Marine Mud Is High in Fish Poop

Will you still enjoy feeling the beach between your toes this summer knowing it’s partly fish feces? In a paper published online this week in the Proceedings of the National Academy of Sciences, researchers report that 14% of the calcium carbonate that makes up the muddy floors of shallow tropical seas is fish poop. Fecal samples from 11 common tropical fish, including barracudas and snappers, reveal that calcium carbonate forms a key component of the excrement. The team estimates that every year, tropical fish excrete 6.1 million kilograms of calcium carbonate, equivalent to the weight of 1000 adult elephants, over an area of 111,577 square kilometers. Each fish may even have its own unique “fecalprint”, with specific sizes and shapes of calcium carbonate crystals (as seen in the black and white image), which could allow future oceanographers to analyze an ocean’s mud to track changes in the numbers and diversity of fish species.

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