Restoring seagrass meadows in England

| 23rd September 2020 |
Seagrass. Photo: Richard Unsworth.
Seagrass meadows support marine life, human livelihoods and the fight against climate breakdown.

Restoring seagrass beds in this way is a first for the UK, and the LIFE Recreation ReMEDIES project is planning to restore 8 hectares of seagrass bed in this way, growing tens of thousands of seedlings over the next three years.

Ocean Conservation Trust scientists and conservation practitioners based at the National Marine Aquarium in Plymouth are tending to tanks of rotting seagrass. Their work is a vital step in safeguarding this important habitat for future generations.

A widely distributed temperate seagrass species commonly referred to as eelgrass (Zostera marina) once formed extensive meadows around the coastal waters of the British Isles but are now categorised as being nationally scarce.

Large scale simultaneous die-offs of Z. marina meadows were observed on both sides of the Atlantic and Pacific oceans in an outbreak of ‘wasting disease’ in the 1920s and 1930s, leading to a 90 percent reduction in habitat cover.

Pressures

In recent decades, populations of Z. marina have continued to decline. Increased nutrient loading in the water is a major issue, increasing their susceptibility to disease and promoting the growth of epiphytic algae, seagrass lose their ability to absorb light and eventually die.

Alongside reduced water quality, seagrass habitat is also threatened by coastal development and poor land use, including disturbance from marine activities.

For example, seagrass can be damaged by the anchoring, mooring and launching of boats, can be trampled by walkers and bait collectors and can be removed by destructive fishing practices.

In combination, the result of these pressures is that almost half of the Z. marina habitat of Britain has been lost in the past 25 years, with the remaining habitat being fragmented, in poor health and considered in unfavourable condition. Year on year, global seagrass habitat continues to decline at an estimated rate of 7 percent, meaning that in less than two decades, this important habitat may have disappeared.

Seagrasses are angiosperms, flowering plants that produce seed, and as such are truly unique in the marine environment. Capable of reproducing vegetatively, creating clone plants by growth of the rhizome (root), they can also reproduce sexually, where flowering, pollination, the production of seed and seed dispersal all occurs underwater.

The evolutionary move of these flowering plants into saltwater have resulted in some of the most productive ecosystems on earth, rivalling tropical rain forests and coral reefs in terms of productivity and the ecosystem services they provide.

Restoration

Providing a variety of critical ecosystem services, seagrass meadows reduce the impact of costal erosion, support fisheries, improve water quality, provide us with oxygen and store significant amounts of carbon.

Seagrass beds act as nursery habitat to many fish and invertebrate species, with one fifth of the world’s largest commercial fisheries reliant upon them for the refuge, shelter and food they provide. Species of note include Alaskan walleye pollack, and Atlantic and Pacific herring and cod populations.

Trapping and stabilising sediment, seagrass beds reduce wave energy and can be a vital tool in the fight against coastal erosion. Additionally, the sediment trapped by seagrass locks in carbon 35 times more efficiently than tropical rainforests by area, making this an extremely important habitat in the fight against climate change.

Improved water quality, reduced pollution and increased management and awareness of marine habitat use is essential in protecting the seagrass habitat that remains in our oceans. In the last 20 years, massive strides have been taken to slow the rate of loss and try to reverse the declining trend.

However, seagrass meadows are not returning to the condition they were once in, and seagrass restoration is now thought to be the way forward in recovering the lost ecological function and ecosystem services seagrass meadows provide.

Cultivation

The Ocean Conservation Trust are partners in a large-scale marine restoration project to do exactly this, restore seagrass beds. The LIFE Recreation ReMEDIES project, Reducing and Mitigating Erosion and Disturbance Impacts affEcting the seabed, will be the first of its kind to collect seagrass seed and cultivate and replant seagrass at this scale in England.

A team of divers, scientists and conservationists at the Ocean Conservation Trust collected approximately 800,000 Z. marina seed this year. Picking the reproductive seed-bearing shoots of Z. marina by hand, the team spent 50 hours underwater.

Working in this way the divers can ensure the root of the plant is left undisturbed, allowing the plant to regrow and maintaining the health of the bed. In a specially built cultivation facility, the seagrass is currently being held in large recirculation tanks in conditions replicating that of their natural marine environment.

Here the seed-bearing shoots rot as they would naturally, the seed drop out, are separated from the vegetative material, cleaned and stored for replanting.

Using seed for large-scale restoration of seagrass has gained considerable momentum in the past decade. Previous restorative efforts have relied upon the transplant of adult plants, but this can be highly labour intensive and potentially damaging to the donor bed.

Regeneration

Seed mortality and failed germination in the marine environment is thought to be extremely high, with losses occurring due to predation, disease, competition, movement to unsuitable germination sites or smothering by organic material to name a few. Collecting seed instead of adult plants therefore utilises a resource that may otherwise be lost.

Growing seed in a laboratory environment allows replication of the conditions required to produce maximum germination and seedling development. Grown in small hessian bags, like sandbags, after approximately three months the seedlings can be transplanted back to the sea, to locations where they will have the best chance of success.

Restoring seagrass beds in this way is a first for the UK, and the LIFE Recreation ReMEDIES project is planning to restore 8 hectares of seagrass bed in this way, growing tens of thousands of seedlings over the next three years.

You can now view the purpose-built cultivation facility for this pioneering project as part of a visit to the National Marine Aquarium.

Looking through the window to tank after tank of small sandbags illuminated under neon blue lighting, you might be forgiven for failing to notice the small seagrass seedlings, currently less than 10cm in height, or for failing to realise their potential to regenerate once abundant seagrass meadows, their potential to support marine life, and the livelihoods of those who rely on it, and their potential in the fight against climate change.

This Author 

Emma Nolan is the cultivation officer at the Ocean Conservation Trust for the LIFE Recreation ReMEDIES project. LIFE Recreation ReMEDIES is financially supported by LIFE, a financial instrument of the European Commission.

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