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Warmer oceans causing commercial fish shortage

Climate change is driving a collapse of the marine food chain, an Australian study published by the University of Adelaide on Wednesday has found.

The study found that rising ocean temperatures was reducing the flow of energy from algae at the bottom of the chain to herbivores or predators, harming commercial fish stocks.

"Healthy food webs are important for maintenance of species diversity and provide a source of income and food for millions of people worldwide," Hadayet Ullah, lead author of the study, said in a media release on Wednesday.

"Therefore, it is important to understand how climate change is altering marine food webs in the near future."

Researchers constructed 12 large 1,600-liter fish tanks to mimic conditions in a warming ocean caused by greenhouse gas emissions and introduced a range of species to the tanks including algae, fish, snails, sponges, and shrimp.

The small ecosystem was maintained under future climate conditions for six months, during which time the growth, survival, and productivity of every species were tracked.

"Whilst climate change increased the productivity of plants, this was mainly due to an expansion of cyanobacteria (small blue-green algae)," Ullah said.

"This increased primary productivity does not support food webs, however, because these cyanobacteria are largely unpalatable and they are not consumed by herbivores."

Ullah was supervised by Ivan Nagelkerken, a professor of ecology and environmental science, who described understanding how ecosystems would cope with a warmer climate as a major challenge in ecological research.

"If we are to adequately forecast the impacts of climate change on ocean food webs and fisheries productivity, we need more complex and realistic approaches, that provide more reliable data for sophisticated food web models," Nagelkerken said.

Xinhua / PNA