Mystical Meadows

The Magical World of Underwater Seagrass Prairies

As you dip below the waves, you enter a world with many unique habitats and species unlike any you can find at the surface. However, there is one habitat that you would be surprised to see diving: an underwater prairie of seagrass. 

If you were to swim through a seagrass meadow without much prior thought, you would be surprised by how powerful these plants are and the many benefits they provide to the world’s ecosystem. 

Between the blades of a seagrass meadow in Porthdinllaen Wales. Photo credit: Jake Davies

What Makes Seagrass Important and Unique? 

Seagrass Ecosystem Services

Seagrasses aren’t just any ordinary plant. They are true plants similar to those found on land, and they are the only flowering plant that can live in seawater and undergo pollination. As a plant, they provide essential services known as ecosystem services, such as the production of oxygen and the capture of carbon dioxide from the atmosphere, which helps mitigate climate change. 

Due to their ability to produce oxygen, seagrasses are often called the ‘lungs of the sea.’ In fact, some seagrass species can produce up to 10 litres of oxygen per square meter!

However, these mighty plants offer even more critical services such as: 

• The storage of carbon dioxide

• Nursery areas for a range of commercially important species

• Coastal protection through the dampening of wave energy

• Sediment stabilisation

• Purification of water

These ecosystem services are beneficial to a diverse range of marine species as well as people. The underwater canopies create nursery habitats for many invertebrates and fish species, but also many organisms live amongst the roots and grow on the blades themselves. Therefore seagrasses are an important element in the larger food web of the area. 

Seagrass is also a large part of the diet for many species, such as the Green Sea Turtle (Chelonia mydas) and dugong  (Dugong dugon). 

Aerial view of a Green sea turtle amongst seagrass in Gili Meno, Indonesia. Photo credit: Jake Davies

For people, seagrass has been a valuable resource for thousands of years, with uses such as fertiliser, insulation, or even making furniture, mattresses, and bags. Moreover, the diversity linked to seagrass ecosystems directly results in food that many people living near these environments rely on for much of their diet.  

Reproduction of Seagrasses

There is much more than that meets the eye to these underwater plants. Remember, they are true plants, so they reproduce through cloning or sexually with seeds in ways similar to plants above water. For this to occur, pollination is required. This can be achieved either by the pollen travelling through the water column or even by invertebrates found amongst the meadow. 

The reproductive shoots tend to be much taller and more prominent, as we can see with the UK’s eelgrass species (Zostera marina). When looking closer at these shoots, you can see the flowers and, later, the development of seeds that form within the pods that will eventually fall to the seafloor. 

Seeds developing within the reproductive shoot of eelgrass (Zostera marina). Photo credit: Jake Davies

Seagrass Meadows Around the World 

There are more than 70 different species of seagrass that can be found off the coast of every continent except Antarctica. Seagrass thrived everywhere from temperate to tropical seas and along the intertidal shore down to approximately 60 meters. 

Since they are plants needing light for photosynthesis, they are most prevalent within the shallow coastal waters from one to five meters deep. It’s incredible to think that seagrasses are so diverse and distributed globally, yet many aren’t aware of this vital habitat. 

Impacts to Seagrass

Seagrasses are crucial marine habitats, yet they are facing a range of threats, both natural and from human impacts. Unfortunately, over the past few decades, the surface area of seagrass meadows has decreased globally. Studies have revealed that seagrasses have been disappearing at a rate of 110 km2 per year since 1980. Even more jarring, since 1879, up to 29% of the known areal extent of meadows have disappeared. 

Threats such as physical modification, nutrient and sediment pollution, over-exploitation, the introduction of nonnative species, and global climate change have all played a role in reducing the extent of seagrass. 

Direct loss of seagrass can also result from physical damage from human impacts such as anchors, propellers, fishing gears, and coastal engineering. Even natural events scuba divers, cyclones, and tsunamis can physically damage meadows.  

Scarring that has led to the removal of seagrass from a seagrass meadow. Photo credit: Jake Davies

But it’s not just direct damage that threatens seagrass. As sensitive habitats, the indirect impacts from poor water quality driven by increased nutrient and sediment runoff can lead to poor seagrass conditions and reduction in seagrass meadows. 

However, it’s not all bad news. Effective management of seagrass areas and increased knowledge of seagrass meadows have helped reduce impacts. In some places, meadows have even been increasing in extent. 

Around the world, numerous restoration projects provide a helping hand in restoring seagrasses. For example, in Wales, a successful restoration project was carried out by Project Seagrass in a small bay in South Wales through planting seagrass seeds called Seagrass Ocean Rescue. Since the success of this pilot project, many more initiatives and projects have been set up all around the UK to restore seagrass meadows. 

Diving In Underwater Seagrass Meadows

Diving or snorkelling in a seagrass meadow is unlike exploring any other marine habitat. However, no matter where you are in the world, these habitats don’t disappoint. If you are in the tropics, you will likely find some charismatic creatures such as turtles that love to feed on the grass. In temperate areas such as the UK, you can find a diverse range of marine animals that make you feel like you’ve been transported to a more tropical setting. 

Green turtle swimming over seagrass in Gili Meno, Indonesia. Photo credit: Jake Davies

You can be part of a network that helps better understand the ecology and distribution of seagrasses worldwide by submitting seagrass sightings to the SeagrassSpotter app developed by Project Seagrass. By uploading a photo and sharing some information, you can share data about meadows that may be unknown to the project and aid in scientific research into these crucial marine habitats.