inquiry + innovation
Who’s Peeing in the Global Pool?* By Elizabeth Preston
A giant database of the underwater excretions of fish, frogs, and other creatures could help scientists understand the effects of fishing and climate change.
* 12
miamian magazine
Reprinted from The Atlantic. © 2017 The Atlantic Monthly Group, LLC. All rights reserved. Used under license.
Compiling more than 10,000 lines of data on the waste products of aquatic animals, from lake trout to pond insects to ocean shellfish, was more time-consuming than ecologist Michael Vanni expected. But he didn’t mind. “I love data on fish pee,” he says. Vanni, of Miami University, and his co-author, Peter McIntyre, of the University of Wisconsin, Madison, had plunged into the project for their own research. But they soon realized the giant dataset they put together could be a resource for other scientists, too — all that work on animal waste didn’t have to go to waste itself. Why anyone cares about fish pee or frog pee or snail pee in the first place has to do with recycling. Nutrients in an ecosystem are used over and over again as they cycle through the food chain. In a forest, for example, when leaves fall to the ground, fungi and bacteria break them down and return their nutrients to the soil, where plants can use them again. Especially in aquatic environments, Vanni says, animals do a lot of this recycling. When fish excrete nitrogen and phosphorus, algae can take the molecules back up. To understand this accounting for a given ecosystem, it would help to be able to look at any animal and predict how much recycling it’s doing. That’s what Vanni and McIntyre wanted to know: “Are there ways that we can predict how much nitrogen and phosphorus an animal will excrete?” Vanni asks. “Are there general rules across all animal life?” To answer the question, they gathered as much data as they could find on excretion by animals living in water, whether freshwater or ocean — in other words, anything peeing in the global pool. Vanni says collecting these data for a small animal is pretty straightforward. You put the animal in a container of water, wait a given amount of time, then measure what it left behind. As long as you don’t stress the animal too much in the process — “You don’t want to literally scare the pee out of them” — you’ll get a decent idea of what it excretes. (A word on poop: In fish, just as in mammals, some