Ocean acidification is thought to exert a major impact on calcifying organisms, including corals. While previous studies have reported changes in the physiological response of corals to environmental change, none have described changes in expression of the ubiquitous host pigments—fluorescent proteins (FPs)—to ocean acidification. The function of FPs in corals is controversial, with the most common consideration being that these primarily regulate the light environment in the coral tissue and protect the host from harmful UV radiation. Here, we provide for the first time experimental evidence that increased fluorescence of colonies of the coral Stylophora pistillata is independent of stress and can be regulated by a non-stressful decrease in pH. Stylophora pistillata is the most abundant and among the most resilient coral species in the northern Gulf of Eilat/Aqaba (GoE/A). Fragmented “sub-colonies” (n = 72) incubated for 33 days under three pH treatments (ambient, 7.9, and 7.6), under ambient light, and running seawater showed no stress or adverse physiological performance, but did display significantly higher fluorescence, with lower pH. Neither the average number of planulae shed from the experimental sub-colonies nor planulae green fluorescent protein (GFP) expression changed significantly among pH treatments. Sub-colonies incubated under the lower-than-ambient pH conditions showed an increase in both total protein and GFP expression. Since extensive protein synthesis requires a high level of transcription, we suggest that GFP constitutes a UV protection mechanism against potential RNA as well as against DNA damage caused by UV exposure. Manipulating the regulation of FPs in adult corals and planulae, under controlled and combined effects of pH, light, and temperature, is crucial if we are to obtain a better understanding of the role played by this group of proteins in cnidarians.
Bibliographical noteFunding Information:
Acknowledgements We thank the Interuniversity Institute for Marine Sciences at Eilat (IUI for the logistical support. We are indebted to Tom Shlesinger, Hanna Rapuano, Dror Komet, Yoav Lindemann, and Jessica Bellworthy for help in field work and aquaria maintenance and Dr. Roi Holtzman and Itai Granot for statistical advice. Special thanks are due to Naomi Paz for copy editing the manuscript. This study was partially supported by the Israel Science Foundation (ISF) No. 341/12 and the U.S. Middle East Regional Cooperation (MERC) Program Agency for International Development (MERC/USAID) No. M32-037 to Y.L.
© 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
- Global climate change
- Ocean acidification
- Stony corals