title: Red fluorescence increases with depth in reef fishes, supporting a visual function, not UV protection.
abstract: Why do some marine fishes exhibit striking patterns of natural red fluorescence? In this study, we contrast two non-exclusive hypotheses: (i) that UV absorption by fluorescent pigments offers significant photoprotection in shallow water, where UV irradiance is strongest; and (ii) that red fluorescence enhances visual contrast at depths below -10 m, where most light in the 'red' 600-700 nm range has been absorbed. Whereas the photoprotection hypothesis predicts fluorescence to be stronger near the surface and weaker in deeper water, the visual contrast hypothesis predicts the opposite. We used fluorometry to measure red fluorescence brightness in vivo in individuals belonging to eight common small reef fish species with conspicuously red fluorescent eyes. Fluorescence was significantly brighter in specimens from the -20 m sites than in those from -5 m sites in six out of eight species. No difference was found in the remaining two. Our results support the visual contrast hypothesis. We discuss the possible roles fluorescence may play in fish visual ecology and highlight the possibility that fluorescent light emission from the eyes in particular may be used to detect cryptic prey.
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Melissa G
authors.initials: MG
authors.lastname: Meadows
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Anthes
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Dangelmayer
authors.affiliation: Department of Marine Science, Faculty of Science, Suez Canal University, Ismailia, Egypt.
authors.forename: Magdy A
authors.initials: MA
authors.lastname: Alwany
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Gerlach
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Schulte
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Dennis
authors.initials: D
authors.lastname: Sprenger
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Theobald
authors.affiliation: Animal Evolutionary Ecology, Institution for Evolution and Ecology, Department of Biology, Faculty of Science, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany nico.michiels@uni-tuebingen.de.
authors.forename: Nico K
authors.initials: NK
authors.lastname: Michiels
mesh_terms: D000818:Animals; D005127:Eye Color; D005399:Fishes / Q000502:physiology*; D005453:Fluorescence; D005470:Fluorometry; D009792:Oceans and Seas; D010858:Pigmentation / Q000502:physiology; D014466:Ultraviolet Rays / Q000009:adverse effects; D014796:Visual Perception / Q000502:physiology*
keywords: colour contrast; fluorescence; marine fish; photoprotection; visual ecology