How to make kelp aquaculture a better — and more economical — carbon sink

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The researchers claim to have developed a kelp aquaculture model for the Gulf of Maine that maximizes carbon sequestration and the profitability of this natural carbon sink.

The researchers, from the University of Maine in collaboration with Conscience Bay Research, note that “wild macroalgae are one of the most extensive and productive stocks of vegetative biomass, but they grow mainly in rocky areas near the shore. , which are not conducive to long-term localized exploitation”. [carbon] sequestration, which only occurs when macroalgae are incorporated into deep ocean sediments deeper than 1,000 meters or remineralized at depths below the permanent thermocline in areas of the ocean where carbon is prevented from returning to the atmosphere”.

However, they argue that kelp farming in areas such as the Gulf of Maine could replicate this process of carbon sequestration if the kelp is transported to a deep-water “sink site” and then deposited deep in the ocean where carbon can be sequestered.

“Farming kelp for large-scale carbon dioxide removal is an idea that has recently caught the attention of the research community, the private sector and the aquaculture industry. The purpose of our analysis was to inject some realism into the conversation about the costs and environmental impact of this emerging technology. Many consider the Gulf of Maine not only a national leader in sustainable seafood production, but also a potential carbon sink. More information is needed to help guide the potential development of carbon dioxide removal from the oceans,” said Struan Coleman, lead author of the study and research associate at UMaine, in a press release. hurry.

“Farming kelp for carbon sequestration is not competitive at the moment, but there are important pathways to reduce the cost of producing kelp, which is good for everyone,” added Damian Brady, co. – author of the study and associate professor of oceanography at UMaine.

“We focused on the cost of production because if it’s not competitive with other carbon sequestration approaches, like direct air capture, it may dictate where future production funding is. research will be undertaken,” he continued.

The researchers created a detailed model for kelp aquaculture in the region. By tinkering with 18 different variables – including assumptions about labor requirements for harvesting, where the electricity is coming from, and the size of the PVC coils in the nursery where the kelp spores or gametophytes attach and grow – they were able to reduce the cost of carbon sequestration through kelp aquaculture from $17,048 per tonne of carbon dioxide equivalent to $1,257.

The results represent a significant decrease in costs for carbon dioxide removal in kelp aquaculture; however, the industry cost target for these technologies is around $100 per tonne of carbon dioxide equivalent in order to be economically viable.

“This means the industry will need to innovate beyond how farms are currently run if removing carbon dioxide from macroalgae is to be economically viable,” study co-author Adam St Gelais said. and Aquaculture Innovation Specialist at the UMaine Aquaculture Research Institute. “Additionally – and equally important for scaling up – this model provides pathways to reduce production costs and reduce production-related emissions for growing kelp, regardless of its end use. . The insights from the model can be applied now to help growers increase yield and increase margins through optimization as they seek to grow. »

Six steps to reduce costs

Although it is not possible to optimize all the parameters described, scientists have identified six steps that will have the greatest impact on production costs, energy consumption and monitoring in kelp aquaculture .

First, farms should have the ability to move to larger, contiguous offshore sites to more efficiently use ocean space and reduce the risk farmers assume when accepting a lease for a kelp farm. .

Farmers should also automate the sowing and harvesting process, take advantage of selective breeding to increase yields, and assess the cost-benefit of nursery crops of gametophytes as opposed to spores, as they are cheaper and provide better selective breeding.

“Our findings are consistent with many research and development needs that the kelp aquaculture industry has been working on for decades. I think the real value of our approach was in looking at how variables such as yield, energy use in the nursery, and farm design impact the cost structure of kelp farms at a relatively large scale. If this industry is to continue to grow, whether it is contributing to food supply chains or removing carbon dioxide, we will need to address these issues,” Coleman said.

Kelp farms in the Gulf of Maine can also decarbonize by using electricity from renewable sources and using low greenhouse gas impact materials with a long lifespan. Finally, they need to develop inexpensive and accurate monitoring techniques for carbon dioxide removal from the oceans to reduce the uncertainty of carbon budgeting.

“Our team is excited to continue this work over the next two years and hope to accelerate kelp cultivation along the technology cost curve. We relied heavily on our initial analysis to identify the most impactful levers we could pull to answer pressing research and development questions. Through a combination of field studies and modeling, we hope to de-risk promising designs and technologies,” Coleman said.

The study was published in August 2022 in Marine Science Frontiers.

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