Skip to content Skip to footer

Green, Green Seagrass of Home

This article is by Monica Chin and has been published in her weekly column ‘Underwater With Monica’ in Asia Times Pulse

OLYMPUS DIGITAL CAMERA

From my last article, you have now understood about wild seaweed (Sargassum) and its contribution to the ecosystem. Now let me share my knowledge about ‘Seagrass’.

When I was a kid, I thought seagrass was like the grass we have on land.  I thought they were the same. I was wrong. I don’t know about you but I was never thought about this in school. So, let’s dive into the amazing world of seagrass.

What Are Seagrasses? A Plant, Not A Seaweed

Even though seagrasses and seaweeds look superficially similar, they are very different. Seagrasses belong to a group of plants that include grasses, lilies and palms. Like their relatives, seagrasses have leaves, roots and veins, and produce flowers and seeds. The roots and rhizomes (thicker horizontal stems) of seagrasses extend into the sediment of the seafloor and are used to store and absorb nutrients, as well as anchor the plants. The entire genome of one seagrass, we understand how these plants adapted to life in the sea, how they may respond to climate warming, and the evolution of salt tolerance in crop plants.

Creation of Living Habitat

Seagrasses are often called nursery habitats because the leafy underwater canopy they create provides shelter for small invertebrates (like crabs and shrimp and other types of crustaceans), small fish and juveniles of larger fish species. The accumulation of smaller organisms amongst and on the seagrass blades, as well as the seagrass itself, attracts bigger animals. As a result, seagrasses can be home to many types of fish, sharks, turtles, marine mammals (dugongs), octopus, squid, cuttlefish, snails, bivalves, sponges, shrimp, crabs, copepods, isopods and amphipods, polychaete worms, sea urchins and sea anemones—and the list goes on and on.

Some of these organisms are permanent residents in seagrass meadows, while others are temporary visitors. A single acre of seagrass can support upwards of 40,000 fish and 50 million small invertebrates, and there are often tens to hundreds more animals in a seagrass bed compared to adjacent bare sandy areas. Hundreds of species live in the seagrass!

A number of the species that depend on seagrasses are important for commercial and recreational fisheries. In fact, in all regions of the world fishermen will specifically seek out seagrass beds for their abundance of fish. It is because of the wide variety of different species that live amongst the grasses that seagrass beds often form important “biodiversity hotspots.” Not only do seagrasses support a diversity of marine life, but populations of a given seagrass species can themselves be very genetically diverse and this diversity itself is linked to higher animal abundances. and breeding. The sea grass ecosystem is considered to be very productive and is seen as a nursery ground for many marine organisms. It also acts as a sediment stabilizer, provides a suitable substratum and a good source of food for marine herbivores, and is a source of fodder and manure.

With 16 recorded species of seagrasses in Malaysia and Malaysia ranks third in the world for seagrass diversity. The most diverse and highly developed seagrass communities are found in Sabah, Sarawak, and the southern and eastern portions of Peninsular Malaysia.  Seagrass meadows in Malaysia also play an important role in supporting coastal marine communities and in maintaining diverse flora and fauna.

Foundation of Coastal Food Webs

Seagrass beds are important feeding grounds for thousands of species around the world, and they support this diverse food web in three different ways. Some organisms—primarily large grazers like manatees, dugongs, green sea turtles and geese—eat the living leaves directly, and seagrass forms a major component of their diets. For example, an adult dugong eats about 64 to 88 pounds (28 to 40 kg) of seagrass a day, while an adult green sea turtle can eat about 4.5 pounds (2 kg) per day. Many of these large grazers are endangered, in large part because of habitat destruction and hunting, but once they were very common. These abundant large grazers probably kept seagrass meadows cropped short like a putting green.

I never knew about all these. The epiphytic organisms growing on the surface of the seagrass blades provide other sources of food.  Some epiphytic bacteria can extract nitrogen from the environment and make it available to larger animals. Small invertebrate mesograzers, such as crustaceans and snails, feed on epiphytes, and in doing so can help keep the seagrass clean, I called ‘Seagrass Cleaner” acting as housekeepers that promote seagrass growth. They are in turn consumed by larger crustaceans, fish and birds and are important links in the coastal food web. But this partnership isn’t always positive. Occasionally when some mesograzer species are at very high densities they can create thick masses of mucus and sediment tubes that block light to the seagrass leaves, and they can even eat the seagrass directly.

And I learned that dead seagrass leaves also play an important role in coastal ecosystems. When the leaves die, they decay on the sediment or are washed onto the beach, supporting a diverse community of decomposers that thrive on rotting material. Some of these living and dead seagrass blades are also washed to other areas of the ocean, feeding organisms in ecosystems as far as the Deep Sea.

Blue Carbon – Seagrasses are capable of capturing and storing a large amount of carbon from the atmosphere. Similar to how trees take carbon from the air to build their trunks, seagrasses take carbon from the water to build their leaves and roots. As parts of the seagrass plants and associated organisms die and decay, they can collect on the seafloor and become buried, trapped in the sediment. It has been estimated that in this way the world’s seagrass meadows can capture up to 83 million metric tons of carbon each year.

The carbon stored in sediments from coastal ecosystems including seagrass meadows, mangrove forests and salt marshes is known as “blue carbon” because it is stored in the sea. While seagrasses occupy only 0.1 percent of the total ocean floor, they are estimated to be responsible for up to 11 percent of the organic carbon buried in the ocean. One acre of seagrass can sequester 740 pounds of carbon per year (83 g carbon per square meter per year), the same amount emitted by a car traveling around 3,860 miles (6,212 km).

Fun facts

  • A single acre of seagrass can support upwards of 40,000 fish and 50 million small invertebrates
  • Malaysia ranks third in the world for seagrass diversity. The most diverse and highly developed seagrass communities are found in Sabah, Sarawak, and the southern and eastern portions of Peninsular Malaysia. 
  • adult dugong eats about 64 to 88 pounds (28 to 40 kg) of seagrass a day, while an adult green sea turtle can eat about 4.5 pounds (2 kg) per day. These abundant large grazers probably kept seagrass meadows cropped short like a putting green.
  • Seagrasses are capable of capturing and storing a large amount of carbon from the atmosphere. seagrasses take carbon from the water to build their leaves and roots.
Show CommentsClose Comments

Leave a comment

Our biggest stories delivered
to your inbox