That Class on Seagrass

The marine environment is home to some of the most incredible habitats on Earth: vibrant coral reefs, vast open oceans, mysterious deep-seas – awe-inspiring places that never fail to captivate our collective imagination. Today, however, we will be exploring another marine habitat that often falls under the radar… seagrass beds! 

At first glance, seagrass beds may seem dull, lacking the visual appeal or grandeur of the more well-known marine ecosystems. However, they more than make up for it in terms of their sheer ecological importance and varied functions!

So, what makes an ordinary-looking patch of grass on the seabed so special?

Well, dear reader, I’m sure you’d be very surprised!

Learning Our A-B-Sea(grass)

Seagrasses are unique in the fact that they are the only marine flowering plant on Earth. Almost all species of seagrasses can go through their entire lifecycle – including pollination and seed dispersal – underwater¹, and will die if exposed out of the water for prolonged periods of time. Still, like any other plant, they require sunlight for photosynthesis and hence are confined to the photic zone (“sunlit” zone) of the ocean². Seagrasses can be found in shallow coastal waters all over the globe², usually spreading across a large area to form seagrass beds (also known as seagrass meadows).

Walk along Singapore’s coastlines and you will easily find patches of green scattered along the beach. Are these all seagrass? Well, not necessarily so! People often confuse seaweeds with seagrasses, and although they may look very similar, they are actually very different organisms. Seaweeds (including the yummy kinds that we eat!) generally refer to macroalgae, which are also capable of photosynthesis, but are much simpler in structure.

Seagrasses have traditional plant features such as roots, ‘true’ leaves and veins to transport water and nutrients. Algae, on the other hand, are anchored by a structure known as a ‘holdfast’ and rely on diffusion to transport nutrients around its body².

Tiny but Mighty

With the confusion out of the way, let us now look at the importance of seagrass meadows in the marine ecosystem. These habitats harbour a wealth of biodiversity, with an immense productivity that can rival those of coral reefs³. 

Certain herbivorous animals, from parrotfishes to turtles, rely on the seagrass directly for sustenance. Dugongs and manatees in particular also feed mainly on seagrass⁴. Coupled with their large, stocky bodies, it is easy to see why these gentle giants are also commonly known as sea-cows!

Even for us landlubbers, seagrass ecosystems provide numerous tangible benefits in the form of ecosystem services. They act as nurseries for many commercially important fish⁵, with juveniles taking refuge amongst the thick vegetation before they are large enough to take on the dangers of the open sea. Many people in coastal communities also directly harvest shellfish from seagrass meadows in shallow waters for sustenance and their livelihoods⁶.

An increasing body of research is also pointing to the importance of seagrass beds as a ‘blue carbon’ sink⁷. Like wetlands (check out Xue Shen’s article here) and other coastal habitats, they sequester massive amounts of carbon and effectively ‘lock’ it away from the atmosphere for thousands of years. In fact, studies have shown that seagrass beds can sequester carbon over 30 times faster than rainforests⁸. This is doubly important given the urgency of our ongoing climate emergency!

Underwater “Deforestation”?

Knowing the numerous benefits they bring about, we should definitely be worried about the increasing devastation of our seagrass communities. Seagrass beds all around the world are under threat from destructive fishing methods, increasing ocean temperatures and land reclamation^2,9. Nutrient runoff can also lead to algal and jellyfish ‘blooms’, which effectively block out life-giving sunlight to seagrass, causing massive die-offs ^2,10.

In Singapore, it is estimated that we have lost around 45% of our seagrass since the 1960s⁹. Many of the larger surviving meadows are now found around offshore islands such as Pulau Ubin (including at the renowned Chek Jawa) and Pulau Semakau. While seagrass monitoring programs have been running since 2007¹⁰, more can be done to protect these underappreciated habitats!

For many of us, terrestrial grasses may not seem like the most interesting organisms ever, much less sea-grasses. However, these mundane-looking aquatic plants are in fact of utmost importance to marine life and humans alike. They are havens housing all sorts of creatures, and their continued survival will be crucial in our fight against climate change. Yet, these amazing habitats only receive a miniscule proportion of the attention given to the much ‘prettier’ coral reefs. 

Perhaps it’s time for us to look beneath the surface (both literally and metaphorically!) and truly appreciate our seagrasses – our unsung heroes of the sea.

For more on local seagrass check out Team SeaGrass’ article.