Seagrass might just save us all

A seagrass meadow in daytime
Seagrass is the only flowering plant able to live in seawater and pollinate whilst submerged

A seagrass meadow is probably the most important habitat in the world right now

Editorial by Ocean Desk editor Jules Powis

Seagrass may look pretty ordinary but it has the potential to help humankind with some of our biggest environmental problems.

Seagrass loves carbon

The ocean’s been absorbing about 90 percent of the excess heat from global warming for decades now. As seawater warms up, it can’t hold onto oxygen as well so carbon dioxide levels rise. Vast amounts of human-driven carbon dioxide in the atmosphere is also dissolving into the sea.

Seagrass is astonishingly good at removing CO2 from seawater: absorbing and storing carbon 35 times faster than a tropical rainforest of the same area. This captured carbon gets buried in the seafloor sediment when the plant dies, it isn’t recycled back into the environment.

Short infographic on the oceans absorbing carbon dioxide

Why is this a thing? Increased levels of CO2 is making the sea more acidic, which is increasingly effecting the ability of corals, oysters and many plankton to form their protective shells. Everything in the marine food web depends on plankton either directly or indirectly. Much of the shellfish we eat begins life as drifting plankton, slowing the acidification of the ocean is vital to avoid ecosystem collapse.

Seagrass currently accounts for a whopping 10-15 percent of global ocean carbon storage despite only taking up a tiny 0.2 percent of the seafloor. It’s been declining globally at about 7 percent a year since at least 1990 – what would happen if we restored seagrass habitats globally and reversed that statistic?

Seagrass supports fish stocks

Seagrass has other properties that we need right now: it’s a vital habitat, harbouring up to 40 times more marine life than seabeds without it. Seagrass meadows are vital for our fisheries. They provide they ideal nursery habitat for many types of juvenile fish like cod, plaice and pollock – and of course the endangered seahorse.

British seagrass meadow with a  seahorses
UK seagrass meadows house species such as seahorses and sea snails
Image: Nature Picture Library

Seagrass is dependent on high levels of light for photosynthesis so it’s only found in shallow water. Perfect conditions for juvenile fish, but this preference also means that seagrass helps to protect our coastline from erosion by knitting the loose coastal sediment together with its root system. This will be an increasingly important benefit for the more extreme weather we are predicted.

Seagrass cleans-up

As if the case for restoring seagrass beds off the coast of Britain wasn’t watertight enough, new research from Europe shows how Mediterranean seagrass might help humanity out with yet another giant problem of its own making: the eight million tons of plastic that ends up in the world’s oceans every year.

A species of seagrass called Posidonia oceanica found in the Mediterranean
A species of seagrass called Posidonia oceanica found in the Mediterranean
Image: University of Barcelona / Jordi Regàs

When blades of a type of seagrass called Posidonia oceanica fall or break off, their fibres can form tangled masses called ‘Neptune balls’. Researchers found that Neptune balls trap small fragments of plastic which then wash ashore. This may not sound like a big deal but a study in Spain estimated that 867 million pieces of plastic is being captured by seagrass each year in the Mediterranean, representing a continuous purge of plastic from the ocean.

When blades of the seagrass break or fall off, their fibres can form tangled masses called 'Neptune balls', this image shows three of them.
When blades of the seagrass break or fall off, their fibres can form tangled masses called ‘Neptune balls’ | Image: University of Barcelona

Seagrass in danger

Seagrass meadows were once common around the British coast, but more than 90 percent have been lost within the last century. This is down to many factors but partly as a result of runoff pollution from land and physical destruction of the seabed by dredging and fishing gear.

There is hope, however. Last summer, 750,000 seagrass seeds were planted in the seabed off Pembrokeshire to create a new 20,000 square metre meadow. Another 250,000 seeds will be gathered later this year and added to the meadow in November as part of Britain’s largest seagrass project by Swansea University, WWF and Sky Ocean Rescue.

We should absolutely try to restore as many of Britain’s lost seagrass habitats as we can. And if we do manage to save them, they’ll help to save us.

A diver checking seagrass in a seagrass meadow
Seagrass Ocean Rescue project | Image: Swansea University 


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