Acid levels threaten oceans

The chemistry of the world’s oceans is being altered at a speed not seen since the extinction of the dinosaurs over 65 million years ago, according to a United Nations study released on 2 December.

Around 25 per cent of the world’s CO2 emissions are being absorbed into the seas and oceans where it converts to carbonic acid.

The report says that the ocean’s pH levels have decreased by 30 per cent, and the concentration of carbonate ions — which are used by organisms to make shells and reef systems — has fallen by 16 per cent since the industrial revolution.

This findings directly relate to fish and other organisms in Cayman waters such as sea urchins, molluscs and coral reef systems.

“Calcium carbonate is the dominant building material of a multitude of invertebrate reef species including the corals themselves,” said Tim Austin, assistant director of research and assessment at the Cayman Islands Department of Environment. “Other important species such as sea urchins, conchs and coralline algae also depend on the availability of calcium carbonate to build their skeletons and shells.”

Impacts in Cayman

He said that studying ocean acidity is such a new topic and relatively poorly understood that it has not been high on the DoE’s priorities for separate monitoring in Cayman, so they can’t say categorically what the impacts have been or are likely to be, but the DOE does know some of the effects.

“The increased acidity of the ocean will impact these species making it harder to grow and increasing the eroding forces on existing structures like the reef framework and living organism’s shells,” he said. “There are also some concerns around the additional energy required to compensate for the increased acidity (more hydrogen ions) by species that maintain a specific ‘blood’ pH. This regulatory system requires energy and will mean that resources are diverted from growth and reproduction.”

Cayman will receive this threat, like many of the communities that rely on the waters for so much.

“The DoE is aware of the threats of ocean acidification and will actively work to keep up to date with the appropriate current scientific knowledge and will continue to monitor Cayman’s marine environment for signs of stress and wherever possible will recommend appropriate management interventions,” Mr. Austin added.

Fish, including shellfish, contribute to 15 per cent of animal protein for three billion people worldwide, and a further one billion people rely on fisheries for their primary source of protein.

The report also says it is anticipating that future ocean acidification is likely to affect adult and juvenile coral growth and recruitment, coralline red algae growth, reed structural integrity and potentially even the density of bio-eroding grazers and predators.

Tropical reefs provide shelter and food for an estimated 25 per cent of known marine fish species, and account for between 9 per cent and 12 per cent of world fish landings.

Carol Turley from the UK’s Plymouth Marine Laboratory was the lead author of the report, which was compiled in collaboration with scientists from other organisations including the National Oceanography Centre in Southampton and the Intergovernmental Oceanographic Commission of UNESCO.

“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,” Ms Turley said in a statement. “We need to start thinking about the risk to food security.”

She added that research indicated that adult lobsters — like the Caribbean Spiny Lobster found in Cayman waters — 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.

Under-Secretary General and UNEP Executive Director Achim Steiner said in a statement: “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.”

Call to action

The report calls on governments, policy-makers 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;

Determine the vulnerability to ocean acidification of human communities dependent on marine resources;

Identify species that are more flexible to change and assess how there may affect ecosystems and food security;

Reduce other pressures on food fish stocks and provide the best chance of success through, for example, marine spatial planning or re-evaluating available resources and their usage;

Assess the options for the development of environmentally sustainable ‘aquaculture’ options using species that may be more resistant to lowered pH;

And embrace the science of ocean acidification into fisheries management tools.

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