Composition, distribution and toxicity of spring phytoplankton community in the San Jorge Gulf - Argentine Patagonia

Abstract

San Jorge Gulf (SJG) is one of the most productive regions in the southwestern Atlantic Ocean, supporting a diverse community and key commercial species for fisheries. However, phytoplankton composition and dy-namics in the area remain poorly studied, and most previous works have focused only on toxigenic phyto-plankton. This study provides the first comprehensive assessment of the entire phytoplankton community (0.2–200 μm) in the SJG, northern waters (NW), and adjacent shelf waters (AW), as well as its relation to hy-drographic conditions during two spring seasons. Furthermore, the occurrence of toxigenic species and the accumulation of toxins in benthic organisms are addressed. High biomass concentrations were observed in the SJG during both springs, with peaks of 706 μgC L􀀁 1 in 2016 and 487 μgC L􀀁 1 in 2017, associated with the North thermal Front System (NFS). Distinct hydrographic conditions were recorded in the two years, mainly reflecting differences in sampling time and in the penetration of the Patagonian Current (PC) into the gulf, which indicated different stages of the spring bloom. Microplanktonic diatoms such as Corethron pennatum, Leptocylindrus danicus, and Thalassiosira spp., dominated most sampling stations during both springs, particularly in the SJG, whereas nanoplanktonic chain-forming diatoms and dinoflagellates contributed substantially to total biomass in the NW and AW. The dinoflagellate Alexandrium catenella was the most abundant toxigenic species, associated with the detection of paralytic shellfish toxins (PSTs) in plankton samples as well as in several benthic organisms.