Small swimmers may play huge role in churning the seas

Author: Carolyn Gramling / Source: Science News for Students

Animals swim by pushing on the water around their bodies. Even small ocean swimmers such as krill — tiny shrimplike animals — make mini currents with each kick. And if there are lots of these tiny creatures? Together they may be powerful enough to stir up water hundreds of meters (yards) deep, a new study suggests.

That water mixing is important because many nutrients are unevenly spread throughout the ocean. Near the surface, microscopic marine plants and bacteria use sunlight to make food. In the process, they use up mineral nutrients in the water. These include nitrogen and phosphorus. So shallow water gets sapped of these nutrients. But deeper water contains lots of such nutrients. Stirring up the ocean helps carry the nutrient-rich deep water up toward the surface where plants can use it.

Wind, tides and large currents all help mix the ocean. But swimming animals move water, too. And researchers wanted to know whether small but very abundant critters might play a role. They were thinking about centimeter (half-inch) sized krill and even tinier crustaceans known as copepods (KOH-puh-podz).

John Dabiri works at Stanford University in California. He studies how fluids move around objects, including animals. Early on, he says, scientists didn’t think creatures as small as krill could have much effect on a big ocean. “The original thinking is that these animals would flap their appendages and create little eddies about the same size as their bodies,” he says.

But then, measurements of krill migrating in the ocean suggested that they might stir up more turbulence than researchers had at first thought possible.

So did computer programs used to predict the flow of water around swimming jellyfish and copepods.

In 2014, Dabiri coauthored a study to measure how water moved around swimming brine shrimp in a lab. Brine shrimp are small crustaceans that look similar to krill. Brine shrimp in tanks created jets and eddies in the water much larger than themselves, that study showed. “But there was skepticism about whether those lab results were relevant to the ocean,” Dabiri says.

Why? Ocean water is not uniform. Some spots are warmer, others cooler. Some parts have more salt than others. Such differences can divide the water into layers, each having its own…

Click here to read more

The post Small swimmers may play huge role in churning the seas appeared first on FeedBox.