Aquaculture for all

Shellfish Trade Could Disappear to Acidification

Health Water quality Economics +2 more

GENERAL - Ocean acidification may cause a serious decline in the harvest of molluscs, such as mussels, and a major economic downturn in the industries that depend on them could follow.

A new study in Environmental Research Letters reveals that in the US ocean acidification could cause shellfish revenues to drop by over one third in the next 50 years, writes Kate Ravilious, a contributing editor to environmentalresearchweb.

Ocean acidification is a side effect of human industrial activity. As atmospheric carbon dioxide levels rise, more carbon dioxide is dissolved in ocean surface waters, producing carbonic acid and pushing up the acidity of the water. This change in environment is bad news for a number of ocean species. In particular calcifying organisms, such as coral, many plankton and molluscs, will find it increasingly difficult to construct their shells or skeletons.

The average acidity of ocean water has increased by 30 per cent since pre-industrial times and there are already signs that this is having an impact. A number of coral reefs, including the Great Barrier Reef along the east coast of Australia, have started to bleach and dissolve.

By 2060 it is estimated that average ocean acidity could have increased by as much as 120%, with potentially catastrophic consequences for many marine organisms.

Sarah Cooley and Scott Doney, from Woods Hole Oceanographic Institution, US, have calculated what kind of economic impact this rising acidity might have on commercial fisheries. Using IPCC projections of carbon dioxide emissions they monitored the likely increase in ocean acidity over the next 50 years.

They then used data from laboratory studies on the effects of acidification on molluscs, to show that mollusc harvests in the US could be expected to decline by between 10 and 25% over the next 60 years.

Currently mollusc sales generate about $750 million per year in the US, nearly 20% of total US fisheries revenue. By 2060 Cooley and Doney calculate that between $75 and $187 m (in today's equivalent terms) will be lost from the mollusc trade every year. This amounts to a loss of up to $1.4 bn over the next 50 years.

In addition there could be substantial indirect economic costs to businesses that rely on the fishing industry, such as the restaurant trade.

For some countries, the consequences could be even more severe. "Global population isn't going to grow evenly throughout the world, and some of the regions that are experiencing fastest population growth depend on their fisheries and aquaculture for protein," Cooley told environmentalresearchweb. Southeast Asia, South Africa and island nations in the South Pacific are likely to be particularly hard hit this way.

To make things worse it is not only molluscs that will be adversely affected by ocean acidification. "The species that depend on molluscs and corals for food or habitat could be harmed as well," said Cooley.

A recent study showed that ocean acidification could affect the way sound is transmitted in the ocean, which could impact on fish and mammal migration. Meanwhile, another study indicates that fish may lose some of their sense of smell as a result of increased acidification, an essential sense for hunting, finding a mate and recognising territory.

All in all, ocean acidification is likely to be a major problem – a fact recognised by The Royal Society, which is concerned that this topic may be left off the agenda at the United Nations Climate Conference in Copenhagen. Martin Rees, president of the Royal Society, recently said, "everybody knows that the increasing concentration of carbon dioxide in the atmosphere leads to climate change. But it has another environmental effect – ocean acidification – which hasn't received much political attention. Unless global CO2 emissions can be cut by at least 50% by 2050 and more thereafter, we could confront an underwater catastrophe, with irreversible changes in the makeup of our marine biodiversity. The effects will be seen worldwide, threatening food security, reducing coastal protection and damaging the local economies that may be least able to tolerate it. Copenhagen must address this very real and serious threat."

Cooley and Doney believe that a certain amount of ocean acidification is now inevitable, and that we need to start considering adaptation strategies to lessen the pressure on marine ecosystems. "Limiting nutrient runoff from land helps coastal ecosystems stay healthy, and fishing rules can be adjusted to reduce pressure on valuable species, for example," said Cooley.

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