Vertical distribution and composition of mesozooplankton in Bahía Blanca estuary (Argentina)

MENÉNDEZ MARÍA CLARA; HOFFMEYER MÓNICA SUSANA; PICCOLO MARÍA CINTIA; BIANCALANA FLORENCIA; FERNÁNDEZ SEVERINI MELISA DAIANA

João Pessoa, Paraiba, Brasil

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

Universidad Federal de Paraiba

Composition, abundance and tide-induced variability in the mesozooplankton community of Bahía Blanca Estuary were analyzed at the inner zone of this area during 2 tidal series of 14 hours each (April and August, 2005). Zooplankton samples were collected at two depths (close to the surface and bottom) every 3 hours. Submersible pumps discharging water into 200 µm mesh nets were used. Salinity and temperature vertical profiles were obtained with a multiparameter probe. Nineteen mesozooplankton taxa were found during both months. In general, taxa richness was higher at the bottom than at surface where the contribution of benthic forms was important. Total  mesozooplankton abundances were higher in August (315-3109.38 ind.m-3) than in April (68.13-3471.24 ind.m-3). In April, highest total abundance was found at surface during ebb and the calanoid copepod Acartia tonsa was the most important taxa. Tidal phases and depths influenced significantly on its abundance (p<0.05). In August, highest total abundance values were registered during ebb (surface and bottom) and flood (bottom). Eurytemora americana was the most abundant species and was followed by A. tonsa, harpacticoid copepods, Cirripedia nauplii and Polychaeta larvae, all of which had no significant contribution to total abundance. No significant depth and tide abundance differences were found for E. americana. The differences observed among tide states in April may indicate that the vertical distribution of A. tonsa responds to the tide-induced water volume. However, factors other than tide seem to have influenced the distribution of E. americana in August.