Variação espacial do fitoplâncton na Bacia de Santos (23º - 28º) no verão de 2021/2022, determinada por pigmentos marcadores

Abstract

Phytoplankton, the main primary producer and base of the food chain in pelagic systems, plays a fundamental role in the ecological and biogeochemical processes of the marine environment. For a better understanding of the dynamics of processes in pelagic ecosystems, it is essential to determine the composition and biomass of this community. Environmental factors, such as salinity, temperature, light incidence and nutrient availability (N, P) in the water column, influence the variation of phytoplankton groups. It is necessary to understand the diversity of the phytoplankton community, and not just its biomass, in order to identify which environmental factors influence its composition. The study of the composition of the phytoplankton community can be carried out by means of its pigmentary profiles, since certain pigments or combinations of pigments are unequivocal markers of phytoplankton groups. The present study aims to identify and quantify the main phytoplankton groups of the Santos Basin (BS), analyzing the horizontal and vertical spatial variation of phytoplankton and pointing out their relationship with the main abiotic factors. HPLC pigments from samples collected between December 2021 and March 2022, in the summer period, were analyzed at 59 stations located along eight transects perpendicular to the coastline, ranging from the internal continental shelf to the oceanic region. At each sampling station, samples were collected at three depths (surface, beginning of maximum chlorophyll depth, and maximum chlorophyll depth). From pigmentary profiles of phytoplankton groups taken from the literature and from CHEMTAX processing, it was possible to identify the presence of pigmentary diatoms 1 and 2, pigmentary dinoflagellates 1 and 2, pelagophyceous, cryptophyceous, pigmentary haptophycea 6 and 8, pigmentary prasinophycea 1 and 3B, pigmentary type 2 cyanobacteria and the genus Prochlorococcus. Thus, from the pigmentary signature of these groups, it was possible to observe their vertical and horizontal distribution, correlating with abiotic environmental variables in the Santos Basin. The southern end of the basin was influenced of cold-water parcels from the south, while the central and northern portions were influenced by the intrusion of ACAS into the euphotic zone. Cyanobacteria predominated mainly in the oceanic portion of the basin. It was possible to observe the occurrence of vortices in the oceanic region, related to phytoplankton biomass. HPLC analysis allowed the identification and quantification of organisms with a smaller phytoplankton size fraction.