[LUM#12] Toward Depopulated Oceans
Reducing greenhouse gas emissions would (also) protect marine biodiversity. A new study shows that global warming will drastically reduce the abundance of marine life.
A warmer, less populated ocean. That is the outlook for 2100, according to the most comprehensive analysis to date of the effects of climate change on marine ecosystems. According to this study, if greenhouse gas emissions continue at the current rate, 17% of the global biomass of marine animals could disappear by 2100. “This refers to the total weight of marine animals such as fish, invertebrates, and marine mammals in the ocean,” explain Yunne Shin and Olivier Maury, co-authors of the study and researchers at the Marbec laboratory ( Marine Biodiversity, Exploitation, and Conservation).
Endangered large marine animals
Why does global warming affect ocean populations? “Two major processes are at work: increased energy dissipation and decreased primary production, ” explains Olivier Maury. “Rising water temperatures will accelerate all biological processes because metabolism is faster in a warmer environment. This phenomenon leads to increased energy dissipation.” A faster metabolism therefore implies an increased need for resources.
Bad news: the amount of available resources is actually set to decline—what researchers call a decline in primary production: “ “It’s actually phytoplankton, ” explains Yunne Shin. “These microscopic plant cells form the basis of all ocean food chains, and with global warming and ocean acidification, phytoplankton density will decline.” Estimates suggest a decline of between 8% and 12% globally.
This decline in primary production will have a greater impact on large marine animals, many of which are already in a precarious situation. “The decline in phytoplankton has more significant repercussions higher up the food chain; it’s a domino effect known as the trophic amplification process, ” explain Yunne Shin and Olivier Maury.
Severe stress
Global warming will therefore have varying consequences depending on the species, but also depending on the region. And it is the intertropical zones that will bear the brunt of the impact. “According to some models, water temperatures could reach 35 degrees in certain regions of the western Pacific, which will become uninhabitable.” The result: ocean populations will migrate toward the poles, completely redrawing the world’s maps.
While it is possible that we will see an increase in biomass in certain polar regions around the Arctic and Antarctic, it is certain that we will observe a drastic decline in many temperate and tropical ocean regions: “Biomass there will decline very sharply, by 40 to 50 percent, even though these are areas where marine biodiversity is already severely impacted by human activities,” explains Yunne Shin.
And the consequences will not be limited to marine life: “These are precisely the regions where human populations depend directly on ocean resources for food,” adds Olivier Maury, “so this is also a matter of global food security.” In these regions, climate change will thus pose a major threat not only to marine ecosystems but also to human societies.
Prevention and Adaptation
For researchers, the key word in light of these scenarios is “anticipation .” “We must, of course, do everything we can to limit CO2 emissions, but we must also reevaluate measures to preserve biodiversity and manage fisheries in light of climate change, ” they recommend. This new study thus provides further incentive to develop sustainable and adaptive fisheries that will help feed the 11 billion people who will inhabit the planet by 2100.
“On the one hand, the human population is set to grow, and on the other, marine resources—which play a vital role in global food security—are at risk of declining by as much as 30 to 35 percent, according to some models, ” warns Olivier Maury. “It is urgent that policymakers at all levels take our findings to heart. Our scenarios can help us anticipate threats and develop prevention and adaptation strategies. The challenge is clear: we must avoid what we cannot manage, and equip ourselves to manage what we cannot avoid.”
Unique expertise
To develop these scenarios, 35 researchers from 12 countries and 4 continents have come together under the international FishMIP consortium (Fisheries and Marine Ecosystem Model Intercomparison Project), a group of experts and modelers working on the dynamics of marine ecosystems in the context of climate change. According to their simulations, marine animal biomass will decline regardless of the CO2 emission scenarios considered. “This decline would, however, be limited to 5% if global warming were limited to 2 degrees, ” the researchers note.
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