The zooplankton biodiversity of some freshwater environments in Parnaíba basin (Piauí, Northeastern Brazil).

The plankton fauna of the state of Piauí, Northeastern Brazil, especially in the Parnaíba basin, is still poorly known; the results of most studies of the subject have not been published and can only be found in grey literature (unpublished scientific works), such as course completion work and consulting reports. Thus, this paper presents data from samples taken recently from different water bodies in Piauí and represents the second study to be published on the region's zooplankton since the pioneering work of Spandl (1926). A total of 38 species were recorded, including 23 new occurrences of rotifers, 10 of cladocerans and 2 of copepods for the state of Piauí. The greatest richness was observed for the rotifers, of which the genus Brachionus must be highlighted, especially at the Joana reservoir. Among the crustaceans, the greatest richness was observed at the Bezerra reservoir, where cladocerans of the genus Bosmina were prominent. The rotifers Brachionus havanaensis Rousselet, 1911 and Filinia longiseta (Ehrenberg, 1834); the cladocerans Diaphanosoma spinulosum Herbst, 1967 and Moina micrura Kurz, 1874; and the copepods Notodiaptomus cearensis Wright, 1936 and Thermocyclops decipiens Kiefer, 1927 occurred in all or in most environments in which the respective groups were studied. The results presented here expand the taxonomic list of zooplankton for the state of Piauí, including a total fauna of 30 species of rotifers, 15 of cladocerans and 3 of copepods. The zooplankton richness was considered low in the studied reservoirs compared to other freshwater ecosystems from Northeastern Brazil; however, the few studies developed in the Parnaíba basin suggest that the diversity for these organisms should be higher.

Cladocerans (Branchiopoda) of a tropical estuary in Brazil.

The study was conducted in the Capibaribe river estuary in Recife (Brazil) to assess the role played by cladocerans in a eutrophic environment. Samplings were carried out monthly at 4 fixed stations along the estuary from July 1987 to June 1988. Collections were made with a plankton net of 65 micrometers mesh size. Six cladocerans species were registered: Penilia avirostris, Diaphanosoma spinulosum, Chlydorus barroisi, Ceriodaphnia rigaudi, Ilyocryptus spinifer, and Moina micrura. The most frequent species was Moina micrura with 49%. The only true marine species was Penilia avirostris, which was registered at station 1 (close to the river mouth), during high and low tide and in the dry season. The Cladocera average density decreased from 329 ind.m'3 (August 1987, high tide) to 2 ind.m(-3) (March 1988, high tide) due to the high load of organic and chemical pollution received by the estuary. At all stations, D. spinulosum, M. micrura, and C. barroisi occurred with a wide distribution, mainly during the rainy season. C. rigaudi and I. spinifer were rare, occurring only during the rainy season. Cladocerans played an important role in the food webs of the plankton community of the Capibaribe tropical estuary and the dominance of a few small species indicated a hypereutrophic environment. A high level of disturbance was indicated by the decline in diversity of specialized species and the increase in abundance of opportunistic species like M. micrura.

Cladocerans (Branchiopoda) of a tropical estuary in Brazil

O estudo foi realizado no estuário do rio Capibaribe em Recife (Brasil) para avaliar o papel desempenhado pelos cladóceras em um ambiente eutrófico. As amostragens foram feitas mensalmente em 4 estações fixas no período de julho de 1987 a junho de 1988. As coletas foram realizadas com uma rede de plâncton com 65 micrômetros de abertura de malha. Foram identificadas 6 espécies de cladóceras: Penilia avirostris, Diaphanosoma spinulosum, Chydorus barroisi, Ceriodaphnia rigaudi, Ilyocryptus spinifer e Moina micrura. A mais freqüente foi Moina micrura, com 49%. A única espécie marinha foi Penilia avirostris, registrada na estação 1 (próxima à desembocadura), durante as preamares e baixa-mares e no período seco. A densidade média dos cladóceros diminuiu de 329 ind.m-3 (agosto/87, preamar) para 2 ind.m-3 (março/88, preamar) em razão de uma forte carga de poluição química e orgânica recebida pelo estuário. D. spinulosum, M. micrura e C. barroisi ocorreram em todas as estações, apresentando ampla distribuição, principalmente no período chuvoso. C. rigaudi e I. spinifer foram raras, ocorrendo apenas durante o período chuvoso. Os cladóceros tiveram importante papel na teia alimentar planctônica do estuário e a dominância de poucas espécies com pequenas dimensões indicou um ambiente hipereutrófico. O declínio da diversidade de espécies especializadas e o aumento de espécies oportunísticas como M. micrura indicam altos níveis de perturbações antropogênicas.