This is Scientific American 60 Second Science.

I'm Christopher in Dangata.

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Every day the largest mass migration on the planet happens in the world's oceans.

Tiny fish, jellies, and shrimpy things

feed at the waters surface by night,

and by day they hide in darker waters

a few hundred meters below.

The ocean is a dangerous place and so swimming down to depth is your best bet to avoid predators.

Danieli Bianchi, an oceanographer at the University of Washington.

Bianchi and his team tracked these ocean migrations with sonar data, and they found

that the creatures descend to areas of deep water where certain species of bacteria hang

out.

Those bacteria snack on nutrients that float down from the surface, so-called

marine snow, but Bianchi says the migrating creatures may also deliver food to

the bacteria in the form of ammonia in the creature's urine.

The bacteria metabolize the ammonia to produce energy in nitrogen gas, effectively removing

the nitrogen from the food chain and sending it in gaseous form back into the

atmosphere. Then other bacteria fix that nitrogen gas back into food chains on

land and in the ocean where it eventually finds its way into amino acids, some of which make up the proteins in us.

The findings appear in the proceedings of the National Academy of Sciences.

There are about 20 times more of these tiny fish than there are

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