CONICET | Buscador de Institutos y Recursos Humanos

Surf zones of sandy beaches are poorly studied in comparison to estuarine an continental shelf waters, specifically because of the difficulties experienced in sampling in high-energy environments. The zooplankton of these areas, therefore, has received less attention than that in other coastal systems. The aim of this study was to investigate the seasonal patterns and tidal height effects (high tide/low tide) on the surf zooplankton community in a temperate southwestern Atlantic sandy beach. We also aimed to evaluate the influence of some environmental variables (water temperature, salinity, chlorophyll-a, suspended particulate matter and particulate organic carbon) on the community structure and to compare the surf community to nearby coastal zone (< to 50 m). Sampling was carried out from September 2009 to November 2010, with a monthly frequency during autumn-winter and bi-monthly during spring-summer. All samples were collected in a fixed station during high and low tide, using a conical net with a 300 µm mesh size. The net was hand-pulled parallel to the cost across 200 m, for 15-20 minutes. Surf waters hosted a very rich zooplanktonic community that were numerically dominated by crustaceans (30-99% of total abundance), especially two calanoid copepods: Acartia tonsa and Paracalanus parvus. The apparent low phytoplankton production detected in surf waters would be compensated by large quantities of detritus and suspended matter that could be an alternative food source for copepods that inhabit surf waters. Total abundances exhibited a strong seasonal variation, ranging from 2.42 (Spring 2009) to 11076.9 ind. m-3 (Autumn 2010). The tidal height was not a significant source of zooplankton variation, probably other factors are more influential at this short-term time scale. Surf waters were inhabited by a typical zooplanktonic community, coexisting both estuarine and neritic organisms. Most of the observed species were similar to those described for coastal waters, but others like A. tonsa were practically restricted to this particular zone. Water temperature, in combination with suspended particulate matter and chlorophyll-a, explained the observed temporal zooplankton pattern. Results obtained in this study highlight the importance of the surf waters of sandy beaches and will be useful for further studies and/or monitoring programs conducted in similar high-energy, turbulent, and turbid ecosystems.