Contribution of aloricate ciliates to the diet of Acartia clausi and Centropages hamatus in coastal waters

Abstract

Clearance rates on natural assemblages of aloricate ciliates were determined for Acartia c l a u s ~ and Centropages hamatusm coastal waters of the Kattegat, the Skagerrak and the Baltic. Ciliate concentrations ranged from 0 06 to 2.9 pgC 1-' equal to 0.4 to 2.9 % of phytoplankton carbon. Clearance rates for A. clausi ranged from 7.9 to 15.0 m1 pgdw-' d-l (27.7 to 52.5 m1 female-' d-l) and for C. hamatus from 3.8 to 14.7 m1 p,gdw-' d-' (32.3 to 125.0 m1 female-' d-l). Clearance increased with ciliate size for both species, reaching a plateau for c~liates > 25 Ci m ESD for A clausi but not for C. hamatus. The size-dependent clearance rates were similar to previously reported rates on phytoplankton and no sign of size-independent preference for ciliates was observed. Copepod ingestion of cihate carbon was always < 10 % and generally < 1 % of total carbon ingestion calculated from egg production measure