Bacteria inside fish guts help regulate ocean chemistry
Tiny mineral pellets excreted by fish act as a planetary thermostat, helping the ocean absorb carbon dioxide and preventing the water from becoming too acidic.
Every time a marine fish takes a drink of salty seawater, it kickstarts a biological desalination plant inside its own gut. To keep from dehydrating, teleost fish—a massive group including everything from goldfish to tuna—must strip excess calcium and magnesium from the water they swallow. They turn these minerals into tiny, hard crystals called ichthyocarbonates, which they then expel as a constant rain of white pellets. These microscopic stones are not just waste; they are alkaline buffers that neutralize acidity in the deep ocean, maintaining the delicate chemical balance required for marine life to thrive.