No abstract

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.

Snorkeling about an hour after sunrise, November 6 th , 2016, we observed high densities of pteropods (Creseis acicula (Rang, 1828); visually estimated >3 pteropods l-1) swarming in the waters above the shallow coral reef of Eilat, Israel. Many pteropods were captured by massive corals with large polyps (Merulinidae: Dipsastraea spp., Favites spp., Platygyra sp. and others). Some of the captured pteropods exceeded one cm in length. In some corals, we observed single polyps ingesting up to three pteropods (Fig 1 A, B). Empty shells were found on the bottom beneath the corals. Neither captured pteropods nor empty shells were found in or around corals with small polyps, including Acropora spp.,