Tidal and seasonal changes in the mesozooplankton community in a highly turbid and mixed estuary (Bahía Blanca, Argentina)

MARÍA C. MENÉNDEZ; M. SOFIA DUTTO; FLORENCIA BIANCALANA; MARÍA C. PICCOLO; MÓNICA S. HOFFMEYER

Pucón

Simposio; 5th International Zooplankton Production Symposium; 2011

The role of seasonal and semidiurnal tidal cycles on the mesozooplankton dynamics was investigated in the inner zone of the Bahía Blanca Estuary, Argentina. Hydrological data and mesozooplankton samples were obtained bimonthly from December 2004 to April 2006, during 14-h tidal cycles. All data concerning precipitations and winds were obtained from a meteorological station and water level was recorded with a tide gauge. The mesozooplankton community was represented by 33 taxa. The taxa richness was higher near the bottom, where the contribution of benthic forms was more relevant. The highest abundances were observed during summer (>5500 ind. m-3) and the lowest during winter (<70 ind. m-3). The mesozooplankton community was largely dominated by Acartia tonsa and Eurytemora americana. Due to their numerical importance, these copepods directed the tendency of the total mesozooplankton abundance. Multivariate analysis revealed significant seasonal differences in the mesozooplankton community structure, especially in terms of number of organisms. Seasonal differences in composition and abundance are well explained by the natural change of abiotic and biotic conditions, although temperature played a key role in structuring the mesozooplankton community. Short-term temporal variations were also attributed to semidiurnal tidal cycles. Zooplankton reached significantly higher abundances during the ebb tide, suggesting that local hydrological conditions are responsible for the spatial variations. The obtained results show how variable the mesozooplankton community structure can be over different time-scales. All this information may help to a better understanding of the zooplankton variability in the Bahía Blanca estuary and other temperate, turbid and mixed systems.