The role of the seasonal and semi-diurnal tidal cycle on mesozooplankton variability in a shallow mixed estuary (Bahía Blanca, Argentina)

Abstract

The role of the seasonal and semi-diurnal tidal cycle on mesozooplankton dynamics was investigated in the inner zone of the Bahía Blanca Estuary (BBE), Argentina. Hydrological data and mesozooplankton samples were obtained bimonthly from December 2004 to April 2006, during 14 h tidal cycles. The mesozooplankton community was represented by 33 taxa. Taxa richness was greater near the bottom, where the contribution of benthic forms was notable. Abundances were greatest during summer (>5500 ind. m -3) and lowest during winter (<70 ind. m -3). The mesozooplankton community was dominated by Acartia tonsa and Eurytemora americana. Multivariate analyses revealed significant seasonal differences in community structure, especially in terms of density. Seasonal differences in community structure are well explained by the natural change of abiotic and biotic conditions, but temperature played a key role in structuring the mesozooplankton community. The zooplankton was significantly more abundant during the ebb, suggesting that local hydrological conditions are responsible for the spatial variations. The results demonstrate how variable the mesozooplankton community structure can be over different time-scales and provide a better understanding of zooplankton variability in the BBE and other temperate, turbid, mixed systems.