The acid threatens the all-powerful cod | Cosmos

For cod facing the effects of climate change, it is not heat but acid that threatens.

Ocean acidification – caused by the penetration of atmospheric carbon dioxide into the water and the drop in its pH – means that the success of two species of northern cod is narrower, which means that # 39, one of the largest fisheries in the world will be threatened if temperatures are not increased limited to 1.5 degrees Celsius, reveals a new study.

The researchers, led by Flemming Dahlke of the Alfred Wegener Institute in Germany, found that cod embryos can survive only in a limited temperature range, and that this range decreases under more acidic conditions.

Researchers predict that Atlantic cod (Gadus Morhuai) would not be able to reproduce below the Arctic Circle by 2100 as part of an "as usual" emission scenario. Polar cod (Boreogadus saida) faces an even more dangerous future because it not only needs colder water, but also depends on the ocean ice for its habitat.

The study is another example suggesting that if global average temperatures continue to rise steadily, entire ecosystems will collapse in this century.

"Given the embryonic intolerance to ocean warming and acidification, we show that with relentless greenhouse gas emissions, the large areas currently used for spawning will be less suitable for Atlantic cod recruitment. and polar cod, which could lead to cascading effects on badociated ecosystem services networks, "write the authors in the journal Progress of science.

The consequences of the decline of cod are not limited to fishing.

The authors note that polar cod is "an essential food for many marine birds and mammals", while the Norwegian Atlantic cod fishery generates $ 1.1 billion annually.

"Estimating changes in the quality of spawning habitat for these focal species is therefore of great socio-ecological importance," the authors say.

Changing the habitat of a large fishery would also complicate regulation. It will become more difficult to manage stocks under existing regulations when fish have changed location and breeding behavior.

"The potential movement of commercially important fish stocks across management boundaries and exclusive economic zones is a major challenge, not only for fishermen and national ecologists, but also for international agencies and regulations, which are aimed at avoid overexploitation, resource conflicts and degradation of virgin ecosystems. the Arctic, "write the authors.

Yet there is hope. Dahlke and his colleagues say that in the context of an aggressive decarbonization plan, cod fishing could avoid serious consequences.

"Our results also highlight that mitigation measures, as provided for in the Paris Agreement, can mitigate the effects of climate change on both species," the authors report.

This is particularly encouraging given that climate change resulting from ocean warming, acidification and sea ice loss is expected to have greater effects than most other regions.

Realistically, however, the global community will need to act quickly to avoid a warming of 1.5 degrees Celsius.

"Given that the current CO₂ Emissions trajectories offer a 1% chance of limiting global warming to 1.5 ° C compared to pre-industrial levels, our results recommend immediate emission reductions according to scenarios compatible with a 1% warming, 5 ° C to avoid irreversible damage to ecosystems in the Arctic and elsewhere, "scientists conclude.