Reef-building corals lose out to softer cousins due warming

Alister Doyle PlanetArk 26 Mar 13;

Climate change is likely to make reef-building stony corals lose out to softer cousins in a damaging shift for many types of fish that use reefs as hideaways and nurseries for their young, a study showed.

Soft corals such as mushroom-shaped yellow leather coral, which lack a hard outer skeleton, were far more abundant than hard corals off Iwotorishima, an island off south Japan where volcanic vents make the waters slightly acidic, it said.

A build-up of carbon dioxide in the atmosphere is turning the oceans more acidic in a process likely to hamper the ability of creatures such as lobsters, crabs, mussels or stony corals to build protective outer layers.

"Soft coral has the potential to be a winner in coral reefs," lead author Shihori Inoue of the University of Tokyo told Reuters by e-mail of the findings, the first study of likely winners and losers among soft and hard corals.

"Reef communities may shift from reef-building hard corals to non-reef-building soft corals under (carbon dioxide levels) predicted by the end of this century," the authors wrote in Monday's edition of the journal Nature Climate Change.

When it reacts with water, carbon dioxide in the atmosphere can form carbonic acid. That damages hard corals, tiny animals that secrete calcium carbonate to form their stony protective layer.

"When combined with their ability for rapid colonization, soft corals may out compete hard corals in coral reef environments subject to ocean acidification," the scientists wrote.

CLOWNFISH

"Hard corals are important reef builders and provide complex three-dimensional habitats for many reef organisms," they wrote, adding that a shift could have damaging effects for many fish and other marine creatures that live around reefs.

A community of soft coral "hardly works like hard coral as a nest for small living organism such as ... shrimp, and little fish," Inoue said. The 2003 animated movie "Saving Nemo" shows how clownfish live and grow around reefs.

Covering less than one percent of the ocean floor, reefs support about 25 percent of all marine life, with over 4,000 species of fish alone, according to the International Coral Reef Initiative which seeks to protect reefs.

The scientists said that the levels of carbon dioxide in the water off Iwotorishima, an island near Okinawa in the Pacific, corresponded varied from equivalent to 550 parts per million (ppm) of carbon dioxide in the atmosphere to as high as 970. Both levels are within the range seen as possible by 2100 according to the U.N. panel of climate scientists.

Current atmospheric levels are about 395 ppm, a sharp rise from 280 ppm before the Industrial Revolution. And emissions of carbon dioxide are continuing to rise - China, the United States and the European Union are the top emitters.

Other studies have also shown that stony coral reefs are vulnerable to rises in temperature that can cause a whitening that can lead to death.

Gas vents in the Mediterranean and corals around a carbon dioxide seep off Papua New Guinea have also been used to study the likely future conditions of the oceans.

"Soft coral may not always be the winner in acidified waters. In temperate oceans, it has been shown that algae or sea anemones can be winners at high-carbon dioxide vents," they wrote.

(Reporting by Alister Doyle; Editing by Jason Webb)

Climate change brings opportunities
Coralcoe Science Alert 26 Mar 13;

Climate change will bring both big opportunities and threats to the fish-dependent nations of the Pacific, international scientists say.

While the coral reef fisheries of Pacific islands are likely to take a major hit from warming and ocean acidification, there is potential for well-managed tuna stocks to grow, improving both national food security and economic prospects in many countries.

The finding appears in the journal Nature Climate Change and is the work of a team of marine scientists from Australia, France, New Caledonia and Fiji.

“Nowhere else in the world do so many countries and territories depend as heavily on fish and shellfish for economic development, government revenue, food security and livelihoods, they point out, adding fishing accounts for 25% or more of the GDP of 12 of the 22 Pacific countries.

“Fish is also a cornerstone of food security in the region,” says Professor Morgan Pratchett of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.

“The tropical Pacific has warmed substantially over the past 50 years,” the report says. “This has reduced the sea’s salinity over large areas and is a trend we expect to see continue as tropical rainfall rises.

“The outlook for El Nino events is still unclear, but there are expected to be fewer, stronger tropical cyclones. Some important currents will weaken. The ocean will continue to acidify with further increases in atmospheric CO2, much of which dissolves in seawater. Sea levels will rise between a half and one metre by 2100. All these changes will affect fish – and the people and communities that depend on them.”

The researchers consider that the Pacific Warm Pool – an immense area of hot water north of Papua New Guinea – is liable to expand, and this may cause a decline in the plankton on which tuna feed.

This will cause tuna to shift their feeding and breeding grounds towards the south and east Pacific, meaning that countries lying to the east of 170 degrees may emerge as ‘winners’ and gain more fish, while others to the west may be ‘losers’.

Overall, there could be a ‘net gain’ in the Pacific tuna catch, provided the stocks are well managed and fishing pressure controlled, the report indicates.

For coral reef fisheries the outlook is uniformly dire: “Even under good management (for example, controlling runoff), coral cover is expected to decrease from the present-day maximum of 40% to 1-30% by 2035 and 10-20% by 2050,” due mainly to bleaching, says Professor Pratchett, who was responsible for analysis of coastal fisheries projections.

“At the same time mangroves and seagrass beds – important as fish nurseries – are also likely to suffer.”

A projected 20 per cent decline in coral reef fish, shellfish and crustacean harvests is likely to have a significant effect on regional food security, the scientists caution.

“In countries (such as) PNG, Samoa, the Solomon Islands and Vanuatu, even well-managed coastal fisheries will not supply the 35 kg of fish per capita per year recommended for good nutrition in the years to come owing to the limited areas of coral reef relative to population size, and rapid population growth.”

Good management of tuna stocks, especially, could in fact enhance regional food security under climate change, they add.

The paper “Mixed responses of tropical Pacific fisheries and aquaculture to climate change” by Johann D. Bell1, Alexandre Ganachaud, Peter C. Gehrke, Shane P. Griffiths, Alistair J. Hobday, Ove Hoegh-Guldberg, Johanna E. Johnson, Robert Le Borgne, Patrick Lehodey, Janice M. Lough, Richard J. Matear, Timothy D. Pickering, Morgan S. Pratchett, Alex Sen Gupta, Inna Senina and Michelle Waycott appears in Nature Climate Change.