Feeding dynamics of larval Pacific herring (Clupea pallasi) on natural prey assemblages: The importance of protists

Abstract

The role of protists in the diet of larval Pacific herring (Clupea pallasi) was examined in laboratory incubations conducted in May and June 2008 using a natural assemblage of microplankton (10-200μm). Available prey consisted of protists (diatoms, dinoflagellates, aloricate ciliates, and loricate ciliates) and metazoans (trochophores, bivalve larvae, rotifers, copepod nauplii, and gastropod larvae). We used a prey enumeration technique that included soft-bodied heterotrophic protists (aloricate ciliates and athecate dinoflagellates) in the diet. We observed significant consumption of aloricate ciliates, loricate ciliates, bivalve larvae, dinoflagellates, and other available prey 73-200μm. Clearance rates (mLlarva -1h -1) and an electivity index E * were used as measures of prey selectivity. The herring larvae showed strong selection for bivalve larvae and 73-200μm available prey; however, across all valid experiments, protist prey were selected for at rates comparable to metazoans. Ingestion rates (μgClarva -1h -1) showed that the majority of larval carbon intake was from diatoms and aloricate ciliates. The results of this study illustrate that there is a direct trophic link between larval herring and the microbial food web, and protists may make up a substantial portion of the larval fish diet, possibly alleviating food limitation. © 2012 Blackwell Publishing Ltd.