Functional response of a surface‐deposit feeder, Saccoglossus kowalewkii

The feeding behavior of a surface‐deposit‐feeding acorn worm (Saccoglossus kowalevskii) was examined with chlorophyll a (Chl a) and protein concentrations as measures of food quality, and a functional response curve was determined. The results suggest that S. kowalevskii is responding to either the microalgal and diatom populations in the available sediment or another component of its food source closely correlated with Chl a concentration. Egestion rate increased with increasing Chl a to a maximum at intermediate concentrations [3–12 µg Chl a (g sediment)−1], followed by a gradual decline in egestion rate as Chl a concentration continued to increase. Functional response data such as presented here are necessary for determining which components of the sedimentary milieu are nutritionally and behaviorally important to deposit feeders, for interpreting flow and sediment transport experiments, and for developing and testing feeding models.