Detection and Characterization of Mycosporine-like Amino Acids in the Sea Surface Microlayer of the Baltic Sea during Summer

The Sea Surface Microlayer (SML) in aquatic environments is a thin layer (1–100 μm) at the air-water boundary, characterized by unique biogeochemical properties distinct from the underlying water. The production of organic biofilms and surfactants within the SML stabilizes the layer, often leading to a "slick-like" environment. The organic matrix within the SML can trap phytoplankton, subjecting them to intense light and ultraviolet (UV) radiation. Mycosporine-like amino acids (MAAs) are pigments produced by certain types of phytoplankton, exhibiting photoprotective absorption bands in UV and visible wavelengths. While numerous studies have documented MAAs in surface waters, particularly in equatorial regions, there is limited documentation of MAAs produced specifically within the SML. Here, we present data collected from the Baltic Sea near the summer solstice under both slick and non-slick conditions. Using High-Performance Liquid Chromatography (HPLC), we detected MAAs in SML samples. Absorption spectra measured from these samples revealed distinct UV absorption peaks characteristic of MAAs. Interestingly, many corresponding subsurface water samples contained either no detectable MAAs or only trace amounts. These findings highlight the unique environment of the SML and the biological acclimations that the neuston undergo to survive under these conditions.