“The story goes something like this: Tiny marine organisms called phytoplankton absorb carbon from the water and air around them. As the plankton are eaten by increasingly larger creatures, the carbon then travels up the food chain and into fish. Those fish then release a lot of it back into the ocean through their poop, much of which sinks to the seafloor and can store away carbon for centuries. The scientific term for carbon storage is sequestration.
“We think this is one of the most effective carbon-sequestration mechanisms in the ocean,” Bianchi told Vox. “It reaches the deep layers, where carbon is sequestered for hundreds or thousands of years.”
Carbon that’s stored in the deep sea is carbon that’s not making the oceans more acidic or trapping heat in the atmosphere. In other words, fish poop could be a bulwark against climate change.
The problem is that commercial fishing has sliced the global fish population to a fraction of its former level. As scientists figure out the importance of fish poop, they’re also recognizing a new danger of large-scale fishing. Beyond putting ecosystems at risk, the industry is messing with big nutrient cycles — and perhaps eating into an important carbon sink.”
https://www.vox.com/down-to-earth/22713250/fish-poop-oceans-carbon-climate-change