Longitudinal distribution of cladocerans (Crustacea) in a Brazilian tropical reservoir.
TAKAHASHI1, E.M., LANSAC-TÔHA1, F.A., VELHO1, L.F.M. & BONECKER1,C.C.
1 Nupélia, Postgraduate Course in Ecology of Continental Aquatic Environments, State University of Maringá.
Av. Colombo, 5790, Maringá-PR, 87020-900, Brazil.
ABSTRACT: This paper compares patterns of longitudinal variation in species richness and abundance of planktonic and non-planktonic cladocerans in a Brazilian tropical reservoir. We also tested if the spatial distribution exhibited by planktonic cladocerans is in accordance with one of the patterns proposed by Marzolf (1990). Samples were taken in the pelagic region, at eight stations along the longitudinal axis of the reservoir, during two hydrological periods (wet and dry seasons of 1998 and 1999). Twelve species of seven families were identified. Highest species richness and abundance of planktonic cladocerans were recorded in the transition zone during both seasons. The ANOVA results showed significant differences in planktonic species richness and abundance among zones. Planktonic species richness was significantly greater in the wet season than in the dry season, whereas abundance did not significantly differ among seasons. For non-planktonic species, higher values of abundance and species richness were observed in fluvial zone. Our results suggest that in the transition zone, a combination of hydraulic effects and the contribution of river discharge, nutrients and food resource supply promote the establishment and development of large planktonic cladoceran populations. On the other hand, the high current velocity in the fluvial zone determines the input of non-planktonic species into this zone.
Key-words: Cladocera, abundance, species richness, longitudinal distribution, reservoir.