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Michele Roux/Ocean Image Library

Michele Roux/Ocean Image Library

What lies beneath – Shining the spotlight on seagrass


What is the only flowering plant that lives in the sea? Clue: it has something in common with the largest animal that has ever lived. Like the ancient forebears of the mighty, record-breaking blue whale, the ancestors of the plants collectively known as seagrass were originally terrestrial species – land-dwellers, in other words – that have since made their home in the ocean.

The expression ‘out of sight, out of mind’ perfectly encapsulates the lot of seagrass. Superficially, it’s the submarine equivalent of a suburban lawn, which goes some way to explaining why this unassuming underdog of the undersea world has been largely unheralded. Far from being merely part of the scenery, seagrass does, in fact, play several pivotal roles on our planet.

What is seagrass?

Seagrasses are marine plants that evolved from a variety of land-based species and recolonised the ocean many millions of years ago. Not to be confused with seaweed, which are algae with no real roots, stems or leaves, seagrasses are flowering plants that produce fruit and seeds. Despite their name, they are more closely related to lilies, palms and gingers than to true grasses.

Anchored to the seabed by their roots, seagrasses spread in a similar way to nettles in a garden, sending out horizontal stems called rhizomes that knit together and produce new growth. Over time, they form extensive carpets known as seagrass meadows.

Seagrass meadow. © Matt Curnock / Ocean Image Library

Seagrass meadow. © Matt Curnock / Ocean Image Library

Seagrass meadow bathed in sunlight.

Where is seagrass found?

Seagrass occurs in shallow coastal waters throughout much of the world, with the exception of Antarctica. Some of the 70-plus species of seagrass are adapted to life in cold climates, while others thrive in warmer waters. Access to sunlight – which the plant needs in order to photosynthesise – is the limiting factor; provided that the water is clear enough, it can grow at depths exceeding 50 metres. Many types of seagrass can survive exposure at low tide.

Why is seagrass important?

By pulling carbon out of the atmosphere and storing it in their leaves, stems and roots, plants play an important role in slowing the rate of climate change. Seagrass is no exception. One of the unsung blue carbon heroes, it’s a key ally in our fight against global heating, capable of sequestering and storing carbon in much greater volumes and at much faster rates than, for example, tropical forests – up to 35 times faster, according to the latest research.

The carbon in seagrass meadows is stored mainly in sediments that are held in place by the plants’ root system and, if undisturbed, can remain intact for millennia. One particular seagrass meadow in Spain’s Portlligat Bay has accumulated carbon-rich deposits that are up to 10 metres deep and more than 6,000 years old.

The enormous carbon sink capacity of healthy seagrass meadows is just one of the many economic and ecological benefits they provide. They also protect against storm surges, prevent coastal erosion, regulate water quality, provide habitat for commercially important marine species, and improve food security for coastal communities.

Seagrass forms the botanical bedrock of one of the world’s most productive ecosystems. It provides an important haven for myriad marine species from shrimps to seahorses. It is also a vital food source for the endangered green turtle and the dugong, whose colloquial name ‘sea cow’ sums up its dependence on these marine pastures. A seagrass meadow supports around 40 times more animals than a sandy seabed.

Dugong grazing on seagrass. © Anett Szaszi/ Ocean Image Library

Dugong grazing on seagrass. © Anett Szaszi/ Ocean Image Library

Dugong grazing on seagrass.

What are the main threats to seagrass?

Arguably the greatest threat to seagrass is our apparent indifference to its fate.

Despite their global importance, seagrass meadows have been neglected, mistreated and inexorably degraded by human activities. As a result, they are dwindling – and, in many areas, disappearing completely – at an alarming rate.

An estimated 90% of the seagrass around the UK has been lost, a figure that has been described as catastrophic. Elsewhere, a shortage of data means that the true extent of seagrass depletion across the globe is sometimes harder to quantify, but it is thought that we have lost a third of the world’s seagrass within the last century. There are numerous instances of entire pastures being wiped from the map.

Coastal development and pollution have taken a particularly heavy toll. Sediments, chemicals and agricultural waste washed into the ocean diminish water quality to the point where seagrass cannot survive.

Seagrass by coastal development. © Ben Jones / Ocean Image Library

Seagrass by coastal development. © Ben Jones / Ocean Image Library

Coastal development is contributing to the dramatic decline in seagrass meadows.

Unsustainable levels of fishing also have a knock-on effect on these delicately balanced ecosystems. Removal of apex predators such as sharks, for example, leads to an increase in numbers of herbivorous fish. Conversely, a reduction in the fish population may result in a population explosion among sea urchins, which then overgraze their meadow home.

Other activities such as bottom-trawling and dredging serve to compound the damage. A habitat that has taken many millennia to establish itself can be destroyed virtually overnight.

These plants may be allies in the fight against climate change, but they are also among its many casualties; seagrass density has been shown to reduce as a result of sudden and repeated spikes in ocean temperature. Literally rooted to the spot, a seagrass meadow cannot migrate to cooler climes.

When degraded or destroyed, seagrass meadows will release carbon back to the atmosphere and ocean. We urgently need to ensure that the world’s remaining seagrass habitat is protected from further disturbance. Without appropriate safeguards to conserve these habitats, it is estimated that a further 30-40% of the remaining seagrass cover could disappear by the end of the century.

How Fauna & Flora is helping to protect seagrass

Fauna & Flora is working with our in-country partners to safeguard seagrass meadows and the rich biodiversity and carbon stocks they support at many of our project sites across the globe, from the UK to far-flung corners of Indonesia.

In the marine paradise of Raja Ampat at the epicentre of the Coral Triangle, Fauna & Flora has worked closely with Yayasan Nazaret Papua, an Indigenous People’s NGO, to establish a customary protection zone for dugongs and their seagrass habitat. We aim to ensure that these seagrass meadows are incorporated into Indonesia’s official protected area network.

The slow-growing Neptune grass Posidonia oceanica is endemic to the Mediterranean. It is threatened by destructive fishing practices, as well as tourism, coastal development, aquaculture and sand extraction. In Türkiye, Fauna & Flora is working with Akdeniz Koruma Derneği, our in-country partner, to build the resilience of the marine ecosystem – including the remaining seagrass meadows – via a network of effectively managed marine protected areas.

As part of the national action plan for sea turtles that it helped draft, Fauna & Flora’s Cambodia marine team is advocating greater protection for turtle foraging habitats, including the seagrass beds on which green turtles depend for food. It has also conducted seagrass surveys and produced a brace of short animated films highlighting their mutual dependence.

Scotland’s coastline and inshore waters support a wealth of marine species and ecosystems, much of it crucial to local livelihoods, but all too often its coastal communities have not been given a voice in how their seas are managed. Fauna & Flora works closely with coastal communities and local NGOs to support their efforts to ensure a better future for Scotland’s inshore waters, including its globally important seagrass beds.

Seagrass (Posidonia oceanica) bed, Turkey. © Zafer Kizilkaya

Seagrass (Posidonia oceanica) bed, Turkey. © Zafer Kizilkaya

Juvenile fish sheltering in a bed of Neptune grass, Türkiye.

Marianne Teoh and student conducting seagrass surveys in Cambodia. © Paul Colley

Marianne Teoh and student conducting seagrass surveys in Cambodia. © Paul Colley

Marine Teoh and student conducting seagrass surveys in Cambodia.

© Kieran Murray / Fauna & Flora

Saving seagrass

Plant blindness is one of the main threats to the world’s plants. They receive far less conservation attention than their animal counterparts, and are disappearing unnoticed at an alarming rate.

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© Kieran Murray / Fauna & Flora