Long-term study of zooplankton in the estuarine system of Ribeira Bay, near a power plant (Rio de Janeiro, Brazil)

Abstract

The structure of the zooplankton community in an estuary adjacent to the Admiral Á lvaro Alberto Nuclear Power Plant at Angra dos Reis, state of Rio de Janeiro, Brazil was studied from 2001 through 2005. At that time, the power plant had been operating for 20 years. The results were compared with a previous study in 1991-1993. The zooplankton was sampled 4 times a year, in vertical hauls using a 150 lm net, at two fixed points near the plant's intake and discharge sites. Temperature, salinity, and chlorophyll a were measured. The water of Ribeira Bay is warm, with salinities typical of Coastal Water and more saline waters. Zooplankton density at the discharge site (Mean: 245,434 ind m -3 , SD: 335,358 ind m -3 ) was higher than that at the intake site (Mean: 84,634 ind m -3 , SD: 101,409 ind m -3 ). A total of 121 mesozooplankton taxa were recorded from 2001 to 2005. Copepoda constituted the most common taxon and comprised more than 57% of the total zooplankton, followed by cladocers and gastropod larvae. A seasonal zooplankton cycle was observed only during 2004; in other years, the plankton varied only between years. Overall mesozooplankton abundance at the discharge site was similar to levels reported from the inner zone of this estuary in 1991-1993. Surface temperature was the important factor structuring the zooplankton community at the discharge site. No effect on the mesozooplankton by passage through the condensers could be discerned, and no permanent negative influence on the plankton populations could be detected.