratum normally provides the ideal culture site for mussels. It is not only ease in installation of culture facilities, but also offers high productivity sites and more abundance in natural food.
3.2.1.6 Source of seed
Potential site should have natural stock and spatfall in large quantity enough for the culture operation. Transport seed from outside is justified if is necessary for the initial operation.
3.2.2 Potential area
The potential areas suitable for culture mussel on stake, suspended line from the fixed structure, long-line and raft are Tanjung Balai, North Sumatra; Teluk Bintan, Riau; Kuala Tungkal, Kg. Laut, Jambi; Kuala Penet, Maringgai in Lampung; Banten bay, Ketapang, Tangerang, Gagara Menyan, Tarumajaya in West Java, Seribu island, Jakarta; Jepara, Central Java; Kenjeran, Pasuruan, Probolinggo, and Kwanyar in East Java; and Labuan Lombok, West Nusatenggara. The total area is around 19 700 ha (Table 5)
The native rock oyster is reported being cultured on stake at Kwanyar, Bangkalan in Madura island, but on a limited scale. Besides on stake culture, the oyster can be also cultured on rack or suspended from floating raft.
3.3.1 Ecological criteria for assessment of site
Some ecological criteria for assessing the suitable site for culture of oysters are similar to mussels. Among of those are bottom substratum, water movement, and turbidity which are already discussed in section 3.2. The ecological requirements for oysters that need to be assessed in relation to site selection are following.
3.3.1.1 Salinity
Optimal salinity for the growth of oyster depends on the species. Crassostrea rivularis, C. iredalei and C. commercial are known to thrive in salinity ranging between 28 and 32 ppt whereas Saccostrea cucullata prefers salinity ranging between 30–34 ppt. S. lugubis can thrive in salinity ranging between 1–30 ppt, C. belcheri prefers salinity between 22–28 ppt. and S. echinata has a good growth in salinity between 16–30 ppt
3.3.1.2 Water depth
Water depth requires for the oyster culture operation depending on the culture practice implied. In inter-tidal zone where the water depth is less than 1.5 m (MTL), the oysters can grow on rocks, concrete slabs provided on the seabed. For the pole and stake method, water depth is deeper than 2.5m is suitable. If the water depth is deeper than 2.5m rafts, hanging and long-line method can be applied.
3.3.2 Potential site
The potential areas suitable for oyster culture under those system are Ketapang, Tangerang, Tarumajay in West Java; Demak, Jepara in Central Java; Kenjera, Pasuruan, Probolinggo, Kwanyar in East Java; Lombok, (Sepi bay and Blongas bay, Gambang bay, Batu Nampar), and Sumbawa (Sape bay, Lb. Pototono, Monta, Waha Wera, Sangor, Donggo, and Bolo) in West Nusatenggara, Kupang bay Timor, East Nusatenggara; and Maros, South Sulawesi. The Potential area is about 7 850 ha (Table 6).
There are three species of oyster in Indonesia waters suitable for culture of pearl. Among of them are gold-lip (Pinctada maxima), black-lip (P. margaritefera), and wing oyster (Pteria penguin).
3.4.1 Ecological criteria for assessment of potential site
Ecological criteria assessing potential site for pearl culture are salinity, substratum, water depth, current and source of seeds.
3.4.1.1 Salinity
The site should have a salinity ranging between 30 and 35 parts-per-thousand. The salinity should not fluctuate much during the year even in rainy season.
3.4.1.2 Substratum
Substratum of sea bottom should be coarse sand or rock substrate. This parameter is an indicator of good water exchange, low turbidity, and low rate of sedimentation.
3.4.1.3 Water depth
A site should have a water depth ranging from 20–25 m (MTL). This parameter is important for good quality of pearls produced due to continued effect of pressure, salinity, and temperature on color formation of the pearl.
3.4.1.4 Current
A site should have a current speed between 10 and 30 cm/sec to ensure an adequate food supply. Area with water current higher than 40 cm/sec should be avoided. Strong current is not only difficult in installation of culture facilities, difficult to work but also reducing feeding rate of the cultured organism. On contrary the site with slow current tends to associate with high rate of sedimentation, and high turbidity resulting in high mortality and higher chance of having disease infection.
3.4.1.5 Turbidity
The site should have clear oceanic water with transparency of at least 20 m. The site with suspended load higher than 400 mg/l is considered not suitable for pearl culture development. The area with high water turbidity tends to have high rate of fouling from organisms such as barnacles, tube worms, boring worms, boring bivalve, and sponge etc. These fouling organisms complete in food, induce parasites and diseases infection which cause high mortality rate of the cultured organism or poor quality of pearl.
3.4.1.6 Source of seed
The site should be in area within the vicinity of good natural ground of pearl oyster. This is not only ensure the suitability of site, but also to ensure the availability of seed supply for the operation.
3.4.1.7 Natural food
Pearl oyster is a filter feeder. It accepts a wide range plankton including single cell algae such as Conscinodicus, and Chaetoceros.
3.4.2 Potential sites for pearl culture development
Potential areas suitable for pearl culture are found in Tj. Putus, Teluk Lampung, Lampung; Pari island, Jakrta, Banyuwedang bay and Pagametan bay in Bali; Gili Poh, Lombok; and Bero, Sape bay Sumbawa in West Nusatenggara; Lokotai in Central Sulawesi; Aru island (Taberpane, Futujuring) in Southeast Maluku; Bacan in Pulau Niring North Maluku; Likuoang in North Sulawesi, Pababusa in Southeast Sulawesi; Bontang and Berau in East Kalimantan; Kabra Island, Sorong in Irian Jaya. The total estimated area is about 4 125 ha (Table 7).
