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An Exposé of Singapore’s Mangroves
Raffles Museum of Biodiversity Research
http://rmbr.nus.edu.sg
PRIVATE LIVES
The mangrove environment of Singapore
has changed substantially in the last century.
Today, over 90% of this key habitat
has been lost. Yet, the remaining parts have
shown tremendous resilience in surviving,
and in the process, have helped “safeguard”
a very important part of Singapore’s
biodiversity. Following the style and
philosophy of the first book on
seashore organisms, we now share
with the readers the many strange
and interesting tales about the myriad
diversity of plants and animals that
live in mangroves. We hope this will
go a long way to dispel the myth that
mangroves are awful places full
of mosquitoes and sticky mud and
nothing else. Through education,
we hope to influence the next generation
of mangrove conservationists!
We need to keep whatever we have left!
PRIVATE LIVES
An Exposé of
Singapore’s Mangroves
Editors:
Peter K. L. Ng
Wang Luan Keng
Kelvin K. P. Lim
Sponsored by
Contents
Prologue
1
The Suburbs
3
The Master Reclaimers
23
The Lobster Condominium
45
Tree House
63
Front Lines
91
Mud Pack
115
Water World
131
Transit Hotel
143
Top Dogs
159
Rubbish Dump
185
Market Place
191
The Original Singaporeans
201
The Good, The Bad and The Ugly
215
Epilogue
235
Contributors
237
Acknowledgements
237
Further Reading
240
Index
243
“The sharp salt air of the living sea mingles with the odour
of decay; all around is life and death, and every fresh tide
brings change. The moments of my life trickle through my
fingers like sand, grain by grain. I want to save them, to stop
time, but I can only give value to each simple moment.
The sea is teaching me. I have enough time.”
Roxanne Snopek, 2002
Prologue
In 2007, the first book of a new series titled “PRIVATE LIVES” commissioned by
EXXONMOBIL was launched. The book series was conceived to fill the perceived gap
between the more technical Science Centre guide book series which has done a great
service to Singapore natural history over the years, and the more generic pockets guides
that help naturalists identify common animals on the shoreline. The writing style was
designed to tell the stories from the “plant’s” or “animal’s” perspective as far as possible
– and share snippets of “secrets” with the reader. The first book on the seashore has been
well received, and the second book on mangroves is now ready.
In 1999, N. Sivasothi and the first editor edited two books in the Science Centre guide
series which covered mangroves in detail for the first time for Singapore. These two books
was a landmark because it was the first time the Science Centre published two parts of
what was essentially one book! It also emphasised the sheer complexity and diversity of
life that is characteristic of Southeast Asian mangroves, and that despite losing over 90%
of our old mangrove forests, the remaining is still extremely rich. We revisit the
exhilarating world of the mangroves once again in part two of PRIVATE LIVES. Then,
like now, we had to rely on the knowledge and expertise of many colleagues and friends
who know a lot more about the many plants and animals of the mangroves than we do.
They have given us a wealth of data and photographs to help finish this contribution – so
this book should be viewed as a collective effort of many minds; the editors were mainly
tasked with making the stories flow!
1
PROLOGUE
Mangrove swamps are a MUCH MALIGNED ecosystem. The sticky mud and thick forests
give many people the wrong idea of their worth. Some technocrats still view mangroves
as places which are home to disease-carrying mosquitoes and other dangerous animals,
with mud that is so soft that they are like quicksand and therefore endanger human lives.
They see mangroves as “wastelands” that need to be improved so true developments can
take place. Since the catastrophic Indonesian tsunami of 2004, this view has been
altered. Mangroves help reclaim land, mitigate erosion and protect against powerful
waves. They hold a wealth of plants and animals that are extremely valuable for human
sustenance and development. And they are a centre for biodiversity as rich as any
rainforests. The books by Ng & Sivasothi (1999a, b) and Tan et al. (2007) have explained
at length the biological structure and form of mangrove forests, and why this key
ecosystem is so important to life on Earth and their value to mankind. There is no need to
repeat these facts here. Instead, we endeavour to focus on interesting observations and
facts about the denizens in Singapore mangroves. We make no apologies in taking a very
anthropocentric and Singapore-centric approach to these stories. Singapore scientists
have reason to be proud in any case – many of the most interesting discoveries have, in
fact, been made by several generations of locally-based mangrove-loving biologists!
PROLOGUE
2
DEADLY BEAUTY • The Sea Poison Tree or Putat Laut (Barringtonia asiatica) is a
MULTIPLE IDENTITIES • The Mangrove Tit-Berry (Allophyllus cobbe) is an evergreen
source of toxic chemicals known as saponins which can be used as a fish poison. Extracts
of the bark and crushed fruit are poured into the water and fishes which ingest the poison
die. This destructive fishing method kills everything – even unwanted species and
juveniles, and is not sustainable.
shrub or small tree that can grow to 15 m tall or more. It grows in the back mangroves
and on sandy beaches. The spirally arranged, stalked leaves are trifoliate. The trunks provide timber that is not very durable and so have limited use, except as firewood.
The Sea Poison Tree is more often associated with sandy beaches. It grows to 7-20 m tall
and has a short, buttressed trunk and dense crown.
The tiny, white flowers are slightly fragrant and grow in inflorescences. This rather
unspectacular but variable plant belongs to a species-complex i.e. we are not very sure
how many species there really are.
The twigs bear spirally arranged, shortly stalked
leaves that have obovate, slightly fleshy leaf blades that
are shiny green above.
The flowers are up to 15 cm across, with four white
petals, numerous, narrow elongated stamens. They
open at night and are visited by bats, which come for
the nectar and hence pollinate the flowers. The flowers
drop by the next morning.
The fruit is shaped like a lantern. Its fibrous fruit wall
is tough and buoyant, enabling it to float for dispersal.
In Indo-China, it has been reported that the fruits are
eaten, despite being poisonous! Presumably, cooking
neutralises the toxin.
17
THE SUBURBS
The fruits hang in bunches, turning from green to red and fleshy. They are said to be edible.
THE SUBURBS
18
Mangrove communities comprise plants that are not
closely related to one another. Instead, they are similar
in the morphological, physiological and reproductive
adaptations that allow them to grow in a rather unstable
and harsh habitat. For example, to be able to extract
water from a solution, an organism’s body fluids must
be more concentrated than the solution from which
water is to be extracted. Seawater is more concentrated
than the body fluids of most organisms, including
humans, which is why you cannot quench your thirst by
drinking seawater. Hence although seawater is wet to
the touch, it is physiologically dry.
The Master
Reclaimers
True mangrove species tend to grow at the front to middle intertidal zones along
the shoreline. As such, under certain conditions, they can accumulate silt and
mud washed down by rivers and in some ways may be considered to be able
to reclaim land. However, if wave energy is very strong and frequent, mangrove
trees may fall over because of the erosion of the mud from their roots which now
lack a substrate for anchorage. In the event of a tsunami impacting a mangrovelined shore, this forest can absorb some of the energy up to a certain limit
but can be completely swept away as in parts of Aceh, Indonesia, after the
devastating tsunami of 26 December 2004.
23
THE MASTER RECLAMERS
THE MASTER RECLAMERS
24
THE CONDOMINIUM • This large “mud volcano” is created by one of the master
Thalassina anomala emerges from its burrow at night.
builders of the animal world, the Mud Lobster (Thalassina anomala). Some mound
systems extend up to 1-2 metres tall and a few metres across. Some may coalesce to form
huge island masses intersected by networks of streamlets and tidal channels against the
backdrop of trees. Deep underground, the tunnels are connected and may stretch for
hundreds of metres. These animals, through their constant digging, help bring fresh mud
to the surface, recirculate nutrients through the ecosystem and help aerate the soil.
Mud lobster mounds at the Lim Chu Kang mangroves.
Generally, Thalassina mounds may be found below
the low water mark. The size and elaborateness
of the system depends on the stability of the
substrate. Soft sediments become almost fluid
and fall apart underwater whereas more clayey
soils hold their form and offer much more rigidity.
Hence, the mud lobster mounds in smaller tracks
of mangroves such as those around Woodlands
and West Coast or Sungei Pandan tend to be
shorter, discrete mounds whereas those in mature
mangrove systems such as Mandai and Sungei
Buloh Wetland Reserve feature larger mounds
that may coalesce.
47
THE LOBSTER CONDOMINUM
THE LOBSTER CONDOMINUM
48
LEAF WRAPPER • The Ashy Tailorbird (Orthotomus
ruficeps) is predominantly a mangrove resident that is more
often heard than seen. A di-syllabic shrill trill ‘trrree-yip’ is
uttered several times. It hunts for insects in the undergrowth.
The nest is constructed by using a single large leaf with its
two outer edges pulled together and held by strands of
cotton or spider silk drawn through holes pierced along the
leaf edges. Sometimes two or two leaves are used. The nest
is lined with soft cottony material and two to three eggs are
laid. Size: 11-12 cm.
Nest of a tailorbird.
BRIGHT-EYED AND BUSHY TAILED • Of the nine species of squirrels recorded
from Singapore, the Plantain Squirrel (Callosciurus notatus) is perhaps the most frequently
encountered as it can be found even on wayside trees in many housing estates. It appears
to be the only local squirrel that is seen regularly in the mangrove forest. Easily recognised
by its red underside and white and black stripes on the sides of the torso, this diurnal
omnivore is largely arboreal. It can
scamper up tree trunks and leap from
branch to branch with amazing
agility. Size: head and body up to
22 cm, tail to 21 cm.
The Ashy Tailorbird picks up small flying
insects with its forcep-like beak.
The Plaintain Squirrel collecting materials for its nest, which is usually built on a fork in the tree.
BATTY CHARACTER • It is a myth that bats are blind. Some in fact, have very large
eyes and good vision – like fruit bats (family Pteropodidae). These animals are
characterised by their dog-like heads and large eyes. Endowed with excellent night vision,
they generally do not rely on echo-location to fly
around and find food in the dark. They feed on fruits
and nectar. The nectar-feeding varieties act as
pollinators of certain plants and fruit trees. Their
fruit-eating cousins carry fruit to devour far away
from the parent plants. Large seeds are discarded
while small ones are swallowed and passed out with
their faeces. They, therefore, play an extremely
important role in seed dispersal.
The Common Fruit Bat (Cynopterus brachyotis) is probably the most
abundant fruit-eating bat in Singapore. It frequents mangrove, forest,
as well as urban areas. In the daytime, it roosts alone or in groups,
hanging upside-down under palm leaves, under large clumps of
epiphytic ferns, or even in buildings. Size: 65 mm in forearm length.
89
TREE HOUSE
TREE HOUSE
90
TEOCHEW CRAB • One of the old dishes favoured by the Teochew community in
Singapore (and many parts of Southeast Asia) are pickled mangrove crabs comprising
mainly the genus Episesarma (Family Sesarmidae). We often call these Vinegar Crabs
because they are caught fresh and preserved in vinegar, salt and fish sauce. There are at
least four species in Singapore, the Singapore Vinegar Crab (Episesarma singaporense),
Thai Vinegar Crab (E. mederi), Violet Vingear Crab (E. versicolor) and Pink-fingered
Vinegar Crab (E. chengtongense). All are relatively common and they generally separate
themselves along different parts of the mangroves, their niches being slightly different.
Vinegar Crabs feed on a variety of plant matter, both fresh and decaying, and are
important in helping to degrade the mangrove’s organic matter. They normally live in
burrows but are often seen climbing tree-trunks or boardwalk legs high enough to clear
the water level. This behaviour may assist in avoiding aquatic predators such as fishes
and crabs that come in with the tide. By staying motionless out of the water, they avoid
other hunters such as kingfishers and otters. They have also been known to climb as high
as six metres to reach fresh leaves. Size: up to 50 mm.
Vinegar Crabs or Tree Climbing Crabs feed by scraping diatoms and algae off the tree bark. At the slightest
approach by a terrestrial predator including humans, they simply drop off into the water. Here is a crab feeding on
a fallen fruit on the mangrove mud.
The Violet Vinegar Crab (E. versicolor) is the most common species locally – with a distinctive violet palm and
fingers tipped white.
The Pink-fingered Vinegar Crab or Soh’s Vinegar Crab
(E. chengtongense) has a violet palm with pink and white
finger tips. It is usually more common in seaward areas.
109
FRONT LINES
The Singapore Vinegar Crab (E. singaporense) was
originally described from Singapore. It has entirely red
claws and is common in or near mud lobster mounds.
FRONT LINES
110
GIANT MUD CLAM • The Lokan
(Geloina spp.) is a large, thick-shelled clam
that live near the back of the mangroves.
They are often found shallowly buried in
mud. These remarkable molluscs spend
more time out of water than any other
infaunal bivalve. In many rural communities, they are collected with rakes in large
numbers and sold as food. They are meaty
and tasty, and to remove the taste of mud,
it is advisable to soak them in sea water for
a day or two. Size: 70-80 mm.
LONG SIPHONS • Other common infaunal bivalves include ungulinids,
psammobiids, pharids, tellinids and laternulids. They all possess relatively
long siphons which allow them to reside deep in the mud while retaining
the connection to the surface from where they obtain their oxygen and food.
Laternulids, also known as Lantern Shells, are unique in having siphons that
are encrusted with sand. At the tops of the siphons are tactile tentacles which
can detect motions when a shadow falls over the siphons. This may be a
defensive response of this highly specialised shell. Most species of the Tellinids
(or Tellins) are identifiable by their compressed shells with hind ends that are
slightly turned to the left. These bivalves are rarely seen and poorly
studied, but are often significant in their biomass. Just how they
are able to survive the toxic effects of the poisonous hydrogen sulphide and low oxygen
levels deep in the mud still baffles scientists.
IN CAHOOTS WITH BACTERIA! Not far behind in size is Austriella corrugata, a
bivalve that lives deeper inside mud. These rather nondescript and plain bivalves harbour
chemosymbiotic bacteria in their gills. They have developed a symbiotic relationship with
sulphur-oxidising bacteria from which they derive much of their energy requirements.
At the same time, the tissues are arranged so that the symbiotic bacteria are not exposed
to oxygen, which is toxic to sulphur-oxidising bacteria. Size: 51.5 mm.
Austriella corrugata
The pharid, Pharella javanica, is characterised by
long, narrow and thin shells. Size: 60 mm.
The tellinid, Tellina sp., use its long siphon as vacuum
cleaners, sucking up detritus from the mud surface.
The ungulinid, Diplodonta sp. Size: 24.4 mm.
119
MUD PACK
MUD PACK
120
Water World
The mangrove forests get flooded by the tides twice a day. The lower parts
invariably get covered by water daily while the supralittoral areas may only be
completely submerged once every two weeks during the full moon or new moon.
Even during low tide, many pools persist, often between the roots of trees or on
muddy depressions. The mangrove forest is always wet! In the aquatic domain,
fishes dominate! They are the single most successful group of vertebrates in the
mangrove forest!
131
WATER WORLD
WATER WORLD
132
A juvenile Malayan Water Monitor basking in the sun. Like other reptiles, monitor lizards are ectoderms, i.e.,
they are unable to maintain the temperature of their own blood and need to use the sun’s energy to warm up
before they are active again.
The Estuarine Crocodile adapts to living
in the saline environment by removing excess
salt using a special gland in its tongue.
WRESTLE MANIA • The Malayan Water Monitor (Varanus salvator) is common
MAN-EATER • Of all the creatures that survive in Singapore today, the Estuarine
in Singapore where swaggering individuals can be seen patrolling along waterways,
or basking lazily in the sun on canal walls. Large individuals are often mistaken for
crocodiles! When two monitor lizards fight, they stand upright and embrace each other
like a pair of sumo wrestlers. Eventually, they will topple over, and the winner is the one
which manages to pin its opponent down.
Crocodile (Crocodylus porosus) is perhaps the only one large and fearsome animal enough
to qualify for the honourable distinction of man-eater. There are no local reports of man
being taken by crocodiles in modern times. The Estuarine Crocodile is the largest of all
living reptiles. It is known to attain more than eight metres in total length. Wild
crocodiles can occasionally be seen at the Sungei Buloh Wetland Reserve and Pasir Ris
Park, but these tend to be no longer than three metres. There are plenty of fishes in the
reserves to ensure that the resident crocodiles are well-fed, and thus they do not pose a
danger to human visitors.
The Malayan Water Monitor frequents mangroves where a wide variety of food is
available, ranging from crabs and fishes to carcasses washed in by the tide. It has an
excellent sense of smell, thanks to its fork tongue which it flicks in and out of its mouth to
‘taste’ the air. It is a good swimmer and climber. It is a huge lizard, capable of attaining
3 metres in total length, as long as its famous Indonesian cousin, the Komodo Dragon,
but not as bulky. Although it prefers to flee when approached, it is a formidable beast that
will fiercely retaliate with its muscular tail, rake-like claws and sharp teeth if cornered.
The bite of a monitor lizard is venomous due to oral toxin producing glands.
It can also give the intruder a “whip” from its powerful tail.
169
TOP DOGS
Crocodiles exhibit great parental care. Eggs are laid and incubated inside a nest of
vegetation, which is attentively guarded by the mother. She continues to tend to the
hatchlings until they disperse to lead their own lives. Crocodiles are protected by law,
and it is illegal to hunt them for commercial purposes.
A basking Estuarine Crocodile at Sungei Buloh Wetland Reserve.
TOP DOGS
170
Animals, when they need to travel, literally have to make their own way around.
Many birds are fantastic travellers – flying thousands of kilometres from
wintering to nesting sites without any second thought. Some of the greatest
and most interesting avian travellers are no doubt the shorebirds or seabirds.
Their migrations span the globe. The world record is held by the Arctic Tern
(Sterna paradisaea), which travels an unbelievable 20 000 km every year.
Bar-tailed Godwits (Limosa lapponica) hold the world record for the longest
non-stop flight of any migrant, travelling 11 000 km from its breeding grounds
in Alaska to its winter grounds in New Zealand. Considering it is only a bird
weighing 190-630 grams...this is one mean feat!
Transit Hotels
As with all travellers, a mid-journey rest is much appreciated. A place to rest,
recover and feed. And that is why healthy mangrove swamps are so important
– many shorebirds use them as transit hotels. Every year, between the months of
September and March, thousands of birds use Singapore’s mangroves as transit
hotels as we are on the migration route of many species of waders.
In addition, these amazing birds also show a complete change of their plumage
from summer to winter and back to summer, as they fly from breeding ground
to winter ground and vice versa. So like their human counterparts, a change of
clothes is also in the game plan!
143
TRANSIT HOTELS
TRANSIT HOTELS
144
Epilogue
As we now move towards the end of the first decade of the new century, several facts
are painfully obvious. Mangroves are still under grave threat from human destruction.
Although we have lost so much of our mangroves, not all the remaining patches are
protected. It is difficult in land scarce Singapore...the good news being we now have
Sungei Buloh Wetland Reserve, a mangrove boardwalk at Chek Jawa, Pulau Ubin and a
mangrove park at Pasir Ris and Admiralty. The hope is that many of the patches in Kranji,
Mandai, Lim Chu Kang, etc. can also be protected in one form or another. The same
goes for the many nice coastal mangroves on Pulau Tekong, Pulau Ubin and the many
Southern Islands.
These mangrove forests, small though they are, have yielded a disproportionately large
number of new discoveries over the last few decades. The dedication of mangrove
scientists must be lauded. Many new species have been found and named from
Singapore mangroves. Many more new records are being registered. And there are still
many more new species to be discovered. We also know very little about what goes on
in the complex mangrove ecosystem. Much has been written about the value of lowland
rainforests and coral reefs and why their survival is linked to that of the planet. We would
argue that mangroves are also extremely important in this respect. Mangrove forests are
greatly under-appreciated and under-valued...we must not lose them only to then realise
that their loss is fatal to our own survival!
BLOODLINES • The late French carcinologist Raoul Serène was one of the greatest
marine biologists of the last century. During his time as UNESCO expert here in
Singapore in the 1960s, he helped trained many taxonomists, including several on
mangrove crabs, a field for which he was one of the pioneers. The diversity was so
overwhelming that he never managed to formally name all his discoveries. In the 1991,
a young Honours year student in NUS was tasked to study pebble crabs (Family
Leucosiidae) and she discovered a small bottle in the museum labelled “Nursia punctata
n. sp.” by the great man in 1968! New to science the centimetre-wide specimen certainly
was, but more significantly, after making fresh collections and doing more work with her
supervisor, she showed that it was also a new genus! The animal was eventually named
Praosia punctata. Naturalists and biologists do not work alone, but have a strong link with
history. Praosia demonstrates the “bloodlines” modern biologists have with the past. The
present generation of mangrove crab explorers follow the path laid by Raoul Serène, who
in turn, followed the trail blazed by his predecessor, Michael Tweedie.
The Cheryl Crab (Praosia punctata) is a type of Pebble
Crab. It hides in soft mud in small pools or along banks
of streams during the day. It is slow-moving and feed
on small animals in the mud.
And we are only beginning to realise how valuable the mangroves are for us. How many
more bioactive substances do the plants and animals there have for us? How much can
we learn from them about building and architecture? Can they help us reduce erosion?
Can they help with the greening of Singapore? Can they help us desalinate seawater to
help with Singapore’s freshwater needs? We NEED to conserve our mangrove forests.
If nothing else, for our own selfish human needs!
A Smooth Otter that has made
Sungei Buloh Wetland Reserve its home.
235
EPILOGUE
EPILOGUE
236