Ocean acidification and global warming are interfering with the way fish interact in groups, posing a threat to their survival that could affect seafood supplies, experts warn.
Marine ecosystems around the world have shown a greater dominance of warm-water species following rising sea temperatures, with parallel changes in the composition of fish catches since the 1970s, according to a report by the Intergovernmental Panel. on Climate Change (IPCC).
Fishing activities in marine ecosystems provide food, nutrition, income and livelihoods to millions of people in the world, says the IPCC. Globally, total fish catches range between 80 million and 105 million tonnes annually, generating more than US$80 billion in revenue, the report underlines.
“Fish show gregarious behavior and congregate in schools, which helps them get food and protect themselves from predators,” explains Ivan Nagelkerken, professor at the Institute of Environment and the South Seas Ecology Laboratories and author. of a study on the effect, published in Global Change Biology.
Under controlled laboratory conditions, the researchers observed how the species interacted and behaved in new ways with changes in temperature and acidification. Although warming and acidification are different phenomena, both act to the detriment of marine ecosystems.
According to Nagelkerken, mixed banks of tropical and temperate species become less cohesive under future climatic conditions and show slower escape responses to potential threats. Strong school cohesion and coordinated movements, whether for food or to evade predators, are important for fish survival.
“Species are extending their ranges poleward as oceans warm due to climate change,” says Nagelkerken. “This process, known as tropicalization of temperate ecosystems, means that tropical species mix with temperate ones and create new ecological interactions,” he explains.
He argues that tropicalization is altering temperate ecosystems and food webs. “With changes in the habitats of fish and other species, ecosystem services and fish populations could also be altered due to the expansion of the range of the species. New interactions between tropical and temperate species are critical as they mediate the population sizes of these fishes and thus the functioning of food webs.”
The bottom line, says Nagelkerken, is that the abundance of species is changing due to their expanding range. “Tropical species will be more abundant in temperate ecosystems, and some temperate species will be less abundant. This changes the type of fishing and other species that are present in certain places and, consequently, potentially also their catches.”
“With changes in the habitats of fish and other species, ecosystem services and fish populations could also be altered due to the expansion of the range of the species.”
Ivan Nagelkerken, University of Adelaide
He believes that sometimes there will be positive effects on fish catches, for example more tropical fish species, but other times the effects will be negative.
“Altering the behavior of fish schools due to climate change and new species interactions can affect survival and growth rates, and therefore can alter the size of populations and, consequently, potentially also catches. “, Add.
Nagelkerken indicates that natural climate oscillations, such as El Niño and La Niña, can also have an impact. “Depending on the location and specific effect of the oscillations, for example cooling versus warming, they could slow down or exacerbate range extensions in the short term although in the long term the effects of climate change are expected to be stronger” .
Scott Doney, a professor in the Department of Environmental Change at the University of Virginia in Charlottesville, told SciDev.Net that climate change and ocean acidification caused by human emissions of carbon dioxide not only encourage tropical fish to expand their habitat areas towards temperate regions, but that “the physiology and metabolism of fish can be altered by the simultaneous effects of warming sea waters and chemical changes associated with acidification”.
“This systematic laboratory study of multiple environmental factors is an important step forward in understanding the potential impacts of climate change on the oceans,” Doney said.
This article was produced by SciDev.Net Asia-Pacific Newsroom
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