Scaling up Kelp Forest Restoration

Building a kelp nursery to produce and deploy green gravel kelp at scale

Project information
  • Management Plan
  • Total budget: ¬£77,198
  • Budget spent: ¬£59,768
  • Status: In Progress

Underwater forests are an immensely important ecosystem: they support biodiversity, improve water quality and sequester carbon. Despite their significance for marine life and the fight against climate change, the loss of kelp forests from coastlines worldwide has captured much less of the spotlight on deforestation. This is why since 2020, we have been working with SeaForester to restore kelp forests in Portugal where large areas of kelp have disappeared. We have built a kelp nursery to produce and deploy kelp that tests a new method called ‚Äėgreen gravel‚Äô with the potential for large-scale marine reforestation.

Project Timeline

Results of our first kelp restoration trial

Our ultimate goal is to make large scale restoration of kelp forests a reality in Portugal and our first step in this direction was the kelp restoration trial we started with SeaForester in Cascais in November 2020. We deployed spores from healthy kelp populations into 3 sites. The results so far suggest that this spore bag technique will not work in this area, possibly because of the presence of turf algae that outcompete the kelp for rock surface. Although we were disappointed with the result, the information we got out of the project is valuable and is already helping guide our next steps.

Jan from SeaForester monitoring the site of our kelp restoration trial in Cascais on our latest visit. Unfortunately, it seems like bringing kelp spores back to the area was not enough to kickstart restoration. With the lesson learned, we are moving on to the new solutions!

A new technique and successful trials

Green gravel is a kelp restoration technique that was recently developed by the Norwegian Institute for Marine Research (IMR). It involves seeding pebbles with kelp in a lab, allowing the kelp to grow under optimal conditions and only then deploying them in the ocean. The potential is huge because this technique can overcome many of the challenges facing current kelp restoration methods.

Since pebbles can just be dropped from a boat, large areas could be restored without the need for more costly and time-consuming scuba diving work. What’s more, since the kelp is already attached to a substrate (the pebbles) it may grow well even if the underlying reef is degraded and covered in turf algae. The technique worked well in turf-covered reefs in Norway so we hope it will also be useful in addressing this problem in the areas in Cascais where releasing kelps spores is not proving to be enough to bring the kelp back.

The method is now being trialled in more than 10 locations across the world in a collaborative effort coordinated through the Green Gravel Action Group. In Portugal, the SeaForester team, including researchers from the Marine and Environmental Sciences Centre - Politécnico de Leiria, have successfully used the technique in small scale trials. Individuals of the golden kelp, Laminaria Ochroleuca, have been successfully deployed on the ocean floor and have grown well over several months. This is very encouraging and means that we are ready for the next step!

Pebble with kelp growing on it deployed using green gravel technique and being held by diver
One of the pebbles deployed in the sucessful trial in Peniche after growing for several months at sea. Photo credit: Jo√£o Nuno Franco.

Scaling things up

Given the success of the initial trials in Peniche and the great potential of green gravel as a marine reforestation technique, we decided to scale things up. With the support of our Mossy Earth members as well as Not Just Travel, Get Set Hire, Unifrog and WSL Pure, we managed to get the funds needed to build a kelp nursery that will greatly increase the green gravel production capacity in Portugal.

This amounts to a total of 80 boxes which we are mounting in a shelf system which allows each of them to maintain about 200 to 400 pebbles under optimal conditions for the kelp to grow in the lab. Each box is illuminated by an LED light that switches on and off to simulate night and day cycles. Water flows through the boxes and is filtered and cooled so that it is kept suitable for kelp growth.

The kelp nursery will be running year-round with a new batch of kelp pebbles being ready to deploy every 2 to 3 months. Each cycle begins by spraying the pebbles with microscopic immature life stages of the kelp which attach to the pebbles and start growing. To avoid the need to collect this starting material from wild populations every time we are also building a lab setup that allows us to keep a seedstock available year-round. This is a modified fridge contraption that allows the seedstock to be kept at the necessary light and temperature conditions. This makes it much faster and cost-efficient to start each production cycle because it is no longer necessary to find and collect material from wild kelp populations every time.

Altogether this will allow the green gravel technique to be tested at a much larger scale in Portugal!

Kelp nursery under construction in Peniche
Getting the system up and running involves a lot of trial and error. Here you can see the first 2 shelves getting close to completion.

Learn more about the context behind this project

Disappearing seaweed forests

The world’s shallow coastal areas, where sunlight penetrates, are the cradles of the ocean. Here seaweed forests grow supporting a rich and diverse assemblage of marine fauna and flora by providing highly productive three-dimensional habitats. In addition to reducing the loss of biodiversity in oceans, kelp forests also provide ecosystem services by reversing acidification, an important part of climate change mitigation.

Unfortunately, European seaweed forests are disappearing at an alarming rate. Although we lack the data to figure out the actual causes for this decline, these are likely to be important drivers in many areas:

  • Water pollution
  • Climate change affecting water temperatures
  • A build-up of sediment as a result of both human and natural causes
  • Increases in herbivory rates due to overfishing and its impact on coastal ecological communities
  • Increased storm intensity
A healthy kelp forest on the coast of Portugal. Photo credit Jo√£o Nuno Franco
Kelp forests are astonishing 3 dimensional habitats. Restoring them has the potential to help all kinds of marine life. Photo credit Jo√£o Nuno Franco.

Pioneering seaweed restoration work in Europe

Unlike land-based deforestation which has received a lot of attention, the loss of marine forests tends to go mostly unnoticed. This may be due to the fact that the underwater world is out of sight for most of us and its deterioration is therefore not as obvious. As result, there are still very few seaweed restoration projects in Europe and there is a great need to develop greater know-how in this area. This is where our partnership with SeaForester comes in to restore these 'forgotten forests'. SeaForester is an initiative that aims to reverse the alarming disappearance of seaweed forests in the world in order to safeguard the oceans’ vital role of carbon sequestration, maintaining fish stocks and securing the planet’s wellbeing. By joining forces with them in Portugal, we aim to make the large-scale restoration of kelp forests a reality here.


We've had an overwhelming amount of interest in this project which has raised some very interesting ideas from our followers! In this section, we will try to answer some of your most common questions and update it as we make developments.

Would it be possible or practical to try for mixed species reintroductions?

Here are our current thoughts about mixing species, namely Laminaria Ochroleuca and Saccorhiza Polyschides.

  1. Golden kelp forests are often single species and this is not a problem so the analogy of a monoculture plantation on land doesn't really apply and it's not something we need to be worried about.
  2. We could try and use S.Polyschides and it may be that it does better at some of our sites or that in some places there would be some sort of synergistic effect.
  3. We do not want to spread ourselves too thin for now. We are already trying to understand the effect of many variables in the production and deployment process and it seems better for us to focus on a single species for now.
SeaForester is an initiative that aims to reverse the alarming disappearance of seaweed forests in the world in order to safeguard the oceans’ vital role of carbon sequestration, maintaining fish stocks and securing the planet’s wellbeing. 

Sources & further reading

Peer Reviewed Research Section
  1. ‚ÄúGreen gravel: a novel restoration tool to combat kelp forest decline.¬†‚ÄĚ - Fredriksen, S., Filbee-Dexter, K., Norderhaug, K.M.¬†et al., 2020External linkIcon Peer Review
  2. ‚ÄúEcosystem Engineers, Keystone Species‚ÄĚ - de Visser S., Th√©bault E., de Ruiter P 2012External linkIcon Peer Review