Green turtles dive through seagrass meadows

In this whole wide world visible to our eyes, there exists another world underwater that is unseen but essential to marine life. It is places covered by grass-like meadows in shallow, clear waters, where one of Aquameridian protected species – green sea turtles are often found flapping their flippers, swimming and grazing upon as if they are rolling over in a comfy and squishy bed.

Shelter and food for green turtles

Scientists name it seagrass beds. Contrary to what their name suggests, they are actually not true grasses but flowering plants as we see on land, with roots, stems, flowers and long green leaves. They rely on sunlight to covert carbon dioxide into food through photosynthesis. Their habitat not only provides shelter and food to endangered green turtles, but is also critical to mitigate climate change, due to their ability to capture and store up large amounts of carbon dioxide to manage greenhouse gas emission[1]. With the loss of seagrass habitat, green turtles are likely to become homeless and starve to death.

[1] Marine Science and Ecosystems: Seagrass Bed.  Oceana: International.      

Hong Kong seagrass beds

In Hong Kong, seagrass beds are uncommon or rare with a very low distribution and occupy less than 0.1% of the total land area. Among the five seagrass species found in Hong Kong, the most common type is Halophila ovalis. The map above indicates the major distribution of seagrass beds spanning various areas of both the eastern and western territories – Ham Tin, Lai Chi Wo, San Tau, Sheung Pak Nai, Sheung Sze Wan, To Kwa Peng and Yam O.[1] A few of these sites such as Sham Wat and Tai O Salt Pan, lies within Hong Kong South Hope Spot waters, which are protected marine areas of special interest declared by Mission Bluein 2022. This is one of Aquameridian’s significant achievements to save green turtles from extinction, in addition to extension of restricted period in Sham Wan for green turtles nesting by Hong Kong AFCD.

[1] Seagrass in Hong Kong: Distribution.  Agriculture, Fisheries and Conservation Department: Hong Kong.           


Nature strikes a healthy balance

As previously mentioned, seagrass meadows, also known as “blue carbon”, helps create a healthy marine ecosystem as they are responsible for storing up more than 10 percent of all carbon buried annually in the sea, twice as much as the world’s rain forests if calculated by per unit area. Paradoxically to say, important as they are to green turtles as food source, if all the seagrasses are eaten by sea turtles or other marine mammals, it will cause horrendous loss of coastal barriers against storms and bring devastating impacts to our climate![1]Worry not, here comes our seagrass defender – sharks!

Sharks know where to find their preys. They often patrol and rove around seagrass beds to look for food like green turtles. The fear of sharks will keep these grazers away from devouring all seagrasses. Sharks are the best allies of seagrasses to maintain a healthy marine ecosystem. What’s more, they act as a helping hand to marine researchers to discover the world’s largest seagrass system in The Bahamas just a month ago!

[1] Sharks: Meet the seagrass protectors.  National Science Foundation: USA.                   

New discovery of world’s largest seagrass beds

The marine ecosystem in The Bahamas contains the largest sand banks in the world, which are perfect habitats for the growth of seagrasses. Since much of the world’s seagrasses have been lost over the last 50 years, quantitative measurements of the remaining areas of seagrass are difficult to obtain.

But thanks to the help of tiger sharks, a protected species in the Bahamas for more than a decade, scientists are able to uncover an extensive local seagrass ecosystem for the first time. In 2019, scientist Dr Austin Gallagher, used an innovative way to measure the size of seagrass beds by attaching camera tags to tiger sharks throughout The Bahamas, which recorded the sharks swimming over dense and expansive seagrass meadows. The findings help map an estimated area of seagrass habitats up to 92,000 in the Bahamas, which is believed to be the world’s

largest seagrass ecosystem, followed by that in Western Australia[1].

[1] Tiger sharks help map world’s largest seagrass ecosystem.  (2022, November 17).  Dive Magazine: United Kingdom.


Seagrass as humble marine plants

Today, there are approximately 72 different seagrass species that belong to four major groups. Australia claims the title of the most seagrass species in the world. Seagrasses forms dense underwater meadows for a vibrant and diverse community of marine animals, not only green turtles but also coral reef fishes, sea cows and crabs etc. Sharks, green turtles and seagrasses are interconnected species of plants and animals working together to create environmental balance[1].

Although seagrasses often receive little attention from humans, they quietly sit within the mysterious seafloors to form one of the most productive ecosystems in the world. Unnoticeable things in nature, are sometimes more precious than we could imagine. And what is essential is often invisible to our eyes.