EFFECTS OF EUTROPHICATION ON SEASONAL PATTERNS OF MESOZOOPLANKTON IN A TROPICAL RESERVOIR - A 4-YEAR STUDY IN PAMPULHA LAKE, BRAZIL

1. Pampulha Lake has undergone rapid eutrophication. Annual maxima of total phosphorus and conductivity increased steadily from 1993 to 1996 . Nitrogen quickly decreased after macrophyte removal in 1994, but inc reased again in the following years 2. The zooplankton was dominated b y Daphnia gessneri, D. laevis, Diaphanosoma birgei and Thermocyclops d ecipiens. The biomass of major zooplankton organisms, including Daphni a and rotifers, increased during the period covered in this study. 3. Autocorrelation coefficients have confirmed the existence of recurrent seasonal patterns for both chemical and biological variables. 4. Daph nia, calanoid copepods and rotifers showed clear and recurrent seasona l patterns. Cyclopoid copepods and Diaphanosoma had temporal patterns more affected by longterm trophic changes. Other organisms such as Moi na, Ceriodaphnia and Bosmina exhibited high temporal variability with no recurrent patterns. 5. There was a strong and positive correlation between total phosphorus and Daphnia biomass. Seasonal patterns of thi s cladoceran were also inversely associated with sestonic C:P ratios. Thus, Daphnia may be limited primarily by phosphorus and not by total food availability as expressed by particulate carbon. 6. This study su ggests that increasing eutrophication has changed the structure as wel l as seasonal patterns of the zooplankton community in Pampulha Reserv oir.