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Marine biomass will plummet unless greenhouse gases curbed, Dalhousie-led study predicts


Waves roll onto the shore of Halifax Harbour. An international study led by Dalhousie researchers projects that unless rigorous action is taken on curbing greenhouse gas emissions, about 17 per cent of marine biomass will be lost by century’s end. - File
Waves roll onto the shore of Halifax Harbour. An international study led by Dalhousie researchers projects that unless rigorous action is taken on curbing greenhouse gas emissions, about 17 per cent of marine biomass will be lost by century’s end. - File

If we don’t change our ways, the future looks bleak for animals that live in the ocean, a Dalhousie University researcher says.

Derek Tittensor, an adjunct professor at Dalhousie’s biology department, co-authored a comprehensive study that concludes 17 per cent of marine biomass could be lost by century’s end if warming trends linked to greenhouse gas emissions continue.

He and lead author Heike Lotze, also from Dalhousie, worked with more than 30 scientists from across the world over the past six years on the study, which was published Tuesday in the Proceedings of the National Academy of Sciences.

It presents a worrisome view of what will happen to the global biomass — the total weight of marine animals such as fish, invertebrates and mammals — if we don’t cut emissions from fossil fuels such as coal and petroleum.

“We’re not on a fixed path, we do have options and we do have choices that we can make that will help to tackle this or at least adapt to it,” Tittensor said in an interview Wednesday.

Smaller-scale studies have been done on the connection between warming ocean waters and the negative effect on marine animals. But the Dalhousie-led study used a combination of climate and marine ecosystem models for a global perspective on the future of marine biomass.

“In a sense we’re looking at the larger patterns of groups of organisms like large fish, large predators, marine mammals, invertebrates and so on,” Tittensor said. “The focus is on the broad trends on global levels rather than trying to drill down into individual stocks or species or populations.”

The sunny side of rising temperatures

If there’s a bright side to global warming and the oceans, changes in water temperature could be a boon to some commercial fisheries.

“The American lobster is a good example,” Tittensor said. “The fishery in Maine has really benefited from warming waters and the lobster fishery has increased and now that effect may be moving up towards Nova Scotia as the waters warm. This is a change that is continuing, so we’ll continue to see shifts in where species are and where the fisheries may need to be.”

But the wide-angle view provided by this most recent research doesn’t include many upsides.

With every degree of warming, there’s a corresponding five per cent drop in the total amount of biological materials in the oceans, which is quite a significant decline and gets more serious as we move up the food chain, said Tittensor, who is also a senior marine biodiversity scientist with the UN Environment World Conservation Monitoring Centre in Cambridge, U.K.

“We know that food production on land is increasingly put at risk by climate change impacts, such as extreme heat and drought,” said study co-author Jacob Schewe of the Potsdam Institute for Climate Impact Research in Potsdam, Germany, in a news release. “This study adds another disconcerting chapter to the global warming story, by confirming that human-made climate change endangers food resources in the oceans too.”

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