Comprehensive global analysis shows a warmer ocean will hold fewer animals

Climate change could have severe negative effects on ocean life, an international group of researchers reveals. Until now, the full extent of impact of climate change on the distribution and abundance of marine life has been difficult to predict, due to the limitations of individual models. However, by combining a range of climate and ecosystem models, the researchers have revealed a more complete picture.

The findings, published in the Proceedings of the National Academy of Sciences on Tuesday 11 June, reveal that global marine animal biomass – the total weight of marine animals such as fish, invertebrates and mammals in the ocean – will decline under all greenhouse gas emission scenarios, driven largely by increasing temperature and declining production from the tiny marine plants and other organisms at the base of the food web.

The group of 35 researchers from 12 countries and four continents found that the extent of these projected losses can be constrained by reducing greenhouse gas emissions. If we carry on business-as-usual, there was a projected 17% decline in global marine animal biomass by the end of the 21st century. However, if the world works together to minimise emissions of greenhouse gases and mitigates its impacts, this decline could be reduced to just 5%.

FIGURE: Projected changes of marine animal biomass by the end of the 21st century (% increase or % decrease compared to the end of the 20th century) under two IPCC emission scenarios: RCP2.6 assumes strong mitigation, RCP8.6 assumes business-as-usual emissions.

Lead author, Heike Lotze from Dalhousie University in Halifax, Canada said: “Reduction of greenhouse gas emissions will undoubtedly help to safeguard marine life as much as possible against further losses.”

The analysis also suggested that the impacts of climate change may be more severe higher up the food-web. This process, known as ‘trophic amplification’, means that fish and marine mammals may suffer more severe declines compared to phytoplankton.

Derek Tittensor, Senior Marine Biodiversity Scientist at UN Environment World Conservation Monitoring Centre in Cambridge, UK said: “Our findings suggest that larger marine animals, many of which are already of conservation concern, are particularly vulnerable to population declines as a result of climate change, with a domino effect from phytoplankton up the food chain.”

The changes in marine animal biomass also vary geographically. Maps of these projected changes reveal that biomass will decline most in temperate to tropical ocean regions, where marine biodiversity is already affected by cumulative human impacts. This is also likely to have substantial impacts on local communities, who can be highly dependent on seafood supply.

In contrast, many polar regions around the Arctic and Antarctica could show biomass increases, which may provide new opportunities for marine resource use but also challenges to marine management and conservation.

These results provide the most comprehensive outlook on potential climate-driven ecological changes in the ocean to date and can help anticipate changes in valuable marine resources under climate change. As such, the results can help to inform ongoing international climate and biodiversity negotiations. The study has been compiled over the past six years by the international FishMIP consortium, a group of experts and modellers on marine ecosystem dynamics under climate change in collaboration with the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP).


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