‘There will be winners and losers’
By Summit Voice
SUMMIT COUNTY — Global warming impacts to coral reefs are not some far-fetched future scenario, but something that is happening right now, leading marine scientists said this week during the opening session of the International Coral Reef Symposium in Cairns, Australia.
A panel of top researchers at the global powwow said the effects of warmer water and increased carbon dioxide levels are already evident in marine ecoystems.
“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,” said the University of Queensland’s John Pandolfi.
“Tropical coral reef waters are already significantly warmer than they were and the rate of warming is accelerating,” said Janice Lough, of the Australian Institute of Marine Science. “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, during the past century global temperatures have warmed by 0.7 Celsius, while sea surface temperatures in tropical regions have warmed by 0.5 degrees Celsius. This increase in baseline temperatures has already resulted in widespread coral bleaching events and outbreaks of coral diseases.
Current projections suggest the tropical oceans could be 1 to 3 degrees Celsius warmer by the end of this century.
Lough focuses on long-term growth histories from massive coral skeletons. Even with the modest amount of warming to date — compared to future projections — coral growth rates are responding to these observed temperature changes.
Several reefs, including the Great Barrier Reef, have witnessed slower massive coral growth in recent decades, while cooler reef sites off Western Australia have, initially, responded by increasing their growth rates. The latter is unlikely to be sustainable, given the setbacks in growth following coral bleaching and, as temperatures continue to warm, optimum temperatures for coral growth are exceeded, she said.
Pandolfi said there is large variation in the vulnerability of coral reef species in their response to temperature change and ocean acidification, so some taxa may survive but others could go extinct. In addition, 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.
Pandolfi added that ultimately the global community must act to reduce greenhouse gas emissions. But new science is also showing that, given that the impact on corals will be more variable than first realized, our management approaches must become more sophisticated, with particular focus on reducing local threats such as overexploitation and pollution. Managing reefs for local stress will ensure maximum health as they continue to confront a changing global climate.
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, said Philip L. Munday, of James Cook University.
“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.”
Over time, he said, more carbon dioxide dissolved in the ocean can also cause abnormal behavior in fish leading to reduced survival. In a recent study, Munday and his team examined the changes to fish in tanks with artificially high levels of carbon dioxide. They found neurological changes that resulted in fish being less effective at avoiding predators, because of adverse impacts to their sense of smell and an increased tendency to stray further from reef areas where they can hide. At the same time, some fish showed, over generations, an ability to adjust to temperatures changes.
“Like coral, there will be winners and losers and the communities of fish we see on reefs in the future are likely to be different to those of today,” Munday said.
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.