Ultraviolet sunscreen on the coral reef: from coral to fish
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2012-05
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University of Hawaii at Manoa
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Abstract
Mycosporine-like amino acids (MAAs) are UVR-absorbing compounds ubiquitous in the aquatic environment. Metazoans appear to obtain them from their diet or from symbiotic microorganisms. The study of MAAs has been complicated by the lack of commercially available standards. Use of tandem mass spectrometry renders this problem tractable. My dissertation exploited the availability of previously published MAA fragmentation patterns to identify MAAs in the mucus of the corallivorous territorial butterflyfish, Chaetodon multicinctus. I next adapted both a powerful HPLC separation procedure and a tandem mass spectrometry technique to not only identify, but also quantify, MAAs in the absence of standards. With this method I examined MAAs through the trophic chain in C. multicinctus and its coral prey, Pocillopora meandrina, Porites compressa and Porites lobata. Specimens from three depths provided non-overlapping levels of downwelling UVR irradiance to investigate if the four species studied modulated their MAA content with exposure level. I found that the MAAs present in Chaetodon multicinctus epithelial mucus are different from the MAAs in their diet: some, like mycosporine-glycine, abundant in the coral diet, are not detectable in fish mucus and some, present in the epidermal mucus such as palythene and usujirene, are not found in the diet. These results are consistent with prior research on fish eyes, sea urchins, and pteropods. They suggest the possibility of selective uptake, translocation and transformation of MAAs by metazoan consumer organisms. The details of these processes are unknown. MAA concentrations in the three coral species decreased with increasing depth and the associated UVR reduction. This pattern was, however, not observed in the fish probably due to a ceiling effect. A model is proposed to illustrate this possibility. The corals also showed an interesting difference in MAAs diversity perhaps due to differences in their Symbiodinium: Porites spp. known to have low diversity of symbionts also had a low diversity of MAAs compared to Pocillopora meandrina that harbors a greater diversity of zooxanthellae. My work also resulted in the addition of several MSĀ² patterns useful for identification. Further, the discovery of up to four new MAAs suggests the value of continuing to investigate these intriguing metabolites.
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MAA, Mycosporine-like amino acids, Sunscreen, Ultraviolet radiation, Fishes
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Zoology.
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