Unexplored seagrass meadows around Ile Plate grab ICS’s attention

The Island Conservation Society (ICS) has started to map Seychelles’ fourth-largest known seagrass meadows located around Ile Plate, a vital carbon store and mitigation mechanism against climate change.

Seagrass have evolved from land plants and, like terrestrial plants, have veins, roots and leaves. As true plants growing on the ocean floor or seabed, they also have a flowering season and can reproduce underwater. They form meadows on the ocean floor, which provide food and shelter to different marine life, from sea turtles to crabs. Yet, not much is known about these green barriers that, similar to mangroves, help to keep our oceans clean by removing harmful algae and stabilising the sand. More importantly, seagrass creates a highly efficient carbon sink by storing significant amounts of carbon in their sediments and biomass and playing a crucial role in global carbon cycling and climate change mitigation.  

In 2020, a project to map the seagrass meadows in Seychelles was launched. The Seychelles Seagrass Mapping and Carbon Assessment Project revealed that there are 1,599 square kilometers of seagrass in the Seychelles Exclusive Economic Zone (EEZ). Surprisingly, it also revealed that Ile Plate accounts for 7.9% of this total area, ranking it as the fourth largest area where seagrass was found in Seychelles, surpassing other areas renowned for their high biodiversity, such as Aldabra Atoll, Farquhar Atoll and Cosmoledo Atoll. Only Providence (14.4%), Mahé Rim (24.5%), and Amirantes Bank (34.1%) outranked Ile Plate in the density of seagrass found through this project. Despite the significance of this project, several questions remain about the areas which had been mapped, for example, what the meadows were made of, how widespread they were and what habitat they were supporting.   

Looking at the lagoon from the air or even from the beach, “we could see these large expansive meadows – in some areas all you can see is seagrass. You can take only a few steps towards the ocean and end up knee-deep in seagrass here,” says Diary Rakotondrazara, who is the Conservation Officer of ICS on Ile Plate.
To better understand this habitat, the team has initiated an in-depth review of seagrass meadows around the lagoon. At low tide, the meadows around Ile Plate are easily accessible, and the team does not have to snorkel to view underwater environments.

“We use a 50-meter line across an area which is checked at every 5-meter interval. At each interval, we observe an area of one meter square where we identify the species we found, the amount of seagrass there is, the height of the seagrass and if there are any algae. We then take pictures and record the GPS coordinates of the area first at the beginning and then at the end.”

By analysing all this information, the team will be able to confirm the density and distribution of the island’s seagrass. There are at least 72 known species of seagrass globally, 12 of which are found in Seychelles.
So far, the team has identified at least three seagrass species around the island, but their density varies. The most common species of seagrass found in the lagoon are Thalassodendron ciliatum, known as “Gomon zerb levantay” or Fan seagrass and Thalassia hemprichii, known as “Gomon torti” or “Gomon zerb torti” or Turtle seagrass. In addition, the team has also identified several patches of Syringodium filiforme, known as “Gomon zerb sed” or “Gomon zerb spageti” in Creole or Casuarina seagrass or Spaghetti seagrass. These are mostly located a few meters from the beach and, according to the initial mapping exercise, are not common in the Outer Islands, such as Ile Plate.

Seagrass “was always a target of our conservation strategy on Ile Plate,” says Rakotondrazara, adding that unlike the other five islands where ICS has a conservation center, the role of seagrass towards the thriving marine life around the island could not be overlooked. 

“Thanks to these meadows, we can now confirm that Ile Plate is a nursery and foraging area for juvenile sea turtles and that they are actively using the island for nesting throughout the year. We can also confirm that the island is a major hub for elasmobranchs, which is another major milestone for conservation of the island.”

As helpful as seagrass is to the marine ecosystem, ICS is also enlisting the help of its partners on the island to help improve their understanding and find ways to protect these seagrass meadows against marine activities such as anchoring and snorkeling. Visitors are already being sensitised about seagrass through informational displays that provide more information about the different seagrasses they may encounter during their stay on the island.

“We’re just beginning to realise how important the seagrass meadows are,” Rakotondrazara says. “As such, unlike other places in the world where seagrass is underrated or overlooked, we want to make this a priority for conservation on Ile Plate.”
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Whilst the survey will be an extensive exercise and part of the regular monthly conservation activities by ICS on Ile Plate, it will also build on the initial Seychelles Seagrass Mapping and Carbon Assessment Project. Furthermore, the details about what’s in the meadows will help to inform future projects around Ile Plate and feed into Seychelles’ national database of information on seagrass. 

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