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

• Published in: Ecohydrology & Hydrobiology 2022-07, Vol.22 (3), p.435-453
• Main Authors: Cavalcanti, Lisana F., do N Feitosa, Fernando A., Cutrim, Marco V.J., Montes, Manuel de J.F., Lourenço, Caio B., Furtado, Jordana A., dos S Sá, Ana Karoline D.
• Format: Article
• Language: English
• Subjects: chlorophyll a; diversity hotspot; ecohydrology; Generalized Additive Model; Maranhão Reentrances; phytoplankton
• ISSN: 1642-3593
• DOI: 10.1016/j.ecohyd.2022.02.002

Biodiversity maintenance is a main goal in ecology. Hence, phytoplankton diversity and biomass were analyzed in a coastal bay (Cumã 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 services and elevated fish production. An ecohydrology-based approach was applied to identify the main factors that drive the patterns of phytoplankton diversity and biomass, considering 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 Cumã Bay were governed primarily by elevated precipitation and macrotidal dynamics, resulting in two different functional zones based on environmental variability: the freshwater influence zone and marine influence zone. Seasonally, the maximum freshwater discharge, low salinity and light availability promoted cell abundance and biomass increase, with blooms of Skeletonema costatum, 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 environmental 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.