Growth Rate of Giant Clam Tridacna gigas at Bikini Atoll as Revealed by Radioautography.

At Bikini Atoll, radioactivity from strontium-90 deposited in the growing shell of a giant clam, presumably during the testing of nuclear weapons in 1956 and 1958, produced unmistakable lines on radioautographs made from transverse sections of the shell. The regular banding seen in the sections is interpreted as annular in nature. One annulus precedes the 1956 layer of radioactivity, two intervene in 1958, and six follow to the time of collection, so that this clam (length, 52 centimeters) was in its 9th year of life.