Posts Tagged ‘coral reef resilience’

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)

How Resilient Are Coral Reefs?

Thursday, August 2nd, 2012

On the Pacific coast of Panama, coral reefs exist in a fairly narrow band of tropics compressed between cold water currents that flow south along the California coast and north along the Peruvian coast. Not exactly the extensive coral reefs of the South Pacific, but still, they are there.

Sea surface temperatures in the tropical Pacific. That’s supposed to be Central America in the upper right, Indonesia in the lower left. Blue indicates cool water, red to yellow increasingly warm water. The ocean currents compress the tropics in the Eastern Pacific compared with the Western Pacific (pord.ussd.edu)

An elegant piece of research published last month in Science indicates that reefs may be resilient, able to cease growth during harsh times, and then regrow once conditions improve. The Pacific Panama reefs are about 7000 years old, but from 4000 years ago to about 1500 years ago, they quit growing. Then they started to grow again.

The 2500 years of no growth is correlated with a long period of intense El Nino and La Nina activity. If the greater stress of these events caused the reefs to stop growing, then the same should have occurred broadly around the tropical Pacific. This appears to be true.

How does a dormant or dying reef reef recover? In the case of the Panama reefs, it is very likely that as conditions improved, the reefs were recolonized from remnants of reefs that had survived in sites less affected by the stressful times.

Cauliflower coral, Pocillopora damicornis, dominates the coral community of the reefs off the west coast of Panama. According to cores made into several of the reefs, growth of this species ceased for 2500 years (loiczsouthasia.org)

A reasonable conclusion is that if we now just stopped – and reversed – the increase in CO2 emissions that our current coral reefs could recover.

But that’s the kicker, isn’t it? CO2 emissions continue to rise every year, and we have no reason to think they will stabilize, let alone reverse, in any political future we can see.

Earlier this summer, 2000 coral reef biologists got together for one of their regular international meetings. They produced a Consensus Statement that they are all signing, and it is a clear, concise and grim summary of the predicament that coral reefs face as ocean temperatures rise, ocean acidification continues, and other stresses of over-fishing and pollution continue relentlessly. The only hope for coral reefs is for CO2 emissions to be reduced.

This is part of the statement (and here’s the full statement)
“CO2 emissions at the current rate will warm sea surface temperatures by at least 2-3°C, raise sea-level by as much as 1.7 meters, reduce ocean pH from 8.1 to less than 7.9, and increase storm frequency and/or intensity. This combined change in temperature and ocean chemistry has not occurred since the last reef crisis 55 million years ago.”

Coral reefs will not survive what we doing to the planet.
As I and many others have written before, that is beyond sad. We have evolved in a complex, beautiful and who knows how unique world, and we are wrecking it.