Holoplankton and meroplankton communities in surf zone waters of a temperate SW Atlantic sandy beach: Seasonal patterns

Abstract

Sandy beaches and their associated surf zones are the most common type of open shoreline, with significant ecological and socio-economic importance. In this study, we explored the seasonal fluctuations of the surf zone holo- and meroplankton com- munities to understand the underlying environmental variables driving the temporal dynamics of each community. We also defined a surf-zooplankton community on a temperate sandy beach (Monte Hermoso, Argentina) and related the organisms to those reported in a nearby estuary for a better understanding of the connection between adjacent coastal ecosystems. Holoplankton was very abundant (13.52– 11070.4 ind m−3 ) and showed a strong seasonality, mainly related to the specific pat- tern of the two most abundant species: Acartia tonsa (>autumn) and Paracalanus parvus (>winter). This community was affected by seasonal changes in water tem- perature and salinity and variations in the velocity of currents, which showed that hydrodynamic forces were more significant on a short-term time scale than seasonal ones. Meroplankton abundances (1.3–48.05 ind m −3 ) were significantly lower than those recorded for the holoplankton and were mainly dominated by Medusae and larvae of Bivalvia and Decapoda. This fraction also showed a clear seasonal pattern (>abundances in summer), primarily related to the seasonal changes in temperature. The abundances of the main surf-zooplanktonic taxa were high and constant, empha- sizing the importance of these waters as habitats for well-established communities rather than being used as a transient area. Consequently, we proposed a “specific” surf-zooplankton community for a temperate sandy beach, considering resident and non-resident taxa. Finally, the comparison of the surf and estuarine communities in- dicated a faunal relationship between seascapes, highlighting the ecological role of coastal waters in planktonic life.