Cross-Shelf Effects of Climate, Spatial and Hydrological Processes on Shaping Phytoplankton Community Structure and Β-Diversity in an Estuary-Ocean Continuum (Amazon Continental Shelf, Brazil)

Abstract

The Amazon continental shelf is a highly dynamic environment, which experiences the highest river discharge worldwide. Hence, this study investigated the influence of the estuarine plume from the Maranhense Gulf on the phytoplankton community structure and β-diversity. To understand the effects of the regulation mechanisms on shaping phytoplankton community structure and β-diversity along an estuary-ocean continuum in the eastern sector of the Amazon shelf, the study considered spatiotemporal analyses of physical, chemical, and biological variables from May 2019 to June 2020. High temporal environmental heterogeneity was identified in Cumã Bay and significant spatial environmental variability in the estuary-ocean. Based on the thermohaline properties, an estuarine plume was observed alongshore at a distance of approximately 60 km from the coastline. Both phytoplankton community structure and β-diversity varied in time and space. From 189 taxa, thirty-nine indicator species were selected based on their functional traits and indicator value. Skeletonema costatum was considered the best phytoplankton indicator of the estuarine water influence. Turnover was the main component responsible for boosting β-diversity at spatial and temporal scales. The present study provided important information about spatiotemporal changes in phytoplankton community and β-diversity and environmental heterogeneity in a macrotidal ecosystem governed by high freshwater discharge.

Keywords: Maranhão continental shelf, Macrotidal bay, Diatoms, Phytoplankton indicator, Skeletonema costatum, Turnover.