Temporal patterns of alpha and beta diversities of microzooplankton in a eutrophic tidal river in the eastern Amazon.

Tidal rivers are peculiar, yet vastly unknown. These rivers are characterized by dynamic tides without saline intrusion. This unusual environmental configuration should affect the biological communities present in these habitats. Therefore, our main goal was to identify the temporal patterns of the zooplankton communities in tidal rivers and the influence of the environment on these patterns. We applied an approach that investigates the local diversity and turnover of species (i.e., alpha and temporal beta diversities, respectively) to disentangle the temporal dynamics of individual taxonomic groups at tidal rivers. Our findings evidenced that periods of high diversity are always followed by periods of low diversity. We suggest that the temporal variation in the resources exploited by zooplankton, specifically algal biomass, is the major factor driving this temporal pattern. Periods of high rainfall led to species homogenization, whereas periods of high insolation and wind speed (i.e., dry periods) led to heterogenization. Moreover, we evidenced that protozoa was the group with the highest alpha diversity, and its species turnover was constrained by seasonality in a similar way to that of rotifers, with both groups undergoing homogenization during rainy periods. Here, we describe the zooplankton community dynamics in tidal rivers over time, which is a scale often disregarded in ecological studies, and suggest that future research should consider temporal variation associated with extensive spatial replication to disentangle ecological patterns. [ABSTRACT FROM AUTHOR]