Characterization of the Zooplankton Community of the Secondary Wastewater Treatment System of an Oil Refinery in Southern Brazil

Resumen

In the present work, the zooplankton community of a secondary treatment system of an oil refinery was analyzed emphasizing its composition and abundance of organisms. Samples were collected twice a month between January and July 1996 from three stations in the system: entrance, middle, and outlet. Protists, rotifers, and copepods were observed and enumerated in the laboratory. A total of 17 species of protists, 10 species of rotifers, and one species of copepod composed the zooplankton community during the study period. The majority of taxa was present in all three station with exception of one protist genus, and three genera of rotifers. Protists were dominant in the three sampling stations followed by rotifers and copepods. Among protists, Vorticella sp. (Linnaeus, 1767), Paramecium sp. Ehremberg, 1838, Coleps sp. Nitzsch, 1827, and Euglena sp. Ehremberg,1838, were the most abundant taxa during the study period, reaching a maximum mean density of morethan 3.000 cells/L. Brachionus spp. Pallas, 1776,Phylodina sp. Ehremberg, 1830, Trichocerca sp. Lamarck, 1801, Keratella sp. Bori de St. Vincent, 1822, and Notomata sp. Ehremberg, 1830 were the most abundant rotifers in the treatment system, with mean densities that reached more than 250 inds/L. Nauplii of Metacyclops mendocinus (Wierzejski, 1892) were present at all stations reaching a maximum mean abundance of 26 inds/L. Correlation analyses failed to show statistically significantinteractions between environmental variables and zooplankton abundance, suggesting that more complex relationships may be governing the system. Key words: Brachionus, copepods, Metacyclops mendocinus, protists, rotifers