Although seagrasses only cover 0.1% of the ocean, they sequester 10% of the total carbon in the ocean - an incredibly efficient store of organic carbon.
Coastal seagrass beds store up to 83,000 metric tons of carbon per square kilometre – that’s over double a typical terrestrial forest!
What is Seagrass?
Seagrasses are the only flowering plants able to live in seawater and pollinate while submerged. They often grow in large groups giving the appearance of terrestrial grassland – an underwater meadow.
There are four species of seagrass in the UK: two species of tasselweeds and two zostera species, commonly known as eelgrass.
It has been calculated that seagrass is responsible for 15% of the ocean’s total carbon absorption.
Algae or "seaweeds" (left) differ from seagrasses (right) in several ways. Algae on the seafloor have a holdfast and transport nutrients through the body by diffusion, while seagrasses are flowering vascular plants with roots and an internal transport system.
Okay... but why is it so important?
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Primary producers: Tropical seagrass beds are among the most productive ecosystems, rivaling agriculture crops like corn and soybeans. Seagrasses themselves are food for a large number of herbivores including urchins, manatees, and sea turtles. Green sea turtles are a particularly important consumer of seagrasses.
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Sediment stabilizers: Seagrasses efficiently hold sediments in place, preventing resuspension and movement of sediment deposits.
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Nutrient processors: Seagrass beds absorb and transform nutrients in the marine environment.
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Habitat: Seagrass beds are important habitat for adult organisms, vital in the life cycles of some species, and active hunting grounds for other species. Many ecologically and economically important species are dependent on seagrass beds during juvenile phases. Adults of many species hunt in seagrass beds, including snappers, groupers, and sharks.
Sadly, it's under-threat!
Disappearing at a rate of two football fields an hour!
Seagrass meadows are disappearing at an alarming rate, and we’ve already lost an estimated 29% globally in the last century. Why?
Natural Threats
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Heavy storms, floods and droughts that make water conditions unfavourable (unfortunately, now being exacerbated by human-induced climate change).
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Disruption by feeding predators as they search for food, including sea turtles and manatees.
Human Threats
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Removal by resorts who believe their guests prefer a white sandy seabed than a green meadow.
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Irresponsible boating practices including poorly thrown anchors and sailing in too shallow water.
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Agricultural and industrial run-off overwhelming the seagrass’s filtration abilities.
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Destructive fishing practices such as dredging (scraping the seabed, catching everything, then dumping by-catch overboard).
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Blocking out of light in busy harbours and docks.
How much can one football field of seagrass do for the environment?
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Process a year’s worth of treated sewage from 780 people
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Absorb 7,500 miles worth of pollutants omitted by an automobile
The Facts
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Seagrasses are known as the "lungs of the sea" because one square meter of seagrass can generate 10 litres of oxygen every day through photosynthesis.
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Seagrasses evolved roughly 100 million years ago from grass on land, which is why vast marine meadows can be reminiscent of our terrestrial grasslands. Often confused with seaweed (which is a relatively simple algae), seagrasses are organized into four distinct plant.
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There are around 50 different species spread all over the globe.
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They can absorb carbon up to 35x faster than Amazonian rainforest.
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They’re ‘ecosystem engineers’, literally creating the foundations of life. Not only do seagrass meadows pump out a staggering amount of oxygen each day (~100,000 litres per hectare!), they also bring stability to the ocean floor with their extensive root systems.
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A single acre alone can support over a million species - these beautiful, swaying, underwater meadows are home to the two species of seahorses that live in UK waters – the spiny seahorse and the short snouted seahorse – they’re also breeding grounds for cuttlefish and sharks, and nurseries for cod, plaice and pollock.
Our contribution
We donate to Seawilding and Project Seagrass and every £1 donated could help protect 5m2 of endangered seagass around the UK.
