Spatial and temporal variations of mesozooplankton in a shallow system (Bahía Blanca Estuary, Argentina)

MENÉNDEZ, M. C.; PÍCCOLO, M. C.; HOFFMEYER, M. S.; BIANCALANA, F.

Bahía Blanca

Congreso; ECSA 44; 2008

IADO

SPATIAL AND TEMPORAL VARIATION OF MESOZOOPLANKTON IN A SHALLOW SYSTEM (BAHIA BLANCA ESTUARY, ARGENTINA) Menéndez, M. C.*; M. C. Piccolo, M. S. Hoffmeyer and F. Biancalana Instituto Argentino de Oceanografía (IADO-CONICET). Camino La Carrindanga Km 7,5. Casilla de Correo Nº 804 B8000FWB, Bahía Blanca, Argentina. *E-mail: menendez@criba.edu.ar The present study reports on vertical and temporal (tidal and seasonal) variations of the mesozooplankton community in the inner zone of Bahía Blanca estuary. Zooplankton sampling and hydrological measurements (salinity, temperature, chlorophyll-a, phaeopigments, particulate organic matter and suspended particulate matter) were conducted bimonthly from December 2004 to April 2006, during 14-h tidal cycles. Thirty-four mesozooplankton taxa were recorded. Taxa richness was always higher near the bottom than at surface, where the contribution of benthic forms was less relevant. The highest abundances were observed during summer months (>3300 ind m-3), and the lowest during winter (<70 ind m-3). The mesozooplankton community was largely dominated by the calanoid copepods Acartia tonsa and Eurytemora americana. Due to their numerical importance, these copepods directed the tendency of the total mesozooplankton abundance. Different patterns were observed in the abundance variation along the tidal cycle. In general, values were higher during ebb tide at surface or at both depths. The seasonal differences in the mesozooplankton composition and abundance observed during this study are well explained by the natural change of abiotic and biotic conditions. On the other hand, tides played an important role in the mesozooplankton vertical distribution, being responsible for noticeable short-term variations in the community structure and hydrographic conditions. However, in some cases, meteorological events such as winds and rainfall, had a strong influence on this variability.