Zooplankton Biomass in Tropical Reservoirs with Different Trophic States

BONECKER CLAUDIA; NAGAE MARIZA; BLETTLER MARTIN; VELHO LUIZ; LANSAC - TÔHA FABIO

Figueira da Foz, Portugal

Simposio; III Plankton Symposium.; 2005

Zooplankton samples were taken at the surface of the fluvial, transitional and lacustrine zones of three reservoirs (oligotrophic, mesotrophic and eutrophic states) in Southern Brazil (Paraná State). Our hypothesis was that zooplankton communities present higher dry weight values in the transitional zone of the eutrophic reservoir during the dry season Cladocerans contributed 73,60% (0,01-259,86 mgPS.ind-3) of the total dry weight, followed by copepods (22,05%; 0,01-69,69 mgPS.m-3) and rotifers (4,35%; 0,01-11,52 mgPS.m-3). Bosmina hagmanni was the most important species for the zooplankton dry weight (0,01-257,36 mgPS.m-3). Other important species were Notodiaptomus amazonicus, Thermocyclops decipiens, Diaphanosoma spnilosum, Ploesoma truncatum, Synchaeta oblonga, Brachionus calyciflorus, Polyarthra vulgaris, Trichocerca iernis, T. capucina multicrinis and Keratella americana. Higher rotifer dry weight values were registered in the lacustrine zone during the dry season, whereas cladocerans and copepods both had higher values during the wet season, but in different zones (transition and fluvial, respectively). Rotifer dry weight was significantly and positively correlated with chlorophyll-a, total nitrogen, and total phosphorus. Cladoceran dry weight was significantly and positively correlated with chlorophyll-a and total phosphorus. Copepod dry weight was only correlated with total phosphorus. The results suggest that the zooplankton groups’ dry weights were influenced by the trophic state, with greater values in the eutrophic reservoir, but the spatial and temporal variation were distinct for the different groups. The total zooplankton dry weight showed the same variation observed to cladocerans due B. hagmanni contributed with the major part of the community dry weight.