PLANKTONIC SYSTEM OF GUANABARA BAY: A REVIEW

Abstract

Guanabara Bay, one of the most eutrophic tropical systems in tire world, receives large loads of urban and industrial wastes. Its hydrobiology shows temporal trends according to seasonal variations determined by the rainny summer and spatial trends associated to a tidally induced current pattern that create horizontal and vertical gradients. Human impact is strongest along the shores in the inner reaches of the Bay that present high ammonia and phosphorus concentrations (? 650 ?M and ? 308 ?M), and low, transparence (< 1m). All major phytoplankton groups are present, but cyanobacteria and the nanoplankton fraction (flagellates and diotoms < 20 ?m) are dominant, especially in the inner reaches and during summer. Increasing phytoplankton biomass in the main circulation channel for the past two decades indicate a progressive deterioration in water quality. Tire presence/absence of zooplankton populations are good water quality indicator, according to their specific levels of sensitivity to pollution: not very sensitive (appendicularians), sensitive copepods, chaetognats, cladocerans) and very sensitive (siphonophores and thaliaceans). The highest concentrations of fish eggs and larvae are detected closer to the entrance to lhe Bay and along its main circulation channel, in contrast to the lowest concentrations found in the Northwestern region. Water quality is considered an important fator for accurrence of spawning and recruitment. Present research focuses on the components of the microbial web (bacterioplankton, picoplankton and protozooplankton), considered essential for the understanding of energy flow in this system.