Feeding by the planktonic calanoid copepod Acartia clausi Giesbrecht on natural suspended particulate matter of varying quantity and quality

Abstract

The defaecation rate of females of the calanoid copepod Acartia clausi Giesbrecht as a measure of the ingestion rate was measured in relation to quantity and quality of natural suspended particulate matter. In the April–September experiments, phytoplankton was the dominant component of suspended particulate matter and the ambient chlorophyll a concentration was high, ranging from l.11 to 23.91 μg·l −1. The defaecation rate became saturated below the ambient particle concentration and the weight-specific defaecation rate was rectilinearly fitted against particle concentration. In terms of chlorophyll a, the critical concentration for saturation of the weight-specific defaecation rate ranged from 0.616 to 1.710 μg·l −1. In the October–November experiments, the ambient chlorophyll a concentration ranged from 0.27 to 0.53 μg·l −1 and non-living particles became the dominant component. No critical concentration was observed and the slope of the line describing the relationship between particle concentration and weight-specific defaecation rate was greatly reduced in comparison with that obtained in the April–September experiments. The reduction of the slope may be due to the dominance of non-living particles.