Kick-starting seagrass for a climate-proof sea

Once upon a time, seagrass meadows of about 150 square kilometres covered the bottom of the Dutch Wadden Sea. Now, seagrasses have all but disappeared, just like in many other places in the world. But these unique saltwater plants play a vital role in an ecosystem. Ecologists Jeanine Olsen, Tjisse van der Heide, and Laura Govers of the University of Groningen are working to help seagrass return to our waters. On the occasion of the World Seagrass Conference, 17-21 June in Naples, Italy, the BBC premiered a mini documentary on Govers’ work .

FSE Science Newsroom | Charlotte Vlek

Rows of researchers and volunteers walk along the mudflats with an adapted caulking gun, injecting a mix of mud and seagrass seeds into the sediment at specified distances. Elsewhere, 3D-printed biodegradable plastic structures are sunk into the ground to make sure that the newly planted seagrasses don’t immediately wash away. These new techniques for seagrass restoration have brought ecologists Laura Govers and Tjisse van der Heide several successes.

Jeanine Olsen, Emeritus Professor of Molecular Ecology, takes a different approach: she is looking at seagrass genomes in her search for climate-proof seagrass. Currently, seeds and plants for seagrass restoration projects are sometimes imported from warmer regions to stay ahead of the rising temperatures due to climate change. However, Olsen explains that simply taking plants from the Mediterranean Sea and planting them in the Netherlands is a bit too simplistic. Genetic information is needed to figure out whether a plant is compatible.

Why it is important, yet difficult

Attempts at seagrass restoration have been ongoing for decades. This is because seagrasses play a fundamental role as the base for an ecosystem. Seagrass meadows provide shelter and food for marine animals, keep the sediment from eroding, and store a lot of carbon. But once seagrass has disappeared from a place, it’s difficult to get new plants to grow back again. 

This is because seagrass has many beneficial effects on its environment, from which the seagrass benefits in turn: seagrass stabilizes the sediment, traps floating mud particles, dampens the waves, and adds oxygen to the sediment. Unfortunately, these positive effects only occur once a large seagrass meadow has been established. Van der Heide: ‘When trying to grow new seagrass, these positive effects are not taking place yet, and there’s a great chance the small plants are washed away.’

The dispenser injection seeding method

Govers: ‘Before, seagrass shoots with seeds were hung in the sea in mesh bags and the seed would mostly wash out and get lost. Out of millions of seeds, only a few would successfully grow where they were seeded. With our seed injection method, we’ve found a way to give these seeds a better chance.’ Govers investigated exactly at what depth and at what distance from each other these seeds should be injected for optimal results.

Thanks to this method, the largest restored intertidal seagrass meadow worldwide can now be found next to the small Wadden Island Griend. Seagrass meadows can be one of two types: subtidal seagrass always grows underwater, while intertidal seagrass emerges above water during low tide. This last type is typically an annual plant that produces many seeds, which makes it a suitable candidate for the seed injection method. 

Govers plants the seeds in collaboration with local and national organizations, but the method has been picked up worldwide and is now used in restoration projects in England, Wales, France, the US, and Australia, to name a few. ‘Each of these projects makes their own adjustments to our method,’ Govers explains, ‘because what’s effective in one system, can be very ineffective in another.’

Imitating good circumstances

There are fewer success stories about subtidal seagrass—the kind that always grows underwater. These plants are often perennial, and as a result, the positive effects they have on their environment has a bigger factor in their success. ‘So we thought: can we simulate these positive effects?’ Van der Heide says. ‘This way, we can help the plants to get beyond the difficult first step of establishing a new seagrass meadow.’

Van der Heide’s biodegradable structures dampen the waves and stabilize the mud. ‘And it works!’ he reports. ‘But for now it is a case of good concept, bad execution.’ That is because the bioplastic used to produce these structures, in collaboration with the industry, turned out to need a lot of time to degrade. In the meantime they disintegrated, leaving pieces of material floating around in the sea.

But Van der Heide recently obtained a grant to develop new prototypes for seagrass restoration as well as for mussel beds and salt marsh plants. Van der Heide: ‘We bought a second-hand robotic arm from a car factory to be able to 3D-print, and we’re now going to try to develop new materials as well as new shapes. So I’m becoming an industrial designer as well as an ecologist!’

Searching for the best candidates

Seagrass seeds and plants for restoration projects are normally taken from nearby locations, such as the German Wadden area in case of the Dutch Wadden Sea. But, on the basis of the plants’ genome, Olsen and her colleagues from Sweden, Germany, and the US are now able to pinpoint specific genes for ecologically important traits. Olsen: ‘This will help to ensure that the right plants are introduced in the right places.’ 

For instance, Olsen and her colleagues can use this information to find out how plants deal with rising temperatures, varying salinity, cloudy water, or ocean acidification. ‘One of the coolest findings so far,’ Olsen reports, ‘is the fact that genes are often duplicated.’ With two of the same gene, the plant can safely ‘experiment’ with one of them, without the risk of self-extinction.’