Heat-resistant coral reefs: struggle to survive when the Earth heats up

Experts say more than half of the reefs may disappear within the next 50 years, largely due to climate change, causing ocean temperatures to rise. But now, scientists at Stanford have had a basis to prove that some coral reefs are adapting to change and still exist in the process of global warming.

'Of course coral is threatened by environmental changes, but this study has really proven that the fact that corals are more resilient than we thought,' Stenphen Palumbi, biology professor, home Senior research by Stanford Woods Research Institute, said.

Palumbi and his colleagues at Stanford began to study the resilience of coral reefs in the Pacific in 2006 with funding from the Woods Research Institute Environmental Project. The project has been expanded and is currently funded by the International Conservation Organization and Bio-X program at Stanford.

'The most interesting thing is that when coral reefs grow well at temperatures that are as high as ocean temperatures 100 years later,' Palumbi, director of Stanford Hopkins Marine Station, said. 'How do they have this ability?'

Coral is threatened

Coral reefs form the basis for a thriving and thriving ecosystem throughout the tropics. They provide food and shelter for thousands of species, including giant fish colonies, which in turn provide the food for millions of people across the planet.

Corals have a symbiotic relationship with the tiny single-celled algae zooxanthellae. Corals provide the algae where they live, and conversely, algae give coral a source of nutrition. But when temperatures rise and affect single-celled algae, algae stop producing food, and coral pushes algae out of its tissue. Without symbiotic algae, coral reefs die and reveal white bones - this is what scientists call 'bleaching'.

During high temperatures, bleaching has killed a large number of corals. In 2005, in the Caribbean, a heatwave caused more than 50% of bleached coral, and so many corals have not yet recovered, according to the Global Coral Reef Monitoring System, an international cooperation agency of governments, policy makers and marine scientists, including Palumbi.

The secret of dealing with coral

In recent years, scientists have discovered that some corals can withstand bleaching by allowing some species of algae to tolerate symbiosis, while others change algae less resistant to heat with stronger species and better heat resistance. Palumbi's team plans to investigate the distribution of heat-tolerant coral reefs on a global scale, and learn more about biological processes that allow them to adapt to high temperatures.

Coral is weakened but still alive - at Ofu Island, American Samoa. This coral gives algae heat symbiosis, and still grows well in high temperature areas in Ofu. (Photo: Tom Oliver)

In 2006, Palumbi and his graduate student Tom Oliver, now a doctoral researcher at Stanford, went to American Samoa's Ofu Island. Ofu, a tropical reef conservation area, remains in good condition regardless of the warming of the sea.

The island is an ideal place for experiments, Oliver said, with countless corals symbiosis with the most heat-resistant algae and the most common heat-tolerant algae. Ofu also has many different temperatures, allowing the team to test which conditions symbiotic individuals cooperate with corals.

In lower temperature areas, Oliver found that very few corals only symbiosis with heat-resistant species. But in warmer areas, he found that the proportion of corals that are symbiotic only with algae that suffer from heat increases significantly. This proves that some corals remove temperature-sensitive algae, and replace them with heat-resistant algae. The results of the study, along with data from other parts of the tropical Pacific Ocean, were published in the Marine Progress Series last March.

Globally

To test whether the adaptation is on a global scale, the research team turned to Kevin Arrigo, a professor of Earth Environment Systems science at Stanford, an expert on the monitoring of marine microalgae. Remote satellite. Arrigo gathers oceanographic data on many environmental variables, including oceanic acid concentrations, frequency of natural phenomena, and sea surface temperatures.

Oliver then arranged the coral research results in the tropics and compared the Arrigo environmental data. The results show a general trend: in regions with the highest ocean temperatures during the year from 84 to 88 degrees F (ie 29 to 31 degrees Celsius), corals avoid bleaching by symbiosis with many algae more heat resistant.

Most corals will be bleached when the temperature increases by 1.8 degrees F (1 degree C) compared to the normal temperature of that area for many years. However, when there are symbiotic heat-tolerant algae, coral reefs can withstand temperatures higher than the bleaching threshold of 2.6 degrees C (1.5 degrees C). This could help coral reefs survive until the end of the 21st century, Oliver said, depending on how severe the global warming situation is.

In 2007, a report by the United Nations International Panel on Climate Change concluded that by 2100 the surface temperature of the Earth will increase by 3.6 to 8.1 degrees Fahrenheit (ie 2 to 4 , 5 degrees C) compared to the present. In such a context, changing the symbiotic object alone may not be enough to help the coral survive for the next century. However, with other adaptive mechanisms, including natural selection of heat-tolerant algae, corals still have many opportunities to survive, Oliver said.

'These findings indicate that, if there is enough time, many corals can adapt to higher temperature habitats by giving symbiosis to heat-resistant organisms,' he explained. 'Although there is a lot of hope, the study also suggests that the environment may change so quickly that corals cannot afford to adapt. Therefore, our work now moves to calculating the rate of environmental change compared to the rate of coral adaptation. '

Heat-resistant corals turn out to be also better adapted to acid rising in seawater, a phenomenon that occurs when seawater permeates excess carbon dioxide from the air. This finding shows that corals around the world are adapting to both rising temperatures and increasing acidity, Oliver said, and in tropical waters, corals can change symbiotic objects. Use this ability to survive.

Plan for the future

The problem of coral bleaching has been studied at the algae cell level, Oliver explained. However, it is surprising that the molecular biology study of threatened coral and zooxanthellae algae has not been conducted satisfactorily, he added.

To test corals and parasites on it at the molecular level, researchers are currently collaborating with John Pringle, a professor of genetics at Stanford. Pringle and his lab arranged boxes, in which propeller grass, corals and parasitic algae experienced changes in temperature, acidity and light. Research is still ongoing.

'What I hope is that we will discover interesting and interesting insights into the genetic and cellular mechanisms that allow symbiosis to occur, as well as the mechanism that occurs when symbiosis ends because of energy. pressing the temperature, ' Pringle said. 'Hopefully in the long run, these insights will contribute to coral conservation.'

The ultimate goal is to find the protein biomarkers that signal heat stress and the potential heat resistance, Oliver explained. After that, the reef manager can reach the range, take a small sample and check the presence of the biomarker to see how it will adapt to higher temperatures.

'With this tool, managers can identify populations that are more resistant to climate change and prioritize to protect them from the threat of hazards, such as hitting Overfishing and coastal development projects, ' Oliver said.

'Although we are trying to do many things that we have never done before, it is hard to imagine that corals, creatures that have been on Earth for ¼ million years, will only last for 50 years, ' Palumbi said. 'And part of our work will probably be to find coral reefs that have the best resistance to protecting them in particular.'

References:
Oliver TA, Palumbi SR.Distributions of stress-resistant coral symbionts match environmental patterns at local but not regional scales.Marine Ecology Progress Series, 2009;37893 DOI: 10.3354 / meps07871