Seasonal and spatial variations in macrozooplankton quality as food for fish in a SW Atlantic Ocean gulf – the role of lipids and fatty acids

Abstract

Abstract Macrozooplankton nutritional quality is essential information to understand the energy and matter fluxes in marine food webs and their value as prey for fish. Lipid-derived energy density (ED; kJ g− 1) and polyunsaturated fatty acids content (PUFA; µg mg− 1 total lipids) of Euphausia spp. and Munida gregaria were studied along a seasonal cycle (September 2016- November 2016-January 2017), and related with their size and the spatial environmental variability (satellite chlorophyll-a (chl-a) concentration and frontal structures) of the San Jorge Gulf (45°–47°S, 65°30′-67°30ʹW; Argentinean Continental Shelf, SW Atlantic Ocean). This gulf is a key nursery and feeding ground for many commercially and ecologically relevant fish species (e.g. Merluccius hubbsi). While ED was similar in both taxa, PUFA content was significantly higher in Euphausia spp. Quality indices showed seasonal and spatial variations, while the effect of size was non-significant. For both taxa, minimum ED values occurred in winter, while for Euphausia spp. the maximum was observed in summer and for M. gregaria in spring. M. gregaria ED tightly coupled with the seasonal chl-a cycle. PUFA content also varied seasonally, with an opposite trend. Spatially, higher ED and PUFA values occurred in locations with elevated chl-a concentrations. This was mostly manifested in M. gregaria indices and less evident in Euphausia spp. Results provide novel and baseline information of zooplankton, which can be applied in food web models to understand the trophic dynamics of many fish and top predators species in the Argentinean Shelf in the current global change context.