Monday, February 20, 2012

Matang: Romanticising the Mangroves (2)

A small trawler boat crusing by the mangroves of Matang.

A view of Kuala Sepetang fishing village.

Afternoon sees the placid brown rivers of Matang disturbed by incoming fishing boats. The chugging engines tear the calmness of the air previously dominated by whispers of heated updrafts carrying rounds of white bellied eagles (Haliaeetus leucogaster) high in the sky. Crab and prawn pots can be seen stacked highly on these smallish boats. As their bows swing towards wood-planked berths stretching out into the waters from village and warehouses, workers on the boats pulled out blue drums loaded with the day’s catch. The berths were lined with people readying to pull the drums up with metal hooks and strong muscles. The cued thud of the starboard on the berth signals a synchronised hauling of the catch from the deck to the berth in minutes. Once all catches are landed, the captain reverses the boat and head out once more to the sea. In a small frame of time, the fishing village of Kuala Sepetang laid its hands on another couple of tonnes of crustaceans.

The distinctive fishing village jetties of Kuala Sepetang.

A boat heading out to sea.

The livery of Kuala Sepetang’s fishing industry for the last 200 years (1) is an enduring testimony of the importance of ecosystem services provided by the mangroves. Mangroves are major nursery grounds for many fishes that inhabit the open waters of the Straits of Malacca (2). During breeding seasons, commercially important fishes such as groupers (garupa; Epinephelus), catfish (keli; Arius), snappers (ikan merah; Lutjanus) and rays (pari; Neotrigon) head into its murky waters to breed (2). The tangled roots and restrictive channels kept large predators away from the vulnerable young fry while they develop into adults.

 A selection of crustaceans such as flower crabs (Portunus pelagicus), mask crabs (Charybdis feriatus), tiger prawns (Penaeus monodon) and a mantis shrimp (Harpiosquilla sp.) found often near mangroves.

These fishes also share their homes with a myriad of other mangrove residents. The celebrated dried shrimp (Acetes spp.) spreaded on the verandas of village houses, drying under the tropical sun, came from the same habitat as the fishes. The greenish-grey mud crabs (Scylla serrata), bounded and packed in rattan baskets were taken from mud banks in the wake of receding tides.

Roofs of Kuala Sepetang fishing village.

The blood clam (Anadara granosa) is a common mangrove mollusc with characteristic red blood (haemoglobin) which aides in its respiration of dissolved oxygen when the tide is far out from its mudflat habitat (4).

Blood clams (Anadara granosa), an indispensable companion of many Malaysian seafood dishes, clang by their thousands in spinning metal clam-washers. Impurities falling out of the washers form a mound beneath it. This is a mix of spiny murex snails (Murex occa, M. trapa), tiger moon snails (Natica tigrina), rock shells (Thais lacera) and sea cucumbers. The first 3 species are blood clam predators and are also increasingly popular on the menu of seafood lovers. This lot is undeniably a section of the mudflat community, which is a unique ecosystem formed by the deposition of nutrient-rich mud on the seaward side of mangrove coasts.

The well-known charcoal factory near Kuala Sepetang. 

Seafood is not the only major industry in Matang’s mangroves. The continual management of mangroves is motivated by the well-known charcoal industry for centuries. The Khay Hor Charcoal Factory is one of the charcoal producers. A tangy vapour of burning mangrove wood greeted me as I was taken a tour of the factory by veteran charcoal-producer Mr. Chuah Chow Aun. Boats holding mangrove logs from allocated logging plots cruises into a canal and unload their cargo. Here, they are processed into charcoal via slow burning in large traditional clay kilns. In the process, strong vapours emitted from the kiln’s outlets are condensed into tannin acid, commercially used for tightening leather but locally used as mosquito repellent. Mr. Chuah explains that the charcoal produced from Matang’s Rhizophora is dense and odourless, a quality attribute that is reflected by the high demand for his charcoal in Japan.
The canal where the unloading of mangrove logs takes place.

The kilns where mangrove logs are traditionally processed into charcoal.

Dark coloured Tannin acid is a byproduct of charcoal production.

The abundance of useful species is an important lifeline for the people of Kuala Sepetang. However, these are but a handful of species in the midst of the thousands of others which are very much ecologically-intertwined with them. Mangroves as a whole are an integral part of the tropical land and seascape. Its presence gave rise to a unique ecosystem which in turn, influenced other seemingly unrelated ecosystems such as coral reefs and seagrass beds (2). At a time when Malaysia is increasingly losing its mangroves (3), it is crucial to ensure that Matang's mangrove ecology and interactions are not destroyed or altered significantly under such intensive resource harvesting.  As any visitors will realise, the cultural and industrial successes of Matang hangs on the ecological balance of its mangroves.

Scibbles and numbers probably showing charcoal yields. The future of the charcoal industry, like many others in Matang, depends on a responsible, long-term management of mangroves.

(1) Watson, JG 1928, Malayan Forest Records: Mangrove Forests of the Malay Peninsula, Forest Department, Federated Malay States.

(2) Ronnback, P 1999, 'The ecological basis for economic value of seafood production supported by mangrove ecosystems', Ecological Economics, vol. 29, pp. 235-252. (Available from: )

(3) Chiew, H 2008, 'Mangrove status in Malaysia', The Star, 10 June. (Available from: )

(4) Davenport, J and Wong, TM 1986, 'Responses of the blood cockle Anadara granosa (L.) (Bivalvia: Arcidae) to salinity, hypoxia and aerial exposure', Aquaculture, vol. 56, no. 2, pp. 151-162. (Available from: )

Monday, February 13, 2012

Matang: Romanticising the Mangroves (1)

Matang is a land of contrasts. It is where numerous mud creeks wind slowly under the endless verdant cover of mangrove stands. A land sheltering clusters of rickety stilt-houses home to generations of fishermen and wood-cutters while serving, at the same time, a refuge for mangrove wildlife. A land whose ecosystem is among the biggest carbon sinks on Earth (1) and yet home to one of the largest charcoal industry in the country (2). Under this paradoxical coexistence, a surprising synergy unveils. This two-part series begins with a visit to the famous mangroves of Matang.

A small river winding among the mangroves of Matang Permeanant Forest Reserve.

The road crossing Matang’s lowlands is peculiarly straight. Lining both sides of the road are the ubiquitous oil palm and the occasional clusters of coconut stands and kampong houses. I strained my eyes to look beyond the blur of passing palms as the car cruises across this unbroken plain, hoping to catch the glitter of mangrove leaves behind the silhouettes of palm fronds, but there were none. At almost 400kmsq, the mangroves of Matang Permanent Forest Reserve are touted as the largest remaining tract of its kind in Peninsular Malaysia (3). But where is it?

 The Matang Permeanant Forest Reserve is an agglomeration of mud-rich estuaries and islands cloaked in mangroves on the west coast of Peninsular Malaysia. 
(Picture source: 4)

Turning around the corner at the end of the road, the car came into full view of a metalled lane walled by an unbroken line of tall mangroves and dense undergrowth. The mangroves have been hiding just behind the oil palms all this while, continuing under the uniform shadow of its thick canopy. Standing at around 10 metres, this unusually tall mangrove Rhizophora apiculata has a straight trunk with branches that does not appear until right at the canopy. Its wide-arched prop roots often share the forest with the sturdy buttress roots of the Leggadai, Brugueira parviflora, which resembles the roots of lowland rainforest dipterocarps. Indeed it almost feels like I’m deep in a rainforest as I pulled into the Matang PFR visitor centre.

 A 65-years-old Bakau Minyak, Rhizophora apiculata displayed in situ.

The Piai Lasa, Acrostichum speciosum, is a fern highly adapted to life in the mangrove forest. It is one of the fastest-spreading plants in such habitat and hence, often compete with the planted mangrove saplings (5).

Here is the scene of fierce competition between the fast growing Piai Lasa and the planted Rhizophora saplings.

A typical scene in the Matang mangroves.

The entrance signboard to Matang PFR boardwalk.

Contrary to the putrid, mosquito-infested mangrove stereotype, Matang turns out to be exceptionally neat and fresh! A newly build boardwalk brings visitors deep into the mangrove forest heartland. Bird nest ferns and giant bracket fungi hang on the trunks and branches while fallen logs scatter among meadows of mangrove fern Piai Lasa (Acrostichum areum), Jejuru (Acanthus spp.) and mangrove saplings. The ground here, having thick layers of fallen leaves across the seemingly dry forest floor with occasional puddles of water, bears uncanny likeness to the rainforest. A chance encounter with a freshly dug puddle of mud no doubt made by wild boars (Sus scrofa) further enhances such an impression. Only a faint whiff of salty air reminds me that I am still in a mangrove, at least for a while.

Wild boars (Sus scrofa) often dig pits like these for molluscs and crustaceans (content source: 6)

A giant bracket fungi measuring almost half a metre across.

The spike-adorned Nibong, Oncosperma tigillarium, is a common palm in freshwater swamps and lowland rainforests but can also be found in drier parts of the mangrove (Content source: 7).

The Rotan Bakau (mangrove rattan), Calamus erinaceus is another peculiar plant related to the Nibong (8).

Glancing up to the canopy, I was rewarded with another surprising sight-the crown-shyness phenomena, in a mangrove forest! This is the first time I’ve seen this phenomena outside of the dipterocarp rainforest. It turns out that these were the result of abrasion between swaying branches of neighbouring trees brought by strong winds (9).

Upon closer scrutiny, the ground reveals the marine fauna component of this part of the forest. Grazing on the dead leaves are several species of the peculiar Ellobiid snails. These snails are essentially terrestrial (they are pulmonate snails ie. they breathe air through lungs) in adult form but marine in its larval stages. It requires the tides to wash its eggs into the ocean which its larva will develop and eventually settle on suitable lands in adult form. (10)

The Banded Cassidula snail, Cassidula nucleus, is a common resident of mangroves.

The Judas Ear Snail, Ellobium aurisjudae, is another Ellobiid found in mangroves.

A larger ellobiid, the Midas Ear Snail, Ellobium aurismidae.

This Spotted Littorinid snail, Littorina scabra is another well-known mangrove snail commonly found way above the water line on trunks or even leaves! Despite it able to survive above water for a considerable time, it breathes via gills (11).

A small stream winds through the thick mangrove forest.

As I wander further along the boardwalk and towards the river, the undergrowth gradually gets thinner. Eventually, only a few straws of saplings remain amongst the mingling roots of Rhizophora. Here, vivid claws of red, blue, orange and yellow male crabs vey for attention among the drab muddy background. But it is not my attention that they are seeking, as I found out when they scurried straight into their pencil-thin burrows in the ground as I approach them. Upon sensing little threat I pose to them, they eventually return to the surface and waver their oversize claws once again. This time, several drab looking female crabs approaches them. I was witnessing a mating display. 

The unique prop roots of Bakau Kurap, Rhizophora murconata.

The undergrowth grew thinner towards the river banks.

A male Rose Fiddler crab, Uca rosea with its oversized claw.

However, there is one thing about the mangrove forest that is more surprising than others. There are several clearings in the forest and distinct plots with different stages of young Rhizophora, reminding visitors that this is in fact a mangrove silviculture site. Matang PFR has a long history of mangrove forest management stretching back to 1908 and was one of the field sites where benchmark research into mangrove management strategies took place a century ago (4). There are two primary species planted in this heavily-managed ecosystem- Bakau Minyak, Rhizophora apiculata and Bakau Kurap, R.  mucronata. These species are highly sought-after for charcoal production and various structural uses in local communities.

A plot of young Rhizophora trees.

A specific area of the boardwalk built for mangrove sapling planting.

A propagule of the Brugueira. This is the ‘seedling’ which drops from a parent tree after maturing and often ends up lodge in the mud via its projectile-like end. Tidal waters then triggers roots and shoots to sprout into a sapling. (12)

As I rounded a corner and walked alongside the Rhizophora-fringed river, a distant object splashed into the water instantaneously! Adrenalin suddenly surge through me. Thoughts of getting face-to-face with the saltwater crocodile (Crocodylus porosus) flashed before my eyes as I scanned desperately around to catch a glimpse of this rare and endangered beast. Knowing that this is the region where crocodiles were prime game in the 19th Century (13), I am always on the lookout for any of their surviving descendants.  A ripple can be seen on the bank, underneath drooping Nipah (Nypa fruticans) fronds. A reptilian head peeked out from the shadows. Sigh, it was no crocodile but a Water Monitor (Varanus salvator).

The water monitor, Varanus salvator swimming along the river bank. It is an omnipresent resident of many habitats stretching from the coastline right up into the mountains, including certain areas of human settlements.

Thick stands of Rhizophora crowd the banks of the river.

Despite continuous disturbance brought on by the silviculture system, it is the biodiversity component that strikes most awe in me. There is no doubt these disturbances altered the natural ecosystem but the resource that contributed to such disturbances-the Rhizophora mangroves, is paradoxically giving the ecosystem a reason to be conserved and be managed sustainably. Inadvertently, this has also buffered various other flora and fauna from ever-encroaching land uses such as agriculture and aquaculture, which have already consumed and heavily disturbed many stretches of this unique ecosystem that exists between the land and the sea.

 (1) Ong, JE 1993, 'Mangroves-a carbon source and sink', Chemosphere, vol. 27, no. 6, pp. 1097-1107. (Available from: )

(2) pers. comm. Chuah Chow Aun

(3) MTC 2009, 'Matang Mangroves: A Century of Sustainable Management', Timber Malaysia, vol. 15, no. 3, pp. 6-11. (Available from:
(4) Giri, C, n.d., Matang Mangrove Forest, Malaysia. (Available from:
(5) Watson, JG 1928, Malayan Forest Records: Mangrove Forests of the Malay Peninsula, Forest Department, Federated Malay States.

(6) Baker, N 2012, Eurasian wild pig. (Available from:

(7) FAO 2007, Ecocrop: Oncosperma tigillarium. (Available from:
(8) Rattan Species Diversity, 2006. (Available from:

(9) Putz, FE, Parker, GG and Archibald, RM 1984, 'Mechanical Abrasion and Intercrown Spacing', American Midland Naturalist, vol. 112, no. 1, pp. 24-28. (Available from:

(10) Apley ML 1970, 'Field Studies on Life History, Gonadal Cycle and Reproductive Periodicity in Melampus bidentatus (Pulmonata: Ellobiidae)', Malacologia, vol. 10, no. 2, pp. 381-397. (Available from:

(11) Chapman, MG and Underwood, MJ 1999, Seashores: A Beachcomber's Guide, Univeristy of New South Wales Press, Sydney.

(12) Mangroves, 2009. (Available from:

(13) Maxwell, WG 1907, In Malay Forests, William Blackwood and Sons, London.

Sunday, April 24, 2011

Susan Hoi: A Glimpse of Prehistoric Thailand

This was what prehistoric Krabi looked like- a typical tropical freshwater swamp dominated by Nipah palms, Nypa fruticans. Photographed in Kuala Selangor, Malaysia.
Noon at Krabi, Thailand. The fierce sun beats down on a still swamp. Humid whiffs of air from deep peat wind their way out of sturdy intermingling roots of swamp plants. The plants jostle and crowd for every space available in between to capture the glaring sun light for their photosynthetic leaves. Their verdant swaying fronts in the midday breeze capture the flickering reflections of sunlight from a large pool of water nearby. The rippling surface of the water stretches quite a distance, lapping on the mud banks on the other side of the slow meander. Looking down at the shallows, beneath the drifting of faint silt in tea-coloured water,  hundreds, if not thousands of wriggling and crawling snails made their way slowly across the silty bottom. Typical scene in this region of mud, water and mangroves, you might say. Except that the snails are not living in mangrove forests and the water is fresh. And most importantly, the time is some millions of years ago...

The signboard welcoming us at the entrance.

"THE WORLD MOLLUSC FOSSIL SITE-KRABI-THAILAND" displays the signboard welcoming us. The time is 5pm and the sun is dipping silently into the Andaman Sea to the west. The rays, although still casting its golden shine on Krabi's coast, is no way near its fiery midday equivalent. We held our breath. Cramming in a van for 3 excruciating hours from Phuket to Krabi with a driver that drives more like a jet pilot have us fatigued. We are only too eager to burst out of the van and indulge in something more productive, fulfilling. The van finally pulled over a car park lined with stores selling typical seashell souvenirs. There's no doubt what this place is famous for!

The information plaque for Susan Hoi.

Rocks surrounding the two headlands of Ban Laem Pho are the centrepieces of this unusual attraction. (image from Google Earth)

Susan Hoi Jedsibhalanpi or more accurately known as Susan Hoi literally means "seventy-five million years old shell cemetery". You might be wondering how did they found out the age of the shells but I'll come back to that later. Located 7km south of Krabi town at the jutting headlands of Ban Laem Pho coast, Susaan Hoi is a collection of 3 geological formations containing fossilised freshwater shells numbering in the millions. Although inconspicuous and insignificant from afar, the rocky capes are wonders in themselves. It is thought that this geological curiosity is among the only sites around the world, the other being in Japan and the US. This statement is doubtful since there are many fossilised shell beds (shell assemblages) including a recent discovery in Mae Moh coal deposits of northern Thailand, also of freshwater origins. Closer to home, Krabi itself boasts another site in a coal mine with the same layer of fossil freshwater shells believed to be from the same formation as Susan Hoi's.

Tens of thousands of fossil shells cover the entire rock layer.
A detached slab showing the thick deposit of fossil shells.

This brings us to the questions: What exactly is the Susan Hoi formation? and how old is it? Let's answer the latter, for a start. Susan Hoi is, admittedly, not seventy-five million years old. The naming error stems from an old assumption that Susan Hoi comes from the Tertiary period, where the 75 million years ago period is located. It is younger, though no geologists have come to terms with its exact date yet. Primarily, there are two camps when it comes to dating these fossils. On one side, scientists who analysed ancient pollen grains deposited along with the fossil shells concluded that Susan Hoi could only be between early and mid-Miocene (that is, between 23.03 and 5.33 million years ago). On the other hand, paleontologists discovered fossilsed fishes and turtles in the deposits dating back to the Eocene period (56 to 34 million years ago). With such conflicting claims, no dating consensus can be made save the error of the 75 million years old phrase. However, what is more definite can be found in the study of the evolution of the environment leading to Susan Hoi's formation.

Slabs of hard fossil rich rocks break and collapse onto the beach as waves washed away softer deposits around it.

Cracks form across the fossil shell bed as a result of endless weathering from wave action in this dynamic coast.

Waves have been pounding hard on the Susan Hoi's rocks for millenia. In the process, softer deposits and the topsoil layers have gave way and washed down into the sea, leaving the more sturdy layer of fossil shells (a.k.a. shell matrix) jutting out of the formation. Eventually, prolonged weathering cracked the exposed matrix and they collapsed to a pile of giant slabs. In such an event, sections of the entire formation can be seen from a cliff face, especially the more exposed parts of the capes. This gives geologists opportunities to study each layer of rock and interpret them.

Lignite (coal) mixed with clays and fragments of Viviparid snail fossils found beneath the rock layer.

Beneath the shell layer, geologists found a dark band of lignite (better known as coal) interspersed with shale and clay and even some Viviparid snails-indicating an ancient freshwater swamp. Some plants living among its watery habitat, often shed its leaves, while other that died  collapse into the water. These organic material decompose and sink into the depths of the swamp, eventually compressed by the pressure of water and soil deposits above. This compressed layer then becomes lignite. Clay and shale, meanwhile, had their origins as silt and sand washed down from the interior and settled between the dead plants in significant quantities. To produce such thick deposits of silt, one may imagine huge amount of rain battering down on mountains and river banks. In other words, southern Thailand might have been tropical even before Susan Hoi's formation! (Not that this is strange, it is just that climate and environment of the past in many places differ significantly from today's.) Indeed, fossil pollen analysis indicate tropical plants thrive during that period.

As sea levels began to rise, saltwater incursion occurs across the Krabi floodplain, aiding the spread of brackish water habitats, followed by the more salty mangrove wetlands. Pictured here is the floodplain as seen from the limestone peak at Wat Tham Suea.

One of the mangrove plant species is the Rhizophora sp., seen here in present day Krabi.
This freshwater swamp, however, disappear completely after several million years. It is then that the shell bed enters the scene. Apparently, salt water had begun to invade the freshwater swamps, leading to the formation of brackish water habitat instead. Brackish water simply means a mixture of salt and freshwater. This means death to the previous occupants including the freshwater swamp plants, hence the absence of lignite in the shell beds. The disappearance of the freshwater plants allowed the growth of certain algae, which in turn allowed molluscs to thrive. Typical swamp molluscs such as Viviparid snails, Melanoides snails and Mya arenaria clams began to appear in profusion. The algae increase heighten activities of grazing and filtering decomposed materials. Sand and silt continued to deposit along with the mollusc shells. This goes on for several million years. by then, the shell and silt became cemented and formed a 1m thick deposit.

Typical brackish water habitat supports a large specialised molluscan community as seen in this example in Pulau Tioman, Malaysia.

The fossilsed Viviparid snails (family Viviparidae), Taia sp.(?), bounded by clay.

Another species present is the smaller, tall spired Melanoides sp. snails (family Thiaridae).

Peculiarly, this shell deposit stopped short of continual growth and was obliterated by a thick layer of sand, clay, gravel and red laterite! What happened? What occured to the swamp...and the snails? Some people speculate that this may be a result of a severe storm which carried tonnes of earth from upstream and dumped them onto the riverine community. Others said it could be a sudden geological uplift of the floodplain, draining out all the swamp water. Or is it? Either way, the entire swamp ceased to exist. This was replaced by the dryland rainforest which grew on the firm earth burying the shell deposits.

As weathering continues, exposed fossil shells will erode. Here the severity of erosion is shown by the reduced striation features found on the Viviparids as compared to the previous two pictures.

As erosion continues, even the shape of the shells began to look indiscernible.

Fossil casts of the freshwater Viviparids embedded in red clay exposed as erosion rounded the fossil -rich pebbles.

As time passes, the coast gradually crept back towards the shell beds. Wave action have been breaking up all the soil and rocks between the sea and shell deposits. finally, the sea is now lapping once again at the doorstep of the ancient swamp fossils.

Rocks less exposed to wave action produce more pronounced details of the ten of thousands of ancient freshwater shells.

Paradox in this dynamic coast: 
Where the old (fossils) meets new (the orange nerite snail, Nerita chameleon (Linnaeus 1758) )

Paradox in this dynamic coast: 
Where the old (fossils) meets the young ('spiral' eggs belonging to an unidentified species of mollusc)

Paradox in this dynamic coast: 
Where the primitive (fossil snails) meets the advanced (an Onch Slug, family Onchidiidae)

As I stand on the cape, gazing out to the Andaman, I contemplated Susan Hoi's eventual fate. The final rays of sunshine touch gently on broken pieces of fossil rocks illuminated by saltwater spray from relentless pounding of waves down at the waterline. It was such a brief exposure, in geological time, that has afforded us an opportunity to reveal the amazing history of this natural wonder. I knew that, very soon, the shell cemetery will be no more. Mere pebbles rolling beneath the waves, ever breaking into smaller pieces, ending back into the sea, just like a few million years ago.

Sunset over Susan Hoi.

Useful further reading:
1. Udomkan, B, Ratanasthien, B, Takayasu, K, Fyfe, WS, Sato, S, Kandharosa, W, Wongpomchai, P and
Kusakabe, M 2003, 'Fluctutaion of Depositional Environment in the Bang Mark Coal deposit, Krabi Mine, Southern Thailand: Stable Isotope Implication', ScienceAsia, vol. 29, pp. 307-317.
Link: []

2. Watanasak, M, Songtham, W, Mildenhall, D 1995, 'Age Of The Susan Hoi (Shell Fossil Cemetery) Krabi Basin, Southern Thailand', International Conference on Geology, Geotechnology and Mineral Resources of Indochina (Geo-Indo '95), pp163-168. Link: []

3. Boonchai, N, Grote, PJ and Jintasakul, P 2009, 'Paleontological parks and museums and prominent fossil sites in Thailand and their importance in the conservation of fossils' in Paleoparks- The protection and conservation of fossil sites worldwide, ed JH Lipps, BRC Granier, Brest, Book 2009/03, Chapter 7. Link: []