November 10, 2010
"We have a very good scientific understanding of what causes reefs to decline—what we now need is a clearer picture of how to help them back onto the reverse trajectory," says lead author, Terry Hughes from the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University.
Heron Island: where coral reefs routinely survive cyclones. Photo by: Rhett A. Butler.
For example, the authors write that "local sites on exposed reef crests on Heron Island on the Great Barrier Reef routinely lose almost all of their coral cover every decade or so because of cyclones, yet they have retained their ability to recover quickly and show no propensity to undergo a long-term shift to an alternative assemblage."
However, human impacts have proven different from natural ones, such as cyclones. Coral reefs are no longer facing down one disaster that hits and then passes, but several different issues, which the authors call "chronic human impacts" that are on-going causing a failure "to recover from pulses of coral mortality" and eventually wholesale collapse. Unfortunately, such states are becoming increasingly common.
"Over the past century many near-shore reefs on the inner Great Barrier Reef have become covered with sediment and macroalgae, and show little or no capacity to return to their former coral-dominated condition," the scientists write.
Hughes says, "the key to saving the reefs lies in understanding why some reefs degenerate into a mass of weeds and never recover—an event known as a ‘phase shift’—while on other reefs the corals manage to bounce back successfully, showing a quality known as resilience."
The researchers point to a number of places where coral reefs are returning due to mitigating the human impacts that contributed to the decline. For example, ending sewage discharges in Kanehoe Bay in Hawaii has allowed coral to recover; returning populations of sea urchins in parts of the Caribbean have allowed coral to rise against seaweed; and in the Philippines better regulations on overfishing has allowed parrot fish to return, a species which aids coral by eating competitor weeds.
"The coral reef crisis is a crisis of governance, because we know what needs to be done but action (to reduce water pollution, curb greenhouse gasses and prevent over-fishing) is not being taken," says Hughes.
|Great Barrier Reef in Australia. Photo by: Rhett A. Butler.|
Of course, the one big wrench in all of this is climate change. In time ocean acidification, due to increasing carbon emissions, and warming sea temperatures could doom coral reefs even when other resilience measures are taken.
To this the researchers say governments must "confront climate change as the single most important issue for coral reef management and conservation by sharply reducing greenhouse gas emissions."
Hughes adds that, "without urgent action, unchecked global warming and ocean acidification promise to be the ultimate policy failures for coral reefs. Although it is possible to promote the recovery of reefs following bouts of bleaching via local actions such as improving water-quality and protecting herbivores, these interventions alone cannot climate-proof reefs."
For Hughes the message is not yet gloom-and-doom, instead: "the world’s coral reefs can still be saved…if we try harder."
CITATION: Terry P. Hughes, Nicholas A.J. Graham, Jeremy B.C. Jackson, Peter J. Mumby, and Robert S. Steneck. Rising to the challenge of sustaining coral reef resilience. Trends in Ecology and Evolution Vol.25 No.11. doi:10.1016/j.tree.2010.07.011.
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