Oceans failing the acid test, U.N. says

The chemistry of the world's oceans is changing at a rate not seen for 65 million years, with far-reaching implications for marine biodiversity and food security, according to a new United Nations study released Thursday.

"Environmental Consequences of Ocean Acidification," published by the U.N. Environmental Program (UNEP)," warns that production of shellfish, such as mussels, shrimp or lobsters, could be most at risk since they will find it harder to build protective shells. It could also damage coral reefs, vital as nurseries for many commercial fish stocks.

Lead author of the report Carol Turley, from the UK's Plymouth Marine Laboratory said in a statement: "We are seeing an overall negative impact from ocean acidification directly on organisms and on some key ecosystems that help provide food for billions. We need to start thinking about the risk to food security."

Tropical reefs provide shelter and food for around a quarter of all known marine fish species, according to the U.N. report, while over one billion people rely on fish as a key source of protein.

Increasing acidification is likely to affect the growth and structural integrity of coral reef, the study says, and coupled with ocean warming could limit the habitats of crabs, mussels and other shellfish with knock-on effects up and down the food chain.

Other marine biologists studying the impact of ocean acidification, which occurs when carbon dioxide dissolves in seawater, have found it affects the ability of fish to smell.

They have discovered that young fish reared in water with elevated levels of carbon dioxide in the water become unable to distinguish the scent of predators and even seem attracted to their smell.

The researchers showed that in the wild, these fish larvae take greater risks, swimming further from shelter that might hide them from predators. More of the fish larvae also die in the wild, sparking fears that fish populations could struggle to survive and replenish themselves as oceans become more acidic.

British researchers pointed out that with an increase in the acidification of the ocean Britain’s famous salmon runs are in danger. The salmon species rely on tiny shellfish when they go out to sea and feed before returning to rivers like the Tay in Scotland or the Test in Hampshire

“One could see a reduction in salmon,” Dr. Carol Turley said. “Ocean acidification may have significant future impacts on catches of crabs, mussels and other shellfish; species dependent on coral reefs and ones such as salmon that feed on smaller, shell building organisms lower down the food chain know as ptetropods.”

The report, unveiled during the latest round of U.N. climate talks in Cancun, Mexico, says that around a quarter of the world's CO2 emissions are currently being absorbed by the oceans, where they are turned into carbonic acid.

Overall, pH levels in seas and oceans worldwide have fallen by an average of 30 percent since the Industrial Revolution. The report predicts that by the end of this century ocean acidity will have increased 150 percent, if emissions continue to rise at the current rate.

But scientists say there may well be winners and losers as acidification doesn't affect all sea creatures in the same way.

Adult lobsters, for example, may increase their shell-building as pH levels fall, as might brittle stars -- a close relation of the starfish -- but at the cost of muscle formation.

"The ability, or inability, to build calcium-based skeletons may not be the only impact of acidification on the health and viability of an organism: brittle stars perhaps being a case in point," Turley said in a statement.

"It is clearly not enough to look at a species. Scientists will need to study all parts of the life-cycle to see whether certain forms are more or less vulnerable."

Scientists are more certain about the fate of photosynthetic organisms such as seagrasses, saying they are likely to benefit from rising acidification and that some creatures will simply adapt to the changing chemistry of the oceans.

The authors identify a range of measures which policymakers need to consider to stop pH levels falling further, including "rapid and substantial cuts" to CO2 emissions as well as assessing the vulnerability of communities which rely on marine resources.

"Ocean acidification is yet another red flag being raised, carrying planetary health warnings about the uncontrolled growth in greenhouse gas emissions. It is a new and emerging piece in the scientific jigsaw puzzle, but one that is triggering rising concern," Achim Steiner, UNEP executive director, said in a statement.

"Whether ocean acidification on its own proves to be a major or a minor challenge to the marine environment and its food chain remains to be seen," he concluded.

Source:
Cable Network News, "Oceans failing the acid test, U.N. says", accessed December 2, 2010
Reuters, "Ocean acidification may threaten food security: U.N.", accessed December 2, 2010
The Telegraph, "Acidic oceans: fish lose ability to smell danger", accessed December 2, 2010
The Telegraph, "Cancun climate summit: Britain's salmon at risk from ocean acidification", accessed December 2, 2010

King Crab Distributions Limited by Temperature in the Southern Ocean

Invasions of voracious predatory crabs due to global warming could threaten the unique continental-shelf ecosystems of Antarctica, according to newly published findings.

"Nowhere else than in these ecosystems do giant sea spiders and marine pill bugs share the ocean bottom with fish that have antifreeze proteins in their blood," says Rich Aronson, professor of biological sciences at Florida Institute of Technology in Melbourne, Fla. "The shell-cracking crabs, fish, sharks and rays that dominate bottom communities in temperate and tropical zones have been shut out of Antarctica for millions of years because it is simply too cold for them."

Climate change is about to cause a major upheaval in the shallow marine waters of Antarctica. Predatory crabs now are poised to return to warming Antarctic waters and disrupt the primeval marine communities.

"King crabs are ecologically important predators and form the basis of economically significant commercial fisheries," said Dr Sven Thatje, an evolutionary ecologist at the University of Southampton's School of Ocean and Earth Science (SOES), which is based at the National Oceanography Center in Southampton.

Thatje and graduate student Sally Hall studied how water temperature influences the distributions of king crab species in the Southern Ocean, which has some of the coldest waters on Earth. The results appear in the journal Polar Biology.

King crabs are cold blooded, their body temperature being determined largely by that of the surrounding environment. Although many of them live in cold, deep-sea habitats, experiments have shown that their larvae (at right) fail to mature in water temperatures below around half a degree Celsius, even after only brief exposure.

"We tested the hypothesis that the king crab species of the Southern Ocean only thrive above a critical minimum temperature and that it is this thermal barrier that determines their biogeographical distributions in the Southern Ocean," said Thatje.

To do this, Thatje and Hall carefully studied the distribution of seventeen species of king crab living at depths between around 500 and 1600 meters in the Southern Ocean. They collated data from published records, museum collections, commercial fishing records, and reports from scientific research cruises. They then compared these records to water temperatures measured at a range of relevant depths and geographical latitudes.

Consistent with their hypothesis, they found that king crabs occur mostly at locations where the polar water temperature is relatively warm. The coldest waters in which king crabs have been found are between 0.4 and 0.5°C in the Ross Sea (map at left), suggesting that this indeed represents a thermal barrier limiting king crab distributions.

In addition, the records showed that only two species are endemic to waters south of 60 degrees South, suggesting that particular physiological and reproductive adaptations are required for life in the most extreme environments.

The researchers found that gaps in king crab distributions largely coincide with regions of low water temperature, although there are some anomalous absences yet to be explained.

Their findings imply that even relatively small increases in water temperature due to global warming could lead to king crabs moving into new areas.

"Rapidly increasing water temperatures observed along the West Antarctic Peninsula could allow king crabs to spread from the slope of the peninsula to the continental shelf itself," explained Hall.

This could have considerable ecological consequences. King crabs are voracious predators that crush and then feed on their prey, but they and potentially competing predators such as sharks and rays and other predatory crustaceans are largely absent on the high-Antarctic continental shelves.

"The worry is that the sudden appearance of a new predator with few competitors could threaten isolated shelf communities such as those of the Bellingshausen Sea (right) on the west side of the Antarctic Peninsula," said Hall.

The researchers believe that their study provides a baseline against which future changes in the distribution of king crabs expected under global warming can be compared.

The study was supported by the Total Foundation (Abyss2100), the European Union's Sixth Framework Program (FP6) Marine Biodiversity and Ecosystem Functioning (MarBEF) project, and by the Natural Environment Research Council.

Source:
Science Daily, "King Crab Distributions Limited by Temperature in the Southern Ocean", accessed November 8, 2010