The Distribution of Mycosporine-like Amino Acids in Phytoplankton Across a Southern Ocean Transect

Interactions between phytoplankton and solar ultraviolet radiation (UVR: 280 – 400 nm) are undergoing changes dictated by variability in ocean temperature, nutrient availability, the depth of mixed layers, and the O-zone layer. There are a variety of mechanisms for phytoplankton to cope with UVR stress, one of the most prevalent being the presence of mycosporine-like amino acids (MAAs). MAAs are a highly diverse class of small molecules containing either a central cyclohexenone or cyclohexenimine ring with various substitutions, with absorption maxima ranging from 269-362 nm. Despite the importance of these molecules to phytoplankton fitness under UVR stress, knowledge of the diversity and distribution of these molecules in the world’s oceans is relatively limited. Here, we present the distribution of MAAs in phytoplankton in the surface waters of a transect across the Southern Ocean, from 54.0233°S, 176.0422°W to 62.1282°S, 56.1329°W in March and April of 2018. The highest concentration of MAAs (> 0.2 ug/L) were found between 50 and 60°S, as well as in a longitudinal gradient between 137.47 and 144.78°W. MAAs were assigned to taxonomic groupings based on HPLC pigmentation and flow cytometry, and will be discussed in the context of UVR, mixed layer depth, fronts and nutrient availability as drivers for MAA composition.