Our directory of things of interest

University Directory

Coral's susceptibility to bleaching varies with geography, raising conservation hope

Coral's susceptibility to bleaching varies with geography, raising conservation hope
22 Jan
2021
Field observations of corals around the world reveal that not all species are as susceptible to bleaching as previous models predict

Coral bleaching is now a well-known phenomenon. When corals are exposed to heat stress, they expel the symbiotic algae that give them their colour and provide them with a large proportion of their energy needs. In 1998, vast tracts of the Great Barrier Reef were bleached ghostly white. A second recent bleaching event occurred in 2010–2011, when record high rainfalls in eastern Australia caused discharges of freshwater to reduce the salinity of coastal waters. Then, in 2015–16, elevated sea temperatures, combined with a strong El Niño event, caused 93 per cent of coral on the northern section of the Great Barrier Reef to bleach. 

Coral scientists have the diffi cult job of predicting the extent of coral damage under future climate scenarios. A recent study from NOAA’s Atlantic Oceanographic and Meteorological Laboratory predicted that, by 2034, bleaching will occur in 100 per cent of corals if the world at large adopts a fossil-fuel-aggressive climate path. On the other hand, the authors predict that we can delay severe bleaching of corals by 11 years if we instead adopt an ambitious but feasible course of action in which warming is limited to 3.8–4.2°C by the end of the century. 

Coral bleachedCoral bleaching occurs when water temperatures rise, causing corals to expel the symbiotic algae that give them their colour

However, not all scientists are convinced that coral’s adaptability to thermal stress has been modelled accurately. Forecasts such as NOAA’s typically rely on satellite data to measure projected sea-surface temperatures, setting a ‘bleaching threshold’ beyond which corals in a given area will bleach. Some adaptability to thermal stress is usually modelled mathematically. While these models certainly tick the box for mass coverage, they may miss out subtle differences that cause variability in coral’s resilience.

In the aftermath of the bleaching events of 1998 and 2016, coral scientist Tim McClanahan noticed that colleagues at different locations reported varying levels of bleaching. ‘The stuff coming out in the literature didn’t align with what my colleagues in different locations were reporting,’ he says. ‘There were some areas really feeling the effects, but others that weren’t. It was assumed that corals acclimate to thermal stresses at the same rate, but that’s without accounting for the fact that there are many types of corals in many different regions.’

In 2019, a separate team of scientists reported that corals that were predicted to exceed the bleaching threshold, defined by previous climate models, were actually showing a greater ability to adapt to thermal stresses. To investigate, McClanahan launched a study with researchers from 19 tropical research institutions to assess the sensitivities of 226 reefs in 12 countries across 2016, one of the Earth’s warmest years on record. Field observation data of bleaching events were collected and compared with satellite data of coral exposure to high sea temperaturesThe team found that past climate warming models overestimated coral destruction in the Coral Triangle – the region that spans Indonesia, Malaysia, Papua New Guinea, the Philippines and the Solomon Islands, where three quarters of the world’s coral species live. In particular, reefs around the Australian, Indonesian and Fiji-Caroline regions were better able to adapt to thermal stress than was previously thought.

IndonesiaReefs in the coral triangle, a region spanning Indonesia, Malaysia, Papua New Guinea, the Philippines and the Solomon Islands, may be more resilient to thermal stress than previously thought

According to McClanahan, one reason might be that those corals that routinely experience heat oscillations during El Niño events may adapt more quickly to thermal stress. ‘Corals have been growing in these environments for millennia, evolving with the exposure to thermal stresses,’ he points out. With resources for marine conservation constrained, the research suggests that treating the Coral Triangle as a ‘climate refuge’ could be the best bet for targeted conservation action.

SUBSCRIBE TO OUR MONTHLY PRINT MAGAZINE!
Subscribe to Geographical today for just £38 a year. Our monthly print magazine is packed full of cutting-edge stories and stunning phography, perfect for anyone fascinated by the world, its landscapes, people and cultures. From climate change and the environment, to scientific developments and global health, we cover a huge range of topics that span the globe. Plus, every issue includes book recommendations, infographics, maps and more!

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...

Climate

History is littered with examples of fungi helping to digest…

Geophoto

The streets of Philadelphia are home to a small and forgotten…

Geophoto

When photographer Matthew Maran first snapped a fox he had…

Wildlife

Coloradans have voted to reintroduce grey wolves to the state

Energy

Covid-19 provides an opportunity to re-assess the supply chains of…

Geophoto

Andrea DiCenzo is a photojournalist, who has covered conflicts for…

Oceans

Field observations of corals around the world reveal that not…

Climate

The Great Plains of the USA are once again getting…

Climate

Attempts to build a digital twin of the Earth could…

Oceans

Food systems will need to change as the global population…

Wildlife

Zoos do a lot more than welcome excited visitors; closures…

Oceans

 BluHope is back with a day of webinars to promote…

Wildlife

WildEast, a grassroots community initiative, is encouraging volunteers to commit…

Wildlife

With growing global awareness of the risks of hunting and…

Climate

Researchers have identified the extent of microplastic contamination throughout the…

Wildlife

The Thames Estuary has long been home to heavy industry,…

Wildlife

Whydahs and indigobirds, collectively known as the vidua finches, show…

Oceans

Whales sequester an enormous amount of carbon, making their protection…