Spectre of seas without shells

Remember Silent Spring? It was in 1962 that Rachel Carson’s book alerted the world to the problems of the insecticide DDT in the food chain. Birds of prey were particularly vulnerable, with their eggshells becoming so thin they could no longer contain growing embryos. The threat of springtime with no birdsong catapulted the world into a new awareness of ecology and conservation.

Forty-seven years on, a new threat is looming, this time in the sea. Once again the busy rhythm of people is causing an ecological crisis. Not as complicated as modelling global warming, not as simple as banning a pesticide, our newest planetary drama is called ocean acidification. It happens because of the connections between air, water, and shells.

We know that human activities, particularly the burning of coal, oil, petrol and wood, have for the past 200 years increased the amount of carbon dioxide, or CO2, in the atmosphere. While these molecules float around in the air, they act like a blanket keeping Earth warm and eventually changing the whole climate. The warming effects of CO2 have been less than they could have been, however, because about a third of CO2 from the air gets mopped up by the oceans.

What’s good for global climate change, however, is bad for the sea. When you add CO2 to sea water, it becomes more acid. And that means that the carbonate ion, CO3, gets scarcer. That might seem like no big deal, but many marine plants and animals use carbonate, along with calcium, for constructing protection and structure.

Clams, snails, urchins, corals, some algae, and many plankton all use calcium carbonate (CaCO3) to build their shells.

Marine ecologists have only just begun to investigate the potential problems that a more acid ocean might pose to creatures in the sea. What they have found so far is alarming. Tiny plankton, zillions of which form part of the basis of the marine food chain, are usually protected by a robust and complex ball of carbonate.

But when you grow them in more acid conditions, these little shells become thinner and more frail. Even more alarming, experiments with corals show that under acid conditions, some do not make a skeleton. They sit there like a jelly glob with no sign of the complex architecture that makes coral reefs so diverse and so attractive to tourists – and to fish.

This isn’t just a problem for squishy marine critters. Marine aquaculture and multimillion-dollar fisheries such as mussel farming are likely to be affected.

Tourism to coral reefs is another multimillion-dollar industry, and some economies are wholly reliant on it. There is even the suggestion that a more acid ocean could be more corrosive and thus affect shipping and ports.

Abigail Smith, stuff.co.nz, 13 May 2009. Full article.

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