Why climate change might not spell death for the Reef

Sydney Morning Herald 13 Apr 12;

Rising ocean temperatures caused by climate change are unlikely to mean the end of the coral on the Great Barrier Reef, according to a new scientific study.

The Cell Press journal Current Biology this morning published what it says is the first large-scale investigation of climate effects on corals and found while some corals were dying, others were flourishing and adapting to the change in water temperatures.

For the study researchers identified and measured more than 35,000 coral colonies on 33 reefs across the length of the Great Barrier Reef to see how they were responding to warming ocean waters.


In results they have described as ‘‘surprising’’ the study found while one species declined in abundance, other species could rise in number.

One of the researchers, Professor Terry Hughes from James Cook University, said while critical issues remained he now believed rising temperatures were unlikely to mean the end of the coral reef.

‘‘The good news is that, rather than experiencing wholesale destruction, many coral reefs will survive climate change by changing the mix of coral species as the ocean warms and becomes more acidic,’’ he said.

‘‘That’s important for people who rely on the rich and beautiful coral reefs of today for food, tourism, and other livelihoods.’’

He said earlier studies of climate change and corals had been done on a much smaller geographical scale, with a primary focus on total coral cover or counts of species as rather crude indicators of reef health.

‘‘We chose the iconic Great Barrier Reef as our natural laboratory because water temperature varies by 8 to 9 degrees Celsius along its full length from summer to winter, and because there are wide local variations in pH,’’ he said.

‘‘Its regional-scale natural gradients encompass the sorts of conditions that will apply several decades from now under business-as-usual greenhouse gas emissions.’’

The warming of the ocean’s temperatures due to climate change will change the composition of coral reefs and while this will mean the end for some species it will mean others are adapting to survive.

The report also listed other human impact dangers to the reef including over-fishing and pollution and noted some coral had adapted to the new conditions these changes presented.

‘‘The accelerating impact of climate change on coral reefs is of major concern worldwide,’’ the report said.

‘‘Contemporary research on how climate change affects coral reefs has matured beyond the simplistic ‘‘canary in the coal mine’’ concept to a more nuanced recognition that climate-related pressures such as bleaching (due to the loss of symbiotic zooxanthellae) and ocean acidification do not affect all species equally.

‘‘In this context, a critical issue for the future status of reefs will be their ability to maintain functional capacity in the face of the changes in species composition.’’

The report said coral reefs are one of the world’s most complex and vulnerable ecosystems and face an uncertain future in the coming decades as they continue to respond to the impacts of human contact and pollution and the called the findings of the study ‘‘profound’’.

‘‘The flexibility in community composition that we document along latitudinal environmental gradients indicates that climate change is likely to result in a reassortment of coral reef taxa rather than wholesale loss of entire reef ecosystems,’’ it said.

‘‘Our results have profound implications for the future expectations of regional-scale impacts of climate change on coral reefs.

‘‘Importantly, the susceptibility of corals to thermal stress and bleaching, reduced alkalinity, and other climate-related phenomena all vary substantially within and between taxa (the organisms which make up the coral reefs).’’

Under Climate Change, Winners and Losers On the Coral Reef
ScienceDaily 12 Apr 12;

As ocean temperatures rise, some species of corals are likely to succeed at the expense of others, according to a report published online on April 12 in the Cell Press journal Current Biology that details the first large-scale investigation of climate effects on corals.

"The good news is that, rather than experiencing wholesale destruction, many coral reefs will survive climate change by changing the mix of coral species as the ocean warms and becomes more acidic," said Terry Hughes of James Cook University in Australia. "That's important for people who rely on the rich and beautiful coral reefs of today for food, tourism, and other livelihoods."

In an attempt to understand the sorts of changes that may take place as the world's oceans warm, the researchers examined the coral composition of reefs along the entire length of Australia's Great Barrier Reef. Earlier studies of climate change and corals have been done on a much smaller geographical scale, with a primary focus on total coral cover or counts of species as rather crude indicators of reef health.

"We chose the iconic Great Barrier Reef as our natural laboratory because water temperature varies by 8 to 9 degrees Celsius along its full length from summer to winter, and because there are wide local variations in pH," Hughes explained. "Its regional-scale natural gradients encompass the sorts of conditions that will apply several decades from now under business-as-usual greenhouse gas emissions."

In total, the researchers identified and measured more than 35,000 coral colonies on 33 reefs. Their survey revealed surprising flexibility in the assembly of corals. As they saw one species decline in abundance, some other species would tend to rise. The waxing or waning of any given coral species the researchers observed as they moved along the coastline occurred independently of changes to other coral species.

Hughes concludes that corals' response to climate change is likely to be more complicated than many had thought. Although he now believes that rising temperatures are unlikely to mean the end of the coral reef, critical issues remain.

"If susceptible table and branching species are replaced by mound-shaped corals, it would leave fewer nooks and crannies where fish shelter and feed," he said. "Coral reefs are also threatened by much more local impacts, especially by pollution and overfishing. We need to address all of the threats, including climate change, to give coral reefs a fighting chance for the future."

Journal Reference:

Hughes TP, Baird AH,Dinsdale EA, Moltschaniwskyj NA, Pratchett MS, Tanner JE, Willis BL. Assembly rules of reef corals are flexible along a steep climatic gradient. Current Biology, 2012 (in press)