Seagrass

hermit_crab__in_eelgrass - Credit paul naylorhermit_crab__in_eelgrass - Credit paul naylor

Seagrasses are the only flowering plants that are able to live in seawater and able to pollinate while submerged. Seagrass often grow in large groups giving the appearance of terrestrial grassland – a kind of underwater meadow. There are four species of seagrass in the UK, two species of tasselweeds and two zostera species commonly known as eelgrass.

What is it?

The plants’ roots are anchored in mud, sand or fine gravel acting to stabilize the seabed and prevent erosion, which has the further effect of helping to stabilise and defend the wider coastline. The leaves are narrow and long, forming a three-dimensional habitat allowing a wide range of species to inhabit the area. The density of the grasses causes the water currents to slow down and allows nutrients to settle, in turn attracting wildlife.

Where is it found?

Seagrass is dependent on high levels of light for photosynthesis to grow and can therefore only be found in shallow water to a depth of around 4 metres. They are found around the coast of the UK in sheltered areas such as harbours, estuaries, lagoons and bays.


Why is it important?

Seagrass provides important habitat for species ranging from tiny invertebrates, worms and shellfish to young and adult fishes including the commercially important bass.

In well-developed areas the leaves can become colonised by algae, stalked jellyfish and anemones, while the soft sediment surrounding the roots is home to molluscs (bivalves), tiny amphipods, polychaete worms and echinoderms.

The sheltered habitat can provide ideal nurseries for flatfish and even cephalopods hiding from predators and thereby increasing their survival rate. Our two native species of seahorse can also be found living amongst seagrass in the southern UK.

Seagrass is also an important food source for wildfowl such as widgeon and brent geese which feed on exposed seagrass at low tides. It is thought that only 5% of the seagrass is consumed in the form of the plant itself and that the majority of feeding is from decaying matter rich in invertebrates.
It has also been calculated that seagrass absorbs 15% of the ocean’s total carbon absorption.

Is it threatened?

A wasting disease was the cause of a drastic reduction of seagrass in the UK in the 1930’s. The following recovery has been hampered by increased human disturbance such as pollution and physical disturbance from dredging, use of mobile fishing gear and coastal development.

Increasingly high levels of nutrients, such as nitrogen and phosphorus, loading from sewage discharge is extremely toxic to seagrass directly but it also acts to stimulate epiphytic algae growth which can outcompete the seagrass by reducing the available sunlight.

The ability of seagrass to reduce the speed of currents can result in pollutant materials accumulating in the seagrass bed. Several heavy metals have been found to be able to reduce the plants ability to fix nitrogen and thus reducing the viability of the plant.
Alien species, including Spartina anglica and Sargassum Muticom, also affect their viability through competition.

Globally 30,000km2 of seagrass has been lost in the last couple of decades which is equal to 18% of the global area.

What are The Wildlife Trusts doing to help?

Following the assent of the Marine & Coastal Access Act, four regional projects were established to identify potential Marine Conservation Zones within England. The projects are stakeholder led and Wildlife Trust staff sit on all projects, at local, regional and a national level.

These projects will ultimately put forward sites to protect special areas of the sea. Additional work on Marine Protected Areas is also underway in Wales and Scotland, whilst in Northern Ireland we are still campaigning for Marine legislation with a commitment to establishing these areas.

What can I do to help?

Visit wildlifetrusts.org/livingseas to find out how you can help our marine conservation work in the UK.

Depending on where you live, local Wildlife Trust volunteers help out with everything from recording marine wildlife sightings to beach cleans and educational work. Visit our Living Seas pages online or contact your local Trust to find out more.