Variable Ingestion Rate and Its Role in Optimal Foraging Behavior of Marine Deposit Feeders

Tests of optimal foraging theory have focused generally on food item selection by mobile, high—trophic—level predators. Deposit—feeding invertebrates are aquatic organisms with limited mobility and hence limited ability to forage actively for food—rich patches. In addition, there is little evidence for a major role of behaviorally mediated food item choice in these animals, and growing evidence of mechanical limitations in food particle choice. Given such limited food—selection ability, varying ingestion rate in response to changes in food value is likely to be an important animal response affecting feeding energetics. A previously developed optimal foraging model predicted that ingestion rate and food value should covary positively in order to maximize net time rate of energy gain. To test this general prediction, we fed three species of deposit—feeding polychaetes artificial sediments which varied only in protein content (food value); other physical and chemical properties which might affect ingestion rate were kept constant. In support of the model, ingestion rates increased as protein levels increased.