Take Two®

News and culture through the lens of Southern California. Hosted by A Martínez

Giant zooplankton: Nature's water filtering, carbon storing enigma

by Julia Paskin | Take Two®

Kakani Katija and MBARI marine operations staff launch the MiniROV and DeepPIV system from the stern of the research vessel Western Flyer. © 2015 MBARI

A key component to understanding climate change may be within some unusual ocean-dwelling critters. 

Giant zooplankton known as Larvaceans are the subject of a unique study published recently in the journal Science Advances. Thanks to new technology that was developed in order to observe the gelatinous, transparent animals, scientists have been able to see how Larvaceans feed in their natural habitat.

It turns out whenever Larvaceans feed, they create mucus structures known as "houses"--since they also happen to live in them. Their houses help them filter out all the organic material to eat while pushing aside the rest, mainly carbon. Once the houses are all blocked up, the Larvaceans abandon them. The discarded houses then fall to ocean floor, trapping all the carbon with them. 

This relationship between Larvaceans and carbon appears to be a missing piece in the puzzle to understand how carbon cycles through the Earth. It also gives us some insights into how the planet moves carbon from air to sea, and how it could potentially help us address the impacts of climate change.  

https://www.youtube.com/watch?v=L1wFb_ShW7k

Take Two's A Matinez spoke with the study's lead author, Kakani Katija. She's principle engineer at the Monterey Bay Aquarium Research Institute.

GIANT ZOOPLANKTON... Actually not so giant. More like finger sized. 

This frame grab from video shows the mucus "house" of a giant larvacean (Bathochordaeus charon) several hundred meters below the surface of Monterey Bay.
This frame grab from video shows the mucus "house" of a giant larvacean (Bathochordaeus charon) several hundred meters below the surface of Monterey Bay. © 2015 MBARI

It's actually called that [Larvacean] because it looks a lot like a larvae. You can also think about a tadpole. Essentially, they only have a head and a tail.

They're fully transparent, their tissues are gelatinous, so you can see right through them. That's one of the reasons why we don't know much about them. Anything that's gelatinous will just appear like a pile of nothing.

They're not just hungry, they're nature's water filter.

This frame grab from video taken by MBARI's MiniROV shows the inner house of a giant larvacean, with its inner chambers outlined by the red sheet of laser light from the DeepPIV system.
This frame grab from video taken by MBARI's MiniROV shows the inner house of a giant larvacean, with its inner chambers outlined by the red sheet of laser light from the DeepPIV system. © 2015 MBARI

They're able to generate a house made of mucus that's actually a really complex structure that serves as a filter. This animal is then able to push fluid through this filter by moving its tail... That separates food particles like organic carbon, and dead animals from the water around it.   

Small critters with a big role in the global carbon cycle  

These houses also play an important role in cycling carbon in our oceans.... There's this process whereby organisms are able to play a role in moving carbon and CO2 that's in the atmosphere and through the oceans, and ultimately some of that reaches the bottom of the ocean and is sequestered.

So, the more carbon that you can transport and get to stay on the bottom of the ocean, the better it is for minimizing the impacts of ocean acidification and climate change. 

Problems keeping an eye on underwater see-through animals? Turn to robots and lasers, of course!

Illustration of MBARI's MiniROV using the DeepPIV laser system to illuminate a giant larvacean.
Illustration of MBARI's MiniROV using the DeepPIV laser system to illuminate a giant larvacean. Kim Fulton-Bennett © 2017 MBARI
This frame grab from video taken by MBARI's MiniROV shows the inner and outer houses of a giant larvacean (left) and the laser and camera of the DeepPIV system (lower right)
This frame grab from video taken by MBARI's MiniROV shows the inner and outer houses of a giant larvacean (left) and the laser and camera of the DeepPIV system (lower right) © 2015 MBARI

We were using remotely operated vehicles. We also developed instrumentation that allowed us to measure directly what the filtration rates are of these organisms are. That instrument is called a DeepPIV and is made up of a camera, a laser and some optics.  That allows us to take a single laser beam... And then shine that beam through some optics to create a thin sheet of light. So, you can see the interior structures of the house as well as how water moves through it. 

https://www.youtube.com/watch?v=0fCnHyxYVMw

There are a lot of questions we're hoping to address thanks to the development of this new instrumentation. 

Tempting it may be, but playing with nature isn't the answer.

Larvaceans play a really important role in carbon cycling, maybe we'd want to do something to promote their numbers or increase their abundance.... However, whenever you mess with an ecosystem that's in a delicate balance, you might have these unintended consequences where we don't know what will happen.

But we may be able to duplicate what Larvaceans do for our own purposes.  

The first step is figure out how the system functions--how the organism functions. The next question is, if they're doing something that's special, is that something we can reverse engineer and use for another application?

*Quotes edited for clarity*

To hear the full interview with Kakani Katija, click on the blue Media Player above. 

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