AVALON— Underwater autonomous drones pulling kelp around the open ocean might sound like a cinematic feature of a science fiction movie, but it might not be that far off in the future. Scientists from the University of Southern California Wrigley Institute for Environmental Studies and engineers from Marine BioEngery Inc. have found a new aquaculture technique that could help overcome some of the roadblocks to creating macroalgae ocean farms for the purpose of creating an alternative biofuel feedstock, which could be used to fuel boats, cars, planes and more.
Using technology called the “kelp elevator” designed by Marine BioEngery, a private-sector company, a team from USC Wrigley studied the effects of depth cycling on the growth, morphology, and chemical composition of the giant kelp macrocystis pyrifera, a target species for renewable biomass production.
“We’re trying to figure out a way for us as a society to move away from fossil fuel source-based energy,” said Diane Kim, a member of the research team and senior scientist and DEI manager at USC Wrigley Institute.
The results of the study, published Feb. 19 in the journal Renewable and Sustainable Energy Reviews, found depth cycling increased kelp growth, yielding four times more biomass than natural processes.
“That was incredibly exciting to us because essentially this method could be utilized in places like the open ocean,” said Kim.
While the open ocean offers a large area for potential cultivation, the distribution of giant kelp is restricted by the availability of light, nutrients, and hard substrate for attachment. The kelp elevator consists of fiberglass tubes and stainless-steel cables that support the kelp in the open ocean, raising and lowering it to different depths to optimize sunlight exposure and nutrient supply.
In a 100-day study, research divers collected kelp from the wild, affixed it to the kelp elevator, and then deployed it off the shore of Catalina Island, near the USC Wrigley Institute’s marine field station. The elevator raised the kelp near to the surface during the day so it could soak up sunlight, then lowered it about 260 feet at night so it could absorb nutrients in the deeper water.
Researchers compared the kelp grown on the kelp elevator to a control group grown in a native kelp bed where kelp normally thrive near Catalina Island.
“We wanted to see how they responded to that and it turns out they not only survived, but they grew and they grew faster than a control group of kelp that we set out in a natural bay,” said Kim.
The results from the study found giant kelp grown under depth cycling conditions had an average growth rate of 5 percent per day and produced four times more biomass (wet weight) than individuals grown in a kelp bed without depth cycling. Analysis of tissue from the depth cycled kelp suggested the depth cycled kelp were not nitrogen-deficient and assimilated nutrients from deep water, according to the study.
“There’s a lot of potential for improving this, but the first essential question was are they going to survive and then if they do survive, can they grow under those seemingly stressful conditions for natural kelp,” said Kim. “Now that we’ve answered that first fundamental question, we can move on to really figuring out how to optimize this.”
Kelp has been identified as one potential sustainable alternative to conventional petroleum fuels since it requires very few natural resources, it doesn’t require land or fresh water, and is regenerative, the carbon emitted into the atmosphere when the fuel is burned is absorbed by kelp to build its own biomass. It can be converted into a lot of different types of energy including ethanol and methane.
“What we’re really excited about is the conversion of that biomass into a biocrude that can essentially be fed directly into existing refineries, so you don’t need new infrastructure, new technology and so what you end up with is something you can essentially pump into cars that exist today,” said Kim.
Kim said USC researchers are gearing up for another depth cycle trial to address some of the next step, high priority research questions. She said Marine BioEngery Inc. is preparing a pilot scale model of an open farm to develop technologies that can be commercialized, with ideas of autonomous drones one day pulling kelp in the open ocean.
“Just using that space alone [the U.S. Exclusive Economic Zone], we could really cultivate a feedstock, a sustainable feedstock, to supply some of our energy sector,” said Kim.
