Climate change

Rising carbon dioxide levels will change marine habitats and decrease fish diversity

written by Oceanographic Staff

Rising carbon dioxide (CO2) in the atmosphere and the resulting alterations created through ocean acidification will have a severe effect on the ecosystem, impacting reef-forming habitats and the associated fish, according to a new study from the Universities of Plymouth, Palermo and Tsukuba.

The research team has found that elevated dissolved CO2 conditions can lead to a 45% decrease of fish diversity, and that under elevated dissolved CO2 conditions, habitats are dominated by few ephemeral algae. This means that even slightly higher concentrations of CO2 than those existing today could cause profound changes.

carbon dioxide impact fish diversity

“Our findings show that the CO2-induced habitat shifts and food web simplification, which we observed along a volcanic gradient in a climatic transition zone, will impact specialist tropical species favouring temperate generalist fish,” said lead author Dr Carlo Cattano, from the University of Palermo. “Our data also suggests that near-future projected ocean acidification levels will oppose the ongoing poleward expansion of corals (and consequently of reef-associated fish) due to global warming.”

They discovered that, in elevated dissolved CO2 conditions, species such as complex corals and canopy-forming macroalgae mostly disappeared. This shift from complex reefs to habitats dominated by opportunistic low-profile algae led to a 45% decrease of fish diversity, with a loss of coral-associated species and a rearrangement of feeding behaviour.

“Our work at underwater volcanic seeps shows that coastal fish are strongly affected by ocean acidification, with far fewer varieties of fish able to cope with the effects of carbon dioxide in the water,” said Jason Hall-Spencer, Professor of Marine Biology at the University of Plymouth. “This underlines the importance of reducing greenhouse gas emissions to safeguard ocean resources for the future.”

Their study also supports previous research that has demonstrated how ongoing ocean acidification has an extreme ecological effect on habitat changes.

This has shown that decreased seawater pH could impair calcification and accelerate dissolution for many calcifying habitat-formers, while rising CO2 concentrations may favour non-calcifying autotrophs enhancing the primary production and carbon fixation rates.

Therefore, some species will succeed under increasingly acidified conditions, while many others will not. Those fish species that rely on specific resources during their different life stages could disappear as a result. This would lead to massive changes in fish diversity in the near future, with potentially severe consequences for marine ecosystem functioning, alongside the goods and services they provide.

To read the full paper, “Changes in fish communities due to benthic habitat shifts under ocean acidification conditions”, click here.

Photograph by Nicolas Floc’h, courtesy of the University of Plymouth.

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