Drivers of phytoplankton biomass and diversity in a macrotidal bay of the Amazon Mangrove Coast, a Ramsar site

Biodiversity maintenance is a main goal in ecology. Hence, phytoplankton diversity and biomass were analyzed in a coastal bay (Cuma Bay) of the Amazon Macrotidal Mangrove Coast, which has been designated as an international hotspot for conservation (Ramsar site) with high biological productivity and diversity that provides crucial ecosystem ser-vices and elevated fish production. An ecohydrology-based approach was applied to iden-tify the main factors that drive the patterns of phytoplankton diversity and biomass, con-sidering spatio-temporal analyses of physical, chemical, and biological variables from May 2019 to June 2020. Phytoplankton dynamics were investigated using multivariate analyses, correlations, and generalized additive models. Seven indices were tested to select the most efficient biodiversity metric. The hydrological conditions of Cuma Bay were governed pri-marily by elevated precipitation and macrotidal dynamics, resulting in two different func-tional zones based on environmental variability: the freshwater influence zone and marine influence zone. Seasonally, the maximum freshwater discharge, low salinity and light avail-ability promoted cell abundance and biomass increase, with blooms of Skeletonema costa-tum, which reduced the taxonomic diversity of the community in the rainy season. During the dry season, turbid waters resulting from macrotidal dynamics and wind speed limited light penetration and phytoplankton photosynthesis, leading to a higher uniformity in the species distribution. Shannon index was the most sensitive biodiversity metric to environ-mental changes. This study found that deterministic processes governed the community, which rainfall on the Amazon coast, along with wind speed, salinity, light availability and nutrients were the main controlling factors for phytoplankton diversity and richness.(c) 2022 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

Phytoplankton diversity and biomass were analyzed in Cuma Bay of the Amazon Macrotidal Mangrove Coast. The study found that rainfall, wind speed, salinity, light availability, and nutrients were the main controlling factors for phytoplankton diversity and richness.