Coral Reefs Flourish Thanks to … Fish Pee?

By Laura Geggel, Senior Writer | August 17, 2016 12:50pm ET

Getting peed on is a good thing, at least for coral reefs, scientists have found.

When fish let loose, they release phosphorus into the water. This, combined with nitrogen excreted from their gills, is crucial for coral reef survival and growth, according to recent studies.

Now, new research shows just how much this "fishy waste" matters. When scientists studied areas with heavy fishing, they found that almost half of the key nutrients needed to maintain a healthy reef ecosystem were missing.

That's right — large, predator fish are needed to mist the reefs with their pee, study lead author Jacob Allgeier, a postdoctoral researcher at the University of Washington's School of Aquatic and Fishery Sciences, said in a statement.

"Fish hold a large proportion, if not most, of the nutrients in a coral reef in their tissue, and they're also in charge of recycling them," Allgeier said. "If you take the big fish out, you're removing all of those nutrients from the ecosystem."

To study the impact of these nutrients, researchers surveyed 143 fish species at 110 sites across 43 Caribbean coral reefs. Some reefs had few fish because of commercial fishing, whereas others were marine preserves with fishing bans.

Reefs with many large, predator fish had the healthiest levels of nutrients, the researchers found. Meanwhile, reefs with few large fish had about 50 percent fewer nutrients, including phosphorous and nitrogen, which are essential to their survival, the researchers said.

"This study is useful to understand alternative ways fishing is affecting coral reef ecosystems," Allgeier said.

Big fish

When fishers target big fish — such as grouper, snapper and barracuda — the fish, and their pee, disappear, the researchers said.

Normally, fish take shelter in coral reefs during the day, whiling away the time as they relieve themselves. At night, they typically forage for food within the reef communities.

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