Feeding, growth, and fecundity of Capitella sp I in relation to sediment organic concentration

In marine soft-bottom benthic habitats, the disappearance of opportunistic species as succession proceeds following an enrichment or disturbance event is thought to be due to the exhaustion of a food resource. To further inve stigate this hypothesis, feeding rate, growth rate, and reproductive output (measured as embryo number and size) of the opportunistic deposit-feeding polychaete Capitella sp. I were measured in sediments with different protei n concentrations but the same protein source. Feeding rates progressively i ncreased as protein concentration increased over the range of 0.2 to 4.7 mg g(-1); thereafter, feeding rate was constant up to a sediment protein conc entration of 8.1 mg g(-1), the highest used in these experiments. This resp onse is not consistent with the predictions of optimal foraging theory, as applied to deposit feeders. Growth rate showed a similar pattern, progressi vely increasing then reaching a plateau at similar to 23 % d(-1) in sedimen ts with 4.6 to 4.7 mg protein g-l. Capitella sp. I showed decreased fecundi ty and longer generation times (embryo sizes were not significantly differe nt) in sediments with lower protein concentrations and did not reproduce in sediments containing <1 to 2 mg g(-1). These results support the hypothesi s that the disappearance of Capitella sp. I as succession proceeds is due t o decreased fitness in sediments with lower food concentrations and an inab ility to reproduce in sediments below a threshold protein concentration. Sy stematically documenting how variations in sediment protein concentration a ffect the acquisition (feeding rate) and utilization (growth rate, reproduc tive output) of food resources by benthic invertebrates with different life -history strategies will help to elucidate important factors influencing th e distribution of individuals and species in the benthos.