Fluorescence in Caribbean Coral Reef Cnidarians

Mazel, Charles

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Many coral reef cnidarians contain substances that fluoresce: that is, they absorb electromagnetic radiation and reemit it at longer wavelengths. The phenomenon may be manifested as vivid coloration under daylight or ultraviolet illumination, or its effects may be more subtle. The existence of fluorescence in cnidarians has been known for a long time, but there has been little study of its nature and significance. I have developed equipment and techniques for in situ observation and photography of ultraviolet-induced fluorescence, and have made quantitative measurements of fluorescence excitation and emission spectra. The results in this thesis constitute the first reported in situ observations and photographs of ultraviolet-induced fluorescence in cnidarians. The field observations and laboratory measurements reveal a high degree of variability in fluorescence responses both between and within species, and at the same time indicate general features that underlie many of the effects. The results also indicate that the fluorescing substances may be more widespread in zooxanthellate cnidarians than previously thought. The work accounts for the relationship between daylight- and ultraviolet-induced responses, and demonstrates why a research approach that is restricted to one or the other of the methodologies is inadequate. A predictive mathematical model for the contribution of fluorescence to the appearance of cnidarians is developed. Measurements reveal that an orange-fluorescent substance in some cnidarians has the same spectral properties as phycoerythrin, a photosynthetic accessory pigment of the red algae and cyanobacteria. There have been no prior reports of this effect in cnidarian tissues. Structural and spectral evidence indicate that there is a relationship between this orange-fluorescent material and the more prevalent green-fluorescent material. Various environmental influences can produce changes in fluorescence emission in cnidarians. The emitted light provides an external indication of internal molecular states or processes, giving fluorescence the potential to serve as a powerful, non-destructive tool for coral reef sensing and assessment. The work in this thesis addresses a number of the areas relevant to the effect, and leads to a better understanding of the phenomenon and a foundation for approaching future study.