Abundance, biomass and size structure of planktonic ciliates in reservoirs with distinct trophic states
VELHO1, L. F. M., PEREIRA1, D. G., PAGIORO1, T. A., SANTOS1, V. D., PERENHA1, M. C. Z. & LANSAC-TÖHA1, F. A.
1 Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (Nupélia)/PEA
Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900, Maringá, Brasil.
ABSTRACT: The objective of this study was to investigate the distribution patterns of density and biomass, as well as analyze the variation in the body size structure of the planktonic ciliate community in three reservoirs (Paraná State) with distinct trophic status, in two distinct hydrological periods (dry and rainy seasons). Samplings were performed in July (dry) and November (rainy) 2001, in the lacustrine region of the reservoirs Iraí (eutrophic), Rosana (mesotrophic) and Chavantes (oligotrophic). In each reservoir, 1-liter samples were taken from the subsurface and the mixing layer, and immediately preserved. The samples were quantified in inverse microscopy. To estimate biomass values, organisms were measured and their biovolume (mm3 ) calculated from their approximate geometric shape. Carbon content (mg C. L- 1) was estimated using 110 fgC mm-3 factor. Higher abundance values were observed in Iraí Reservoir and lower ones in Chavantes Reservoir. In general, ciliates were more abundant at the surface in all reservoirs. Seasonally, a significant difference in density was observed only for Iraí Reservoir. Oligotrichia and Hymenostomatida were frequently dominant in the different reservoir samplings, layers and periods. Analysis of ciliate community size structure showed that in the three studied reservoirs the community was dominated by small-sized individuals (<40mm). Nevertheless, largesized individuals were best represented in the oligotrophic reservoir. Results suggest that trophic status constituted a preponderant factor in determining patterns of spatial and temporal variation in the density, biomass and body size of the planktonic ciliates.
Key-words: protozooplankton, ciliates, abundance, body size, trophic state.