Linmological characteristics and seasonal changes in density and diversity of the phytoplanktonic community at the Caco Pond, Maranhao State, Brazil

Seasonal changes of the phytoplanktonic community and limnological abiotic characteristics of Caco pond (Maranhtao State, Brazil) was evaluated from two field researches during the rainy (April 1999) and dry (November 1999) seasons. Measurements of twelve chemical and physical variables and phytoplankton collections were carried out at eight sampling stations. The Chlorophyceae and Cyanobacteria groups were in highest fractions during the rainy and dry seasons, respectively. The limnological abiotic variables showed a homogenous spatial distribution. The cluster analysis, using Bray-Curtis distance, distinguished two major groups, represented by the most common and abundant species in both the periods. The results showed that the climate regime, due to the seasonal changes in pluviosity, was a determinant over the phytoplanktonic community structure at Caco pond.