Our oceans and the fight against climate change

By Martin Montague

John F. Kennedy said, “We are tied to the ocean. And when we go back to the sea, whether it is to sail or to watch – we are going back from whence we came.”1

And this quote is more poignant than you might think. We are inexorably linked to the ocean: all life on Earth originates from its depths – and it is crucial for our future, too.

Seagrass and fish species
Scientists say that the ocean provides 50-80% of the oxygen that we breathe. © Cameron D Smith I Getty
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Regulating the climate 

The vast ocean is divided into five “basins” – Arctic, Atlantic, Indian, Pacific, and Southern.2 Collectively, it covers about 71% of our world and is instrumental in the processes that keep us alive.

Firstly, whilst the rainforests may be referred to as “the lungs of the planet”, scientists say it’s actually the ocean that provides 50-80% of the oxygen3we breathe. Then, through a “conveyor belt”4 action, it helps regulate Earth’s climate by transporting heat away from the equator, towards the poles to cool.

But the ocean also proves itself essential in the fight against climate change too. It absorbs 50 times more carbon dioxide5 than our atmosphere – or rather, it’s not the ocean itself… but what lives in it.

Many forms of aquatic life naturally absorb and hold carbon,6 which is taken down to the seabed – and kept there – when they die. From microscopic phytoplankton to gigantic whales, life of all shapes and sizes play a part in feeding these “carbon sinks” (areas that absorb more carbon dioxide than they release).7

And perhaps one of the most incredible forms is the humble seagrass.

Seagrass meadow shore
Seagrass grows in shallow and sheltered coastal areas. © Somnuk Krobkum I Getty


Across the globe, there are more than 70 species of seagrass,8 growing in shallow and sheltered coastal areas. It grows in the vast underwater meadows of 159 countries on six continents, covering 300,000 square kilometres (115,000 square miles).9

Now, that may be an area the size of Italy, but it’s barely 0.2% of the seafloor.10 And this is where the super seagrass comes into its own because it absorbs 10% of the ocean’s carbon each year and captures carbon up to 35 times faster than tropical rainforests.11 

Seagrass builds its leaves and roots using carbon, which it extracts from water through the process of photosynthesis – and it holds on to it, even after death. Dead plant material decomposes slowly on the ocean floor, and this means that the carbon stored within is eventually buried under the seabed.

It’s ironic that such an effective natural solution to climate change is itself under threat from climate change, as temperatures rise and more violent storms ravage seagrass beds.12 Pollution, the long-term development of coastlines, and unregulated fishing have all played additional roles in its decline.

According to the U.N. Environment Programme (UNEP), a seagrass area the size of a football pitch is destroyed every 30 minutes, around the world.13 Globally, it is declining at a rate of about 7% a year – and the UK has lost over 90 per cent of its seagrass in the last century.  

Seagrass is critically endangered and appears on the EU Red List of habitats. Unless action is taken, it is predicted that some seagrasses will go extinct by 2050.14

Seagrass meadow with sun shining through the sea
Across the globe, there are more than 70 species of seagrass. © Lindsay_imagery I Getty

Posidonia Oceanica

One of the most important species of seagrass is Posidonia oceanica. It’s one of the longest-living organisms on the planet and can be found all over the Mediterranean. It’s also especially resistant to microbial degradation, which means when it dies and falls to the sea floor the carbon it has trapped inside is not released again.

Two decades ago, an area of 55,000 hectares of seagrass between Mallorca and Formentera was designated a world heritage site by UNESCO. Posidonia can cope in temperatures of up to 28C,15 but due to climate change, half of the summers since 2000 have exceeded this “thermal limit”. Posidonia is also being destroyed by boats when they drop anchor. This has resulted in a 44% reduction in the meadows of Formentera in just four years, between 2008 and 2012.

Unfortunately, the plant grows very slowly; the damage of just one anchor in a single day could take up to 1,000 years to restore.

Seagrass meadow
Posidonia oceanica is one of the longest-living organisms on the planet. © Damocean I Getty

What can be done?

Experts say that reversing the decline of seagrass will take an international effort. Fortunately, restoration missions are already underway, in places as far afield as Kenya, Mozambique, and the UK.

In the last century, Denmark lost 95 per cent16 of its seagrasses from its estuaries and inlets. Restoration projects have been undertaken there, re-planting in one metre squares in a grid pattern – more than 40,000 shoots in total.

During 2020, the Seagrass Ocean Rescue team at Swansea University, Wales, also took decisive action. A team of volunteers, staff, and members of the local community planted one millions seeds across a two-hectare site in Dale Bay, off the coast of Pembrokeshire.17 

Elsewhere in the UK, the Ocean Conservation Trust (OCT) has opened a seagrass cultivation lab. Here, seagrass is grown in batches, using seed-bearing shoots that have been hand-picked by divers. This was no small task: 17,500 shoots needed to be collected to reach the target of 700,000 seeds required for the operation.In late April 2021, 2,200 bags of these seedlings were planted on the sea bed of Plymouth Sound, England. The hope is that they will flourish into a vast meadow – or the size of six football pitches - and mariners have been asked to stay away, to protect the young plants from damage. It’s the start of a four-year project – and next in line is a stretch of sea between the south coast of England and the Isle of Wight.

Seagrass and sun beams
Experts say that reversing the decline of seagrass will take an international effort. © Damocean I Getty

Meanwhile, in the sunnier climes of the Balearics, the “Posidonia Festival” was been held regularly since 2008, to raise awareness about the wonders of this vivid green plant. Government action to protect Posidonia has intensified in recent years, too. But researchers suggest that adding a financial value to the carbon locked inside the Posidonia could help to encourage funding that could be used to protect and restore it.

This has already proven effective in Gazi Bay, Kenya,19 where their seagrass project has been partially funded through the selling of these so-called “carbon credits”. This is an especially important site because one scientific study has shown that these seagrasses lock in 50% more carbon than is typical for seagrass meadows elsewhere, making them super-efficient.

Measures such as these are all highly significant, as it’s estimated that just one hectare of restored seagrass will capture as much carbon as ten hectares of forest on land. But rising temperatures remain a twofold threat: an increase in storms that tear the shallow-rooted seagrass from its beds, and rising sea-levels that block out the sunlight.

However, seagrass is known to adapt to survive – and gene sequencing of the Zostera marina seagrass20 has shown it has done so on three separate occasions already. Could it be one of Earth’s great survivors that will save us all? As with most things, only time will tell.


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