Beautiful but dumb: Giant clams

The National Zoo has welcomed several new additions to its Invertebrate Exhibit. Ten giant clams arrived in February from the Shedd Aquarium in Chicago and after six weeks in quarantine are now on exhibit in the coral tank. These giant clams are of the Tridacna crocea species, the smallest of the giant clam species, and can grow up to nine inches. The clams currently range in size from 3 to 6 inches and are estimated to be between 3 and 4 years old.

Native to the warm waters of Indo-West Pacific coral reefs, T. crocea come in a variety of patterns and color mixtures. They have multicolored designs, and their mantle is usually decorated with iridescent blue, yellow or green blotches, spots or lines.

“The giant clam is an iconic South Pacific reef invertebrate and this particular species is absolutely beautiful,” said Mike Henley, an animal keeper in the Invertebrate Exhibit. “To some people, the giant clams might not be the most exciting invertebrates, but because they are so content to stay in one place, they make great photo subjects and learning tools.”

Tridacna crocea

Care of these clams involves clean salt water, strong lighting and plenty of “flow,” or water movement. Zoo staff use filters to clean the water, water pumps to simulate ocean currents and waves, and various combinations of high-intensity lights to provide as much of the sun’s wavelengths as they can.

Although the giant clam is classified as of least concern by the International Union for Conservation of Nature, it faces many population threats and is close to being considered vulnerable, according to Henley. Fishers hunt these clams for their meat and shells, and because they are so colorful, they are frequently collected for the pet trade. Giant clams are also threatened by the increasing destruction of their coral-reef habitats.

“If we lose coral reefs, this is one of the beautiful denizens we could lose,” said Henley. “Our hope with the giant clams is that visitors will learn about the amount of biodiversity that coral reefs contain and appreciate their beauty. Anything we can do to demonstrate that is very exciting.”

The Zoo’s Invertebrate Exhibit is home to dozens of invertebrate species, including sea stars, spiny lobsters, giant African millipedes, tarantulas and a giant Pacific octopus. View the Zoo’s Octopus Cam or check out some of the Zoo’s special demonstrations for an up-close-and-personal look at the invertebrates. For more information about giant clams, watch the Zoo’s giant clam video.

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