UV sunscreens in marine organisms: Antipodean
adventures on the dark side of sunlight

Malcolm Shick
University of Maine

Wednesday, December 8, 1999
3:00 p.m.—Pacific Forum

Mycosporine-like amino acids (MAAs) occur in taxonomically diverse marine organisms. Their pronounced absorption of environmental UV wavelengths and the correlation of their concentration with solar exposure suggest a sunscreen function. For example, MAAs decrease in concentration with increasing habitat depth in corals, and photosynthesis in deep-dwelling corals having low levels of MAAs is depressed upon their acute exposure to UV fluences in shallow water. By analogy with structurally similar fungal mycosporines, MAAs have been assumed to be synthesized early in the shikimic acid pathway, and there is now experimental evidence for this in corals. Exposure to UVB radiation is the primary stimulus for shikimic acid pathway-dependent MAA synthesis in Stylophora pistillata. Animals lack this pathway, so MAAs in phototrophic symbioses presumably emanate from the algal endosymbionts, although the compounds may be modified in the host’s cells. MAAs found in non-symbiotic animals are obtained from the diet, and feeding adult sea urchins controlled diets differing in MAA content provides an experimental tool to produce eggs having different MAA concentrations. Developmental and biophysical studies using such eggs confirm UV-sunscreen function for MAAs.