Seagrasses are found on almost all our natural shores! Undisturbed shores tend to have more luxuriant growths, but any natural shore is likely to have some seagrasses.
Where they grow thickly, our seagrass meadows are like underwater forests, teeming with life!
What are seagrasses and why are they important?
Seagrasses are the only flowering plants adapted to grow submerged in the sea. Like other 'normal' land plants, seagrasses have green leaves. These leaves emerge from rhizomes (underground stems) that spread along the soft sediments.
Seagrass meadows are a vital habitat that is often overlooked and loses out in media coverage to the more glamorous reefs. The meadows of seagrass leaves create a miniature underwater forest.
A host of small plants and animals thrive in these thickets, such as this tiny Blue dragon nudibranch (Pteraeolidia ianthinia) seen on Cyrene Reef's meadows. Seagrasses provide shelter for many animals that are not adapted for fast swimming, such as this seahorse seen on Changi's splendid seagrass meadows.
Animals lay their eggs among and on the seagrass blades.Seagrasses also shelter juveniles of larger fishes and animals that later move out into deeper waters, such as this tiny butterflyfish seen on Cyrene Reef. The Star Trackers recently noted that the seagrass meadows on Cyrene Reef are important and possibly the only habitat left in Singapore where baby Knobbly sea stars (Protoreaster nodosus) can be found in large numbers.Many commercially important fishes and sea creatures such as prawns also spend their youth in seagrass meadows.
The underground stems and roots of seagrasses form a mat which stabilises the ground, while their leaves slow the water flow and thus help keep sediments down and the water clear. The leaves also trap sediments and detritus and contribute to the nutrient cycle in the ecosystem. In the stabilised ground, many burrowing creatures make their homes such as the carpet anemones and peacock anemones of Chek Jawa.Few animals can eat seagrasses, because few can digest the cellulose that makes up these plants. Among those that do feed on seagrasses are the Green turtle (Chelonia mydas) and Hawksbill turtle (Eretmochelys imbricata) as well as the Dugong (Dugong dugon). Although dugongs have not been actually seen, dugong feeding trails were observed on Chek Jawa in 2007!Seagrasses do indirectly provide food to a large number of animals. Microscopic algae grow on their leaves and larger seaweeds get entangled among the seagrasses. Many small animals graze on these algae. They are in turn eaten by larger animals. In this way, seagrasses are an important part of the food chain in other ecosystems nearby, such as sandy shores, mangroves and coral reefs.
Seagrass meadows are vital part of a rich and diverse shore. Dead seagrass leaves as they decay, provide nutrients to other ecosystems. By trapping sediments, the meadows keep the water clear for coral reefs to develop nearby. The stabilised areas where seagrasses grow may eventually be colonised by mangroves.
According the Seagrass-Watch site, seagrass meadows are considered the third most valuable ecosystem globally. The average value of seagrasses for their nutrient cycling services and the raw product they provide has been estimated at US$ 19,004 per hectar per year (1994). This value would be significantly greater if the other services of seagrasses were included.
All our seagrasses are listed among the threatened plants of Singapore.
Seagrasses are affected by careless visitors who may unknowingly trample on their delicate underground stems. Nets dragged over seagrasses also uproot them and kill the animals that live there. Marine litter (plastic bags and other rubbish) smother seagrasses. They may also trap and kill small animals. Larger animals may accidentally eat them and die. Seagrasses are also affected by pollution that poison the water. Activities that stir up sediments also obscure sunlight and affects photosynthesis and thus the growth of seagrasses.
However, the most damaging impact to seagrasses is habitat loss due to land reclamation and development of our shores. Seagrasses grow best on flats that are shallow but seldom totally out of water, and relatively calm. Too deep and there is not enough sunlight for photosynthesis; too shallow and the seagrasses are regularly out of water. Reclamation usually results in steeply sloping shores where seagrasses don't grow well.
TeamSeagrass is a group of volunteers comprising ordinary people who come together to monitor our seagrasses. They go out at low tide, even if it's early in the morning, to collect data on the state of health of our seagrass meadows.
Join TeamSeagrass to make a difference for our shores!More links