When it comes to the world’s oceans, big things come in small – microscopic, really – packages.
With feathery, fluttery legs and a minuscule body, oceanic creatures known as zooplankton don’t look like they could pack much of a punch. However, a new study published in Nature suggests that these tiny invertebrates should join the ranks of wind and waves to be considered one of the ocean’s key influencers.
Every night, these tiny shrimp-like creatures swarm together in the trillions as they migrate hundreds of meters from the depths of the sea to its surface to dine on small floating plants called phytoplankton. It’s during this upward migration researchers believe their tiny legs send columns of water down, mixing surface waters with the deep ocean below, moving nutrients around in the process.
And although they are little, zooplankton – meaning “wandering animals” – are fierce.
“Ocean dynamics are directly connected to global climate through interactions with the atmosphere,” said senior author John Dabiri in a statement. “The fact that swimming animals could play a significant role in ocean mixing – an idea that has been almost heretical in oceanography – could therefore have consequences far beyond the immediate waters where the animals reside.”
Teaming up with environmental engineers in the lab, Dabiri and graduate student Isabel Houghton created flow environments in large water tanks that mimic the ocean with saltier, denser water at the bottom. Using brine shrimp, or “sea monkeys”, that are attracted to light, the team alternated LED lights from the top to the bottom of these tanks and used cameras to measure individual eddies surrounding each shrimp. The turbulence from individual organisms aggregated into a much larger “turbulent jet” that was powerful enough to mix the tank’s salt gradient.
“They weren’t just displacing fluid that then returned to its original location,” Houghton said. “Everything mixed irreversibly.”
Zooplankton were thought to only create turbulence in their own size range – they're less than a centimeter long – that wasn’t considered powerful enough to move nutrients. Now, scientists say they have the capacity to mix ocean waters at least regionally.
If shrimp do it, researchers say other ocean-dwelling creatures like jellyfish, fish, squid, and marine mammals could as well.
“Right now, a lot of our ocean climate models don’t include the effect of animals or if they do it’s as passive participants in the process,” said Dabiri. The findings could influence how scientists think about global nutrient cycles like carbon, phosphate, and oxygen, or even ocean currents.
The team hopes to verify their findings in the ocean and, if confirmed, believe they could change the way scientists think about the roles animals play in marine environments and, ultimately, climate change.