Acidifying oceans could threaten marine food chain says UN

Posted: 4 December 2010

The future impact of rising CO2 emissions on the health of seas and oceans may be far more wide-ranging and complex than was previously supposed, a new report released at the UN climate convention meeting in Mexico says. 

The study, entitled The Environmental Consequences of Ocean Acidification, has brought together some of the latest scientific research on ‘ocean acidification', a process triggered by increasing concentrations of dissolved C02 which is changing the sea's chemistry by lowering the pH of the marine environment.

Launched by the UN Environment Programme (UNEP), the report confirms concerns that some organisms, such as corals and shellfish may find it increasingly difficult to form their skeletons in the decades to come making it harder to survive let alone thrive. It also shows that ocean acidification can react together with ocean warming so that animals such as crabs have a reduced range of temperatures they can thrive in.

Bleached coral<bR>&#169 Woolcot Henry 2001
Bleached coral
© Woolcot Henry 2001

This in turn 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 known as ptetropods, for example.

Other new research is spotlighting fresh areas of concern including findings that some species, including the clown fish made famous in the Disney cartoon Finding Nemo, may find it harder to avoid their predators and to find their way home.

If other fish react the same way, this may have implications for the marine food chain upon which billions of people depend directly or indirectly for protein and livelihoods.

Red flag

Achim Steiner, UNEP Executive Director, said: "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".

‘Whether ocean acidification on its own proves to be a major or a minor challenge to the marine environment and its food chain is to date unknown. But the phenomenon comes against a backdrop of already stressed seas and oceans as a result of over-fishing to other forms of environmental degradation. Thus the public might quite rightly ask how many red flags do governments need to see before the message to act gets through," he said.

The report was compiled in collaboration with the Plymouth Marine Laboratory in the United Kingdom and scientists from other organisations including the National Oceanography Centre in Southampton and the Intergovernmental Oceanographic Commission of UNESCO.

Food security

Carol Turley, Co-ordinator for the UK Ocean Acidification Research Programme, and lead author of the new report, said: "As scientists around the world start to investigate the potential impacts of ocean acidification, 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."

Dr. Turley stressed that researchers were working on the frontiers of science in respect to ocean acidification and its potentially complex impact on the marine environment and its organisms.

She added that some research indicated that adult lobsters, for example, might actually increase shell-building in response to falling pH levels whereas it may be the juveniles who are less able to build healthy skeletons.

A similar possibility may arise in respect to adult and juvenile forms of fish with the olfactory or smelling systems of some species of young fish impaired but adults unaffected.

Meanwhile, there is some evidence of other curious changes if emissions continue to rise and concentrations of C02 continue to build-up in the seas and oceans. For example, brittle stars, an important part of the marine food chain, may increase shell-building at the cost of muscle formation, some science suggests.

"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. Meanwhile, 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," said Dr. Turley.

Other key findings

The report points out that there may be "winners" as well as "losers", with photosynthetic organisms such as seagrasses likely to benefit from rising acidification. Yet studies of natural C02  events in the Mediterranean Sea show that although there are some "winners" the ecosystem is likely to be altered in other ways.

It says that many marine organisms have ways of compensating for changes in seawater chemistry, although they may have to spend more energy doing this in an increasingly more acidic ocean. However, studies of mussels and sea urchin species have shown that they have only a partial or no compensation mechanism, potentially making them more vulnerable.

Pointing out that around 80 per cent of fish catches occur in just 10 per cent of the oceans, including key areas such as Continental shelves and estuaries, the report says that "many of these areas are also projected to be very vulnerable to ocean acidification this century";

Fish farming could be the answer to the world's growing demand for fish, but environmental - and social - concerns remain. (Photo by R. Faidutti courtesy UN Food and Agriculture Organization)
Fish farming could be the answer to the world's growing demand for fish, but environmental - and social - concerns remain. Photo credit: FAO/R. Faidutti

The aquaculture industry is the fastest growing food producer worldwide, increasing at a rate of 7 per cent per annum and the proportion of fish produced by aquaculture and consumed by humans worldwide has risen to 50 per cent of total production.  The report says that these industries are now at risk from future ocean acidification both directly through the impact on the organisms themselves and indirectly through the food webs and habitats they depend on.

Tropical reefs provide shelter and food for an estimated 25 per cent of known marine fish species, and account for between 9 and 12 per cent of world fish landings. Consequently, these coral reefs provide food and livelihood security for some 500 million people worldwide. But future ocean acidification is likely to affect adult and juvenile coral growth and recruitment, coralline red algae growth, reef structural integrity and potentially even the density of bio-eroding grazers and predators.

The report calls on governments,  policymakers and others to consider a range of actions including rapid and substantial cuts to man-made CO2 emissions to the atmosphere in order to reduce ocean acidification.

 The full report is available here.