January 18, 2018, by Tim Radford
Reduced energy flow cuts the food available for predators. Image: By Lance Anderson, Unsplash
Marine and freshwater fish could one day be in trouble as ever-rising levels of carbon dioxide affect aquatic life.
LONDON, 18 January, 2018 – New studies warn that global warming is not good news for aquatic life, putting at risk the creatures both of the seas and of inland waterways.
Experiments in Australia confirm that increased temperatures driven by ever-rising atmospheric levels of the greenhouse gas carbon dioxide reduce the flow of energy up the marine food web, which would be bad news for the ocean’s top predators – and some prized fish catches.
Another study finds that ever-greater levels of dissolved carbon dioxide in rivers and lakes could disrupt the dietary supply for creatures higher in the food chain.
Scientists have been warning for years that global warming and ever-increasing levels of acidification could harm ocean productivity. Researchers from the University of Adelaide report in the Public Library of Science journal PLOS Biology that they put the proposition directly to the test.
“Healthy food webs are important for the maintenance of species diversity and provide a source of income and food for millions of people worldwide”
They built 12 huge laboratory aquaria with water temperatures and acidity levels that matched predictions of climate change, and then introduced a range of sea creatures: algae, shrimp, sponges, snails, fishes and so on.
They found that the plants flourished, largely in the form of cyanobacteria, or blue-green algae. “This increased primary productivity does not support food webs, however, because these cyanobacteria are largely unpalatable, and they are not consumed by herbivores,” said Hadayet Ullah, who led the study.
“Healthy food webs are important for the maintenance of species diversity and provide a source of income and food for millions of people worldwide. Therefore, it is important to understand how climate change is altering marine food webs in the near future.”
Alarm, too, about the impact on freshwater species is not new. German biologists had access to data collected every month at four river dams from 1981 to 2015. They report in the journal Current Biology that acidification levels in the reservoirs had steadily increased in that time.
So they tested the response of species of daphnia, the water flea – and a source of food for other freshwater creatures – to changing water chemistry. The higher the acidity, the weaker the response of the water fleas to the scent of nearby predators.
“Many freshwater organisms rely on their sense of smell. If that sense is compromised in other species due to rising CO2 levels this development might have far-reaching consequences for the entire ecosystem,” said Linda Weiss of the Ruhr University of Bochum, who led the study.
“Follow-up studies must now be carried out, in order to determine if the acidification of freshwater systems is a global phenomenon and in what way other species react to rising CO2 levels.” – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.