Blue carbon sequestration and storage potential has increased in seagrass sediments from Northern Morocco

[Geoengineering News]

https://www.nature.com/articles/s43247-025-02966-y

Authors: Nezha Mejjad, Abdelmourhit Laissaoui, Azzouz Benkdad, Fouad Taous, Mohammed El Bouch, Anas Otmani & Moncef Benmansour 

16 December 2025

Abstract

Driven by the essential role of blue carbon ecosystems in mitigating climate change and by scarce regional data, here we aim to quantify carbon sequestration rates and storage in a Moroccan coastal vegetated ecosystem over time using nuclear approaches. The carbon stocks recorded over the past 60 years ranged from 1.35 to 11.07 Mg Corg ha−1 in Merja Kahla and from 3.55 to 54.48 Mg Corg ha−1 and from 3.57 to 104.58 Mg Corg ha−1 in two cores from Merja Zerga. The highest carbon accumulation rates were observed in the top 5 cm of sediment cores, ranging from 14.60 to 53.08 g OC m−2 yr−1, suggesting a noticeable increase in recent years. These findings highlight the need to integrate blue carbon ecosystems into national policies as nature-based solutions for mitigating climate change and for enhancing the management and conservation of coastal and marine resources threatened by human activities.

Source: Communications Earth & Environment 

[Michael Hayes]

Cultivation of seagrass within a closed hull system offers not just high C sequestration rates as soil is built, as found in the wild, but also offers a crop that can be used to produce ethanol, thus making bio-ethylene production possible. If the cultivation hulls are made of high density polyethylene, and bio-ethylene is a primary commodity being produced, this represents a largely self-replicating mCDR infrastructure.

The C locked up in the HDPE hulls can be considered as being stored for an extended period of time, all while the cultivation operation continues to drawdown more CO2 and generating even more bio-ethylene.

This largely self-replicating mCDR system of systems needs no new technology to be deployed today. At the policy level, as the hulls are enclosed and all discharged water can be monitored and, if needed, adjusted, the impact on the surrounding environment should be negligible, thus meeting many policymakers demands. 

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[Tom Goreau]

It is feasible to grow floating solar powered seagrass with PV panels, and I proposed to do so as part of the United Nations Sustainable Floating City Programme.

 

https://unhabitat.org/news/27-apr-2022/un-habitat-and-partners-unveil-oceanix-busan-the-worlds-first-prototype-floating

 

But this would NOT be in a “closed hull system” as you describe (to which CO2 and light would have to be added) but an open system taking up both CO2 and sunlight from the sky above while exporting organic carbon and limestone.

 

True closed systems are possible, but much more complicated to maintain.

 

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[Michael Hayes]

Tom, et al.,

I expect that both open and closed systems will be developed. An important advantage of a closed systems over open systems is that they can be submerged, thus avoiding weather and wave hazards. 

Also, light, temperature, nutrient, and CO2 levels can be optimized for the crop being cultivated. All plants can consume far more CO2 than what the atmosphere provides, and light and temperature control eliminates seasonal limits...just like an enclosed fully controlled greenhouse achieves.

Finally, and I think this is economically very important, enclosed systems can be used to grow terrestrial crops in the marine space as well as aquatic crops. Any one crop system is vulnerable to market swings and diseases moreso than multi crop systems. On-shore shimp farming is the posted child for what a rapid global spread of viral infections can cost. 

Your open system does need support for many reasons, lower startup cost being the primary advantage, yet closed systems can likely pay for their added cost and complexity due to their greater flexibility of use, or greater spread of end products.

Best regards 

[GRETCHEN & RON LARSON]

Michael, Tom,  List  with  1 cc

 

     Thanks to Michael and Tom for keeping this mCDR topic alive. My interest as well - but way less strong than theirs.

 

       Googling today suggests good recent progress on handling seaweed -  applicable via biochar.  Especially Sargassum.

 

     But the most interesting  mCDR article I found showed up just this week.     Non-fee, (but not yet peer-reviewed) at:.

 

 https://www.sciencedirect.com/science/article/pii/S2211926425004941?via%3Dihub

Comprehensive quantification of production costs for large-scale kelp aquaculture and cost reduction opportunities

Z Moscicki, ATS Gelais, S Coleman, A Kinley… - Algal Research, 2025 - Elsevier

 

     A highly realistic techno-economic analysis (TEA) was developed to assess the cost of production (COP, US $ per fresh tonne kelp) for large-scale kelp aquaculture. The TEA resolves feedbacks across structural design and response, operational requirements and decisions, site properties, and biological response. We apply the TEA to a Saccharina latissima farming operation at a 100 m deep, 405 hectare site located 20 km offshore in the Gulf of Maine. Our baseline scenario included a farm previously designed for minimal …

 

       The article showed an amazing (> 5x) possible reduction in costs.  Not Michael's approach, but some parts should be applicable.  Since cost seems to be what has been holding mCDR (and especially mBCR) back, I hope Michael, Tom and others can comment on whether these new much-lower mCDR cost numbers are well-founded.   The methodology seems applicable to all forms of CDR - not just mCDR..

 

Ron

 

 

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