Coral fluorescence: a prey-lure in deep habitats

Plankton show preferential swimming towards fluorescent cues compared to non-fluorescent targets in both the laboratory and the sea. Further, green fluorescence enhances predation success, suggesting a prey-luring effect of fluorescence in corals. Fluorescence is highly prevalent in reef-building corals, nevertheless its biological role is still under ongoing debate. This feature of corals was previously suggested to primarily screen harmful radiation or facilitate coral photosynthesis. In mesophotic coral ecosystems (MCEs; 30-150 m depth) corals experience a limited, blue-shifted light environment. Consequently, in contrast to their shallow conspecifics, they might not be able to rely on photosynthates from their photosymbionts as their main energy source. Here, we experimentally test an alternative hypothesis for coral fluorescence: a prey-lure mechanism for plankton. We show that plankton exhibit preferential swimming towards green fluorescent cues and that compared to other morphs, higher predation rates are recorded in a green fluorescing morph of the mesophotic coral Euphyllia paradivisa. The evidence provided here - that plankton are actively attracted to fluorescent signals - indicates the significant role of fluorescence in amplifying the nutritional sink adjacent to coral reefs.

Automated summary

Research indicates that plankton prefer swimming towards fluorescent cues over non-fluorescent targets, with green fluorescence enhancing predation success in corals, suggesting a prey-luring effect.