Zooplankton composition and vertical distribution in a tropical, monomictic lake (Dom Helvécio Lake, Southeastern Brazil)

MAIA-BARBOSA¹, P.M., ESKINAZI-SANT’ANNA¹, E.M. & BARBOSA¹, F.A.R.

¹ Universidade Federal de Minas Gerais. Laboratório de Ecologia do Zooplâncton/Limnologia. ICB/I3/253. Av. Antônio Carlos, 6627. Pampulha, Belo Horizonte, Brasil. 31270-901. E-mail: maia@mono.icb.ufmg.br

ABSTRACT: In order to determine the influence of the stratification and food availability on the composition and vertical distribution of the zooplankton populations of Dom Helvécio Lake, studies were undertaken during one stratification period (February, 2000) along a 24 h diurnal cycle. Samplings were done in a fixed point of the limnetic region, at five different depths (surface, 3, 6, 9 and 18 meters). The lake showed a well defined stratification, with the thermocline between 3 and 10 m and a general tendency for the increase of the nutrients and chlorophyll-a concentrations starting at the metalimnion. Zooplanktonic community was characterized by the quantitative dominance of rotifers (mainly Ptygura sp and Keratella cochlearis) and Cyclopoida copepods (especially Thermocyclops minutus). The current composition of the community suggests that Dom Helvécio Lake has mesotrophic characteristics. The quality of the available food and bottom-up effects are the possible determinants of the observed pattern of the zooplankton composition. Zooplankton densities were higher at metalimnion and lower at epilimnion. It was observed that different factors influenced the vertical distribution of the zooplanktonic populations in the Lake Dom Helvécio: temperature and oxygen had more effect on rotifers, which were preferentially distributed at the epilimnion while food resources (quality) probably determined the vertical distribution of copepods at the metalimnion.

Key-words: zooplankton, composition, vertical distribution, tropical lake, Brazil.