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The jellyfish <i>Olindias formosus</i>, seen under white light.
Fluorescence in this triplefin blenny may attract prey.
Green fluorescence in a siphonophore. The rest of the body is illuminated in red.
Under mixed light, the central tentacles of this cerianthid tube anemone fluoresce.

Slideshow: Glowing predators of the deep

Hundreds of marine animals fluoresce—all thanks to natural molecules that reemit absorbed light at a different wavelength. Among the brightest of these molecules are the green fluorescent proteins (GFPs). Some species use light from GFPs to create a better environment for the symbiotic algae that live inside them. Others use fluorescence to alter the colors of the light they actively emit by bioluminescence (which may serve as a burglar alarm, drawing attention to nearby predators). Now, a new study finds that GFPs can also help some animals lure prey. The researchers hit on this idea while studying the flower hat jelly, Olindias formosus. This pinstriped jellyfish lives in the western Pacific and catches small prey with its stinging tentacles—each of which has a green fluorescent band near the tip. Using a partitioned tank, the researchers recorded the interest of young rockfish—under a variety of lights—in both the jelly and an artificial, tentacleless jellyfish look-alike, dubbed the blobject, which did not fluoresce. Fish were significantly more attracted to the jellyfish’s tentacles in blue lighting conditions—as found in the jelly's natural environment—under which the fluorescence was excited and visible above the background light, the team reported on 31 July in Biology Open. In a separate experiment, fish chase after the similar-looking visual stimuli of a green laser pointer dot—confirming this strong attraction. The researchers suggest the animals may confuse these fluorescent signals with those from chlorophyll, a pigment that plants and algae use to turn light into chemical energy via photosynthesis. Herbivores may mistake the fluorescence for chlorophyll in the algae they eat; similarly, carnivores may think they have found an herbivore with chlorophyll in its gut. Following these tests, the researchers have also uncovered evidence for similar fluorescent lures in a number of other marine creatures—including some fish, siphonophores, and a mantis shrimp.

(Photo credits: S. Haddock/MBARI/biolum.eemb.ucsb.edu)