Spatial gradients of spring zooplankton assemblages at the open ocean sub-Antarctic Namuncurá Marine Protected Area/Burdwood Bank, SW Atlantic Ocean

The sub-Antarctic Namuncurá Marine Protected Area at Burdwood Bank (NMPA/BB) is an area of favorable conditions for the development of planktonic organisms and the sustenance of numerous species of ecological importance. The current study aimed to evaluate the spatial distribution of the abundance, biomass, community structure, and functional diversity of the mesozooplankton from the NMPA/BB during spring 2014. We also assessed the potential of zooplankton as prey for upper trophic levels, in particular the larvae of the Fuegian sprat (Sprattus fuegensis), a key species in the food web of the NMPA/BB. A total of 26 zooplankton taxa were identified. Nauplii and copepods evidenced the highest abundances, with the latter representing the dominant group in terms of biomass. Copepods showed a strong eastward gradient in their abundance, biomass, and diversity. This spatial structure in the community composition seems to be modulated by a west-to-east decreasing trend in the size of available preys, with nano- and picoplankton playing a major role in the eastern part of the NMPA/BB. Such pattern would be, in turn, a consequence of productivity gradients along hydrographic features. The high abundance of nauplii and copepods suggests that spring is an appropriate time for their reproduction and, given their size structure, they represent an adequate food source for Fuegian sprat larvae. This would be enhanced by anticyclonic cells present in the NMPA/BB, which can gather and retain sprat larvae along with their zooplanktonic preys. The results of our study, which is the first comprehensive approach addressing the zooplanktonic indicators of the NMPA/BB, serve as a baseline for future ecosystem-based policies aiming to manage and protect the natural marine resources sheltered here.