Climate change threatens marine ecosystems

“The situation is analogous to that faced by a human whose immune system is compromised and who may succumb to a disease that would not threaten a healthy person,” says Eileen Claussen, President of the Pew Centre on Global Climate Change.

The Pew report says delicate marine ecosystems such as coral reefs are under threat (see related story). Temperature changes are likely to influence organisms’ metabolism and alter species interactions. Those that are adapted to particular temperature ranges or local resources would have to compete or migrate, or else face extinction.

Changes in rainfall and circulation patterns could lead to increased flooding or drought, with regional temperature changes in the ocean. Increased upwelling and downwelling could alter the availability of essential nutrients to organisms. The result would be the geographic redistribution of marine species. Coastal wetlands migrating inland with rising sea levels might be obstructed by human development.

But not all of the news is bad. A recent report suggested that the process of coral bleaching – whereby coral expel the colourful algae living on them, triggered by rising sea temperatures – may in fact provide a defence against warming waters, allowing new species of algae adapted to higher temperatures to settle and protect the coral (see related story).

And a German study monitoring the effects of temperature change on European cod populations has found that while some species will suffer, others will flourish. As waters become warmer cod populations are predicted to shift to cooler waters in deeper and more northern parts of Europe, with some species disappearing at the southern limit. But according to Professor Hans Poertner of the Alfred-Wegener Institute, “if warming extends to the Arctic, this will be compensated for to some extent by increased productivity in the North.” Some species will thrive as the oceans warm to the optimum temperature within the species’ temperature tolerance range.