learn only 3 things about them ...
Identified by prominent central mid-rib vein.
It deson't flower frequently, and the flowers are small.
is eaten by dugongs.
Where seen? This thin flat needle-like
seagrass is sometimes seen on some of our shores, often mixed with
other seagrasses. But luxuriant growths are more commonly seen on
large natural shores such as Chek Jawa, where it is commonly found
on the seaward side of the sand bars. The preliminary
results of a transact survey of Chek Jawa shows it is widely distributed
in the seagrass lagoon there.
Needle seagrass is found throughout tropical Indo-West Pacific. It
grows well in areas with high disturbance and plays a key role in
stabilising the sediments with its mat of rhizomes and fibrous roots.
Features: Needle seagrass
is common on all our shores, especially on the edges of the sand bars
towards the low water mark. The leaves may be short to very long.
The leaves have three parallel veins which can be quite distinct.
In most, the central mid-rib vein is quite prominent. The leaves emerge
from thin rhizomes (underground stems) which have fine roots. Halodule
uninervis has narrow leaves (0.1-0.3cm), 3-15cm long. These have
a tip with two or three points. Sometimes those with broad leaves
(1cm) are seen. Halodule pinifolia is said to be differentiated
from H. uninervis by a single blunt rounded end, but a single
rhizome may have leaves with one, two or three points. This confusion
suggests the two are not actually separate species.
Sometimes confused with other
ribbon-like seagrasses. Here's more on how
to tell apart ribbon-like seagrasses.
Flowers and fruits: Needle seagrass
has separate male and female plants. The flowers are tiny, usually
forming at the base of the leaf sheath, buried in the sediment and
emerging only for a short period. It produces seeds with a hard seed
coat. Needle seagrass has an unusual way of releasing its seeds directly
into the sediments so the seeds are not washed away by the currents.
Studies suggest the seeds can remain dormant for some time. In this
way, the seeds may help re-establish the species if the parent plants
are destroyed by some natural disturbance. However, needle seagrass
tends to spread more by vegetative growth than through its seeds.
Role in the habitat: Although
tiny, needle seagrass grows rapidly and densely from its underground
stems. Forming a mat, it traps, builds up, and stabilises sediments.
This allows other seagrasses to establish themselves and provides
a more stable environment for burrowing creatures. Needle seagrass
is also one of the seagrasses preferred by dugongs.
Status and threats: Halodule
pinifolia is listed as 'Critically Endangered' while Halodule
uninervis is listed as 'Vulnerable' on the Red List of threatened
plants of Singapore.
Changi, Apr 10
Halodule with very broad blades.
Sentosa, Jun 07
Chek Jawa, Jun 05
Chek Jawa, Aug 05
Sentosa, Jun 07
Short skinny Halodule.
Chek Jawa, Mar 05
Pulau Semakau, May 09
Cyrene Reefs, Aug 11
Cyrene Reefs, Aug 11
seagrass on Singapore shores
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.
seagrasses on the Seagrass-Watch website.
of the Sea: Seeds of Coastal Seagrasses on the CRC Reef Research
Centre website: brief introduction to the ways seagrasses reproduce
and re-establish themselves if affected by natural disturbances,
and how Halodule uninervis 'stores' its seeds in the sediments.
Michelle (et. al). 2004. A Guide to Tropical Seagrasses of
the Indo-West Pacific. 2004. James Cook University. 72 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.
- Hsuan Keng,
S.C. Chin and H. T. W. Tan.1998, The
Concise Flora of Singapore II: Monoctyledons
Singapore University Press. 215 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.