ZOOPLANKTON CHARACTERIZATION IN A SUBTROPICAL RESERVOIR

CLAPS, M. C.; ARDOHAIN, D. M.

Joao Pessoa, Brasil

Simposio; Plankton Symposium IV; 2007

Association for Plankton Research

The Río Tercero Reservoir was built for hydroelectric purposes in 1936. Since 1983 the reservoir has been regulated by the requirements of a nuclear power plant, which uses the water for cooling, with reduction of water level fluctuations. The reservoir became mesotrophic in the last decade related to its water management. Since 1999, the presence of an invasive and exotic species (Limnoperma fortunei) and blooms of a non edible phytoplankton species (Ceratium hirundinella) were recorded in the reservoir. The objective of this investigation is to describe the structure and dynamic of zooplankton related to the mentioned modifications occurred in the environment.The samples were taken where the Nuclear Power Plant pumps water in for cooling in a vertical profile with six levels every two months. Fifty eight species were identified (17 protists, 1 turbellarian, 27 rotifers and 13 crustaceans). Only 14 of them were perennial. Rotifers were always dominant due to the abundance contribution of Keratella cochlearis, Conochilus unicornis, Hexarthra sp. and Polyarthra vulgaris. The mean zooplankton density decreased constantly from 613 individuals.L-1 in 1996 to 231 individuals.L-1 in 2005 whereas the mean species richness fluctuated between 43 species in 1999 to 24 species in 1998 and 2004. The zooplankton biomass decreased suddenly in the last four years related to the minor contribution of the calanoid Notodiaptomus incompositus. The diminution of the zooplankton populations is associated with the low phytoplankton biomass and the repetitive dominance of non palatable algae such as C. hirundinella.Limnoperma fortunei) and blooms of a non edible phytoplankton species (Ceratium hirundinella) were recorded in the reservoir. The objective of this investigation is to describe the structure and dynamic of zooplankton related to the mentioned modifications occurred in the environment.The samples were taken where the Nuclear Power Plant pumps water in for cooling in a vertical profile with six levels every two months. Fifty eight species were identified (17 protists, 1 turbellarian, 27 rotifers and 13 crustaceans). Only 14 of them were perennial. Rotifers were always dominant due to the abundance contribution of Keratella cochlearis, Conochilus unicornis, Hexarthra sp. and Polyarthra vulgaris. The mean zooplankton density decreased constantly from 613 individuals.L-1 in 1996 to 231 individuals.L-1 in 2005 whereas the mean species richness fluctuated between 43 species in 1999 to 24 species in 1998 and 2004. The zooplankton biomass decreased suddenly in the last four years related to the minor contribution of the calanoid Notodiaptomus incompositus. The diminution of the zooplankton populations is associated with the low phytoplankton biomass and the repetitive dominance of non palatable algae such as C. hirundinella.