Mesozooplankton and water masses in the guanabara bay: Ten years monitoring

Abstract

This work was made from the Long Term Ecological Research program-LTER /CNPq, on the mesozooplankton of the Guanabara Bay. Guanabara Bay is one of the most eutrophicated and polluted ecosystem in the world. Its hydrological structure is singular due to a double stratification of its water column: thermal, due to an input of cold water on the bottom from the South Atlantic Central Water, and haline, with low salinity at the surface due to continental flow. In spite of high primary biomass availability, we observed a decay of mesozooplankton community at inner areas of the bay. The main objective of this study is to analyze composition and abundance of the main mesozooplanktonic organisms throughout a ten years monitoring. We hypothesized that there is an effect of hydrological changes on mesozooplankton community due to climate change. Sampling was made 2-3 times per month during 10 years, with a plankton net (mesh size 200 µm) hauled vertically at a fixed station. The mesozooplankton was dominated by the copepods Acartia tonsa, Paracalanus spp, Temora turbinata, Oncea venusta, Oithona hebes, followed by the Appendicularian, Chaetognatha and Cladocera. Variations were due to seasonal influence and stratification of the water column caused by changes in water masses. The reason of undetected long-term variation of the mesozooplankton at Guanabara Bay could be due to insufficient sampling time or/and the partially effective efficiency of the Program for Remediation of Guanabara Bay implemented by the government of Rio de Janeiro State. The continuity of the long-term monitoring is needed to show changes of the density and composition of mesozooplankton at the Guanabara Bay.