AME 35:65-78 (2004)  -  doi:10.3354/ame035065

ABSTRACT: Selection for ciliates in the presence of phytoplankton has been previously shown for some species of copepods. However, the factors determining preference for this heterotrophic prey and how crustacean zooplankton predation can affect the ciliate community are not yet fully understood. In this study, we investigated predation rates on phytoplankton and ciliates by the most abundant copepod and cladoceran species in a coastal area of the oligotrophic NW Mediterranean Sea monthly over an annual cycle. Three major results were apparent. Firstly, ciliates were important contributors to zooplankton diet, representing a median of 37 and 17% of the carbon intake, and 51 and 34% of the nitrogen intake for copepods and cladocerans, respectively. Secondly, ciliates were positively selected in most cases, this selection was species specific and apparently independent of phytoplankton concentration. And finally, in spite of the high clearance rates on ciliates, the impact of the crustacean community on the ciliate standing stock was low (median 2%), suggesting a bottom-up control of the ciliate community.

KEY WORDS: Copepods · Cladocerans · Ciliates · Food web · NW Mediterranean