area presented by the masses of branching corals and their associated flora and fauna must have removed all adsorbable radionuclides not already removed from the water by the plankton soon after fallout. The land organisms contain primarily the long-lived fission products 137¢s and 99sr (Welander, 1967; Welander et al., 1967; Smith and Moore, 1971). As expected, these radionuclides are found associated with those tissues or organs which contain potassium and calcium, respectively, since cesium and potassium behave similarly in metabolism, as do strontium and calcium. We determined the !37’Cs content of tissues of rats collected at Bikini in 1969 and 1970, and the range of 13’cs concentrations in pCi/g dry weight was 340 to 827 in muscle tissue; values for muscle, lung, liver and bone are given in Table 7. The coconut crabs which are terrestrial, except during their larval stages, contain mostly !37cg from among the gamma-emitting radionuclides (Table 8) and are concentrators of 29Sr (Table 9). The spiny lobster, a strictly marine crustacean, contains no detectable 137cg or 99Sr and only small amounts of 60cq (Table 10). There are quantitative and qualitative differences in the radionuclide content of organisms associated with feeding habit. The goatfish, a bottom-feeding carnivore, contains more ®Co and 29’Bi than the convict surgeonfish, a grazing herbivore, or the mullet, a detritus feeder (Tables 11, 12 and 13). Higher order carnivores, the grouper and ulua, also contain more ©%Co (Table 14) than the convict surgeonfish; however, the differences may be associated with age as well as with feeding habit. The smaller, and presumably younger, reef fish of a species contain less 2°Sr than the larger fish of the same species (Table 15). Presumably, the 2[Sr is being accumulated throughout the life of the fish and a steady state has not been reached. Another example of increasing concentration of a radionuclide probably associated with age is the concentration of ®9Co in the kidney of the giant clams Tridacna sp. and Hippopus hippopus (Table 16). By far the highest levels of 60co, as much as 4,000 pCi/g dry, in any organism at Bikini Atoll are in the kidney of these clams. Obviously, there must be an accumulation of ©°Co in the kidney, and the longer the clam lives in an environment where ©°Co is available, the more 68¢o it accumulates in. the kidney, if 69Co has a long biological half-life. This is not a con- centration through the food web, since the clams are filter feeders. 10 ee In addition, the marine organism may absorb radionuclides directly from the water, or radionuclides may be adsorbed on the surface of the organism. Although adsorption is an important means of contamination of organisms by fresh fallout, it is probably no longer important at Bikini, where the last significant fallout occurred in 1958. The astronomically large surface