How reef-building corals attract photosynthetic symbionts

Reef-building corals use green fluorescent protein to attract symbiotic algae, which are crucial for the corals' survival, according to a study. Most reef-building corals acquire the symbiotic alga Symbiodinium from surrounding waters, but how the immobile corals attract free-living Symbiodinium remains unclear. Shunichi Takahashi, Jun Minagawa, and colleagues tested the hypothesis that bright green fluorescence emitted by the corals' green fluorescent protein (GFP) upon exposure to UV/blue light helps recruit the symbionts. Symbiodinium was drawn to weak green light of 510 nm and away from strong purple-blue light of 375-475 nm, suggesting that green fluorescence lures the symbionts toward the corals and away from competing light sources such as sunlight, which includes both green and blue light. The authors observed a 10-fold increase in the density of Symbiodinium drawn to fragments of live Echinophyllia aspera corals when the corals emitted green fluorescence upon exposure to blue light; dead coral skeletons failed to attract the symbionts. Similarly, under blue light exposure in the laboratory, a dome-shaped resin disc that otherwise failed to attract Symbiodinium drew large numbers of the alga when painted with a green fluorescent dye, suggesting that GFP-generated fluorescence, rather than chemical cues, underlies the attraction. Field tests in which traps painted with the dye were placed on a coral reef near Sesoko Island in Okinawa, Japan confirmed the laboratory findings, with green-fluorescent traps attracting 2.5 times as many Symbiodinium cells as control traps. According to the authors, the findings illuminate a key mechanism of coral-algal symbiosis.

Article #18-12257: " Green fluorescence from cnidarian hosts attracts symbiotic algae," by Yusuke Aihara et al.

MEDIA CONTACT: Shunichi Takahashi, National Institute for Basic Biology, Okazaki, JAPAN; tel: +81-564-55-7517; e-mail: shun@nibb.ac.jp

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