Tridacna derasa, or the smooth giant clam, is the second largest giant clam species with a maximum size of around 24 inches. The geographic range of T. derasa primarily encompasses the Coral Triangle region, although it extends east to Tonga and as far west as the Cocos (Keeling) Islands in the eastern Indian Ocean.
T. derasa preferentially inhabits clear offshore waters distant from areas of significant freshwater run-off and seems to favor oceanic environments (i.e., small islands and atolls) more than fringing reefs adjacent to large island masses.
T. derasa has a heavy, plain-colored shell and can be distinguished from other species by the shallow folds of its shell. The mantle is often characterized by elongate patterns of brilliant greens and blues.
Decades of intense, unregulated harvest has driven T. derasa to very low abundance throughout much of its range. Past and ongoing harvest for meat and shells is the primary threat to this and other giant clam species.
| Kingdom | Animalia | Phylum | Mollusca | Class | Bivalvia | Order | Cardiida | Family | Cardiidae | Genus | Tridacna | Species | derasa |
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A grant project in Guam is setting up giant clam aquaculture in two southern villages, Inalåhan and Malesso. Giant clams are a culturally important species in Guam, where they’re also regulated due to overharvesting. Credit: David Burdick
Fifteen of the 83 species included in the Pacific Islands vulnerability assessment. From left to right: Acanthurus achilles, Caranx melampygus, Tripneustes gratilla, Acanthurus triostegus, Scarus rubroviolaceus, Cephalopholis argus, Octopus cyanea, Lutjanus kasmira, Panulirus penicillatus, Triaenodon obesus, Selar crumenophthalmus, Ctenochaetus strigosus, Naso unicornis, Zebrasoma flavescens, Tridacna maxima. Photo credit: Bruce Mundy.