A coral reef refuge in the Red Sea MAOZ FINE* † , HEZI GILDOR ‡ andAMATZIA GENIN † § *The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52900, Israel, †The Interuniversity Institute for Marine Sciences, P.O.B 469, Eilat 88103, Israel, ‡The Fredy & Nadine Herrmann Institute of Earth Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Givat Ram, Jerusalem 91904 Israel, §Department of Ecology Evolution & Behavior, Institute of Life Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904 Israel Abstract The stability and persistence of coral reefs in the decades to come is uncertain due to global warming and repeated bleaching events that will lead to reduced resilience of these ecological and socio-economically important ecosystems. Identifying key refugia is potentially important for future conservation actions. We suggest that the Gulf of Aqaba (GoA) (Red Sea) may serve as a reef refugium due to a unique suite of environmental conditions. Our hypothesis is based on experimental detection of an exceptionally high bleaching threshold of northern Red Sea corals and on the potential dispersal of coral planulae larvae through a selective thermal barrier estimated using an ocean model. We propose that millennia of natural selection in the form of a thermal barrier at the southernmost end of the Red Sea have selected coral genotypes that are less susceptible to thermal stress in the northern Red Sea, delaying bleaching events in the GoA by at least a century. Keywords: climate change, coral bleaching, coral reefs, Gulf of Aqaba, Red Sea Received 9 January 2013; revised version received 6 August 2013 and accepted 7 August 2013 Introduction Coral reefs, Earth’s richest and most diverse ecosystem, are deteriorating rapidly (De’ath et al., 2012) with the possibility that stony corals will no longer dominate reefs (Hoegh-Guldberg et al., 2007) by 2100. This may have severe ecological and socio-economical conse- quences as the recovery from such a state might be slow and prolonged. Among the causes, ocean acidifi- cation and global warming are often considered the most critical issues. The latter, already affecting coral reefs world-wide, is manifested as mass coral bleaching events. Observational and experimental evidence (Hoegh- Guldberg, 1999) indicates that corals bleach when ambient water temperatures exceed the local summer maximum by 0.5–1.5 °C (hereafter ‘bleaching rule’). During bleaching the symbiosis between the coral host and its Symbiodinium dinoflagellates (zooxanthellae) weaken, resulting in the loss of the coral’s main energy source and in deceleration of calcification. As this sym- biosis with Symbiodinium allowed for the prosperity of coral reefs in tropical, oligotrophic waters over a long geological history, an increase in the prevalence of bleaching events is alarming. Susceptibility of coral reefs to and recovery from bleaching events is hitherto unclear (Brown & Cossins, 2011). Repetitive exposures to thermal stress were sug- gested as one of the mechanisms leading to increased tolerance (Brown et al., 2002; Van Woesik et al., 2012; Barshis et al., 2013). Corals occupying areas with vari- able conditions are also reported to have a higher ther- mal resistance (Mcclanahan et al., 2007; Guest et al., 2012) and lower sensitivity to bleaching (Oliver & Palumbi, 2011). Overall, the sensitivity/resilience of corals to bleaching is species specific (Marshall & Baird, 2000) and depends on the coral host, its symbionts (Rowan, 2004; Berkelmans & Van Oppen, 2006) and their acclimatization history (Oliver & Palumbi, 2011). Recent advances in genomic techniques explain the inherent thermal resilience of corals in their ability to express or shut down an array of heat stress-related genes (Desalvo et al., 2010; Barshis et al., 2013; Grana- dos-Cifuentes et al., 2013) these in turn, up or down- regulate expression of cellular mechanism such as heat shock proteins (Leggat et al., 2011), programmed cell death (Kvitt et al., 2011), and antioxidant enzymes (Granados-Cifuentes et al., 2013) which determine the physiological capacity to withstand heat stress. Yet, the general perception is that given the current trends of global warming, an increase in intensity and frequency of mass bleaching events are inevitable and will threa- ten some of the world’s richest reefs. Rinkevich (2005) highlighted the need to conserve the gene pool of reef building corals for possible future reseeding of lost reef areas. Conserving coral gene pool is motivating both in vitro (Hagedorn et al., 2012) and Correspondence: Maoz Fine, tel. +972 8 6360123; fax +972 8 6374329; e-mail: maoz.fine@biu.ac.il © 2013 John Wiley & Sons Ltd 1 Global Change Biology (2013), doi: 10.1111/gcb.12356