Last week was a sad one for the planet, but buried beneath headlines of history's largest carbon polluter telling everyone else to piss off, a team of researchers issued a more hopeful message: Coral reefs, a poster child for impacts of climate change, may not be as doomed as we think.
Image: US Fish and Wildlife Service / Flickr Creative Commons
It's no secret that coral reefs are in bad shape, nor that pollution, overfishing, development and rising temperatures — in short, humans — are to blame. With overheated ocean waters cooking reefs year after year, scientists have issued dire warnings that these ecosystems might not survive the century. But now, a team led by coral reef experts at James Cook University — the same ones who first raised the alarm about the plight of the Great Barrier Reef last year — are adopting a less apocalyptic tone. The reefs aren't doomed yet, the researchers wrote in Nature last week, but we need aggressive conservation strategies in order to save them. And we need to accept that the pristine reefs of the past are no more.
"We're not driving the gloom and doom message that they will all be dead by 2030," lead study author Terry Hughes of the ARC Centre of Excellence for Coral Reef Studies told Gizmodo. "But it's also a dose of realism in that we're saying the reefs of 30 years ago will continue to shift, and attempts to get back to where we were are not going [to work]."
Although they cover less than one per cent of the seafloor, coral reefs are bastions of biodiversity, sheltering a quarter to a third of all marine species. Reefs are also incredibly important to humans, supporting fishing and tourism industries, and providing ecosystem services from water purification to carbon sequestration, whose total value has been estimated at a staggering $US172 billion ($230 billion).
But today, overfishing, ship traffic, pollution and climate change have created a crisis for these delicate ecosystems. For the past three years, this crisis has manifested visibly, as reefs around the globe have suffered the longest, most widespread, and most damaging coral bleaching event on record. The Great Barrier Reef is being hit especially hard, with an estimated 29 per cent of its shallow water corals dying from bleaching in 2016, according to the Australian government. More coral die-off is expected this year as elevated ocean temperatures cause corals to expel the algae they depend on for food, turn ghostly white, and starve.
But as Hughes and colleagues explore in their paper, this alarmist talk masks a more complex — and hopeful — reality. For instance, while the colourful, branching Acropora corals that dominate the northern Great Barrier Reef have been hit hard by bleaching, slower growing, dome-shaped corals appear resilient. Corals are diverse organisms with a range of environmental tolerances, and as temperatures rise, we can expect natural selection to favour those that can take the heat. In fact, scientists are already observing changes at the genetic level that appear to be associated with heat tolerance in certain species.
"Bleaching is not random — there are winners and losers," Hughes said. "And within each species, there's inevitably going to be rapid selection for those that are tougher."
And while rising temperatures are generally considered a bad thing for reefs, a warmer world could cause the habitat range of certain corals to expand north and south of the equator. In the short term, range expansion may even help offset another climate-related threat: Ocean acidification. In reality, Hughes and his colleagues write, it's hard to know how the effects of rising temperatures and rising acidity will impact corals over the next few decades, because laboratory experiments typically simulate much more extreme environmental changes — ones that we still have time to avoid.
"Our knowledge of the chronic impacts of up to 1 [degree] C of further warming on the physiology and demography of reef organisms is surprisingly limited because the temperatures used most commonly in recent thermal experiments are too high," the researchers write. Likewise, lab experiments simulating the effects of ocean acidification typically assume a doubling of atmospheric CO2 over present levels, from 400 to 800 parts per million. We're decades to centuries away from an 800 ppm world; hopefully we never get there. The researchers say studies that simulate more moderate levels of warming and acidification are urgently needed to understand climate change impacts on these complex ecosystems.
But ultimately, Hughes and his colleagues conclude, we need to get the climate under control to give coral reefs a fighting chance. Hughes believe that the goal of the Paris Agreement — to cap the global temperature rise at 2C or less — will allow many reef species to survive, although, he acknowledged, "it certainly won't be comfortable for them."
Importantly, this doesn't mean every species will make it, or that the reefs of the future will look anything like the reefs of the past. As Hughes noted, reefs in the Caribbean will never again resemble those of the pre-Columbian era, thanks to the disappearance of key megafauna like sea turtles and manatees, and the introduction of predatory lion fish. With coral reefs as with land-based ecosystems, Hughes says conservationists have to embrace the fact that change is inevitable.
"We can't preserve the status quo, and we can't go back to the past," Hughes said. "What we should be aiming for is an endpoint that is beneficial to people and is sustainable."
Hughes and his colleagues say we also need to rethink management of reefs, and that humans are going to have to play a much more active role as stewards of these ecosystems in the future. Active management could include propagating corals in the lab, re-introducing critical species that have been lost, pumping cold water up from the deep ocean, or tinkering with coral genetics — in addition to dealing with underlying problems of pollution, development and climate change.
Obviously, this will not be easy or cheap. But it may be doable, and Hughes believes that is a message worth communicating.
"Our take home is that no, they won't [all] be dead if we actually do something about it," he said. "But we better do something quickly. And we have to deal with the root causes."