Production of mycosporine-like amino acids by phytoplankton under ultraviolet radiation exposure in the Sub-Antarctic Zone south of Tasmania

Phytoplankton production of mycosporine-like amino acids (MAAs) against the damaging effects of ultraviolet (UV) radiation, and the associated changes in absorption properties, were examined across different trophic regions south of Tasmania, from the Polar Frontal Zone (PFZ) to the Sub-Antarctic Zone (SAZ) and in sub-tropical waters. The MAA concentration and particulate absorption coefficient were determined in the 0 to 100 m layer across a latitudinal gradient from 54 to 44 degrees south. These spatial observations were complemented with daily incubation experiments at 3 stations located in the PFZ and in the SAZ southeast and southwest of Tasmania. MAAs were widespread, with a predominance of primary MAAs such as porphyra-334 in the PFZ and secondary MAAs such as palythenic acid in the stratified waters in the north of the SAZ. Under surface irradiance levels during deck incubation experiments, phytoplankton from the PFZ and SAZ produced significant amounts of MAAs under UVB radiations, and a fraction was released into the dissolved fraction (generally <20% of the total MAAs). MAA production rates in the north of the SAZ ranged from 0.0009 to 0.0436 mg m(-3) kJ(-1) UVB m(-2) southwest and southeast of Tasmania, respectively. Changes in MAA distribution are discussed in relation to environmental factors (UV radiation exposure, mixing, nutrients) and shifts in the phytoplankton assemblage composition. The strong variability in MAA distribution and composition across the study region is driven primarily by UV radiation exposure and vertical mixing and secondarily by species-specific responses to UV radiation.