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Pigment-based chemotaxonomy of phytoplankton in the Patos Lagoon estuary (Brazil) and adjacent coast

ABSTRACT The composition and distribution of phytoplankton assemblages were studied monthly at two sites in the Patos Lagoon estuary and at one site on the adjacent coast over three years (May 2012–April 2015). Samples were collected for microscopic examination and high-performance-liquid-chromatography pigment analysis. The pigment data were analysed using CHEMTAX software to estimate the contribution of different taxonomic groups to total chlorophyll a (Chl a). Phytoplankton assemblages were generally dominated by diatoms, which contributed, on average, 51% of the total Chl a, especially at the Cassino Beach surf zone, where Asterionellopsis guyunusae was the main species contributing to the high diatom-associated biomass. Cyanobacteria appeared as an important group at the lagoon’s mouth station, contributing, on average, 37% of the total Chl a. Cryptophytes, chlorophytes, prasinophytes and dinoflagellates were less important and contributed, on average, 13, 7, 5 and 3%, respectively, of the total phytoplankton biomass in the region. A good correlation was found between microscopy counts and CHEMTAX biomass estimates for most phytoplankton groups. The relationship, however, was poor for cyanobacteria and green algae, where the pigment-based approach estimated relatively higher biomasses. This discrepancy may be related to either the presence of plant/algae detritus in the samples (captured by the pigment method) and/or an underestimation by the microscopic method. Despite some differences, the pigment-based method successfully described the overall phytoplankton community pattern during the study period. Canonical Correspondence Analysis showed that temperature, salinity and dissolved inorganic nutrients are important driving forces of the observed variation in the phytoplankton community.