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This study investigates the variability in the spectral absorption of phytoplankton in Antarctic waters. A large in situ data set comprising phytoplankton pigments and hyperspectral absorption was measured in the northern tip of Antarctic Peninsula during 2013 and 2014 summers at several depths. A proxy of package effect was estimated from the phytoplankton absorption spectra, independently of chlorophyll a. Variations in the concentration of photosynthetic and photoprotective pigments were discernible by changes in this metric but not in the chlorophyll a specific absorption coefficient of phytoplankton. The fucoxanthin to chlorophyll a ratio correlated positively to package effect due to an increase in cell size of phytoplankton (diatoms) and increasing fucoxanthin content per cell to maximize light harvesting in depth. The package effect was found to covary inversely with photoprotective pigments relative to chlorophyll a, partially due to their contribution to enhance absorption in the blue part of the spectrum. Using a cluster analysis ( k-means algorithm) on the phytoplankton absorption spectra, we illustrate the capacity to identify a regular increase in the degree of package effect. This approach can be useful to classify the phytoplankton assemblages in Antarctic waters according to different degrees of pigment packaging, each one related to a specific pigment composition. Our results demonstrate the potential for this classification at different temporal and spatial scales from ocean color satellite data. This should improve our understanding of deviations in global bio-optical algorithms when applied to the Southern Ocean. [ABSTRACT FROM AUTHOR]

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.

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.