Friday Fellow: Giant Clam

by Piter Kehoma Boll

One more giant is coming to our team, again from the sea, but this time from the bilvavian molluscs. Its name is Tridachna gigas, commonly known as the giant clam.

Found in shallow coral reefs of the Indian and Pacific Oceans, especially around Indonesia, the giant clam can grow up to about 1.2 m, weigh more than 200 kg and live more than 100 years, being the largest living bivalve mollusk.


The giant clam is seen in coral reefs as a giant lump of molluscan material. Watch out, Dory! Photo by flickr user incidencematrix.*

One interesting aspect of the giant clam and its close relatives is that they live in a symbiotic association with some dinoflagellates (the so-called zoxanthellae, also found in corals), having even a special structure, the zooxanthellal tubular system, to house them. During the day, the giant clam exposes its mantle to the light in order to allow the algae to photosynthesize. Part of the nutrients produced by the algae are given to the clam. This allows the giant clam to survive in otherwise nutrient-poor environments, where its standard bivalvian feeding stile, by filtering partiles from the water, would not be enought to allow it to grow properly.


A half-closed shell. Photo by The Central Intelligence Agency.

The giant clam is used as food in many Asian countries, especially Japan and countries from Southeast Asia and Pacific Islands. Additionally, the giant shell is considered a valuable decorative item and can be sold for large amounts of money. Due to such exploitations, the giant clam populations are starting to decline and the species is considered vulnerable by the IUCN.


An empty shell exposed in Aquarium Finisterrae, Galicia, Spain. Photo by Wikimedia user Drow male.**

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Klumpp, D. W., Bayne, B. L., & Hawkins, A. J. S. (1992). Nutrition of the giant clam Tridacna gigas (L.) I. Contribution of filter feeding and photosynthates to respiration and growth. Journal of Experimental Marine Biology and Ecology, 155(1), 105–122. doi:10.1016/0022-0981(92)90030-e

Norton, J. H., Shepherd, M. A., Long, H. M., & Fitt, W. K. (1992). The Zooxanthellal Tubular System in the Giant Clam. The Biological Bulletin, 183(3), 503–506. doi:10.2307/1542028

Wells, S. (1996). Tridacna gigas. The IUCN Red List of Threatened Species doi:10.2305/IUCN.UK.1996.RLTS.T22137A9362283.en. Access on September 1, 2018.

Wikipedia. Giant clam. Available at < >. Access on September 1, 2018.

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*Creative Commons License
This work is licensed under a Creative Commons Attribution 2.0 Generic License.

**Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.


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Filed under Friday Fellow, mollusks

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