Effects of Light and Salinity Stresses in Production of Mycosporine‐Like Amino Acids by Gymnodinium catenatum (Dinophyceae)

Mycosporine‐like amino acids (MAAs) were analyzed in a Portuguese Gymnodinium catenatum strain when transferred to high salinity and high light conditions. Total MAA concentrations increased progressively between 30 and 36 psu, attaining at 36 psu 2.9‐fold the 30 psu treatment. When abruptly transferred to solar light in an outdoor shadowed location, MAA concentration increased steadily along the day for most compounds. After 8 h, mycosporine–glycine, palythene and M‐319 attained or surpassed 25‐fold their initial concentration, while M‐370 only attained 4‐fold concentration. When transferred from halogen to fluorescent light, polar MAAs such as shinorine and porphyra‐334, increased until day two and then declined, while M‐370 increase slowly, becoming the dominant compound from the profile after 1 week. These experiments put into evidence the relation of palythene with M‐319, which was further identified as its acid degradation product, palythine. Acid degradation of M‐370 originated M‐324, while M‐311 seems to be the precursor of M‐370. Under high salinity and high light conditions chain formation was altered toward shorter chains or solitary cells. This alteration can represent a morphological stress sign, which in the natural environment could affect average population speed during daily vertical migrations.