Mesopelagic Fish Secrete Carbon

The mesopelagic zone, or also known as the ocean twilight zone, is an area of the ocean. It is a poorly lit area of the ocean and is located between the productive surface water and the deep sea. It is one of the largest ecosystems of the planet that is the least explored and understood. This habitat is mostly inhibited by fish, squid, jellyfish, and zooplankton. Mesopelagic fish species are the largest and the least studied by marine professionals in the world. Their global biomass consists of at least 1,000 to 10,000 million tons. Many organisms from the mesopelagic zone escalate to the surface to feed during the night and they resettle to greater depth before the sun rises. Due to this lifestyle, mesopelagic organisms play a key role in regulating oceanic food webs, carbon separation, and biogeochemical cycling.

Researchers at the University of Miami uncovered that deep-sea fish, specifically blackbelly rosefish (Helicolenus dactylopterus), play a larger role in Earth's carbon cycle than would be expected. Lying at depths of 350–430 meters, the mesopelagic fish were found to excrete carbonate minerals—predominantly high-magnesium calcite—at rates equivalent to shallow-water species. This process, known as ichthyocarbonate production, was thought but never directly detected in deep-sea environments. The study found that up to 52% of the carbon found in such minerals comes from the diet of these fish, and hence they are really transporting organic carbon into deep oceanic layers. As mesopelagic fish account for approximately an estimated 94% of the overall fish biomass on the planet, their contribution to oceanic alkalinity and carbon sequestration is also substantial.