The Solar Powered Clam
 

Summary

• Giant calms filter feed like other clams
• They also get food from symbiotic algae
• This extra food allows these clams to grow to a massive size
• Giant calms are rare in many areas because they are overfished

Not your average clam

Giant clams (Tridacna species) start life like any other clam, as tiny larvae floating in the water column.  They settle and begin to filter-feed just like other clams.  Unlike most clams, however, Tridacna also get food from the sun.

Regular clams are small, but giant clams can grow up to 4 feet (1.2m) across, and weigh in at 500 pounds (225 kg).  They can grow this big because they are not limited to the food they filter from the water.  Giant clams have access to a virtually inexhaustible supply of food - the sun. This extra food enables these clams to grow much larger than regular filter feeding clams.

Like reef building coral, giant clams have developed a symbiotic relationship with zooxanthellae algae. Giant clams provide zooxanthellae with a safe home. In return, these single-celled algae photosynthesize food from the sun and share it with the giant clam. The zooxanthellae algae living in the giant clam comes from the same genus (Symbiodinium) as coral symbionts.

Big and beautiful...

Giant clams are spectacular with their large size and brightly colored mantles. These color patterns, unique to each clam, are created by zooxanthellae living in the tissues of the clam.

...but big and tasty

Giant clams are becoming rare on some reefs. They are large, tasty, brilliantly colored, and unable to run away. Giant clams are a traditional food source on many tropical islands, but increased harvesting is reducing clam numbers to the point where many populations may be unable to repopulate reefs naturally.  One solution is giant clam farms, which may enable local populations to increase enough to help bring back wild clam numbers.

References

McCarron, S. (2007, May 29). Village Ecology and economy of giant clams in Fiji. Center for Applied Biodiversity Science (CABS). PDF retrieved 8 August 2008 from http://science.conservation.org/portal/server.pt/gateway/PTARGS_0_124186_105801_0_0_18/Giant_Clam_proposal.pdf

National Geographic. (2007, June 27). Giant Clam. National Geographic. Retrieved 8 August 2008 from http://animals.nationalgeographic.com/animals/invertebrates/giant-clam.html

Wikipedia. (2008, August).Giant Clam. Wikipedia. Retrieved 8 August 2008 from http://en.wikipedia.org/wiki/Giant_clam

Yellowlees, D. et al. (2008, February 27). Metabolic interactions between algal symbionts and invertebrate hosts. Plant, cell and environment 31(5): 679-694. Retrieved 11 August 2008 from http://www3.interscience.wiley.com/cgi-bin/fulltext/119398747/HTMLSTART