Materials required:
- Fertile kelp
- Cooler for transportation
- Reproductive kelp solution
- Spray bottle
- Gravel: limestone and/or granite (2-5 cm in diameter)
- Tank(s) for closed seawater system
- Pumps to create water flow for simulated natural environment
- Aquarium cooling unit to maintain temperature for optimal growth
- Germanium dioxide or a UV steriliser to inhibit growth of contaminants
- LED lamps
- pH meter
- Nutrients such as Provasoli Enrichment Solution
- Transport containers for collection and release
- Boat for kelp collection and release
- Standard diving equipment for kelp collection and release (optional)
Steps of implementation:
1. Kelp Collection
- Identify the location for kelp collection where there is an abundance of the desired fertile kelp leaves. Kelp is typically in its peak reproductive phase in spring and fall, but this depends on the species.
- Collect the reproductive tissue of healthy and fertile kelp species by using scissors to cut at the base of the kelp . The reproductive tissue is short, ruffled, darker and often thicker than the infertile blades.
- Place the reproductive tissue in a clean cooler for transportation.
2. Spore Release
- Clean reproductive tissue by rinsing it in fresh water and wiping it gently with a towel to remove small organisms growing on the surface of the kelp blade.
- Induce spore release by first drying the reproductive material on paper towels in a cool, dark place (10-15 ℃) for 2 hours. Then place the reproductive tissue in cold, dark and filtered seawater for up to 48 hours or until the water becomes cloudy. The resulting mixture of seawater and spores is the reproductive kelp solution.
* Spore release may differ depending on the kelp species.
3. Green Gravel Preparation
- Using a spray bottle, spray the reproductive kelp solution onto the gravel pieces.
- Place the sprayed gravel into water tanks filled with seawater.
4. Green Gravel Development
- Incubate the gravel at controlled settings.
- Monitor and control temperature, nutrient availability, light quality, contamination, and air flow.
- Water temperature should be around 11 ℃.
- For the first two weeks, air flow should be maintained at about 20 L per hour, and then increased to 60 L per hour.
- Keep constant light that is suitable for kelp growth. During the final two weeks, use a 12 hour light and 12 hour dark cycle to minimise stress before releasing the kelp to the restoration site.
- Allow kelp to grow about 2-3 cm.
5. Deployment
- Transport green gravel in containers to the restoration location. Deployment has been shown to be more successful in winter months, likely due to reduced competition from existing kelp in the spring.
- Various techniques can be used for deployment.
- Surface release: Place the seeded gravel pieces in buckets and drop them from the surface of the water onto the selected restoration site.
- Manual placement: Place the gravel pieces in a bag, then use diving gear to transport them directly on the seafloor. Distribute the gravel to a spot where there is light, wave protection and hard surface for attachment.
6. Monitor
- Immediately after deployment, record baseline data to measure long-term progress. Make sure to note things such as the date, location, number of gravel units released, deployment method, and conditions of the surrounding environment such as water temperature, light availability, and biodiversity.
- Track the establishment of the kelp by checking placement, growth, survival rate, grazer impact and later on a biodiversity survey.
- There is limited information on detailed monitoring plans. However, one study implemented a monthly monitoring plan for a total of eight months after initial deployment.
*Steps of implementation come from (Source)
Considerations for application:
- Because this method is in its early stages, it has only been tested in limited environmental contexts. Thus, adjustments in methodology need to be made depending on kelp species or geographic location.
- Detailed and reliable protocols are still being established for optimal production and successful scaling initiatives.
- Challenges for successful application include: topography, grazing pressure of sea urchins, rough terrain, and the unexpected appearance of sediment.
- Algae contamination can be an issue when keeping seaweed in controlled environments. Thus, careful monitoring is needed to keep the kelp healthy in its stages of development.
- While collecting fertile kelp leaves is less invasive than removing entire clusters of kelp, frequent collection can risk depleting spore availability, which can compromise the natural ecosystem. Therefore, efficient use of reproductive material is essential to support large-scale restoration efforts.
This intervention contributes to:
Green gravel may be a cost-effective and scalable method for kelp restoration. However, current data on its implementation costs are limited and inconsistent. As a result, definitive conclusions about its economic viability can not be made.
All info from following table came from (Source)
| Factor |
Estimated Value |
| Preparation and facilities (lab) |
£2,866.11 (UK 2020-2021). |
| Labour Time |
Preparation: three days, one person
Field deployment: one day, four people
Monitoring: nine days, two people |
| Maintenance Cost |
Travel: £49.50 (based on UK mileage/fuel rates from 2011-present) *mileage travelled to restoration site over an eight month period
Field deployment (labour): £312.68 (UK April 2023 minimum wage, £10.42)
Monitoring (labour): £1406.70 (UK April 2023 minimum wage, £10.42) |
| Material Cost |
£250 (UK 2020) |
| Total |
£4884.99 = £1221.25 per ㎡
*total GBP values are estimated from various years between 2020-2023. Additionally, the cost of the aquarium personnel to monitor the aquarium controls over the course of the experiment term were not included. |
A separate study estimated that restoring about 314 ㎡ of seafloor required ~ 116kg of green gravel. This process took 54 hours (40 hours of lab time for culturing and maintenance, 14 hours for collection and release). Excluding expenses such as facilities, vessel rentals, and long-term monitoring, estimated costs were about $6.75 USD per ㎡ of restored area (Source).
- Green Gravel Portugal
Along the coast of Portugal, a team of scientists is working to test and scale the green gravel restoration method. They are using the kelp species Laminaria Ochroleuca to optimise the outcome of this restoration method. The goal of this project is to develop reliable methods in green gravel restoration for large scale implementation in Portugal. To support this effort, they operate a year-round kelp nursery to boost production. Additionally, to minimise the need for harvesting new material from kelp populations, they are developing a seedstock system for continuous availability. This project is also partnering with various organizations and local municipalities to encourage marine conservation.
2. Grønn Grus Norway
The Norwegian Institute of Marine Research is advancing their efforts to test green gravel techniques on Norwegian kelp forests. Due to sea urchin overgrazing, the kelp forests along the southern coast have suffered great decline, highlighting the urgent need for effective restoration methods. This project is centered on restoring Sacharrina latissima (sugar kelp) with the aim of developing a cost-effective technique for restoring large areas of kelp forests.
3. Restoring Blue Forests with Green Gravel
This research project, conducted in collaboration with Operation Crayweed and Sydney Institute of Marine Science, aims to restore the crayweed populations along the coast of Sydney, where they have become locally extinct. Crayweed plays a vital role in kelp forest ecosystems by providing food and habitat for a wide range of marine life. Its absence has contributed to significant biodiversity loss, making this restoration technique essential for marine ecosystems.
