Contribution of Unicellular Eukaryotes to the Diet of First-Feeding Capelin Larvae

The feeding success of first-feeding fish larvae is known to influence their survival, and, potentially recruitment. Despite growing evidence of the importance of unicellular eukaryotes (uE) in the diet of fish larvae, contemporary feeding ecology studies almost exclusively focus on crustacean taxa when quantifying preferred prey. Our study investigated the spatiotemporal variability of the uE contribution in the diet of first-feeding capelin. First-feeding capelin larvae and their potential eukaryotic and zooplankton prey (minimum size of 50µm) were sampled on a weekly basis in July-August 2014 in Trinity Bay, Newfoundland, Canada. The guts of a subsample of capelin larvae were dissected to visually describe prey ingested. We also identified prey using genetic markers (18S rDNA) to evaluate the contribution of cryptic microscopic soft-bodied prey to larval diet. Finally we assessed variability in diet composition as a function of spatiotemporal variation in prey availability. This research will provide important information on the role of microplankton organisms (20-200µm) in early larval trophodynamics and in processes driving larval survival and recruitment of this important forage species.