The Gulf of Aqaba/Eilat (GoA), Red Sea, harbors a high-latitude (29°N), yet flourishing and diverse coral reef. In spite of a normal rate of warming (~0.035°C per yr) and the occasional occurrence of extremely hot summers, no mass bleaching has ever been reported from the GoA. The local corals appear to defy the otherwise universal “heating rule” of coral bleaching. On the other hand, mass mortalities of corals occur in the GoA due to algal smothering during unusual spring blooms that follow extremely cold winters. In this talk, I will demonstrate how both phenomena are related to the unique geology and oceanography of the Red Sea, where a shallow sill (137 m) at the Straits of Bab el Mandeb controls the temperature and extent of water exchange with the Indian Ocean. Consequently, the deep Red Sea waters are unusually warm (e.g., 21°C at 2500 m depth), stratification is weak, and vertical mixing during winter reaches depths that greatly exceed any other warm-water ocean on the globe (e.g., >800 m in the cold winter after the Pinatubo eruption in 1991). Those unique oceanographic conditions generate extraordinary spring blooms that kill corals. In the past, during the peak of the last glacial period, when sea level was 120 m below present, the sill left little space for water inflow, causing salinity to dramatically increase, eliminating corals and other metazoa throughout the Red Sea. After sea level rose, some 8000 yrs ago, corals entering the Red Sea form the Indian Ocean could not survive the passage through the straits unless they could survive the local hot waters (32-34°C). This selective barrier for heat-tolerating genotypes means that corals that are found today in the northern GoA can survive much higher temperatures than those occurring in the GoA during summer (~27°C). According to this scenario, under present rate of warming, it will take another ~100 yrs for corals to start bleaching in Eilat. The knowledge gained from the unusual Gulf of Aqaba should be applied to better understand the ecology and evolution of animals under climate change.
Prof. Amatzia Genin is a marine ecologist and biological oceanographer. His major interest is in the coupling between physical and biological processes in the marine environment, focusing on the effects of water motion on fundamental ecological processes, including predator-prey relationships, competition, symbiosis, mass transfer, and behavior. Research at his lab is process-oriented and inter-disciplinary, addressing mechanisms that operate at levels ranging from the individual to the ecosystem. Most of Amatzia’s studies are based on field experiments involving advanced technologies and novel approaches.
Amatzia completed his BSc (1977) and MSc (1981) at the Hebrew University of Jerusalem, Israel and his PhD (1987) at Scripps Institute of Oceanography, UC San Diego, USA. He has been a faculty at the Hebrew University of Jerusalem and a resident researcher at the InterUniversity Institute for Marine Sciences of Eilat (IUI) since 1987. In the past 6 years, he was the scientific director of the IUI. At present, he is on sabbatical leave at the Global Climate Institute, UQ, at Ove Hoegh-Guldberg’s lab.