Seasonal and diel variation of shrimp (Crustacea, Decapoda) on sandbanks of a tropical floodplain river

We studied seasonal and diel changes of shrimp abundance in sandbanks of the Cinaruco River, a tropical floodplain tributary of the Orinoco River. Paired diurnal and nocturnal samples were collected from seven river-channel sandbanks during different periods of an annual hydrological cycle. We collected 3730 shrimp representing two families: Sergestidae (Acetes paraguayensis) and Palaemonidae (six species). Patterns of temporal and spatial variation of shrimp abundance on sandbanks of the Cinaruco indicated responsiveness to both diurnal cycles and the annual hydrological regime. The presence of submerged vegetation and the absence of ridge-and-trough topography on sandbanks were the factors most strongly associated with high shrimp abundance. We conclude that the river's seasonal flow regime and geomorphology create the heterogeneity of hydraulic habitats that is essential for diel movements of shrimp between areas used for nocturnal foraging and diurnal refuge.