Global warming could see certain coral species flourish

By Tim Radford

Rising sea temperatures will make life a bit cosier for at least one organism – a tiny variety of foraminifera (the name means “hole bearer”) called Amphistegina.

Martin Langer of the University of Bonn and colleagues report in the Public Library of Science One that these little single-celled, calcareous creatures (chalky, or containing lime) will be able to extend their natural range as the sea warms – and could possibly help stabilise coastlines under threat as sea levels rise, and coral reefs that are stressed by rising temperatures.

There are thousands of foraminifera species and they exist in their trillions in the ocean, dying to form the calcareous ooze on the bottom of the oceans and the sands of the shallows.

The only limits to their multiplication are the warmth of the water and the supply of marine nutrients, and Amphisteginids in particular require a water temperature of 14°C.

Under business-as-usual scenarios scientists say oceans could be 150% more acidic by 2100

As the oceans warm – and climate scientists expect the warming to be at least 2.5°C by the end of the century – the potential range of these organisms extends.

Professor Langer has tracked these creatures for 9,000 kilometres along the coasts of Somalia, Kenya, Tanzania, Mozambique, South Africa, Namibia and Angola, and they could be heading north and south at a rate of between 2.75 km and 8 km a year.

By 2100, they will have moved another 300 kilometres closer to the poles as the oceans warm.

Acid scavengers

Corals, too, can and should spread away from the tropics as temperatures rise.

But one consequence of extra carbon dioxide in the atmosphere is that the oceans become more acidic, which is bad news for corals as a genus, and very bad news for communities that depend on stable coral reefs, because the skeleton of a coral is aragonite, and vulnerable to increasing acidity.

The shells of foraminifera are calcite, and as the foraminifera multiply, they could be doing what corals have always done: convert the solution in water to calcium carbonate, and in the course of doing so at least remove some of the carbon dioxide from the atmosphere.

“Foraminifera are ecosystem engineers,” said Prof Langer. “With their shells, these protozoa produce up to two kilograms of calcium carbonate per square metre of ocean floor.

This often makes them, after corals, the most important producers of sediment in tropical reef areas.”

Foraminifera have been making marine sediments – and therefore also some of the planet’s terrestrial rocks – for at least 600 million years: they have tended to flourish in times when the planet was significantly warmer.

Prof Langer believes that these little agents of change could spread vigorously in the coming decades and “contribute substantially to future tropical reef island resilience.”

Thomas Lovejoy from the H. John Heinz III Center for Science explains why 2 degrees of warming could devastate the oceans

This article was produced by the Climate News Network

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