Effects of food quality on the functional ingestion response of the copepod Acartia tonsa

Abstract

[Effects of food quality on the functional ingestion response of the copepod Acartia tonsa were determined using 3 algal species 6 to 12 μm in diameter (dinoflagellate Amphidinium carteri, coccolithophorid Hymenomonas carterae, senescent and actively growing diatom Thalassiosira weissflogii), over a wide range of concentrations. The algal cells were characterized by their contents of carbon, nitrogen, protein, carbohydrate, lipid and chlorophyll a, and by dry weight. A. tonsa ingestion rates increased to an asymptote and were fit to the Ivlev model without a feeding threshold at low algal concentrations. Maximum ingestion rates of algal cells were inversely proportional to their protein, nitrogen, and carbon content. Maximum ingestion rates of protein and nitrogen increased with increasing cell content of these variables. In contrast, maximum ingestion rates of algal carbon were generally constant with increasing cellular carbon content. The effects of cellular carbohydrate, lipid, and chlorophyll a content on maximum ingestion rates were variable. The rate at which the ingestion of phytoplankton cells approached the maximum ingestion rate increased with greater protein and nitrogen content. Our results suggest that cellular protein and nitrogen content (or factors related to them) are important in regulating A. tonsa ingestion rates.]