Acidic oceans threaten marine life

Concerns that sea life will struggle for survival as greenhouse gases make the oceans more acidic are amplified today by a study that shows that marine creatures such as snails and crabs will have weakened defences to protect them against predators.

Leaving aside the direct effects of greenhouse gases on climate change, the oceans “mop up” carbon dioxide from the atmosphere so that levels of carbonic acid rise. There are fears that the resulting rise in acidity could particularly affect sea creatures with hard shells because it cuts the availability of calcium carbonate (chalk) – which coral reefs, clams, molluscs and some plankton use to produce their hard skeletons.

The rising acidity of the seas is having a damaging effect on the hard shells of marine creatures like crabs
The acidity of the seas is having a damaging effect on the hard shells of marine creatures like crabs

Now it seems that the rise in the acidity of the seas has another effect on shellfish. Many marine creatures, from crabs and lobsters to molluscs, are able to protect themselves from predators by growing thicker shells when they are under greater threat.

Today, in the journal Biology Letters, Dr Simon Rundle of the University of Plymouth and colleagues there and at the Plymouth Marine Laboratory report that this common ability is disrupted in the case of the common periwinkle, which thickens its shell in the presence of predatory shore crabs. “This thickening was absent when snails grew in acidified seawater; these snails also had disrupted physiologies and behaviour.”

Although the experiments were performed under laboratory conditions that aimed to mimic extreme future acidification scenario “they do suggest, however, that effects of seawater acidification are likely to be more extensive than previously thought and extent beyond direct effects,” said Dr Rundle. “The effects will be even more pronounced.” If this is common, it could alter the way marine food webs work, he added.

One recent study from California State University found that half of the carbon emitted by human activities over the last two centuries has entered the oceans. Another, by the US Livermore National Laboratory, predicts that the release of carbon dioxide during the next several centuries will increase ocean acidity more rapidly than during the past 300 million years, except perhaps during global catastrophes.

Increased acidity may also directly affect the growth and reproduction rates of fish, as well as affecting the plankton populations which they rely on for food, and have potentially disastrous consequences for marine food webs.

Roger Highfield,, 17 October 2007. Article.

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