Giant clams

Giant clams represent an increasingly large proportion of the exports of live invertebrates destined as aquarium specimens. Although additional lighting is often required in order to maintain giant clams, they play an important role in removing nitrates, nitrites and ammonia from aquaria water, elements considered as

Blue starfish, Linckia laevigata

Blue starfish, Linckia laevigata

The most commonly imported sea star in the aquarium trade is Linckia laevigata. According to exporters' data within GMAD this species accounted for 3 per cent (32,509 pieces) of the total trade in invertebrates. Experienced hobbyists warn that they are very difficult to maintain in aquarium conditions79. Their poor survival rate in aquaria may be due to their dietary needs of organically enriched films (or detritus) that typically cover live rock77. They should therefore not be placed in a newly set up tank (less than six months), or one in which there is not enough live rock to explore. Furthermore, they are known to often refuse artificial aquarium food. As common predators of sea stars in captivity are dog-faced puffers (Arothron nigropunct-atus), these two species should not be allowed to coexist in an aquarium. Small parasitic snails (Thyca crystallina) are also known to prey on L. laevigata79.

The nine giant clams (tridacnids) common in trade

The nine giant clams (tridacnids) common in trade

□ Tridacna maxima: the rugose or small giant clam is the most wide-ranging of all giant clam species, being found from the east coast of Africa, through the Indian Ocean and across the Pacific to Polynesia and Pitcairn83. It is still relatively abundant throughout its range although its status in the Indian Ocean is poorly known. It has a distinct brightly coloured mantle (blue, green and brown), which makes it particularly attractive for the aquarium trade. GMAD data show a total of 15,172 specimens as exported from Viet Nam, Fiji, the Solomon Islands, Tonga, Vanuatu, the United States and unknown countries between 1991 and 2001 (importers' data) (or a total of 8,215 from Fiji and the Solomon Islands between 2000 and 2001 based on exporters' data).

□ T. squamosa: the fluted or scaly giant clam has a generally speckled mantle in blue, brown and green. Like T. maxima, it is fairly abundant throughout its range although little is known of its status in the Indian Ocean. GMAD data show a total of 6,711 T. squamosa as exported from Fiji, Indonesia, the Solomon Islands, Vanuatu, Viet Nam and unknown source countries between 1991 and 2001 (importers' data) (or a total of 2,339 from Fiji, Indonesia and the Solomon Islands between 1999 and 2001 based on exporters' data).

□ T. crocea: the crocus or boring giant clam, although smaller, is similar to T. maxima in that it has a brightly coloured mantle. It is assumed to be generally widespread throughout its distribution area, from the west coast of the Malaysian peninsula, the South China Sea, the Coral Sea, southern Japan to southern Australia, to Micronesia and east to Palau83. Like T. maxima it is a popular species in the aquarium trade. GMAD data show a total of 11,685 T. crocea as exported from the Solomon Islands, Vanuatu, Viet Nam and unknown source countries between 1991 and 2001 (importers' data) (or a total of 17,881 from Fiji, Indonesia and the Solomon Islands between 2000 and 2001 based on exporters' data).

□ T. gigas: is considered to be the true giant clam as it can reach dimensions of more than 1.4 m in shell length. The mantle is brown-green with blue or green spots. This species is particularly sought after for food. It has suffered extensive reductions throughout its range due to overexploitation and is extinct in Fiji, Guam, New Caledonia, most areas of the Philippines and the Northern Marianas. Population levels have been dangerously reduced in most of Japan, Taiwan, Tuvalu, the Federated States of Micronesia and Vanuatu. GMAD data show a total of 1,808 T.gigasas exported from the Solomon Islands, Vanuatu and unknown source countries between 1991 and 2000 (importers' data) (or a total of 149 from Palau, Indonesia and the Solomon Islands between

2000 and 2001 based on exporters' data).

□ T. derasa: the smooth or southern giant clam is the second largest species with its shell reaching lengths of up to 60 cm. Its mantle has elongate brown, green and blue patterns. It is known to be fairly abundant in Palau, northern Papua New Guinea, Australia, the Solomon Islands, New Caledonia, Fiji and Tonga. Although it has been reintroduced in a number of locations outside its natural range, wild stocks have only become established in Yap. GMAD data show a total of 24,960 T. derasa exported from the Solomon Islands, Vanuatu and unknown source countries between 1988 and

2001 (importers' data) (or a total of 8,937 from Fiji, Palau, Indonesia and the Solomon Islands between 2000 and 2001 based on exporters' data).

□ T. tevoroa: the deep water devil clam is a rare species that only lives at depths greater than 20 m in the northern Tonga Islands and eastern Fiji Islands. No data in GMAD.

□ T. rosewateri: is a newly described species similar to T. squamosa. It has a very restricted range, only occurring on the Saya de Malha Bank, Mauritius, in the Indian Ocean. No data in GMAD.

□ Hippopus hippopus: the bear paw, horses hoof or strawberry giant clam has a heavy and thick shell with a dull yellow-brown mantle. Its distributional range is similar to that of T. crocea but population numbers are lower and local extinctions have occurred. GMAD data show a total of 58 H. hippopus as exported from the Solomon Islands and unknown source countries between 1999 and 2000 (importers' data) (or a total of 551 from Palau and the Solomon Islands between 2000 and 2001 based on exporters' data).

□ H. porcellanus: the china clam, has a very limited range in the region of Indonesia, the Philippines and Palau. Its appearance is similar to that of H. hippopus. No data in GMAD.

80 81 82 Source: Wells , EUis , Raymakers et al and data from GMAD.

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