Secondary productivity of main microcrustacean species of two tropical reservoirs in Brazil and its relationship with trophic state

Abstract

In view of the importance of the zooplankton community in energy transfer between trophic levels, this study had as objective to estimate the secondary productivity rates of the main microcrustacean in two large tropical reservoirs, Três Marias and Furnas, state of Minas Gerais, Brazil. We included <em>Thermocyclops</em> <em>minutus, Bosminopsis deitersi, Bosmina hagmanni, Ceriodaphnia cornuta</em> and <em>Moina minuta</em> in Três Marias Reservoir, and, in Furnas, these species and also <em>Notodiaptomus henseni, Daphnia ambigua, Ceriodaphnia silvestrii, Diaphanosoma spinulosum, D. fluviatile</em> and <em>Bosmina freyi. </em>With respect to total productivity, higher rates were obtained in the rainy period in both reservoirs (P<0.000), with mean values during the dry and rainy periods of 0.44 and 1.80 mg DW m<sup>-3 </sup>d<sup>-1</sup> for Três Marias Reservoir and 1.50 and 3.10 mg DW m<sup>-3 </sup>d<sup>-1</sup> for Furnas Reservoir, respectively. <em>Thermocyclops minutus</em> was the most important species in terms of density and biomass in Três Marias Reservoir, and <em>M. minuta</em> showed the highest rates of secondary productivity, especially during the rainy period. In Furnas, <em>N. henseni</em> and <em>D. ambigua</em> showed the highest productivity rates in both periods, and <em>C. silvestrii, C. cornuta, D. spinulosum</em> and <em>D. fluviatile</em> were also important during the rainy period. Values of the productivity:biomass ratio were usually lower for the copepods; the cladoceran <em>M. minuta</em> showed the highest values in both reservoirs. The higher microcrustacean secondary productivity rates in Furnas Reservoir are probably the result of greater efficiency in energy transfer between trophic levels, due to the presence of phytoplankton species with better nutritional quality in this environment.