Mycosporine-like amino acids (MAAs) are regarded as powerful sunscreens protecting the algae against harmful UV radiation. The MAA protection efficiency was tested in algal samples by measuring the optimum quantum yield of photosynthesis using photosystem II fluorescence. It could be demonstrated that the recovery of photosynthesis after exposure to enhanced UV radiation is faster in individuals with high MAA content. MAAs can be synthesized in several polar macroalgae in response to different radiation conditions. Although MAA induction patterns are very species-specific, some similarities can be found. Field studies indicate that plants from different growth habitats providing distinct radiation climate can be grouped into 3 physiological categories depending on their MAA content. The first group (I) includes mainly deep water species typically lacking MAAs. The second group (II), algal species found in a broad range of water depths (eu- and sublittoral), which are able to flexibly synthesize and accumulate MAAs. The third group (III) includes supra- and eulittoral taxa, which always contain high MAA concentrations. In laboratory studies, we showed that taxa of the II. and III. group, responded in three different ways based on MAA accumulation when exposed to different radiation conditions (PAR, PAR+UVA, PAR+UVA+UVB). Either they; (a) exhibit highest total MAA concentration under the full artificial spectrum, (b) increase their MAA concentration after exposure to PAR and PAR+UVA or (c) MAA concentration declines after exposure to the full spectrum. Our studies have indicated that when coupled with UVR, exposure to temperature fluctuations ranging from 0 - 10 °C also affect MAA biosynthesis.

Key words: MAA, macroalgae, polar regions, sunscreen, UV radiation