The links among mycosporine-like amino acids (MAAs), algal physiological ecology, and the environment may be viewed from two sides. The UV-absorption spectra of MAAs make them prime candidates for UV-screening compounds, and indeed, numerous studies have shown that a high concentration of MAAs is correlated with various degrees of protection of cellular processes from UV damage. Thus, it might be said that the structure of terrestrial, eulittoral and sublittoral algal communities depends in part on their ability to synthesize effective quantities of MAAs. Corollaries to this hypothesis might include the proposition that those species incapable of synthesizing MAAs will be excluded from UV-containing environments, and that UV is necessary to trigger MAA synthesis. However, a number of studies have demonstrated that triggers of MAA synthesis need not include exposure to UV, but may include the relative availability of nitrogen, osmotic stress, or high levels of photosynthetically active radiation. Furthermore, the response to these factors may vary as a function of other environmental conditions. These issues will be discussed with respect to elucidating the master switch for MAA synthesis.

Key words: algal diversity, global change, high light, mycosporine-like amino acids (MAAs), UV radiation, zonation