Fish are getting smaller

Flickr/ The WorldFish Center

Some animals and plants may shrink in size because of climate change over the next century, threatening food security and human livelihoods, say scientists.

Climate change will lead to higher temperatures and a decrease in rainfall, which, along with the increase in carbon dioxide levels will reduce the growth of a range of crops and protein sources, such as fish, that are crucial for human nutrition, say researchers in an article in Nature Climate Change this week (16 October).

"Climate change will have an effect on some species that had not been previously anticipated," Jennifer Sheridan, co-author of the study and a researcher at the National University of Singapore, told SciDev.Net.

Previous studies have found that global warming is causing earlier migration, breeding and flowering among species but little was known about how the changing climate might affect their size.

"It is necessary to understand which organisms are likely to shrink, and to what degree, in order to make accurate predictions of population trends and ecological interactions in the face of climate change," Sheridan said.

Fossil records from around 56 million years ago show that when temperatures increased by 3-7 degrees Celsius and rainfall decreased by 40 per cent — similar to the changes expected across the world by the end of the century — some insects and spiders more than halved in size.

Similarly, ocean acidification, caused by carbon dioxide emissions, significantly reduces the growth of corals, molluscs and phytoplankton — the basis of the marine food web.

The authors cite studies showing that some plant and several fish species are becoming smaller —fish shrink by up to a fifth for every degree Celsius increase.

Almost a billion people rely on fish as a food source, so humans are likely to be affected by these changes, they say.

"If this is a broad trend among fish it may become harder for small-scale fishers to feed themselves and their communities," Sheridan said.

Prolonged droughts, loss of soil nutrients and frequent fires caused by climate change will also affect crops, making it more challenging to feed people, especially in South Asia where water scarcity will reach alarming levels, Sheridan added.

The scientists warn that more research is needed to determine which species are shrinking and the potential effects this will have on ecosystems.

But Yoram Yom-Tov, professor emeritus of zoology at Tel Aviv University, Israel, told SciDev.Net that changes in body size are a common phenomenon. "Animals are adaptable, and there is no cause for alarm over the fact that animals react to changes in environmental conditions."

Link to full study in Nature Climate Change