Last year, ecologist Roger Bradbury provided a bleak outcome in an opinion piece for the New York Times, saying: “There is no hope of saving the global coral reef ecosystem.” It was a controversial claim, and many other coral scientists see less doom and gloom. “The trajectory is one of decline across the board, but I see areas of incredible resilience in even the most severely hit ecosystems,” says McPherson. “There are so many places you can go where reefs, if not bouncing back, are at least holding their own in a suppressed state.”
Not all corals, or all reefs, are the same. Some, like those in American Samoa, have genetic advantages that allow them to thrive in shallower warmer waters, and some can recruit strains of algae that tolerate higher temperatures. Others grow in waters that are naturally acidic, where carbon dioxide seeps from the ocean floor. Corals can acclimatise to changing conditions, and there’s some evidence that reefs which bleach extensively for one year are better able to handle warmer waters a decade later. And reefs can change at the community level, shifting from sensitive species like the elkhorns to sturdy, robust ones like big boulder corals.
Humans can help, particularly by setting up marine protected areas – underwater national parks – where fishing is verboten. Not only do they allow local reefs a chance to recover, but they can seed nearby areas with coral larvae. “That’s our best weapon in our arsenal right now for coral conservation,” says MacPherson, “but they need to be managed.” While a quarter of the world’s reefs already lie in marine protected areas, many are protected on paper only. Their restrictions have to be actively enforced, and they need strong support from local communities. All of this takes money, education, and expertise.
But in the end, the fate of coral reefs comes down to global warming. “We stop climate change, or that’s that,” says Bruno. “That’s a precondition for conserving almost everything.” Setting up marine reserves, fighting coral diseases, reducing pollution... all of these measures are about buying time.
And with enough time, corals prove to be remarkably resilient. They have lived through several climatic fluctuations, including waters that were far warmer and more acidic than those today. Over geological timescales, corals have endured at least five severe crises, but have never been entirely wiped out. Small populations survived in refuges to restart their rocky kingdoms during more hospitable climates.
The difference, of course, is that these ancient changes played out across millennia, whereas we are causing similar upheavals within the space of decades. Based on the latest report from the Intergovernmental Panel on Climate Change (IPCC), it is entirely plausible that the oceans might be three or four degrees Celsius warmer by the end of the century. “Honestly, if we got to that, most reefs would be toast,” says Bruno. “Usually, one degree of warming is enough to cook and kill most corals. There are very few species that could survive three or four.”
However, those figures are a global average. Not every patch of water will warm equally, and some cold areas may even become more conducive to corals. “We’d lose a lot of what we have,” says Bruno, “but we probably wouldn’t lose everything and we’d gain reefs in some places. We could get close to a world without corals... but reefs aren’t going to go extinct, probably under any global scenario.”
Corals, after all, live in a fine mosaic of salinity, temperature and light, where adjoining areas experience different conditions to their neighbours. It’s that patchiness that creates abundant niches for life, and has turned reefs into engines for evolution. And it’s that patchiness that might help to save them, even if we cannot. “That is my rationale for hope,” says MacPherson.