Warming climate damaging reefs, impacting fish

The impact of a warming climate on reefs is already upon us — complex changes have begun that could fundamentally change what reefs look like in the future. This in turn could impact on fish populations and their availability.

That was the overarching message from a panel of coral reef experts, who are on the forefront of understanding the impact of a rising seawater temperatures and ocean acidification.

The panel included Janice M Lough of the Australian Institute of Marine Science; John M Pandolfi of the University of Queensland; Roberto Iglesias Prieto of the National Autonomous University of Mexico; and Philip L Munday of the James Cook University.

"Tropical coral reef waters are already significantly warmer than they were and the rate of warming is accelerating," said Janice Lough.

"With or without drastic curtailment of greenhouse gas emissions we are facing, for the foreseeable future, changes in the physical environment of present-day coral reefs.

Lough said that over the past century, global temperatures have warmed by 0.7 degrees Celsius and those of the surface tropical oceans by 0.5 degree Celsius. This raising of baseline temperatures has already resulted in widespread coral bleaching events and outbreaks of coral diseases. Current projections indicate that the tropical oceans could be 1-3 degree Celsius warmer by the end of this century, according to an Australian Institute statement.

Pandolfi elaborated that coral reefs that are already degraded from human pressures, such as overfishing or land-based pollution, will be much less likely to handle the increase in temperature and ocean acidity.

"There will be winners and losers in climate change and ocean acidification, but reefs will demonstrably change and, for most people's idea of what reefs are, not for the better," says Pandolfi.

Munday said changes to coral reef habitat caused by climate change will also potentially lead to changed fish populations. The direct impacts, which are already occurring, are reduced coral cover and less habitat structure for fish.

"That will mean fewer species and lower fish abundance," Munday said. "Some species will fair better than others. For example, fish that eat coral will be more severely impacted, but overall we can expect a decline in fish numbers.

Roberto Iglesias-Prieto underscored that these changes will ultimately have severe impacts on the millions of people worldwide who depend on reefs for food, income and storm protection. Reefs also contribute to national economies through such sectors as tourism and commercial fisheries.

"To truly understand the impacts of climate change on reefs, you have to be an ecologist, an economist and a political scientist," Iglesias-Prieto said.

These findings were presented at International Coral Reef Symposium 2012 in Australia.