Temporal and spatial variability of mycosporine-like amino acids and pigments in three edible red seaweeds from western Ireland

The content of photosynthetic pigments (chlorophyll a and phycobiliproteins) and UV-absorbing mycosporine-like amino acids (MAAs) was investigated in three commercially important red macroalgae, Palmaria palmata, Chondrus crispus, and Porphyra dioica, with respect to seasonal changes at three locations in Galway Bay (western Ireland). Several parameters, including light, temperature, salinity, and nutrients, were measured over a 12-month sampling period, in an attempt to correlate changes in the content of compounds with variations in environmental factors. Pigments followed a distinct seasonal pattern, similar for the three species, which correlated in most cases with changes of seasonal environmental factors. As irradiance and temperature decreased in autumn, chlorophyll a and phycobiliprotein concentrations increased and remained high throughout winter, typically reaching maximum levels by late winter, early spring. By contrast, an increase in total MAA contents in all species was induced by increasing daily light doses and irradiance levels, from winter to spring, but without clear significant correlations with light and/or temperature. This could be explained by the low nutrient concentrations observed in summer months, limiting the synthesis and accumulation of MAAs, even when exposed to high irradiance levels. Nutrient availability, in particular nitrate, appears to be a limiting factor for the red algal species under investigation to synthetize MAA compounds when exposed to extreme light/irradiance stress. This study provides therefore the first available account of the seasonal variability of pigments and MAAs in these three commercially and ecologically important edible red seaweeds from Ireland.