Surviving harsh environments becomes a death-trap for specialist corals
The success of corals that adapt to survive in the world鈥檚 hottest sea could contribute to their demise through global warming, according to new research.
Warm water corals depend on a vital partnership with unicellular algae of the genus Symbiodinium. Damage to the algal symbiont through heat stress can result in the breakdown of the association, leading to fatal coral bleaching. Most corals fall victim to bleaching at water temperatures above 32潞C. However, corals from the PAG region survive summer peak temperatures of up to 35潞C on a regular basis.
The senior author of the study, Professor J枚rg Wiedenmann from Ocean and Earth Science at the University of Southampton, explains: 鈥淚t was not clear whether this resilience is related to the presence of a new type of symbiotic alga (Symbiodinium thermophilum) that was recently discovered by our team in this region. Therefore, we used molecular markers to identify the algal partners of three coral species along the coast of the southern Gulf and the adjacent Gulf of Oman. We found that this special symbiont indeed seems to play an integral role for coral survival in the world鈥檚 hottest sea.鈥�
The researchers studied corals along 1000 km of coastline in the southern PAG, a region where the world鈥檚 warmest coral reef habitats are separated from the wider Indian Ocean by the narrow Strait of Hormuz. Notably, the PAG features not only record temperatures, but the water is also exceptionally salty.
Professor Wiedenmann, who runs the University鈥檚 Coral Reef Laboratory based at the National Oceanography Centre Southampton, continues: 鈥淎s soon as you leave the Gulf, corals start to host different symbionts. This 鈥榩artner exchange鈥� starts when the salinity of the water approaches normal oceanic levels.鈥�
Lead-author Dr Cecilia D鈥橝ngelo, Senior Research Fellow at the University of Southampton, says: 鈥淲e have simulated these conditions in our laboratory and found that corals from the Gulf lose their exceptional heat stress tolerance when they need to cope at the same time with salinity levels commonly found in coral reefs elsewhere. This may explain why the PAG-typical coral-alga associations are rarely found in the less salty water or the Gulf of Oman 鈥�
Dr D鈥橝ngelo adds: 鈥淪ome corals may potentially escape their fate in waters heated by global warming by shifting their geographic distribution. However, our findings indicate that in addition to barriers such as landmasses, the lack of suitable substrate for settlement and adverse currents, the dependence on certain local environmental conditions may represent an invisible fence that could trap corals in their endangered habitat.鈥�
With rising ocean temperatures anticipated to cause a loss of most warm water reefs within the next 100 years, it has been discussed whether heat tolerant corals adapted to hot environments, such as PAG, could be used to replenish reefs damaged by global warming elsewhere.
Professor Wiedenmann comments: 鈥淥ur results suggest that the transplantation of corals over large geographic distances is not a straight-forward solution to restore reefs since they may struggle to adjust to different environmental factors apart from the temperature in the new habitat. Efforts to protect coral reefs should rather focus on other measures including the reduction of nutrient enrichment, sedimentation, overfishing and destructive coastal development. At the same time all attempts should be made to reduce CO2 emissions to prevent further global warming.鈥�
References:
Cecilia D鈥橝ngelo, Benjamin C.C. Hume, John Burt, Edward G. Smith, Eric P. Achterberg and J枚rg Wiedenmann (2015). Local adaptation constrains the distribution potential of heat-tolerant Symbiodinium from the Persian/Arabian Gulf. The ISME Journal, DOI 10.1038/ismej.2015.80
Hume, B.C.C. et al. Symbiodinium thermophilum sp. nov., a thermotolerant symbiotic alga prevalent in corals of the world鈥檚 hottest sea, the Persian/Arabian Gulf. Sci. Rep. 5, 8562; DOI:10.1038/srep08562 (2015).
D鈥橝ngelo, C. and Wiedenmann, J. "Impacts of Nutrient Enrichment on Coral Reefs: New Perspectives and Implications for Coastal Management and Reef Survival." Current Opinion in Environmental Sustainability 7, (2014): 82-93.
Contact:
Dr. Andreas Villwock (91探花, Comunication & Media), Phone: +49-431-600-2802, presse(at)geomar.de
Glenn Harris, Media Relations, University of Southampton, Phone: +44-23 8059 3212, E-Mail G.Harris(at)soton.ac.uk
