Saving Our Seagrass: The Ocean’s Forgotten Ecosystem
Did you know that hiding just beneath the ripples of the ocean in the world’s shallow coastal waters lie great meadows of swaying flowering plants? Looking much like our land-based fields and grasslands, seagrasses often take over expanses of the seafloor not too far from where we walk barefoot on the sand. Whilst coral reefs, mangroves and dark empty expanses often come to mind when we think about marine habitats, seagrasses are actually one of the most important aquatic realms, despite being relatively unknown and forgotten.
Surprisingly, there are thought to be over 60 species of seagrass in the world which come in a variety of shapes and sizes. Often, seagrass is confused with seaweed but it is actually much more closely related to the plants which line our gardens and hedgerows. Seagrasses are one of the only flowering plants that are able to live and reproduce whilst being submerged in seawater, making them pretty unique in the world of flora. These swishing marine meadows are found on every continent in the world except Antarctica and are often lying along gently sloping protected shorelines, with great hotspots being the warm waters swirling around South East Asia, the Caribbean and East Africa. These grasses evolved 100 million years ago whilst dinosaurs were stamping across the land above and over time, they have become an extremely important ecosystem.
As these plants rely heavily on sunlight to grow, they are mostly found in shallow waters less than four metres deep. Here they anchor their roots tightly into the mud, sand or fine gravel which covers the seabed and creates a calm, safe haven for many wildlife species. The thick tangle of grass forces the water travelling through the meadow to slow down which means the area’s sheltered waters are the perfect home for young fish, crabs and even seahorses. The slowing of the sea also reduces the speed and size of the waves which crash onto the shoreline, reducing the erosion which eats away at our beaches and cliffs. In amongst the roots of the seagrass hide molluscs, worms and small shrimp-like creatures known as amphipods. The slender leaves themselves house algae, anemones and even unusual stalked jellyfish. At low tide, parts of the seagrass bed are exposed and so wildfowl such as geese flock in for a few hours to feed on the exposed leaves. This flurry of marine life attracts larger animals such as sharks, turtles, manatees and octopuses, depending on where in the world you are of course. It is for this reason that seagrasses are sometimes known as ‘ecosystem engineers’. This phrase means that they often dramatically alter the environment around them and in turn impact all the other living beings that are nearby too. In fact, seagrass meadows are thought to house 40 times more animals than patches of bare sand!
Seagrass beds however, are incredibly important to us humans too. Amazingly, 15% of all the carbon that is taken into the ocean is absorbed by seagrass despite seagrass beds covering only 0.2% of the ocean floor! This means that these forgotten habitats are actually an essential natural solution to the increasing effects of climate change. Whilst we often hear about the wonders of our rainforests and how they absorb carbon and keep it out of our atmosphere, seagrass actually captures carbon 35 times faster than our heralded tropical rainforests! So whilst planting trees on land is one solution, replenishing and protecting seagrass beds is another important step that should be taken if we are serious about tackling climate change before it is too late.
Despite their importance in terms of both aquatic life and carbon sequestration, seagrasses around the world are disappearing quickly, yet because they are hidden under the waves, no one is really taking any notice. Globally, 30,000 square kilometres of seagrass has been lost over the last few decades, 18% of all the world’s seagrass meadows. At the current rate, we are losing two football pitches worth of seagrass every single hour. Alongside the loss of these plants are the creatures that live amongst them, with large grazers like manatees and green sea turtles, which rely on seagrass for the majority of their food intake, being especially at risk.
In the Atlantic, a wasting disease in the 1930s posed a large threat to seagrass beds as it attacked the leaves and prevented photosynthesis taking place, effectively killing the plants. However, it is thought that the swathes of seagrass could have bounced back if it weren’t for an increasing level of human interference. Physical damage is one of the reasons our seagrass beds are in such bad condition today as an increasing amount of maritime traffic comes hand in hand with an increased number of damaging boat propellors, mooring chains, dredgers and fishing nets. Often these heavy objects damage not just the leaves but the roots, making recovery a lot more uncertain. When boats are driven through shallow waters for example, their propellors can leave a long scar mark on the seabed which causes the seagrass environment to fragment. This means lots of smaller patches of seagrass emerge which erode much more easily whilst tiny creatures such as crabs and molluscs may not be able to travel the new distance which exists between these patches of food and shelter.
The second biggest threat to seagrass beds around the world is an increasing level of pollution. In areas where there is a high level of sewage discharge into the ocean, there is also an abundance of nutrients which are toxic to seagrass but favoured by algae. This leads not only to a decline in seagrass but also a boom in algae which then smothers the remaining grass and steals the majority of the sunlight which is crucial for growth. Chemical fertilisers which run off agricultural land also have a similar effect whilst disturbed seafloor sediment from boat traffic can cause the water to turn murky whilst smothering the grass and again, blocking out the essential sunlight. The issue of pollution is made worse by the fact that seagrass meadows slow down the water travelling through them and cause any suspended sediments to fall to the ocean floor, effectively trapping pollutants and toxic particles in the seagrass beds.
However, all is not lost as scientists have found that seagrass beds can bounce back surprisingly quickly once all pressures on them have been removed. Multiple seagrass restoration projects are now underway around the world as seeds are collected sustainably from remaining seagrass beds, cultivated in labs before being painstakingly replanted into new locations. Virginia has one of the most successful seagrass projects in the world which actually started all the way back in 1999. 74.5 million eelgrass seeds were planted into an area of ocean roughly one square mile large in size. Now, 20 years on, the seagrass meadow has spread on its own and covers almost 13 square miles whilst a diverse range of fish and invertebrates are returning to the area. More recently, some researchers are turning to look at the root of the problem by generating new ‘seagrass-friendly’ boat mooring designs to reduce the damage occurring in ports and harbours.
There is even a worldwide seagrass citizen science project taking place so anyone can get involved in helping to protect this underrated ocean ecosystem. ‘Seagrass Spotter’ has both a website and an app that you can use to log any location where you have seen seagrass. You are able to upload photos of your sighting and they even have a really simple identification guide. The idea of getting local people involved in this project is to allow scientists to gain a much greater set of data than they ever could on their own. Divers, fishermen, wildlife enthusiasts and tourists around the world are helping researchers better understand the health and distribution of seagrass beds which will ultimately aid their conservation. If we know where the meadows are, we can campaign for marine protected areas to be placed around them whilst tightening regulations on the land nearby to ensure minimal pollutants are running into the ocean. It can also provide us with a fantastic global monitoring network to measure our progress in conserving and restoring these habitats.
For so long, conservationists have focussed on key megafauna but these single species do not underpin and sustain whole ecosystems like seagrass beds do. Seagrass is a crucial element of our oceans as it forms the very base of the food chain, impacting every other animal above it. It is also key in our work to combat climate change and so it seems about time that we pay this incredible ecosystem the attention it deserves and needs to survive.
By Neve McCracken-Heywood