Zooplankton dynamics in a tropical Amazon estuary

While some data are available on plankton diversity in Amazonian coastal ecosystems, little is known about the seasonal variation in the zooplankton community of the Taperacu estuary. In order to identify the zooplankton species in this estuary and to evaluate the relationship between these species and hydrological parameters, 48 samples were collected at a fixed station located in this estuary during rainy and dry season months. Salinity, temperature, pH, and dissolved oxygen varied significantly between seasons, and were directly influenced by rainfall. Chlorophyll a concentrations did not vary seasonally, although significant variation was recorded in nutrient concentrations. The zooplankton included seven phyla, of which the subclass Copepoda was the most diverse, with 17 species identified. Of these, the most important in terms of density and frequency were Pseudodiaptomus marshi, Oithona oswaldocruzi, Acartia lilljeborgii, Paracalanus quasimodo, Oithona hebes, Parvocalanus crassirostris, and Acartia tonsa. Fluctuations in diversity, evenness, and richness were associated with changes in salinity and density of the different taxa. A cluster analysis revealed the formation of two distinct groups, which were determined by rainfall patterns. Overall, the population structure of the zooplankton in the Taperacu estuary was influenced primarily by rainfall, which affected the salinity of the system, and secondarily by the strong local hydrodynamics (in particular tidal currents) and mixing processes, which in turn regulate the importation and exportation of species and the distribution of zooplankton organisms in the water.