Changes in the plankton community according to oceanographic variability in a shallow subtropical shelf: SW Atlantic

Abstract

Copepods play a key role in marine ecosystems, acting as major primary consumers grazing on phytoplankton or feeding on microzooplankton. Plankton communities are mostly structured by nutrient availability and water temperature. The Subtropical Southwestern Atlantic Shelf has oligotrophic conditions due to the predominance of the Tropical Water in the upper layers. Its condition can change due to cold water upwelling in summer, the northwards spreading of the Plata Plume Water in winter, and local freshwater discharges. This study aimed to investigate the temporal and spatial variability in plankton community in the shallow shelf off the Brazilian coast (~ 27°S to 48°W). Results of the PERMANOVA analysis and co-occurrence networks revealed distinct seasonal communities. During winter the water was homogeneous, which supported the even distribution of the dominant species and the prevalence of the herbivore food chain throughout the area. During summer the herbivore food chain occurred in the bay area, being displaced by the microbial food chain toward the shelf. The plankton community is determined by the homogeneity of the water during winter and by the environmental heterogeneity during summer.