Taxonomic composition and temporal changes in phytoplankton community of Lake
Quebra-Pote (Maranhão State, Brazil)
NOGUEIRA1, N.M.C., BARBIEIRI2, R., COSTA NETO2, J.P. & ROCHA3, O.
1 Programa de Pós Graduação em Ecologia e Recursos Naturais e 3 Depto. de Ecologia e Biologia Evolutiva. Universidade Federal de São Carlos, C. P. 676, São Carlos, SP.
nanogueira@elo.com.br; doro@power.ufscar.br
2 Universidade Federal do Maranhão, Labohidro. Av. dos Portugueses s/n Bacanga, São Luís – Maranhão CEP 65000-000.
ABSTRACT: The phytoplankton of Lake Quebra-Pote was examined by intervals during a hydrological cycle, in order to record temporal changes in the species composition and in the abundance of main groups of algae. Physical and chemical characteristics of water were also analyzed. Five samplings were carried out in different periods of the hydrological cycle: drought (1997), rising water, flooding, water falling and drought (1998). A total of 102 taxa were found: 15 Bacillariophyceae, 26 Chlorophyceae, 1 Chrysophyceae, 19 Cyanophyceae, 1 Dinophyceae, 17 Euglenophyceae, 1 Xanthophyceae and 22 Zygnematophyceae; these data indicate a diversified algal community. Most taxa constitute new records for Maranhão, partly because phycological inventories are rare and partly due to the intrinsic peculiarity of the local flora, which was different from those in Lake Caçó and the interdunal lakes of Lençóis Maranhenses, inventoried in earlier papers. Turbulence, rainfall and water-level fluctuations were considered the main factors controlling the successional dynamics. The Cyanophyceae class was the most abundant and dominant group in three periods sampled quantitatively: water rising (38%), water falling (48%) and drought (54%). Bacillariophyceae was the most abundant class only in the flooding period, representing 48% of the phytoplankton community. Turbulence, precipitation and water-level fluctuations probably controlled this change. The highest algal densities occurred in the drought period. However the dominance of Cyanophyceae, a lowquality food resource, may conduct to a food chain via detritus, whereas during the flooding the abundant Bacillariophyceae may support a herbivorous food chain and higher secondary productivity.
Key-words: phytoplankton, floodplain lakes, flooding pulse, Lake Quebra-Pote, algae, biodiversity.