Phytoplankton Assemblages And Optical Properties In A Coastal Region Of The South Brazil Bight

Phytoplankton assemblages in the inner portion of the South Brazil Bight are studied at a coastal time-series station (2012-2017). Diagnostic pigment analysis (DPA) coupled with a hierarchical cluster analysis were applied to generate and evaluate a locally tuned model to retrieve phytoplankton groups. These results are intercompared with phytoplankton taxonomy (microscopy analysis) and phytoplankton bio-optical properties (i. e., specific absorption coefficient a(ph)*(lambda), package effect index Q(a)* (440) and size indices S-f and SI). Overall, phytoplankton bio-optical properties were well related to the DPA phytoplankton groups and size fractions. Samples with high proportions of diatoms, dinoflagellates, and cryptophytes usually presented low or intermediate values of a(ph)*(lambda), Q(a)* (440), S-f , and SI. When cyanobacteria and green algae proportions were high, the values of these indices were also higher. The locally-tuned model overestimated the chlorophyll-a fraction in diatoms and underestimated that in nanophytoplankton and dinoflagellates, compared with the biomass estimated from microscopic size measurements. The area is characterized mainly by oligo-mesotrophic conditions, with a mixed assemblage, and episodic events of phytoplankton blooms. Dominance of diatoms were associated with low sea surface temperature and high total chlorophyll-a under the influence of nutrient-enriched waters mixed within the Coastal Water, especially in upwelling events during spring-summer. On the other hand, cyanobacteria were associated with high sea surface temperature and low total chlorophyll-a. Surface waters were dominated by the Coastal Water. Episodic events with the intrusion of low salinity and temperature waters suggested the presence of the Rio de La Plata River Plume Water in autumn-winter. High salinity and low-temperature waters indicated surface intrusions of the South Atlantic Central Water, in spring-summer, either by local upwelling or the Cape Frio Upwelling Front, characterizing a highly dynamic environment influencing the phytoplankton assemblages.