Algae offers hope of surviving in hot acid seas

A scanning electron micrograph of a single coccolithophore cell of the species Emiliania huxleyi

After Friday's depressing news that ocean acidification is the worst it has been in 300 million years, we start the week with a similar subject but on a slightly more optimistic note.

A new report suggests that tiny marine algae may be able to evolve fast enough to cope with climate change, which would means some ocean life would be more resilient to rising temperatures and acidification than we thought.

The study found that one type of microscopic algae that can produce 500 generations a year can still thrive when exposed to warmer temperatures and levels of ocean acidification predicted for the mid-2100s.

"Evolutionary processes need to be considered when predicting the effects of a warming and acidifying ocean on phytoplankton," according to the German-led study in the journal Nature Climate Change.

The phytoplankton species tested was Emiliania huxleyi, a type of one-celled marine plant known as a coccolithophore. They live in large numbers throughout the upper layers of the ocean.

The phytoplankton are an important source of food for fish and other ocean life and also absorb large amounts of carbon dioxide as they grow. Their huge blooms can sometimes be seen from space.

NASA's Earth Observatory website has a good introduction to coccolithophores.

Unlike any other plant in the ocean, coccolithophores surround themselves with a microscopic plating made of limestone (calcite). These scales, known as coccoliths, are shaped like hubcaps and are only three one-thousandths of a millimeter in diameter.

And this is how they help mop up carbon dioxide.

In the long term, the plants seem to be good for the environment. Coccolithophores make their coccoliths out of one part carbon, one part calcium and three parts oxygen (CaCO3). So each time a molecule of coccolith is made, one less carbon atom is allowed to roam freely in the world to form greenhouse gases and contribute to global warming. Three hundred twenty pounds of carbon go into every ton of coccoliths produced. All of this material sinks harmlessly to the bottom of the ocean to form sediment.

Thorsten Reusch, an author of the study at the GEOMAR Helmholtz-Centre for Ocean Research in Kiel, warned that the findings about were only for one species of algae in a laboratory test, in water with no predators or disease.

Stephen Palumbi, a professor of biology at Stanford University – whose marvellous book Extreme Life of the Sea was excerpted in Cosmos last month – told Reuters that there was evidence that some coral reefs or sea urchins could be more resilient than expected to ocean changes.

"What we don't know is how far these mechanisms will go. I suspect personally that they will not solve the future climate problem because climate is changing far too fast."

"But perhaps these abilities will give some important marine life a few more decades than we previously thought," he said.

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