Temporal variation of zooplankton on a tropical Amazonian beach

Pinheiro, S.C.C., Magalhães, A., Costa, V.B. da, Pereira, L.C.C. and Costa, R.M. da, 2013. Temporal variation of zooplankton on a tropical Amazonian beach. To assess the spatial and temporal variation in zooplankton populations at Ajuruteua Beach, northern Brazil, monthly samples were taken between August, 2004, and July, 2005, at three fixed stations, during the spring (flood/ebb) tide. The zooplankton community was characterized by the absence of any significant spatial or seasonal variation in density, diversity or evenness. However, density was significantly higher during the ebb tides, with mean values ranging from 4,967±670.0 ind.m−3 in July (flood tide) to 38,213±15,157 ind.m−3 in April (ebb tide). A similar tidal pattern was recorded for the density of copepods. The dominant copepod species were Euterpina acutifrons (47.0±30.5 to 18,313±2,431 ind.m−3) and Paracalanus quasimodo (420.0±60.0 to 11,260±7,203 ind.m−3) and, together with Oithona hebes and O. oswaldocruzi, were responsible for the peaks in zooplankton density recorded in April. Monthly zooplankton diversity (1.8±0.2 to 3.0±0.1 bits.ind−1) was relatively high overall, whereas evenness varied from 0.4±0.0 to 0.8±0.0, with both indices presenting significantly lower values in November. The absence of any significant seasonal trend in total zooplankton during the present study may have been related to atypical precipitation patterns during the study period, when surface waters were abnormally warm (~1.5°C). Overall, zooplankton community structure at Ajuruteua Beach was indirectly related to the local rainfall regime, which affected the physical, chemical, and biological parameters of the water, influencing the temporal dynamics of these organisms.