Analysis of fluorescent and non-fluorescent sea anemones from the Mediterranean Sea during a bleaching event

We examined the physiological responses to bleaching of two shallow water anemones, Anemonia sulcata var. smaragdina and A. rustica, common to the Mediterranean Sea. The tentacle coloration of A. sulcata var. smaragdina is caused by proteins homologous to the green fluorescent protein (GFP) from Aequorea victoria. Minor amounts of the transcripts for the same GFP-like proteins were also detected in tentacles of the non-fluorescent Anemonia rustica. During a bleaching event observed in the Mediterranean Sea, representatives of both species lost ∼ 90% of their zooxanthellae, indicating that the green fluorescent host pigmentation had no influence on the degree of bleaching of the two sea anemone species. Interestingly, the content of fluorescent proteins was also significantly reduced in bleached individuals of A. sulcata. The content of mycosporine-like aminoacids (MAAs) was essentially unaltered in bleached specimens. Bleached anemones were characterized by increased levels of superoxide dismutase activity, whereas the catalase activity in these animals was significantly reduced. The latter results indicate that oxidative stress might have been involved in the observed bleaching of Anemonia spp.