Ecosystem - Mangroves

Naked Facts:

NF#1: Read them from here !
Great and important facts! Do read them.

NF#2: Seagrasses need the mangroves.
a) Mangroves can slow down the speed of water from inland, therefore causing fine silt to settle around the mangrove forests.
b) But if these fine silt reach the waters, they will cloud the water, block the sunlight and the seagrasses will not be able to make food (photosynthesize) and flourish.
NF#3: No durians with mangroves?Read more about this here.
Did you know?
a) It is believed that the earliest species of mangroves came from the Southeast Asian region.
b) There are more mangrove species in this region than anywhere else in the world.

Too much information
NF#4: Pollution Controller
a) Mangroves help to control some forms of pollution, including excess amounts of nitrogen and phosphorous, petroleum products, and halogenated compounds from reaching the seas. Mangroves stop these contaminants from polluting the ocean waters through a process called rhizofiltration. But the over-existence of these pollutants can kill the mangrove trees.b) Rhizofiltration is the filtering of water through a mass of roots to remove toxic substances or excess nutrients.

For more reading on the importance of mangroves, you may click here.

Related Links:
1. Mangrove Climbers
2. Bushes in the mangroves

Slithery Snakes

Naked Facts (General information about snakes):

• All snakes are carnivorous or you can say they only eat meat.
• Some snakes have a venomous bite, which they use to kill their prey before eating it.
• Other snakes kill their prey by constriction or called 'wrapping you up and then squeezing you to death'.
  
• Still others swallow their prey whole and alive.
• Snakes are covered in scales. Most snakes use specialized belly scales to travel, gripping surfaces.
  
• They shed their skin periodically. The primary purpose of shedding is to grow; shedding also removes external parasites.
• Venom VS poison: The term poisonous snake is mostly false - poison is inhaled or ingested whereas venom is injected. A venomous snake is a snake that uses modified saliva, venom, delivered through fangs in its mouth, to immobilize or kill its prey.

Too Much Information:

• Unlike other reptiles, shedding for snakes is usually done in one piece, like pulling off a sock, with the snake rubbing its nose against something rough, like a rock, for instance, creating a rip in the skin around the nose and the mouth until the skin is completely removed.
• It is a common misconception that snakes actually dislocate their lower jaw to consume large prey. Actually as snakes do not chew their food and have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull, allowing them to open their mouths wide enough to swallow their prey whole, even if it is larger in diameter than the snake itself.

Fabulous four (Mangrove) snakes:

Common Characteristics:

• All of them are aquatic.
• Their eyes are positioned on the top of their heads so that they can remain with their body submerged in water and yet are able to see above the surface.
• All of them have poisonous fangs on the back of their jaws, but their venom is not known to have any serious effects on humans.
• All of them give birth to living young, and appear to be largely nocturnal in habits.

Dog-faced Water snake or Bockadam, Cerberus rynchops feeds largely on fish trapped in mud puddles during the low tide.

Yellow-lipped Water snake, Gerarda prevostiana, is less common. It specialises in feeding on newly-moulted crabs.

Cantor’s Water snake, Cantoria violacea, is a rarely seen and extremely long species with markings similar to that of the venomous sea snakes (family Elapidae, or Hydrophiidae). It feeds on snapping shrimps.

Crab-eating Water snake, Fordonia leucobalia, is believed to live mainly in mud-lobster mounds and feeds on hard-shelled crabs.

Monitor Lizards: Cleaner of the Mangroves

Naked Facts:

• Monitor lizards are the “cleaners” of the mangrove habitat as they eat anything that they can swallow therefore helping to make sure there is no too much of any living things in the mangrove.
  
• Their long list of 'diet' consists of (here goes): tiny insects, crabs, molluscs, snakes, eggs (of birds and crocodiles), fishes (including eels up to 1m long), rodents, small mouse deer, other monitor lizards and even human faeces. But they are particularly fond of dead bodies.
• They have known to eat prey almost as big as themselves: a 1.2m long monitor lizard ate a snake 1.3m long.

• Corny Joke: As long you try not to look ‘delicious’, they are not known to consume humans.
• Message behind joke: Observe but not disturb them.
  

• The Water Monitor's main hunting technique is to run after prey that it has spotted, rather than stalking and ambushing.
• Like snakes, they have a forked tongue that they stick in and out regularly to "smell" their prey and other tasty titbits.
• Water Monitor Lizards are highly mobile. They can swim, run faster than most of us can run and even climb trees.
• Monitors can survive in habitats (such as the mangrove forests) that wouldn't be able to support other large carnivores as they are cold blooded (If you need to drag time, you might want to explain the difference between warm and cold blooded).

Did you know?

• Komodo Dragons are a member of the monitor lizard family, Varanidae.

Too Much Information:

• They have been seen swimming far out at sea and can remain underwater for up to half an hour.
• They climb to search for food as well as to escape predators. The young usually stay in trees for safety. If cornered up a tree, they will jump into the safety of a stream or river.
• As scavengers, Water Monitors keep the habitat neat and tidy, and also control populations of their prey. They in turn provide food for larger carnivores such as crocodiles and birds of prey. Small young Water Monitors are particularly vulnerable even to large birds such as herons.

More about the Monitor Lizard.

R(A) link (Watch how two monitor lizards mate):
http://www.youtube.com/watch?v=XDEnkGBSpyA

Vinegar Crabs aka Tree Climbing Crabs

Name the Creature Activity (Something you can try with kids if a Vinegar Crab is spotted on a tree):

Guide: "Hey, we have a crab on a tree here (point to crab)."

Guide: "Let's say we want to name this crab, what name would you give it?"

Kid A: "Tree crab?"

Guide: "But how did it get up there?"

Kid A: "Climb! Oh, Tree-climbing crab!"

Disclaimer: Might not work every time.

Naked Facts:

• During low tides, you can find them on the forest/mangrove floor feeding on leaves.
• During high tides, you can usually find them at a height high enough to clear the water level and they will remain motionless on tree-trunks, leaves or boardwalk legs.
• This is probably a predator-avoidance behaviour, especially with the many predatory species of fish and crabs that hunt with the incoming tide. Out of the water, they remain motionless to avoid other predators like kingfishers, monitor lizards and otters.
• At night time or dusk, they have been seen climbing up trees to heights of more than six meters to graze on algae as well as eating leaves.

• Food fact (1): The Teochew are known to pickle this crab in black sauce with vinegar, and take it with porridge. That’s why they are also called vinegar crabs.
  
• Food fact (2): The Thais like it salted, with the roe or simply fried whole.

• National Education: There is a tree climbing crab named the Singapore vinegar crab (E. singaporense), it is a common species of the tree climbing crab (Episesarma) and has entirely red claws. It is commonly sighted in or near mud lobster mounds.

Too Much Information:

• They are usually burrowing crabs, digging holes at the base of trees and mud lobster mounds.
• They are considered pests of mangrove plantations for their habit of attacking propagules (seeds of the Lenggadai, a threaten species of mangrove).
• Tree Climbing Crabs are known to scavenge meat like many other crabs.

Reference and more about Tree Climbing Crabs

Snails and clams of the mangroves

Telescopium snail (Telescopium telescopium) Family Potamididae

It is also called 'Rodong' or 'Berongan' in Malay. 8-15cm. It can stay out of water for long periods of time. It eats detritus and algae, using its highly extendable proboscis to gather edible bits from the mud surface at low tide. It is eaten in some places and is said to be delicious when steamed and eaten with chilli.

Belongkeng snails (Family Ellobidae)

Ellobium sp. on the left is usually found on the ground.
Pythia sp. on the right is sometimes seen on leaves of mangrove trees.
These snails are sometimes seen on leaves and trunks of mangrove trees or on the mud in the back mangroves. They are sometimes also called Mangrove helmet shell snails. Empty shells of dead snails are sometimes also washed up on shores near mangroves.

1-5cm. Shells thick. They breathe air (instead of through gills like most other marine snails) and all lack an operculum to seal the shell opening. They graze on algae growing on mangrove trees and debris.

Mangrove jingle clam (Enigmonia aenigmatica) Family Anomiidae

Like shiny scales, these bivalves are common seen on leaves, trunks and roots of mangrove trees. They usually settle at a height between the high spring and high neap tide.

To about 3cm. The two-part shell is thin and lustrous. Usually oval, sometimes irregular. Colours range from beige, purplish to blackish.

One valve is stuck to a hard surface (leaves, tree trunk, roots) and this valve is usually flat. The other valve is usually slightly conical in shape. The valve that is stuck to the hard surface has a notch or hole in it. The animal secretes byssus threads through the hole to stick to the hard surface. A young animal is more mobile and can move around by using its extendible foot. A young animal is relatively broader than a more mature animal.

Fiddlers: macho crabs of the shore

The Big Useless Claw Story
Messages: "every inch of the shore is alive, every step kills, stick to the death zone"

For a shore walk (you can go straight to Step 3 if you're on a boardwalk)
Step 1: "Stay very still and you will see some interesting animals on the sand. They are very small and very sensitive to your footsteps. If you wave your arms around they will think you are a bird and will hide. Pretend you are a tree and they will come out."

This will make visitors get used to not stomping around. To be still and look carefully for small things that will only come out when there is no disturbance.

Step 2: If it's taking a while for the crabs to come out "While we wait, let's look around us and I'll tell you about some of the special ecosystems we can see on Semakau. Meanwhile DON'T MOVE!"

Step 3: Once crabs are active, "How many claws does the crab have?" Eventually someone will say "One".

Step 4: "Actually it has two claws. The big claw is so big that it misses the mouth. It has a much tinier claw that it uses to feed itself. Can you see one feeding?"

Step 5: "Only the male crabs have one big useless claw. The females have two small claws so they can feed twice as fast."

Step 6: "Why do you think the males have one big useless claw?" Usual guesses: to find food, for fighting, for defence from predators. Explain briefly and clearly why these are not the case. Goad them with "Why do all boys have big useless things? Like sports cars?" Eventually someone, usually a girl or a small child, will say "To attract girls"

If the visitors have been very very still, you can say "These tiny crabs are all over the place. You can see some near your feet too! See!!! Every inch of the shore is alive with creatures. Some of them are small and buried in the sand. Every step we take on the shore will most definitely squash something."

For shore walk
"We have designated a trail on the shore. It is a death zone. Just like any nature park in Singapore. At Sungei Buloh or Bukit Timah, we don't walk anywhere we want to but have to stick to a trail. Otherwise, a larger and larger area will become 'botak' as footsteps kill off small plants and animals.

"To minimise this death zone, please stay close to me and try to stay in a single file."

If you are not the first group "Follow the trail made by the group in front. Then you don't kill things that they haven't already killed."

For boardwalk
"It's great to have a boardwalk, so we can have a look at these animals without killing them!"

Tips on dealing with fiddlers

Please do NOT pick up fiddlers. Visitors will do as we do and not as we say. In any case, if we catch them and put them down far away from their burrow, they will be stressed and may not be able to find protection and then die.

Please do NOT dig up fiddlers either. This is destructive to the habitat, and encourages visitors to dig up everything they want to see. Instead, encourage them to be patient and wait for animals to come out and go about their normal business.

Naked Facts:

The male waves his large pincer in a style and rhythm unique to his species in order to attract the ladies. Fiddler crabs got their name for this behaviour, which resembles a musician playing on his fiddle. Interactive activity: You can do the fiddler movement using one of your arms to demonstrate to visitors how fiddler crabs fiddle.

The eyes of a fiddler crab are mounted on long stalk giving it a good all-round view of the air and the horizon. This is for potential mate, rival and early predator detection. When the crab scuttles back into its burrow, the eyestalks fold down into grooves along the body.

Interactive activity: Use two fingers from each hand to illustrate this point.

The larger claw can be its either right or left claw. If an adult male loses its fiddler claw, the remaining claw grows to the same size as the lost claw, the claw it regenerates becomes the smaller claw.

Sex sells: When a male Fiddler crab succeeds in persuading a female to mate with him, they retire into his burrow. The female may remain there until the eggs hatch. The eggs hatch into free-swimming larvae that drift with the plankton, changing into yet another form before settling down and developing into fiddler crabs.

Too Much Information

Fiddler crab species are distinguished by the structure of the male's enlarged pincer. They are not reliably distinguished by the colour of bodies, pincers. The species of females is hard to distinguish.

Fiddler crabs cannot swim and prefer to breathe air. So at high tide, they hide in their burrows, plugging the entrance with a ball of sand to trap some air inside. However, they need water to keep their gill chambers wet as well as to process their food. They absorb water from the wet sand through hairs on their legs.

Porcelain fiddler crab (Uca annulipes)

Distinguishing features of the enlarged pincer of the male

• outer side is smooth and does not have a triangular depression (most observable difference)
• the movable upper finger extends past the immobile lower finger.
• has a ridge of bumps on inside or the 'palm' of the pincer.

Orange fiddler crab (Uca vocans)

Distinguishing features of enlarged pincer of the male

• has a bumpy outer face.
• the tips of the claws are flattened and sabre-like.
  
• the immobile lower finger has a long groove on the outside.

Mudskippers: frog, snake or fish?

Thoughtful question: "Is it a fish, a snake or a frog?".

Fish! "Yes, it's a fish. But how can it move around out of water? How do you think it breathes out of water?"

"How do YOU breathe underwater when you go diving?"

"Just like the way we bring two tanks of air for scuba diving, the fish brings two tanks of water in its gill chambers. Which is why it has such 'puffy cheeks'."

Naked Facts

Mudskippers have to regularly replenish the water in their gill chambers, so they cannot stay far from water. But mudskippers can actually ‘breathe’ (absorb) air through their skin (as long it remains moist) . This is why they often roll in puddles and keep their tails in water, leading some early observers to believe that mudskippers breathed through their tails!

Mudskippers skip by flipping their muscular bodies. They skim over mud as well as the water surface. They can catapult themselves for a distance of up to 60cm and actually move faster on land and on the water surface than by swimming with their bodies in water.

A distinctive and endearing feature of mudskippers is that their huge goggly eyes at the top of their heads. Unlike other fishes, mudskippers prefer to swim with their heads above water, thus giving them a good 360 degree view.

Corny Joke: Their eyes are like a CCTV in action.

Interesting Fact: Mudskippers can also tolerate high levels of toxic substances such as cyanide.

Too Much Information

Gold-spotted mudskipper (Periophthalmus chrysospilos) Family Gobiidae

They tend to move around in groups, often in amusing 'herds', nervously moving just out of your reach. Sometimes they move in a line, following what seems to be the leader.

To about 12cm. Gaily speckled with orange spots on the undersides. The male raises his bright orange-and-black dorsal fin to court females and intimidate rival males. It eats small crabs, prawns and insects.

Giant mudskipper (Periophthalmodon schlosseri) Family Gobiidae

To about 27cm long, it is the largest of our mudskippers. It has a black stripe along the side of its body.

It builds a pool in with deep tunnels in the mud as a nursery for its young. At low tide, they are often in or near their pool. At high tide, they might be seen clinging to mangrove tree roots.

An aggressive hunter, it eats mainly prawns, small crabs and insects. It may even snack on smaller mudskippers!

Yellow-spotted mudskippers (Periophthalmus walailake) Family Gobiidae

To about 13cm long, it has a greyish body with scattered yellowish spots. There are brownish spots on the upper body. The first dorsal fin is reddish with a broad black band and narrow white margin.

It was previously confused for the juveniles of the Giant mudskipper (Periophthalmodon schlosseri). Unlike the Giant mudskipper, the Yellow-spotted mudskipper does not have a broad black band along the body length.

It is said to be nocturnal, leaving its burrow at night to forage and returning to the burrow in the morning.

Assorted smaller mudskippers

We can't really be sure what they are, especially if they are viewed from the boardwalk. They could be juveniles of larger mudskippers or different species of small mudskippers.

Mudskippers are probably the only fish with movable eyelids!
To keep their eyes moist when they are on land, the eyes can be retracted to dip them into water that collects at the bottom of the eye socket. Their retinas have rod receptors above and cones below, giving them colour vision above and monochrome vision below!

They can absorb gaseous oxygen through blood-rich membranes at the back of the mouth and throat and they also absorb air through their skin which is rich with blood capillaries, so long as the skin remains moist.

Mudlobster Condo

Mudlobster formations are found around the old prawn pond and inside the back mangroves (where the Nipah palms start getting abundant).
Three NAKED facts

Question: Can you guess what animal makes those funny volcano shapes in the mud?

naked fact#1: Without mudlobsters there will be fewer plants and animals in the mangroves.

Those volcanoes are the result of mudlobsters that dig deep in the soft mud. As they burrow about, mounds are created without them even knowing what happens above ground. Mudlobsters are seldom seen above ground.

The mound is like a cosy condo for all kinds of animals. These animals make little holes and tunnels to live in. These animals include crabs, ants, spiders, worms, clams, snakes, and shrimps.

Some plants also appear to grow better on these mounds.

Corny joke: The condo even comes with a swimming pool!

Water is trapped in the mound system forming pools which shelter fish and swimming animals at low tide.

naked fact #2: Mudlobsters are like earthworms. As they burrow and dig, they loosen the mud and allow air and oxygen-rich water to penetrate the otherwise oxygen-poor ground. This allows other animals and plants to make use of the mud.

naked fact #3: The Mudlobster is listed among the threatened animals in Singapore as their preferred habitats are lost or degraded. If it disappears, so will its 'condo' and the plants and animals living there.

Other interesting things to look for at mudlobster mounds

How many plants and animals can you see growing on the mound?

How can you tell whether the mound is an old one or one that is freshly made?

How high do you think a mudlobster mound can get? Records are 2m above the ground, which is taller than an adult human being! I've seen mounds at Lim Chu Kang that are as tall as me.

Too Much Information about Mudlobsters

This photo was taken of a mudlobster on Chek Jawa before deferment. It was spotted by Zeehan as we were having lunch on the big rock where the intertidal walks usually start! We don't know why it was wandering about in the open. We brought it to the prawn pond and left it there hoping it will burrow to safety.
Mudlobsters are not lobsters! Mudlobsters (Thalassina anomala) are more closely related to ghost shrimps of the genus Callianasa. A mudlobster can grow to about 30cm long.

What do they eat? No one knows for sure. They are believed to eat mud.

Can eat or not? There isn't really much of a mudlobster to eat. But they are eaten in some places. They are considered a nuisance by fish and prawn farmers as their digging activities undermine the bunds (raised edges of mud) that surround fish and prawn ponds.
Ubin villagers believed that mud lobsters can be eaten to treat asthma, but no scientific study has confirmed that.

Ferocious mud ant! There is a kind of ant that is found on mudlobster mounds that has a really nasty evil malignant bite. It's name is suitably Odontomachus malignus. I've been bitten by these tiny ants before, their bite really hurts! More about them on the Guide to the Mangroves of Singapore

Links
Guide to the Mangroves of Singapore

No durians without mangroves?

Three NAKED facts

Question: How many of you like durians?

Question: What do you think pollinates the durian flowers?
If no one guesses right away. "I'll give you some clues: the durian flower looks like a pom-pom, it's white and it blooms at night" Eventually someone will guess bats.
naked fact #1: These bats only drink nectar and eat pollen. They don't eat fruits, they don't eat insects.

Question: "How often does the durian tree flower?"
Eventually they will realise once or twice a year. (We get durians year-round in Singapore because we import them from different places)

Question: "So what do these bats feed on when the durian is not in bloom?" If these bats relied only on durian flowers, they would starve to death.

naked fact #2: Mangrove trees like the Perepat (Sonneratia) have similar pom-pom-like flowers. Bats also feed on the nectar and pollen produced by these trees.
Such trees bloom more regularly and thus support a population of these bats. With more bats, more durians are likely to be pollinated.

naked fact #3: Without mangroves we may have fewer or even no durians!

Where to do this story? Preferably where the visitors can see a Perepat (Sonneratia) tree. As it is a long story, don't do it where it's hot, or mosquito-infested.

To ID a durian tree: the long narrow leaves are dull green on the upperside and bronzy on the underside. The branches are somewhat angular and usually sparsely leafed.
Of course if there are durians on the tree, that's a dead giveaway!

Bushes in the mangroves

Ximenia americana

This shrub can grow quite tall, with fluffy white flowers that turn into oval fruits that ripen to yellow.
Sea holly (Acanthus sp.)

Common low shrubs often growing on mudlobster mounds. Some leaves may not be so spiky, an a single plant may have spiky and non-spiky leaves.
The flowers may be white with blue or purple tinges, developing into cylindrical fruits.

Getting to the root of mangroves

Three NAKED facts

naked fact #1: Mangrove trees have weird roots!
Question: Can you describe the different kinds of weird roots that you see?
Stilt roots (Rhizophora)
Pencil-like roots (Avicennia)
Knee roots (Bruguiera)

Thoughtful question: Can you think of reasons why mangrove trees have such strange roots?
Imagine you had to stay all your life on the soft squishy mud without moving. And the tide comes in and covers you up. And waves wash against you. What do you think you need to have?

• To grow upright and not fall over? Stilt roots!
  
• To breathe when the tide is high? Pencil-like roots! (Stilt roots are breathing roots too!)

Mangrove trees have shallow roots. Those with pencil-like breathing roots form a kind of raft, with thick roots growing horizontally and the pencil-like parts growing upright from these thick roots.
naked fact #2: You can tell what kind of mangrove tree it is by the kind of roots it has!

After explaining, you can remind them along the way and perhaps get them to guess. If they get it right a lot of time you can congratulate them and say they are now very good with mangrove trees!

Stilt roots (Rhizophora)
Straight pencil-like roots (Avicennia)
Conical pencil-like roots (Sonneratia)
Knee roots (Bruguiera)

naked fact #3: Mangrove trees are the root of life, and source of your seafood!

The tangle of roots in the mangroves results in a rich variety of marine life in the mangroves.

• Animals to settle on the roots (clams, snails, barnacles), as well as seaweeds.
• These provide food for other animals.
• Small animals hide among the roots where bigger animals can't get at them.
  
• Roots protect the mud and sand from being washed away by waves. Here burrowing animals can settle down.
  

Many of our favourite seafood come from mangroves and the seagrass areas near mangroves

Question: What is YOUR favourite seafood?
Stay in mangroves all their lives: Mud crab, mussels, clams
Stay in mangroves when they are young: big prawns, baby fishes of grouper and other fishes. These go into deeper waters when they grow up.
Found in seagrass areas: flower crab, sting ray, baby fishes

Mangrove climbers

Ant-house plant (Dischidia sp.)

This strange climber often found on mangrove trees, has two kinds of leaves. Smaller, 'normal' looking ones that are still somewhat fat. And clumps of large hollow leaves.
Ants eventually take up residence in these inflated leaves. Here the ants find safety. Meanwhile, the plant benefits by absorbing the leftover food and rubbish that the ants accumulate inside their 'house'. The plant grows roots into these inflated leaves to absorb these nutrients that are rather scarce in a mangrove.

Hoya climber (Hoya sp.)

Another climber with fat leaves, a water-conserving adaptation to the mangrove habitat where freshwater is scarce.
The climber produces a ball of waxy flowers that develop into long narrow pods full of seeds.

Derris (Derris trifloliata)

A climber commonly seen in our mangroves, it often twists around a young tree so the tree trunk becomes deformed as it grows bigger. Eventually, the tree's growth breaks the climber, but the twisted scars remain.
This climber has pretty pink flowers that develop into flat pods.

Links to more about some of these climbers
on the Guide to the Mangroves of Singapore
Common Derris (Derris trifoliata)

Nipah (Nypa fruticans)

This is a palm, like a coconut palm. But instead of a vertical stem, it has horizontal underground stems with tall leaves sprouting from the stem. The long palm leaves are used as roofing or 'attap' in traditional kampung houses.This palm is the source of 'attap-chee' which is the young seed. The part we eat is the source of food for the seedling (on the right is a photo of a sprouting seed).
This is the long stalk of tiny male flowers that produce pollen. Tiny stingless bees often gather at blossoming male flowers and pack the pollen baskets on their legs full of yellow pollen.
The female flowers are in the form of a ball. The yellow one is ready to attract pollinators through the little slits. This ball then turns into a ball of fruits.
The sap in a branch of blooms is full of sugars. Traditionally, the sap is collected and may be processed into 'gula melaka' or sweet brown sugar, also used in many of our deserts. Or fermented to produce the alcoholic 'toddy'.

Links to more about Nipah
on the Guide to the Mangroves of Singapore
Nipah (Nypa fruticans)

Nyireh (Xylocarpus)

Nyireh bunga (Xylocarpus granatum)

Flowers are tiny pinkish.

The fruits are large and look like cannon- or bowling-balls! Inside are a few irregularly shaped nuts arranged like a puzzle.
It has buttress roots. Doesn't have pencil like roots.

The timber is used to build boats and make furniture. Bark dyes used on cloths.

Links to more about Nyireh
from the Guide to the Mangroves of Singapore
Nyireh bunga (Xylocarpus granatum)

This is rare
Nyireh batu (Xylocarpus moluccensis)

Perepat (Sonneratia alba)

The breathing roots are large, conical with pointed tips.
The flowers have hard sepals that are green on the outside and pinkish on the inside. The flowers bloom at night. The petals are small and white. What is seen as a big pom-pom are a bunch of many many stamens (that produce pollen). These usually drop off the morning after the bloom, and the mud may be littered with hundreds of these tiny white stamens.
Fruits rounded, with the sepals forming a star-shape behind them.

More about the role of Perepat in durians

Links to more on Perepat
from the Guide to the Mangroves of Singapore
Perepat (Sonneratia alba)

These are rare
Berembang (Sonneratia caseolaris)
Gedabu (Sonneratia ovata)

Bruguiera

All Bruguiera have knee roots.Bakau putih (Bruguiera cylindrica)

Flowers small with pale hard sepals and tiny white petals. The petals usually wither away by mid-day.
Seedlings cylindrical, slender with backward pointing sepals (the thing that looks like a crown)

The wood from the tree is used for fish stakes, pilings, railway sleepers, heavy pillars and beams and other construction. It is also favoured as firewood and for conversion into charcoal as it produces the most heat among mangrove woods. The bark is astringent and used to treat malaria, cure fish poisoning, diarrhoea and fever.

Tumu (Bruguiera gymnorhiza)

Flowers with red hard plasticky sepals (sometimes bright red, sometimes pale pink) and brown furry petals. The petals usually wither away soon after blooming.
Seedling short and fat.

Links to more Bruguiera
on the Guide to the Mangroves of Singapore
Bakau putih (Bruguiera cylindrica)
Tumu (Bruguiera gymnorhiza)

This one is rare
Lenggadai (Bruguiera praviflora)

Bakau (Rhizophora)

All Rhizophora have stilt roots.All Rhizophora have small dots on the underside of the leaf.

Bakau kurap (Rhizophora mucronata) and Bakau (Rhizophora stylosa)
These two species are hard to differentiate in the field.

Flowers more elegant and held on long stalks from the branch.
Seedlings tend to dangle on long stalks from the branch too.

Bakau minyak (Rhizophora apiculata)
Flowers sturdy and stuck close to the branch.
Seedlings long and stuck close to the branch.

Links to more about Bakau
on the Guide to the Mangroves of Singapore
Bakau minyak (Rhizophora apiculata)
Bakau kurap (Rhizophora mucronata)
Bakau (Rhizophora stylosa)