Abstract
This study evaluated the biomass distribution of microcrustaceans in three subtropical reservoirs in Brazil and the relationship among these distributions and some limnological variables in the reservoirs. The hypothesis was that the microcrustacean biomass is distributed according to Marzolf´s third model, proposed in 1990 for zooplankton density in tropical reservoirs. The planktonic microcrustacean biomass ranged from 261.5 mg DW m -3 (Irai reservoir, transition zone, dry season) to 0.03 mg DW m -3 (Segredo reservoir, fluvial zone, wet season). The highest biomass values were registered in the transition zone, but this longitudinal variation was not significant. The total biomass was related to the trophic state of each reservoir, and a higher difference was observed among the reservoirs than within them. The longitudinal biomass distribution was also related with the longitudinal distribution of chlorophyll-a and showed the same pattern described in Marzolf´s third model. In this way, the results suggested that this model developed for density zooplankton could be employed for the longitudinal distribution of zooplankton biomass in the studied reservoirs.
Highlights
Cladocerans and copepods are important groups of reservoir zooplankton, usually representing a major part of the zooplankton community biomass (De Manuel and Jaume, 1994; Rocha et al, 1995; Ghadouani et al, 1998)
The planktonic microcrustacean biomass ranged from 261.5 mg DW m-3 (Iraí reservoir, transition zone, dry season) to 0.03 mg DW m-3 (Segredo reservoir, fluvial zone, wet season)
The microcrustacean biomass values recorded for these reservoirs (Iraí reservoir = 101.5 mg DW m-3, Mourão reservoir = 6.8 mg DW m-3, Segredo reservoir = 6.8 mg DW m-3) were relatively similar to values obtained by other authors for tropical reservoirs with similar trophic status (Infante, 1993; González et al, 2002; PintoCoelho et al, 2005)
Summary
Cladocerans and copepods are important groups of reservoir zooplankton, usually representing a major part of the zooplankton community biomass (De Manuel and Jaume, 1994; Rocha et al, 1995; Ghadouani et al, 1998) These microcrustaceans participate actively in the energy flow and nutrient cycling of aquatic systems since they are characterized as efficient filter feeders and predators on bacteria and phytoplankton, and due to their importance as a food resource for other invertebrates and fishes. Reservoirs show typically both abiotic and biotic gradients upstream towards the dam, especially on account of the progressive settlement of particles and materials transported in the inflowing river water. Based on this longitudinal gradient, Marzolf (1990) proposed three gradient models to describe the distribution of zooplankton
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