Abstract In tropical reservoirs, limnological factors are responsible for changes in plankton and vary at temporal and vertical scales. The aim of this study was to evaluate the effects of temporal and vertical variation of the water column on phytoplankton and zooplankton dynamics in two tropical reservoirs (mesotrophic and supereutrophic) in Northeastern Brazil. Monthly collections from three depths in the limnetic region of the reservoirs were performed to analyze the phytoplankton, zooplankton, and limnological variables. The temporal and vertical variation of the physical and chemical water variables, including their interactions, influenced the phytoplankton and zooplankton community. In the supereutrophic reservoir, decreased nitrogen and increased phosphorus and temperature contributed to the dominance of Microcystis panniformis Komárek, Komárková-Legnerová, Sant’Anna, M.T.P.Azevedo & P.A.C.Senna. Conversely, Planktothrix agardhii (Gomont) Anagnostidis & Komárek was dominant under high nitrogen concentrations and low temperatures. In the mesotrophic reservoir, the desmids were dominant and showed a positive relationship with nitrogen. Copepoda Calanoida was dominant and correlated to phytoplankton in both reservoirs. The results showed that nitrogen forms directly influenced phytoplankton, and the importance of nitrogen for management strategies of tropical reservoirs, as well as demonstrated the ability of Calanoida to adapt to different trophic conditions and phytoplankton compositions.

Resumo Trichodesmium é um gênero tipicamente planctônico cujos tricomas estão dispostos em fascículos ou radialmente em colônias. Com base em estudos morfológicos, existem 11 espécies de Trichodesmium descritas, das quais nove são para ambientes marinhos e apenas duas para águas continentais. Este gênero é conhecido principalmente por sua capacidade de formar florações e produzir toxinas em ambientes marinhos tropicais e subtropicais. Contudo, não há informações sobre produção de toxinas por suas espécies de água-doce. Foi apenas com os estudos moleculares que a taxonomia das espécies marinhas começou a ser resolvida. Contudo, até o presente, não há material disponível para a realização de estudos moleculares com as espécies de ambientes continentais. Durantes o estudo das microalgas do Estado de São Paulo, uma população similar a Trichodesmium foi encontrada em uma lagoa utilizada para recreação. Os organismos analisados formavam fascículos compostos por tricomas homocitados e não atenuados, com aerótopos presentes; características que os tornam diferentes de outras espécies de Trichodesmium. Assim, descrevemos a espécie Trichodesmium brasiliense sp. nov. a partir da análise de espécimes de águas continentais brasileiras. Adicionalmente, sugerimos a revisão de algumas citações da literatura brasileira para T. lacustre e inclusão dessas na sinonímia da nova espécie descrita.

Abstract Trichodesmium is a typical planktic genus in which trichomes are disposed either in fascicles or radially in rounded colonies. Based on morphological studies, there are eleven species of Trichodesmium, out of which nine are from marine environments and only two from freshwaters. Trichodesmium is mainly known for its capacity to form blooms and produce toxins in marine tropical and subtropical environments. There is no information about the capacity of the freshwater Trichodesmium species to produce toxins. It was only with molecular studies that the taxonomy of marine Trichodesmium started to be solved. However, up to now, no material has been available for molecular analyses of freshwater species. During the studies of microalgae from São Paulo state, a population resembling Trichodesmium was found in a recreational pond. The analyzed organisms formed fascicles of homocyted and not attenuated trichomes and cells with gas vesicles, a set of features that makes them different from the other freshwater Trichodesmium species. Thus, we have described the species Trichodesmium brasiliense sp. nov. based on material from Brazilian inland water. Also, we have suggested revision of some Brazilian literature citations of T. lacustre and their inclusion in the synonym of this new species.