Posts Tagged ‘coral reefs and climate change’

The Partial Recovery of Coral Reefs.

Wednesday, May 27th, 2015

The damage to coral reefs varies of course. It’s greatest in the Caribbean and the Western Pacific – Indonesia, PNG, the Philippines, Guam. It’s least where humans can’t easily get to them – near isolated islands like Pitcairn and Easter, and around atolls scattered in the Pacific, hundreds of km from human communities.

A coral reef in the Philippines, reduced to rubble, similar to many in the Caribbean (wwf.org)

A coral reef in the Philippines, reduced to rubble, similar to many in the Caribbean (wwf.org)

Pristine reefs, with angel fish, healthy corals, even top predators, are now very rare, existing isolated far from human communities (kidsdiscover.com)

Pristine reefs, with angel fish, healthy corals, even top predators, are now very rare, exist isolated far from human communities (kidsdiscover.com)

And that variation is intriguing. If we reduced the stresses we can actually control – pollution, destruction and overfishing – will that make the reefs more resilient to the challenges of climate change? We can find out only by reducing those stresses.

Meanwhile, what happens to a reef, not wrecked by pollution and other destructive events, if overfishing is reduced? Will it recover any? some? all? of its lost ecological complexity? Marine Protected Areas (MPAs) that are large, old and isolated are recognized to be the ideal solution, but in much of the tropics where humans live in any abundance they are impractical, even impossible: completely restricting fishing is not an option.

Coral reefs of the world. Far too many people live far too close to far too many of them, for instance in the Caribbean and the Western Pacific (oceanservice.noaa.com)

Coral reefs of the world. Far too many people live far too close to far too many of them, for instance in the Caribbean and the Western Pacific (oceanservice.noaa.com)

Now a new and remarkable study indicates that some limited management can go a long way. We don’t have detailed long-term data on coral reefs to guide us, but we do now have current and recent data on a lot of reefs. A team of coral reef biologists has assessed what is known about the current status and recent history of 832 coral reefs, ranging from the most damaged to the most pristine (only 20 of the 832 are considered to be pristine).

The team compared fish biomass on the reefs – finding 1000 kg or more per hectare on a pristine reef, less than half that amount on overfished reefs, and as low as 10% of that amount on the most overfished reefs.

These illustrations are from the Nature article assessing 832 coral reefs. You will need to go to the article to see the details. a and b: The fish biomass on fished reefs is a small fraction of what exists on unfished reefs (red, extremely overfished; green, unfished). c: The less the fish biomass, the longer the time to full recovery when fishing is completely restricted  - 50-60 years for the most damaged. d: With limited regulations in place, ecological complexity (functional return) gradually increases (nature.com),

These illustrations are from the Nature article assessing 832 coral reefs. You will need to go to the article to see the details. a and b: The fish biomass of fished reefs is a small fraction of what exists on unfished reefs (red, extremely overfished; green, unfished). c: The less the fish biomass, the longer the time to full recovery if fishing is completely restricted – 50-60 years for the most damaged. d: With limited regulations in place, ecological complexity (functional return) gradually increases (nature.com),

Unexpectedly, limited regulations can still have considerable impact. For instance, protecting herbivorous grazers, scrapers and browsers (Parrot Fish come to mind) reduces algal cover, promotes coral dominance once again, and raises fish biomass. Eliminating the most damaging fishing gear, like beach seines, also helps fish recovery. Restricting access to the reef to those with negotiated rights to fish there while excluding external fishers helps even more. Sustainable fishing becomes possible.

Parrotfish (this is the Bicolor Parrotfish) are critical herbivores on a coral reef, sraping back algae (ecology.com)

Parrotfish (this is the Bicolor Parrotfish) are critical herbivores on a coral reef, sraping back algae (ecology.com)

Currently most reefs anywhere near human communities are hardly managed at all. Now we know that with limited regulations, a reef can recover to about half of its pristine fish biomass, and when it does, it is much less likely to collapse.

So sustainable fishing on somewhat recovered coral reefs is a target we can realistically aim for, an outcome so very clearly worthwhile in itself. These are grounds for a little optimism.

Will such changes then also make the reefs more resilient to the stresses of rising ocean temperatures and acidification associated with climate change? Coral reef biologists predict that they will, but though the theory is sound, it is untested.

Let’s find out. It’s the least we can do.

What Coral Reefs Can Teach Us

Tuesday, September 30th, 2014

On many coral reefs, the living corals have died, the reef has turned to rubble, and diverse algae have overgrown the rubble. So far, about 80% of coral cover on Caribbean reefs has been lost, and about 50% has been lost on the reefs in the tropical Pacific. Ecologists call this shift in ecosystem structure a phase shift, or ‘regime change’.

This global coral reef disaster is not a new and sudden response to some new stress. The shift to algae has been coming for 3 or 4 decades, and the stresses responsible include overfishing of both predators and herbivores, pollution, demolition, hurricanes, diseases of both corals and sea urchins, along with ocean warming and coral bleaching. Sea level rise and ocean acidification pose ever greater threats in the decades ahead.

Surviving coral reefs around Indonesia are still fished illegally with dynamite (solcomhouse.com)

Surviving coral reefs around Indonesia are still fished illegally with dynamite (solcomhouse.com)

If we could stop the fishing, the pollution, and the habitat destruction, as we do in no-take Marine Protected Areas, and assuming for the moment that the ocean is not going to get too warm, too high, or too acidic too quickly, what kind of coral reef recovery is then possible?

If herbivores like parrot fish and sea urchins return to a reef, they can clear the algae off pieces of the substrate, and coral larvae have a chance to colonize. Whether they succeed depends on many factors: light, current, predators, competition, chance, and even the ‘taste’ of the reef. But recovery is at least possible.

To help coral reefs recovery, corals are grown for a year or two and then transplanted to a damaged reef (digitaljournal.com)

To help coral reefs recovery, corals are grown for a year or two and then transplanted to a damaged reef (digitaljournal.com)

Of course we cannot pretend that climate change will not devastate coral reefs, no matter how resilient they might be now. Even under ideal conditions, recovery would take decades, and time is something we don’t have much of.

But coral reefs may still have a lot to teach us. We know now that shifts from one stable phase to another stable phase of an ecosystem can take decades, and is likely to be the result of accumulating and interacting stresses. Such a shift may start without our recognizing it for decades, and once we finally recognize it, there may then be little we can do about it. As the climate warms, we are likely to see this play out repeatedly in both marine and terrestrial ecosystems.

Can it also occur at a planetary scale, shifting us from a cool and dry planet to a hothouse planet? It has happened before. Perhaps it has already started, a result of accumulating stresses that we have caused, passing a tipping point we have not noticed.

Or perhaps we have not reached that point, and we can recover some of what we have lost, like no-take zones in MPAs. Perhaps we can still slow the process enough so that the outcome is one we and most of our co-existing species can tolerate as we too explore the limits of our resilience.

Coral reefs as we remember them (plaza.ufl.edu)

Coral reefs as we remember them (plaza.ufl.edu)

The Great Barrier Reef : We Barely Knew You

Wednesday, August 6th, 2014

We are going to lose our coral reefs within the next century – including the greatest of them all, the Great Barrier Reef. Warming ocean temperatures, coral bleaching, and ocean acidification will kill them. This is without the overfishing, habitat destruction and pollution that already seriously stress them. Some very tolerant and adaptable coral species will probably persist, but the reefs will crumble.

The Great Barrier Reef extends for 1430 miles close to the coast of northeast Australia, with 3000 separate reefs or cays, and hundreds of islands (cairnsdiveadventures.com.au)

The Great Barrier Reef extends for 1430 miles close to the coast of northeast Australia, with 3000 separate reefs or cays, and hundreds of islands (cairnsdiveadventures.com.au)

Coral reef biologists continue to have depressing annual meetings. Individuals, scientists, NGOs and other organizations all continue to search for ways to protect reefs and give them more time to adapt to what lies ahead. But what lies ahead is bleak indeed.

What to do? Just accept it and watch it happen? Find some way to prevent it? Though much has been written about this, Ian McCalman’s new book The Reef is an intriguing contribution.

Historian Iain McCalman book The Reef takes us from Captain Cook's imperial invasion to the impact of current climate change,

Historian Iain McCalman book The Reef takes us from Captain Cook’s imperial invasion to the impact of current climate change,

It is, to start with, a very fine book. It tells the history of our emerging understanding of the Great Barrier Reef through the journals and accounts of 20 people, in 20 chapters, starting with Captain Cook’s trip up the GBR Inner Passage in 1770, one he was lucky to survive with his repaired ship still floating.

Captain Cook on his first trip mapped the coasts of New Zealand and Eastern Australia (gbrexperience.com)

Captain Cook on his first trip mapped the coasts of New Zealand and Eastern Australia (gbrexperience.com)

Then some of the naturalists on board subsequent navigating trips by other ships used the opportunity to get to know the Aborigines and the geology and some of the biology of the reef. The naturalists mainly counted species, all well known long before that by the coastal Aborigines.

Some castaways from ships wrecked on various parts of the reef at the north end near Torres Straight were saved and adopted by Aborigines, and lived to tell their remarkable stories about the people who were radically different from their popular reputation as savage, violent and ignorant cannibals.

And then in the early 1900s came the trained naturalists and scientists who began more serious study of the reef. Maurice Young’s year long expedition in 1929, leading a team of 14 scientists (amazingly for its time, 6 were women) revealed a lot about corals and their commensal and possibly symbiotic algae (known as zooxanthellae).

The colors of coral come from their symbiotic zooxanthellae that are expelled when ocean surface temperatures rise a couple of degrees, bleaching the corals (lovethesepics.com)

The colors of coral come from their symbiotic zooxanthellae that are expelled when ocean surface temperatures rise a couple of degrees, bleaching the corals (lovethesepics.com)

Yonge and the team wrote extensively about the year, drawing attention to the great uniqueness of the GBR – and unintentionally attracted hordes of tourists with all their collateral damage. So close to the mainland, the unprotected reef became stressed by resorts, pollution, uncontrolled fishing, destructive dynamiting, and growing interest by oil and gas companies.

All of this provoked the increasing concern of the conservationists and ecologists emerging over the past half century. In 1979, after great conflict among the players, the GBR Marine Park was finally created. In 1981 UNESCO designated it a World Heritage Site.

McCalman concludes the personal narratives with an account of the naturalist and coral expert, Charlie Veron, who early on recognized the growing threats to coral reefs from climate change. He published his own fine book in 2009 with the sobering title A Reef in Time: the GBR from Beginning to End.

Charlie Veron's book tells the history of the GBR and its imminent end (amazon.com)

Charlie Veron’s book tells the history of the GBR and its imminent end (amazon.com)

At the very end of his book, McCalman tries not to leave us in fatalistic despair about the reef by sharing the anecdotes of some very resilient humans, determined to not give up.

But that is not enough.

The only real hope for any kind of coral reef survival is rapid reduction of CO2 emissions. We need to dispel the myths that prevent the US, Canada and other nations from taking action. And we need to nourish plausible new ideas, like the cap-and-dividend proposal of US Congressman Chris Van Hollen which even libertarians seem to like.

But all of this has happened far too quickly. Just under three centuries will have passed from our ‘discovery’ of the GBR to its probable destruction at our hands.

We thought we would have more time together.