Image Credit: Caiger / Woods Hole Oceanographic Institute
Why is the mesopelagic zone important?
The Ocean Twilight Zone, or Mesopelagic Zone, extends from 200 to 1,000 meters below the ocean’s surface. Though it makes up just 20% of the ocean’s volume, it may contain up to 90% of all fish biomass, forming a vital link between surface waters and the deep sea.
- Unique Biodiversity: This zone hosts a huge variety of species, most of which remain undiscovered.
- Essential Food Source: Many top predators—like sharks, tuna, swordfish, and marine mammals—depend on mesopelagic creatures such as jellyfish, squid, shrimp, and fish.
- Climate Regulation: Each day, billions of mesopelagic animals migrate to the surface to feed, transporting carbon back down and helping sequester 2–6 gigatons of carbon annually—more than double the emissions from all cars worldwide. Most of this carbon stays in the twilight zone or sinks even deeper, reducing atmospheric CO₂.
Why is action needed?
Expanding fisheries into the mesopelagic zone could harm ocean ecosystems and weaken climate resilience. As traditional fish stocks decline due to climate change, industries are eyeing mesopelagic species, like lanternfish, for their omega-3 content. Meanwhile, the zone is already threatened by warming, deoxygenation, and deep-sea mining, which can cause toxic pollution.
How do we advocate to protect the mesopelagic zone?
IUCN Motion 035: Protection of Mesopelagic Ecosystem Integrity
In October 2025, Marine Conservation Institute, in partnership with the Ocean Conservancy and the Environmental Defense Fund, proposed IUCN Motion 035: Protection of mesopelagic ecosystem integrity at the IUCN World Conservation Congress in Abu Dhabi, UAE.
The motion called for applying a precautionary approach to the expansion of fishing and other activities that may impact life in the mesopelagic zone until there is a better understanding of how these activities could have an effect on mesopelagic species, ocean food webs, and climate.
The motion passed with a large majority and is now an IUCN Resolution, demonstrating growing momentum to protect the incredible biodiversity of this zone before the damage is irreversible.
To learn more about the mesopelagic zone and Motion 035, watch this webinar hosted by our colleagues at the Environmental Defense Fund:
Join us in advocating for the protection of the Ocean Twilight Zone, ensuring a healthier ocean for future generations.
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