EFFECTS OF DIET AND STARVATION ON FEEDING IN THE SCAVENGING NEOGASTROPOD BULLIA-DIGITALIS (DILLWYN)

Effects of body size, diet and starvation on feeding time, feeding cyc le, feeding rate, absorption efficiency and growth potential in Bullia digitalis have been studied. Fed whelks were starved for 1, 4 or 8 wk before presentation of a poor-quality diet, jellyfish, or a rich one, the tunicate Pyura. Feeding lime had a negative relationship to body size, ranging from 1 to 3 h for small whelks to between 0.6 to 1 h for adults. Diet affected feeding time only at the 1 wk starvation level when jellyfish was eaten in a shorter time. After prolonged starvation , it took a longer time to ingest either diet, indicating a detrimenta l effect on the physical process of feeding. Predicting the length of feeding cycles from body size was undependable since postfeeding durat ion became erratic after a long starvation period. Jellyfish feeding c ycles shortened with protracted starvation unlike Pyura cycles, which showed no clear relationship with starvation interval. More Pyura was eaten than jellyfish as mg dry wt . meal(-1) but as wet wt, 2 to 3 tim es more jellyfish was consumed. Starvation had no effect on meal size. Feeding rate (mg dry . d(-1)) was correlated positively with body siz e, while the influence of diet was marginal. Starvation had no effect on rates of jellyfish consumption whereas Pyura rates peaked after 1 w k but declined significantly with longer food deprivation. Absorption efficiencies were higher for Pyura than for jellyfish but both decline d with increasing starvation. In contrast to Pyura, a diet of jellyfis h resulted in negative growth potential for all whelk sizes and it is concluded that diet is the chief factor determining growth, rather tha n differences in meal size or feeding rates. Application of optimal fo raging theory to B. digitalis is discussed.