Ecology of Peridinium gatunense and Peridinium umbonatum (Dinophyceae) in a shallow, tropical, oligotrophic reservoir (IAG Pond), São Paulo, southeast Brazil.

ODA^1,2, A.C.R. & BICUDO², C.E.M.

¹ Curso de Pós-graduação em Ciências Biológicas, Área Biologia Vegetal, Universidade Estadual Paulista, “campus” de Rio Claro, SP.

² Seção de Ecologia, Instituto de Botânica, Caixa postal 4005, 01061-970 São Paulo, SP.

cbicudo@terra.com.br

 ABSTRACT: Two dinoflagellate (Dinophyceae) species, Peridinium gatunense Nygaard and Peridinium umbonatum Stein were studied at the IAG Pond, a tropical, shallow, oligotrophic reservoir located at the Parque Estadual das Fontes do Ipiranga Biological Reserve (23^o 38’ 18,9” S and 46^o 37’ 16,3” W), southeast of the municipality of São Paulo, Brazil. Samples were gathered monthly from August 1998 to July 1999 at one fixed station of the reservoir (limnetic region, maximum depth ± 4.70 m), at five depths [subsurface (± 20 cm below surface), 1 m, 2 m, 3 m, and bottom (15-20 cm from the bottom)] to study temporal and vertical distribution of the two species. Both species showed very similar seasonal distribution, i.e. both were present during the mixing period (April-July 1999 and August-October 1998) distributed throughout the water column, although their greatest densities were detected in the reservoir superficial layers. During the same period, nutrient depletion was pronounced, except for high amounts of orthosilicate and DO. During the remaining months (rainy period, November 1998-March 1999), an increase of TN, NO2 -1, NO3 -1, PO4, TDP, free CO2, total CO2, and HCO3 - and a significant increase in chlorophyll a concentration were registered, indicating that the phytoplankton community total density was highly due to nutrient availability. The two Peridinium species greatest development occurred during a period of evident limnological stress (nutrient depletion), with less intraspecific competition, suggesting their preference for oligotrophic conditions.

Key-words: autoecology, urban reservoir, indicating organisms, dinoflagellates, Brazil.