Around the world coral reefs are facing threats brought by climate change and dramatic shifts in sea temperatures. While ocean warming has been the primary focus for scientists and ocean policy managers, cold events can also cause large-scale coral bleaching events. A new study by scientists at Scripps Institution of Oceanography at UC San Diego compared damage to corals exposed to heat as well as cold stress. The results reveal that cool temperatures can inflict more damage in the short term, but heat is more destructive in the long run.
The study is published in the Feb. 2 issue of Scientific Reports, a publication of the Nature Publishing Group.
Climate change is widely known to produce warming conditions in the oceans, but extreme cold-water events have become more frequent and intense as well. In 2010, for example, coral reefs around the world faced one of the coldest winters and one of the hottest summers on record.
During a unique experiment conducted by former Scripps Oceanography student Melissa Roth and current Scripps scientist Dimitri Deheyn, corals subjected to cold temperatures suffered greater growth impairment and other measurable damage in just days compared with heat treated corals. Yet the researchers found that corals were eventually able to adjust to the chilly conditions, stabilize their health and continue to grow. However, over the long term corals subjected to heat suffered more greatly than those in cold, with evidence of severe bleaching and growth stoppage, a trajectory that leads to death.
"These results show distinct responses between cold and heat-treated corals on different time scales," said Roth, now based at Lawrence Berkeley National Laboratory. "On a short time scale, the cold event was actually more harmful to the corals than an equivalent warming event, but over time, these corals were able to acclimate to the cold. Therefore, these corals showed more resilience to seawater cooling than seawater warming."
The coral's ability to adjust to cool temperatures surprised the researchers, who say the study's results highlight the complexities of monitoring coral health in response to varying environmental factors.
During the investigations-conducted inside Scripps' Experimental Aquarium-the researchers tracked the overall coral health and the stress of their symbiotic algae, sometimes called "zooxanthellae." The symbiosis is an essential component for reef-building corals because the symbionts provide corals with most of their energy. Accordingly, the researchers found that the cold both disrupted the photosynthetic system of the symbionts and greatly reduced coral growth.
"Global warming is associated with increases but also decreases of temperatures," said Deheyn, a project scientist in Scripps' Marine Biology Research Division. "Not much has been known about the comparative effects of temperature decrease on corals. These results are important because they show that corals react differently to temperature differences, which is critical for future management of coral reefs in the realm of climate change."
The study was coauthored by Scripps researcher Ralf Goericke of the Integrative Oceanography Division.
The research was supported by the National Science Foundation (NSF), an NSF Graduate Research Fellowship and the Air Force Office of Scientific Research's Biomimetics, Biomaterials and Biointerfacial Sciences program. Birch Aquarium at Scripps provided logistical and technical support for the experiments.
Scripps Institution of Oceanography at the University of California, San Diego, is one of the oldest, largest, and most important centers for global science research and education in the world. Now in its second century of discovery, the scientific scope of the institution has grown to include biological, physical, chemical, geological, geophysical, and atmospheric studies of the earth as a system. Hundreds of research programs covering a wide range of scientific areas are under way today on every continent and in every ocean. The institution has a staff of more than 1,400 and annual expenditures of approximately $195 million from federal, state, and private sources. Scripps operates robotic networks and one of the largest U.S. academic fleets. Birch Aquarium at Scripps serves as the interpretive center of the institution and showcases Scripps research and a diverse array of marine life through exhibits and programming for more than 430,000 visitors each year. Learn more at scripps.ucsd.edu.
About UC San Diego
The University of California, San Diego is a student-centered, research-focused, service-oriented public institution that provides opportunity for all. Recognized as one of the top 15 research universities worldwide and born of a culture of collaboration, UC San Diego sparks discoveries that advance society, drive economic growth and positively impact the world. Our students, who learn from Nobel laureates, MacArthur Fellows and National Academy members, are committed to public service. For the sixth consecutive year, UC San Diego has been ranked first in the nation based on research, civic engagement and social mobility. We are one campus with multiple pillars of excellence, a top ten public university that is transforming lives, shaping new disciplines and advancing the frontiers of knowledge. Learn more at www.ucsd.edu.