Effects of ultraviolet (UV) radiation on marine microalgal-invertebrate symbioses .2. The synthesis of mycosporine-like amino acids in response to exposure to UV in Anthopleura elegantissima and Cassiopeia xamachana

The response pf two symbiotic associations, that between Anthopleura elegantissima and Symbiodinium californium, and Cassiopeia xamachana and S. microadriaticum, to artificial ultraviolet (UV) radiation (280-400 nm) was studied by analysis of the intact associations and of the partners in isolation. After 8 wk exposure to UV, the concentrations of mycosporine-like amino acids (MAAs) were high in symbiotic A. elegantissima, but there was no significant difference in the concentrations of these compounds in anemones not exposed to UV and those that were exposed to UV. The concentration of MAAs was higher in aposymbiotic A. elegantissima exposed to UV than in those not exposed to UV. MAAs were neither detected in S. californium in culture, in the culture medium, nor in the algae freshly isolated from A. elegantissima. These observations suggest that the anemones are not obtaining MAAs from the algae, but probably from an exogenous source. By contrast, S. microadriaticum in culture releases three MAAs to the culture medium. Aposymbiotic scyphistomae of C. xamachana produced no MAAs even when exposed to UV, whereas symbiotic ephyrae and adult jellyfish, assayed after removal of the algae, contained the same three MAAs found in S. microadriaticum. Taken together, these data suggest that S. microadriaticum synthesizes MAAs and transports them to the host.