Soft-bodied zooplankton predators and competitors of larval herring (Clupea harengus pallasi) at herring spawning grounds in British Columbia
Canadian Journal of Fisheries and Aquatic Sciences 473: 505-515
The soft-bodied zooplankton predators and the microzooplankton foods of herring larvae were collected at 28 herring spawning grounds in British Columbia Canada in April 1984, when herring larvae (Clupea harengus pallasi) hatched. The same predator species were found throughout coastal B.C., but total densities varied over three orders of magnitude. Barkley Sound had the highest densities, and bays in northern B.C. and the Strait of Georgia had higher densities that open shorelines in both regions. Eight of 18 species of soft-bodied predators contained herring larvae. The hydromedusan Aequorea victoria was the most important predator, and consumed 0.4% of the herring larvae.cntdot.d-1 in Fanny Bay, and 12.5, 3.9, and 0%.cntdot.d-1 over three consecutive days in Kulleet Bay as larval densities decreased. Herring larvae ate copepod nauplii (84.4%) and other microzooplankton. Densities of these prey varied between 0.8 and 37.cntdot.L-1 among 21 locations sampled. Only three species of hydromedusae showed extensive dietary overlap (90-100%) with larval herring. Soft-bodied predators consumed < 1%.cntdot.d-1 of the microzooplankton in 17 locations, and could have affected densities in only one of the 21 locations. The ratios of microzooplankton to predator densities varied over 1000-fold, suggesting great differences in the chances for herring larval survival among various locations.