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Abstract This review summarizes the state of knowledge on athecate dinoflagellates occurring within the South Atlantic Ocean and Atlantic sector of the Southern Ocean. We compiled data from 105 articles and selected 33 addressing any aspect of athecate dinoflagellate studies. Our aim is to discuss the patterns in athecate dinoflagellate distribution by building a thorough species list and an occurrence map based on species recorded in coastal and oceanic waters. We found 69 species totaling 141 occurrences in the entire South Atlantic Ocean basin. Contradicting global trends, most species distributed throughout this region are subtropical. We linked this trend to a higher local effort in dinoflagellate research instead of higher biodiversity, especially when compared to usual hotspots in biodiversity attributed to tropical oceans. The Subantarctic and Antarctic regions had a low number of occurrences, with 12 and 5, respectively. Except for the occurrence of Gyrodinium lachryma in the Antarctic Zone, all records are unique, poorly described and never recorded again for species such as Gymnodinium baccatum and Gymnodinium antarcticum. This demonstrates that the state of knowledge regarding athecate dinoflagellates in the South Atlantic and especially in the Antarctic region is still limited due to a lack of directed investigation.

Abstract Diatoms are successful in occupying a wide range of ecological niches and biomes along the global ocean. Although there is a recognized importance of diatoms for the Southern Ocean ecosystems and biogeochemical cycles, the current knowledge on their ecology and distribution along the impacted Antarctic coastal regions remains generalized at best. HPLC–CHEMTAX approaches have been extensively used to this purpose, providing valuable information about the whole phytoplankton community, even for those small-size species which are normally difficult to identify by light microscopy. Despite that, the chemotaxonomic method has reserved minimal focus on great diversity of types associated with diatom genera or species. Here, we show a coupling between the key genera and the corresponding chemotaxonomic subgroup type-A or type-B of diatoms via HPLC–CHEMTAX and microscopic analysis, using chlorophyll–c 1 and chlorophyll–c 3 as biomarker pigments, respectively. The results demonstrated strong correlations for nine of the fifteen most abundant diatom genera observed along the Northern Antarctic Peninsula, from which five (four) were statistically associated with chlorophyll–c 1 (chlorophyll–c 3). Our study highlights the importance to observe diatoms in greater detail, beyond being only one functional group, for a better understanding on their responses under a climate change scenario.

Cyanobacterial blooms in marine and freshwater environments may be favored by shifts in physical water column parameters due to warming under climate change. The Patos Lagoon (PL), a subtropical coastal environment in southern Brazil, is known for recurrent blooms of Microcystis aeruginosa complex (MAC). Here, we analyze the variability of these blooms and their relation to changes in wind direction and speed, rainfall and freshwater run-off from 2000 to 2017. Also, we discuss both longer time-series of air temperature and rainfall and a review of local studies with microcystins produced by these noxious species. Since the 1980s, MAC blooms were associated to negative anomalies in annual precipitation that occur during La Niña periods and, in the last years (2001–2014), accompanied by a trend in low river discharge. MAC blooms were conspicuous from December to March, i.e., austral summer, with massive patches seen in satellite images as for 2017. We suggest that low rainfall and run-off years under NE wind-driven hydrodynamics might accumulate MAC biomass in the west margin of the PL system. In contrast, a positive, long-term trend in precipitation (from 1950 to 2016; slope = 3.9868 mm/yr, p < 0.05) should imply in high river discharge and, consequently, advection of this biomass to the adjacent coastal region. Due to the proximity to urban areas, the blooms can represent recreational and economic hazards to the region.