-19- lable | 5 BS Lo- nd rary tsotopes. declined to a a maximum of 10 d/m/g four days post-Nectar, and level of 3,000 d/m/g at 305 days and 537 days (Fig. 1). a Gut with content The hermit crab gut with its content was generally more vari- ronlly Levels of activity were 8,500 d/m/g pre-Nectar, reached able than liver in levels of activity, first month post-Nectar. particularly during the This difference is to be expected since Vity digested food would have variable amounts of surface contamination te and not all crabs would feed on the same thing at any one time. Initially, following the Nectar test, the gut had the: highest level of activity of all tissues (5 x 10° d/m/g). 1é8 The activity in the gut also had the shortest ecological half life of all tissues during the first 100 days post-Nectar. By 100 days, the levels of activity in gut and liver approached each other and their ecological half lives were about the same, although the gut remains so variable from collection to collection that only an approximation can be made. The activity in the carapace by 100 days was higher than that in the gut even though the latter had the highest initial activity. This variation is, of course, due to the different rates of decline, which reflect selection of the longlived isotope gr70 by the carapace. No chemical analyses of gut samples were made. Gill The rate of decline of activity of the gill of the crab tis more rapid than the rateof decay of mixed fission produds during the first 10 to 20 days post-Nectar, but thereafter approximates pa”