Small Migrating Animals' Urine Dramatically Affects Ocean Chemsitry

Researchers at the University of Washington found that the release of ammonia by small migrating animals dramatically affects the chemistry of ocean.

The largest migration on earth is the movement of small animals, right from the surface of open oceans to the sunless depths where they seek shelter to avoid attacks from predators. In the latest study, the researchers found that during the daylight hours below the ocean surface, the small animals produce ammonia that is equivalent to human urine. This released ammonia is known to play a key role in marine chemistry, especially in the low-oxygen zones.

"I'm very fascinated by these massive migrations," said lead author Daniele Bianchi, a postdoctoral researcher in the UW School of Oceanography. "To me, it's exciting to think about the effects of animal behavior on a large scale in the ocean."

It is often assumed that peeing into the vast ocean won't have any detrimental effect, but animals like zooplankton, crustaceans like krill and fish that measure a few inches long, compensate for their tiny structure with the widespread abundance throughout the world's oceans.

After spending the night time near the ocean surface, the small animals swim to a distance of 650-2,000 feet in a couple of hours. They expel solid waste that falls as pellets and water is also produced gradually.

Prior to this, the same team had revealed that animals spend most of their time in the low-oxygen water. The oxygen in the water is then consumed by the marine bacteria as they decompose the sinking dead material, eventually creating a low-oxygen zone a few hundred feet below the surface. It was also revealed that animals contribute the low-oxygen zones by using the little oxygen left to breathe.

"The animals really seem to stop in low-oxygen regions, which is sort of puzzling," Bianchi said. "Some speculated these zones might protect them from larger predators."

After solving this, the next mystery was on the bodily functions. To solve this, the researchers gathered data from underwater sonar surveys and calculated the number of animals that migrate and to which depth and where. They measured the combined effect of daytime digestion. They noticed that in few parts of the ocean, ammonia is being released from animals that drive a huge part of the oxygen-free conversion of ammonium and other molecules to nitrogen gas.

"We still think bacteria do most of the job, but the effect of animals is enough to alter the rates of these reactions and maybe help explain some of the measurements," Bianchi said.

The finding appears in the Proceedings of the National Academy of Sciences.