Seagrass meadows: Britain’s most important and threatened habitat

Seagrass – a little harshly described as the most important aspect of British biodiversity that nobody has heard of.

Well the ‘important’ bit is certainly right – and enough people have heard of it and treasure it – for the ‘Great British Seagrass Fightback’ to be well underway.

Time was when vast swathes of our sheltered estuaries and even some more open beaches shone green in the summer sun with huge gently swaying underwater fields of seagrass just a metre or two down on the seabed.

As rainforests are to animal species, so seagrass is to a huge range of marine animal species. Scientists have found tens of thousands of sea animals in just a hectare of seagrass. From tiny invertebrates to crabs, fish and even British seahorses – yes we have them too.

Trouble is, we have lost around 90% of UK seagrass groves in just the last thirty years. Human encroachment and dredging have played a part, but the biggest cause appears to have been sewage pollution on the watch of the privatised water monopolies. It isn’t just human swimmers scared off by the muck.

Fightback underway

Now though the fightback is underway. Tucked between the idyllic estuary at Laugherne in southwest Wales where Dylan Thomas wrote, and the machine gun and shellfire of a coastal army range, at a huge 50-acre nursery owned by a wetland restoration company, Salix, you find Project Seagrass.

It’s the largest effort yet to cultivate two of the four British species and replant them at sites in Wales, southern England, northeast Scotland and Orkney.

So far the Welsh results look promising but it is painstaking work. Tiny, frail seedlings planted into seawater ponds under a polytunnel with a ripple machine to replicate the effect of wild tidal marine zones. You need a polytunnel to stop the Welsh rain diluting the salinity of the growing ponds.

The grass seed comes in tiny thin pods after the plants flower. To begin with, divers plucked these from remaining healthy seagrass fields in north Wales. That still happens but the good news is they are able to grow their own seed now at the Laugherne experimental site.

The importance of seagrass

Much is at stake. We like to think of UK peat bogs as our rainforests when it comes to carbon sequestration. But seagrass fields outdo rainforests by some margin on that score. As well as teeming with marine wildlife.

The race is now on to get replanting around at least five UK sites but clearly we will have to improve our track record on sewage discharge to help the groves return to their former glory.

There are openly practical benefits as well. Like reed beds, seagrass is also a highly effective means of dispersing and buffering tidal surges, so its use in flood mitigation is only now beginning to be understood.

Moreover the benefits for inshore fisheries are obvious. Replant the seagrass groves and the fish and crabs arrive in abundance once again.