José Galizia Tundisi

A bacia hidrográfica do Tietê/Jacaré: estudo de caso em pesquisa e gerenciamento

A bacia do Tiete/Jacare e uma das 22 Unidades de Gestao de Recursos Hidricos (Ugrhis) do Estado de Sao Paulo. Um estudo desenvolvido de 2005 a 2007 detalhou as principais caracteristicas dessa bacia hidrografica, os usos do solo, a cobertura vegetal, as fontes pontuais e nao-pontuais de eutrofizacao e contaminacao e as vulnerabilidades da bacia, que conta com 34 municipios e uma populacao de 1.200.000 habitantes. A montagem de um banco de dados com as informacoes ecologicas, hidrologicas, climatologicas e economicas possibilitou estabelecer um programa de planejamento e gestao baseado em vulnerabilidades da bacia hidrografica, impactos das mudancas globais e futuras perspectivas para a gestao dos recursos hidricos. Um indice de qualidade da bacia hidrografica foi desenvolvido com a finalidade de apoiar o planejamento de longo prazo e a gestao de aguas superficiais e subterrâneas.

Predation on Ceriodaphnia cornuta and Brachionus calyciflorus by two Mesocyclops species coexisting in Barra Bonita reservoir (SP, Brazil)

Feeding experiments with two species of carnivorous copepod, Mesocyclops longisetus (Thiebaud) and Mesocyclops kieferi Van de Velde from Barra Bonita, a eutrophic reservoir in São Paulo, Brasil, were performed using two common types of prey: Ceriodaphnia cornuta, a cladoceran, with a mean body length of 464 µm (including spines) or 393 µm (without spines), and Brachionus calyciflorus, a rotifer with a mean body length of 350 µm (including spines) or 279 µm (without spines).Both species showed higher consumption rates on Brachionus than on Ceriodaphnia. For Mesocyclops longisetus, the average rates were: 2.19 prey ind−1 h−1 (Brachionus), and 1.30 prey ind−1 h−1 (Ceriodaphnia). For Mesocyclops kieferi, the rates were 1.85 prey ind−1 h−1 (Brachionus) and 0.60 prey ind−1 h−1 (Ceriodaphnia). These experimental data are discussed with reference to the dynamics of the predator and prey populations in the reservoir.

Predation on and by pelagic Turbellaria in some lakes in Brazil

Planktonic Turbellaria are of common occurrence in both natural and man-made lakes in Brazil. Experiments were performed in 1987 and 1989 to determine which zooplankton species are consumed by predatory Mesostoma sp. from three natural lakes in the Rio Doce Valley. Experiments were also performed in 1989 with a yet unidentified flatworm from Barra Bonita reservoir. Both predators consumed Daphnia and Ceriodaphnia at a high rate: 4 individuals per day in the case of Mesostoma sp., a large species and 1.5 ind day−1 in the case of the smaller species from Barra Bonita reservoir. Consumption of copepod nauplii, copepodids and adults was much lower, and Ostracoda were not consumed at all. Experiments on food selectivity showed a clear preference by the flatworms for cladocerans.In the lakes studied, flatworms are heavily preyed upon by larvae of Chaoborus and by Mesocyclops species.Turbellaria densities in the natural lakes were around 300 individuals per cubic meter, whereas in Barra Bonita reservoir, 1000 individuals per cubic meter was a mean value in a fifteen days study.

Impact of Holoshestes heterodon Eigenmann (Pisces: Characidae) on the plankton community of a subtropical reservoir: the importance of predation by Chaoborus larvae

We analyzed the effects of planktivorous Holeshestes heterodon Eigenmann (Characidae) predation on the plankton community of a small subtropical reservoir, using four enclosures (volume about 17.5 m3), open to the sediment, established in the littoral zone. Two enclosures were stocked with fish (mean TL 5.7 cm), at a density of about 4–5 fish m−3 (approx. 8 g m−3), whereas two remained fishless. The experiment lasted a little longer than one month. In the fish enclosures, most Crustacea and Chaoborus larvae remained scarce, probably as a result of visually selective fish predation. In both fishless enclosures, Chaoborus larvae became abundant. However, in only one of these did large individuals become relatively numerous; this discrepancy in the demographic structure of the Chaoborus populations between the two fishless enclosures is unexplained. Only in the fishless enclosure without appreciable numbers of large Chaoborus did densities of Crustacea increase greatly. It is suggested that in the enclosure containing large Chaoborus individuals, crustacean populations were prevented from developing due to predation pressure, while the small Chaoborus larvae of the other enclosure could not readily consume these prey. Rotifers were low in abundance in the absence of fish, probably as a consequence of Chaoborus predation. Phytoplankton density increased in all four enclosures, due probably to the lack of water flow. Only in the fishless enclosure with high densities of crustaceans did phytoplankton abundance decrease markedly at the end of the experiment, perhaps because of grazing losses.

Spatial variation of zooplankton groups in a tropical reservoir (Broa Reservoir, São Paulo State-Brazil)

In this paper the spatial variation of zooplanktonic groups(cladocerans, rotifers, nauplii and adults of copepods) in the Broareservoir was studied using geostatistical tools. The variation inthe density of cladocerans and nauplii and adults of copepods isstructured along the geographic space in the form of gradients, whichimplies the rejection of the hypothesis of spatial homogeneity andrandomness. In other words, the variation in the density of thesegroups is not distributed randomly over the geographic space. Thepatterns of spatial variation observed can be attributed to differentfactors (advection, behavioral mechanisms and limnological factors).The last conclusion is congruent with the multiple forces hypothesis(Pinel-Alloul, 1995; Pinel-Alloul et al., 1995). Implications tosampling methodology are also discussed.