Short-term variability of copepod abundance in Jurumirim Reservoir, Sao Paulo, Brazil.

E A Panarelli,R Henry,M G Nogueira

doi:10.1590/s1519-69842001000400007

Abstract

Short-term variability in composition and abundance of copepod populations were studied during the dry (winter) and rainy (summer) seasons, at the dam region of Jurumirim Reservoir, São Paulo, Brazil. An intensive sampling program was carried out during 30 days in each period of the year. Samples and measurements were taken every other day at 0, 5, 10, 15, 20 and 25 m depths. The relationship between variability of the populations and some environmental factors was analyzed. The main species were: Argyrodiaptomus furcatus (Sars), Notodiaptomus iheringi (Wright), Mesocyclops longisetus (Thiébaud), Thermocyclops decipiens (Fischer), and T. minutus (Lowndes). Thermocyclops minutus was the most abundant species in dry season and its abundance varied significantly between sampling days. A large increase in abundance of calanoids occurred during the rainy season. This increase was correlated with higher temperature values. At that time, Notodiaptomus iheringi was dominant. This species showed significant short-term variations in abundance in both dry and rainy seasons. Significant variation in density of populations within the same sampling period might result from either the dispersion pattern of the populations or continuous substitution of the water masses. Significant correlation was observed between copepod abundance and temperature, especially for species of calanoids and there was also some correlations between densities of particular species of copepods and some phytoplankton taxa, mainly during the dry season. As for vertical distribution, most organisms were found between the surface and 15 m deep. During the rainy season, there was some evidence of the occurrence of spatial segregation between species of cyclopoids and calanoids, with the cyclopoids in a deeper position within the water column.

Highlights

Population adaptation to the limnetic environment is the result of a complex evolutionary process mediated by interactions between biotic and abiotic factors
Studies on short-term variability are of major importance for understanding the dynamics plankton communities in this kind of ecosystem, which can be subject to the natural variations and to variations imposed by the operational system for electricity production
The aim of this study is to investigate patterns in short-term variability of zooplancton abundance in the lacustrine zone of a tropical reservoir (Jurumirim Reservoir), located in the State of São Paulo, Brazil

Summary

Introduction

Population adaptation to the limnetic environment is the result of a complex evolutionary process mediated by interactions between biotic and abiotic factors. Variations in the environment can promote cyclic or erratic changes in the activities of the organisms, short-and long-term fluctuations in the abundance of populations or even substitution of the species. Information on how the structure of a community changes, at different temporal scales, can contribute to a better understanding of the functioning and evolution of the ecosystem. Information about shortterm fluctuations in density are scarce, despite the fact they can have an important role in plankton dynamics in tropical zones. Studies on short-term variability are of major importance for understanding the dynamics plankton communities in this kind of ecosystem, which can be subject to the natural variations and to variations imposed by the operational system for electricity production

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