Critically Endangered
Giant clam
Tridacna gigas
Giant clam is a bivalve in the family Cardiidae (order Cardiida) — Tridacna gigas, recorded as Critically Endangered.
Appearance
By day, the clam opens its shell and extends its mantle tissue so that the algae receive the sunlight they need to photosynthesise.
One of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans, they may weigh more than 200 kilograms (440 lb), measure as much as 120 cm (47 in) across, and have an average lifespan in the wild of more than 100 years.
Range and habitat
The giant clam lives on flat coral sand or broken coral and may be found at depths of as great as 20 m (66 ft). Its range covers the Indo-Pacific, but populations are diminishing quickly and the giant clam has become extinct in many areas where it was once common. The maxima clam has the largest geographical distribution among giant clam species. It may be found off high- or low-elevation islands, in lagoons or fringing reefs.
Pins are Wikidata “endemic to” fields. Orange dots, when present, are GBIF occurrence tiles — survey bias included.
Breeding
This flexibility in reproduction reduces the burden of finding a compatible mate, while simultaneously doubling the number of offspring produced. Since giant clams cannot move themselves, they adopt broadcast spawning, releasing sperm and eggs into the water.
A transmitter substance called spawning induced substance (SIS) helps synchronize the release of sperm and eggs to ensure fertilization.
In crisis
The species is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES) meaning international trade (among them in parts and derivatives) is regulated. T. Gigas has been reported as locally extinct in peninsular Malaysia, while T. Derasa and Hippopus porcellanus are restricted to Eastern Malaysia. Restocked individuals in the Philippines have successfully dispersed their own spawned larvae to at least several hundred meters away after only ten years.
Giant clam is Critically Endangered on this catalog because that is the IUCN category stored on Wikidata. Confirm the official criteria and any later count on iucnredlist.org.
Sources
Written for this catalog from the English Wikipedia article on Giant clam, Wikidata item Q751784. Family and order context is original field-guide writing about the group, not a copied assessment of this one species. Wikipedia text is CC BY-SA. Not an IUCN assessment. Counts, when quoted, can change — confirm them on the recovery programme and on iucnredlist.org.
