On a sunny but bitterly cold February day a line of small children snaked their way from Dale to Dale Fort on the Haverfordwest estuary. They were the last of more than 2,000 volunteers who over the last year have collected, stored and inserted seagrass seeds into little hessian bags, ready for planting.

These seagrass seeds were soon to join others on the seafloor a few hundred metres off-shore from Dale to restore two hectares of seagrass meadow. This restoration is the latest attempt to reverse a century of destruction.

In the UK we can only estimate the loss but in Denmark, seagrass (eelgrass) records dating back to the 1880s give a very grim and accurate picture. At the turn of the last century fishing was vital to the Danish economy and catches were falling. It was known then that seagrass meadows were a vital habitat for young sea fish such as cod and plaice and so in 1908 botanist Carl Ostenfeld was commissioned to survey the seagrasses then found in all the estuaries and inlets of Denmark.

That study provided a clear benchmark against which to measure the loss of seagrass in Denmark, a loss that currently stands at 95 per cent.

Children help place seagrass seeds inside hessian bags, ready for planting

The situation in the UK is much the same. According to Swansea University’s Dr Richard Unsworth: ‘Once every estuary in the UK had its seagrass meadows, from the Humber to the Thames, the Morey Firth to the Mersey. Now, seagrass is found in perhaps five per cent of that area.’

Why does this matter? Seagrass is not only a keystone species providing a nurturing habitat for fish and invertebrates, seagrass also sequesters carbon, at a rate in marine habitats only bettered by mangrove forest. Seagrass also stabilises the shore and absorbs energy, reducing the impact of storms. 

Boat anchors are one cause of damage to seagrass; dredging and seashore development another. But the main culprit is river water pollution, particularly nutrients from fertiliser and sewage. These excess nutrients cause algal growth that blankets the seagrass, cutting out light, and then later, when it dies off and rots, removes all oxygen. Excess nitrogen also makes it more likely that a devastating disease – eelgrass wasting disease – breaks out.

This problem of eutrophication has lessened in the last few decades thanks to the clean water regulations brought in during the 1980s, so that now some estuaries are again fit for seagrass growth. Dale is near the mouth of the Haverfordwest estuary and the water is relatively clean. Further in, nearer Haverfordwest, the nutrient load is still too high for seagrass, thanks mainly to agricultural run off. 

Active restoration can accelerate the slow pace of natural restoration (the edges of an existing meadow extend by only a few centimetres each year). Swansea scientists have spent six years perfecting a planting system. Small degradable hessian bags are strung on a rope at metre intervals, each filled with sand and around 50 seagrass seeds. These ropes are weighed at each end and manually dropped onto the seafloor from a small boat. The bag protects the seeds from being eaten by crabs and the sand provides a neutral, aerobic environment that enhances seed germination. The seedlings grow through the weave of the hessian and the bags decompose.

At Dale the seeds were collected in the summer of 2019 by volunteers from the Channel Islands and the Isle of Man. Divers, snorkelers and folk simply wading out during low tide gathered around a million seeds. The blades containing the seeds were snapped off – causing no harm to the plant – and then taken to laboratories where they were prepared.

The team go out on the boat to begin planting the seed bags

Meanwhile, in Denmark, students cut out seagrass divots from surviving, thriving meadows and planted them out in one metre squares in a grid pattern, a pattern now easily seen from drone footage as the plants establish.

Restoring seagrass meadows is one essential component for restoring fisheries. Banning dredging is another. Allowing kelp regrowth and the seafloor to again become stabilised by oyster beds leads to ever clearer waters and improving conditions for seagrass growth.

Nature recently published an article called ‘Rebuilding marine life’. In it Professor Callum Roberts from the University of York said: ‘Overfishing and climate change are tightening their grip, but there is hope in the science of restoration…’ One of the overarching messages is, if you stop killing sea life and protect it, then it does come back. We can turn the oceans around and we know it makes sense economically, for human wellbeing and, of course, for the environment.

In the seagrass planting in Dale, there is that hope.