Ultraviolet radiation is recognized only recently as an important environmental parameter for marine animals. The strong scattering properties of UV light in the sea create unique opportunities for signal detection. It is now known that UV-A radiation (320-400 nni wavelength) is present in a biologically useful intensity up to 400 m deep in clear oceanic water. UV radiation on shallow tropical reefs can be a destructive agent and many reef organisms produce special, UV-absorbing compounds to protect their tissues against radiation damage. Many animals have UV-blocking compounds in their eyes to reduce chromatic aberration and radiation damage and are blind to UV radiation. Recently it was realized that many reef animals lack UV-blocking compounds in their eyes and are sacrificing focusing precision and risking potential damage to their eyes in exchange for the advantages of UV vision. Unique UV-sensitive visual pigments have evolved for the purpose of UV perception. Science knows little about the distribution of this perceptual ability or the form of the UV-perceptual world that may be very different from our own. This study will explore the UV visual world of reef fishes - a world that is denied to human visual senses. It will examine the hypothesis that the phylogenetic origins of UV vision in fishes centered on detection of pelagic objects such as zooplankton. UV vision while present for food detection, would likely be evolutionarily co-opted for other functions such as communication. Work will proceed on three fronts. Spectrophotometry will indicate species that lack UV-blocking compounds in their eyes and thus likely have UV vision. UV vision will be confirmed by microspectrophotometry. Using the comparative method, work will study families that include zooplanktivores and other feeding guilds. Species that use UV vision for food detection will likely have other functions such as social communication. Field work with a UV-sensitive underwater video system will describe the fixed and changing UV colorations of fish and their background. Pilot studies have indicated various types of coloration that are not evident in the human-visible spectrum. Some include a complete reversal of the bright/dark reflecting areas that humans perceive. Imaging will concentrate on reef sites such as cleaning stations that are visited by many species that undergo coloration changes during cleaning. Both visible and UV contrast of the colorations that are found will be quantified to explore hypotheses as to the use of UV for close range social communication and longer range broadcast signals. Thirdly, when species are found with interesting UV coloration, field and aquarium studies will establish the likely communication functions of the UV colors. Understanding both the uses, and phylogenetic distribution, of UV vision and coloration will help us understand the evolution of UV vision and better predict the responses of organisms to changes in UV radiation incident on our oceans. This understanding will also result in better appreciation of the signal detection/transmission value of UV radiation in aquatic media. Knowledge of the existence of unsuspected UV color patterns in the fishes will greatly improve the validity of future studies of the ecology and behavior of these species. At this time, we may literally be `calling black, white!` For species important to commercial and sport fisheries, knowledge of their visual world will impact the design of visual lures as well as visual barriers intended to exclude unwanted `bycatch`. It is hoped that the total benefits will rival those that resulted from appreciation of the UV-visual world of terrestrial insects. As an additional benefit, the survey of fish coloration will also result in knowledge of the UV-absorbing characteristics of corals and algae in the environment on a scale that was heretofore impossible. This knowledge may lead to improvement of our understanding, management and conservation of our sustainable shallow reef environments in a world of increasing UV radiation.
