INFLUENCE OF REGIONAL FACTORS ON ZOOPLANKTON STRUCTURE

CLAPS, M. C.; GABELLONE NA,; NESCHUK, N. C.

Joao Pesso, Brasil

Simposio; Plankton Symposium IV; 2007

Association for Plankton Research

The structure and dynamics of the zooplankton were seasonally analyzed in a saline lowland river (basin area: 150000 Km2). The samples were taken from the main channel and tributaries (15 sampling stations) during 1997-1999. One hundred and seventy five species were identified (54 protists, 89 rotifers and 32 crustaceans). Rotifers were the most abundant group with predominance of loricate species (Brachionus plicatilis, Brachionus angularis and Keratella tropica) tolerant to high conductivities or salinity variations. The crustaceans were important in the headwaters, where the river is directly connected to large shallow lakes. These environments contributed inocula to the river mainly during flood periods. The protists were in low densities along the longitudinal axis but in the headwater sector, Paramecium caudatum and Stentor roeseli were abundant and Tintinidium fluviatile was conspicuous in some tributaries and in the lower river sector. Zooplankton density peaks were recorded in the middle sector of the basin coinciding with the highest conductivity values (maximum: 4685 individuals L-1 with 7390 ìS.cm-1). The spatial heterogeneity of the zooplankton composition in the Salado River basin was associated with differences in the ionic composition (geological features), conductivity and, phytoplankton biomass (chlorophyll “a” concentration), among other river characteristics. We concluded that, to obtain a good knowledge of the regional zooplankton characteristics of a semi-arid basin, it is necessary to include the main channel and tributaries that represent sub-catchments in order to identify the pattern and processes of the zooplankton community