Vertical distribution and composition of mesozooplankton in the Bahía Blanca Estuary

MARÍA C. MENÉNDEZ; MÓNICA S. HOFFMEYER; MARÍA C. PICCOLO; FLORENCIA BIANCALANA; MELISA D. FERNÁNDEZ SEVERINI

João Pessoa, Brasil

Simposio; IV Plankton Symposium y I Congresso Brasileiro de Plâncton; 2007

Universidad Federal de Paraíba

Composition, abundance and tide-induced variability in the mesozooplankton community were analyzed during 2 tidal series of 14 hours (April and August, 2005) at the inner zone of the Bahía Blanca Estuary. Zooplankton samples were taken every 3 hours in two depths (close to the surface and bottom). Submersibles pumps discharging into 200 µm mesh nets were used. Salinity and temperature vertical profiles were obtained with a multiparameter sonde. Nineteen mesozooplankton taxa were found in both months. In general, taxa richness at bottom was higher than at surface being important the contribution of benthic forms. Total mesozooplankton abundances were higher on August (315 – 3109.38 ind m-3) than on April (68.13 - 3471.24 ind m-3). On April, the highest total abundance was found during ebb at surface and the calanoid copepod Acartia tonsa was by far the most important taxa. Tidal phases and depth influenced significantly the abundance of this specie (p<0.05). On August, the highest values of total abundance were registered during ebb (surface and bottom) and flood (bottom). Eurytemora americana dominated the mesozooplankton community following by A. tonsa, harpacticoid copepods, Cirripedia nauplii and Polychaeta larvae which were played a minor role. For this specie not significant depth and tide differences were found. The differences observed among tide states on April would indicate that the vertical distribution could be responded to the volume of water induced by tides. However, different factors could influence the distribution of organism on August.