Potential zooplankton preys (Copepoda and Appendicularia) for Engraulis anchoita in relation to early larval and spawning distributions in the Patagonian frontal system (SW Atlantic Ocean)

We investigated the spatial distribution of the abundance, biomass and size of zooplankton (nauplii, calanoids, cyclopoids and appendicularians) in relation to the distribution of first-feeding larvae and eggs of Engraulis anchoita across the frontal system of Peninsula Valdes. Twelve samples of zooplankton and ichthyoplankton were taken with small Bongo (67 mu m) and Pairovet (200 mu m) nets during the spring of 2004 along two transects. The total abundance of zooplankton and the chlorophyll a concentration were higher in homogeneous waters, while total biomasses were higher in stratified waters. Temperature was negatively correlated with biological variables and was the main factor affecting the zooplankton distribution. In both transects, abundance peaks of first-feeding larvae were detected at coastal stations along with the smallest fraction of zooplankton (<500 mu m), while the largest fraction was dominant at the external stations, coinciding with the highest egg abundance. The physical structure of this front generates different levels of food availability for first-feeding larvae. Calanoids (southern transect) and cyclopoids (northern transect) are predominant followed by nauplii and appendicularians. The biomass of zooplankton preys contributes to the carbon transfer to the upper trophic levels and is probably important for the survival and growth of anchovy larvae in this frontal system.