While snorkeling we swam over giant clams that were well over two feet (0.6 meters) in length! These clams gather some of their food by filtering ocean water through an internal pair of gills, but the majority of their food comes from a symbiotic relationship the clam has with algae. The algae (called zooxanthelle) are protected within the clam’s fleshy mantle and they use the sun’s energy to produce sugars, as well as some amino and fatty acids. Some of these nutrients are released directly into the bloodstream of the clam. The symbiotic algae give giant clams their attractive colours.