Family Cymodoceaceae and Family Hydrocharitaceae
updated Dec 2019
learn only 3 things about them ...
| Not all seagrasses look like land grasses.
They grow from underground stems and will be damaged if
they are stepped upon. Avoid stepping on seagrasses.
eat mainly seagrasses!
seen? Seagrasses are found on almost all our shores. Undisturbed shores
tend to have more luxuriant growths, but any natural shore is likely
to have some, albeit sparse, growths of seagrasses. Where they grow
thickly, our seagrass meadows are like underwater forests, teeming
What are seagrasses? Seagrasses are the only flowering
plants adapted to grow submerged in the sea. Seagrasses generally
grow in intertidal areas to depths of 30m. Seagrasses do not belong
to the same family of plants as the land grasses (Family Graminae).
Despite the name, the leaves of seagrasses are not always grass-like.
Seagrasses in Singapore belong to either the Family Cymodoceaceae
or Family Hydrocharitaceae.
Lush seagrass meadows at East Coast Park, Feb 2019
|Features: Like other 'normal'
land plants, seagrasses have green leaves where photosynthesis takes
place. These leaves have veins to transport water around (called a
Seagrass leaves emerge from rhizomes (underground stems). These rhizomes
spread along the soft sediments. Roots anchor the plant. Thus seagrass
form a firm mat over the sea bottom. Unlike land plants, seagrass
absorb water and nutrients through all parts of the plant, not just
the roots. Seagrasses also have air canals in their leaves and rhizomes
so they can 'breathe' while underwater.
Sometimes confused with green
seaweeds. Unlike seagrasses, seaweeds lack veins, roots that absorb
nutrients, and do not produce flowers or fruits. Here's more on how
to apart seagrasses and green seaweeds.
leaves have veins.
Chek Jawa, Jul 02
Seagrass have underground stems with roots
Chek Jawa, Aug 05
Fern seagrass has a leaf made up
of little leaflets
Chek Jawa, Jun 05
|Seagrass flowers: Seagrass flowers
are usually small and inconspicuous. Water plays a big role in pollination. One study of a temperate seagrass (not found in Singapore) suggest that they may be pollinated by zooplankton and tiny bottom dwelling animals.
Their seeds are also dispersed by water. In some species, the same
plant produces male and female flowers. In others, male and female
flowers are produced in separate plants.
However, seagrasses seldom flower. They spread mainly through vegetative
reproduction through their underground rhizomes. Thus seagrasses do
not easily colonise new places.
Seagrasses need the sea: Seagrasses
dry out easily because, unlike land plants, their leaves and stems
lack a waxy covering. They can tolerate short periods out of water,
but must be submerged most of the time.
Keep off the grass! Seagrasses
can rapidly regrow their leaves. However, if their underground stems
are damaged, it takes them longer to recover. So please do not step
on the seagrasses.
|Role of seagrasses: 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. Seagrasses
provide shelter for many animals that are not adapted for fast swimming
(e.g., the seahorse and filefish). These include juveniles of larger
fishes and animals that later move out into deeper waters and include
commercially important fishes and sea creatures. Seagrass leaves also
provide a place for animals to lay
their eggs, and for small animals to settle
| The Star
Trackers have 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
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.
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 sea turtles such as the Green turtle (Chelonia mydas) and Hawksbill turtle
(Eretmochelys imbricata) as well as the Dugong (Dugong dugon).
A fresh dugong feeding trail!
Chek Jawa, Jan 07
Dugong feeding trails
Cyrene Reef, May 19
|However, seagrasses do provide food indirectly. 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 hectare per year (1994). This value would be significantly
greater if the other services of seagrasses were included.
Human uses: In Southeast Asia,
especially in the Philippines, seagrasses are used in all kinds of
ways. They are woven into baskets, used to thatch roofs, stuffed into
mattresses and used a fertiliser. A durable fibre useful for fishing
nets is also made from the Tape seagrass (Enhalus acoroides). Modern rugs are also woven out of seagrasses.
Status and threats: 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.
Bleaching following oil spill in May 10.
Chek Jawa, Jun 10
Bleaching, cause unknown.
Sentosa, Apr 11
Burnt, cause unknown.
Sentosa, Apr 11
| 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
Where are the animals in the seagrass meadows? Many are well camouflaged or hide in burrows. Some are tiny. Look
carefully and avoid stepping on lush patches of seagrasses.
Where can we explore seagrass meadows in
Singapore? Labrador has the last large mainland seagrass meadows. There are also narrow
and patchy seagrass areas at Changi. Among our northern islands, there
are vast seagrass meadows at Chek
Jawa on Pulau
Ubin. While on our Southern islands, there are extensive seagrass
meadows at Pulau
Semakau and some at Sentosa.
of seagrasses on Singapore shores
on Singapore shores
Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity
red are those listed among the threatened plants of Singapore
from Davison, G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The
Singapore Red Data Book: Threatened plants and animals of Singapore.
+from NParks BIodiversity Centre
Hydrocharitaceae (marine species only)
- L. J. McKenzie, S. M. Yaakub, R. Tan, J. Seymour & R. L. Yoshida Pp. 60-77. 29 June 2016. Seagrass habitats in Singapore: Environmental drivers and key processes. The Raffles Bulletin of Zoology 2016 Supplement No. 34 (Part I of II).
- Siti M Yaakub, Lim RLF, Lim WL & Todd PA (2013) The diversity and distribution of seagrass in Singapore. Nature in Singapore, 6: 105–111.
- Lee Q, Siti Maryam Yaakub, Ng NK, Erftemeije PLA & Todd PA (2012) The crab fauna of three seagrass meadows in Singapore: a pilot study. Nature in Singapore, 5: 363–368.
L.J., Yaakub, S.M., and Yoshida, R.L. (2007). Seagrass-Watch:
Guidelines for TeamSeagrass Singapore Participants (PDF).
Proceedings of a training workshop, National Parks Board, Biodiversity
Centre, Singapore, 24th-25th March 2007 (DPI&F, Cairns). 32pp.
- Tan, Hugh
T.W. L.M. Chou, Darren C. J. Yeo and Peter K.L. Ng. 2007. The
Natural Heritage of Singapore.
Second edition. Prentice Hall. 271 pp.
G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore
Red Data Book: Threatened plants and animals of Singapore.
Nature Society (Singapore). 285 pp.
H. P. & Menez, E. G., 1997.Field
Guide to the Common Mangroves, Seagrasses and Algae of the Philippines.
Bookmark, Inc., the Philippines. 197 pp.
Michelle (et. al). 2004. A Guide to Tropical Seagrasses of
the Indo-West Pacific. 2004. James Cook University. 72 pp.
John M. 2000. Marine
Plants of Australia
University of Western Australia Press. 300pp.
- Lim, S.,
P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life
and Times of Labrador Beach. Division of Biology, School of
Science, Nanyang Technological University & Department of Zoology,
the National University of Singapore. 160 pp.
- Ong, Jin
Eong & Gong, Wooi Khoon (eds.), 2001. The
Encyclopedia of Malaysia (Vol. 6): The Seas
Didier Millet, Malaysia. 144 pp.
- Hsuan Keng,
S.C. Chin and H. T. W. Tan.1998, The
Concise Flora of Singapore II: Monoctyledons
Singapore University Press. 215 pp.
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