The Devil clam (formerly known as Tridacna tevoroa) is a marine bivalve (having two shells joined at a hinge) and is so named because of its appearance with contrasting dark and bright colours.

The Devil clam is different from other clams in that the mantle does not overhang the edge of the shell as in other clam. . They are one of the largest clams in the world and published documents have recorded Devil clam shells at a maximum of 50 cm in length.

Distribution

This clam has been recorded mainly in the oceanic barrier reefs of Tonga and eastern Lau group of Fiji. A website on the internet suggests that Devil clams have also been found off the outer reefs of the Great Barrier Reef in Australia. The map points out the general eastern Lau area.

TRIDACNA MBALAVUANA map

Habitat Ecology and Behaviour

The habitat of the Devil clam is quite unusual for a clam. It is usually found in the clear oceanic water of barrier reefs, at a maximum of depth of 33 m. Other clams, other than T. derasa, are only found at a maximum depth of 10 m. In less clear water, the Devil clams are found at shallower depths. There is some documentation on Giant clams, the group to which the Devil clams and T. derasa belong. Some ecological information is available on the World Wide Web; and experiments on the culture and translocations of Giant clams for the marine aquarium trade have been conducted in Tonga.

Studies on the Devil clam have shown that they this incredible ability to live at such great depths because of its ability to increase its photosynthetic efficiency at great depths, while being dependent on the symbiotic zooxanthellae which occur on their exposed mantle. Like other clams and bivalves, Devil clams are filter feeders, and have particularly been able to obtain nutrients at great depths and low light intensity. Devil clams have morphologically adapted to life in deep sea and low light intensity (which the zooxanthellae would need for photosynthesis).

Threats

Devil clams are naturally rare. Over-harvesting for consumption and for the marine aquarium trade because of their role as potential biofilters in aquarium tanks are possible threats to this species.

Conservation Status

This species is protected under Appendix I of CITES and is listed as Vulnerable in the IUCN Redlist of Threatened Species. The IUCN records show that the available information on the species is outdated, and will need to be reviewed. Marine biologists of the University of the South Pacific in Fiji have commented on the rarity of the species in the wild highlighting the need to conduct further research and conserve this Giant clam.