The hills of the mainland northeast New Territories tumble to the sea, meeting the waters of Mirs Bay along a serrated coastline with a jumble of small stream mouths, inlets, bays and headlands. Rocks, islets and islands are scattered across the inshore waters. A stretch of mainland coast and the nearby shores of the three largest islands – Double Island, Crescent Island and Crooked Island – encircle a natural harbour known as Double Haven (Yan Chau Tong).
This is one of the loveliest areas in Hong Kong. There are only scattered, small villages, most of which are partly or wholly deserted, with ruined houses often being covered by vegetation that is reclaiming the landscape. Much of the coast and the Double Haven islands are within Plover Cove Country Park; Yan Chau Tong Marine Park protects most of Double Haven, and the bay by Lai Chi Wo.
The area is geologically rich, with volcanic rocks, together with sediments that were mostly produced by erosion after the volcanoes fell silent. Southernmost Double Haven is dominated by these younger sedimentary rocks – they form the southern coast of Crescent Island, as well as much of the land just to the west, around Sam A Chung. These rocks are siltstones and sandstones, plus conglomerates with larger, rounded pebbles, laid down during the Cretaceous as rivers prone to flooding surged across alluvial plains below the rapidly eroding remnants of volcanoes.
The sedimentary rocks include the reddish sandstones flanking Hung Shek Mun (Red Rock Channel), between the western tip of Double Island (Wong Wan Chau) and the mainland New Territories. They formed in a “basin” – a low lying area created by movement along faults, with the southernmost fault running southwest from Bluff Head, and a parallel northern fault through Sha Tak Kok.
Rocks in the same formation extend westwards, along the southern slopes of Tiu Tang Lung, to the Pat Sin Leng range. Above and below them are layers of older fuff, which was created from thick layers of incandescent volcanic ash that was blasted from volcanoes during major eruptions in the Middle Jurassic.
It might seem odd that rocks should be sandwiched between layers of an older rock formation – as normally, rocks should become younger from bottom to top. Here, the answer lies in a relatively young fault, occurring 60 to 90 million years ago. This is a thrust fault, with the tuff pushed up from north to south.
The fault runs through the headland south of Lai Chi Wo, on through tiny Fu Wong Chau, and runs just above the south coast of Double Island, the remainder of which is formed of tuff. This same tuff forms westernmost Crescent Island (Ngo Mei Chau), much of southern Crooked Island (Kat O) and islets the west of it, as well as most of the mainland around and west of Lai Chi Wo.
But another fault slices southeast – northwest through the island group, and along its east are younger volcanic rocks that form most of Crescent and Crooked Islands, and Yeung Chau. These rocks are mainly tuffs and rhyolite lava, and though related to other volcanic rocks in much of eastern Hong Kong, they may have formed here, perhaps in and near vents formed along the active fault line. There are also some layers of sedimentary rocks – mudstones and limestone.
The fault cuts through the southeast peninsula of Crooked Island, where erosion has cut through it to form a distinct “notch”.
At the very north tip of Crooked Island are more sedimentary rocks. They’re the youngest rocks in the area (perhaps from the Late Cretaceous: 100 to 65 million years ago), and are evidently talus, formed of rock debris that accumulated at the base of a cliff in an arid landscape.
To the east of Double Haven, Round Island is formed of sediments closely related to those of Port Island (Chek Chau).
With volcanic activity over, and an end to major earth movements that once created landforms here, erosion has continued working on the landscape, removing landforms such as the cliffs that once towered above northern Double Haven, and sculpting the rocks until during the last ice age there were hills cut by valleys, above a broad coastal plain. As the ice age came to an end from around 8000 years ago, vast ice sheets nearer the poles melted, and the sea rose, flooding in across the coastal plain. At Mirs Bay including Double Haven, hilltops became islands, valleys became channels and estuaries (rias). Sea level stabilised around 6000 years ago.
History
The Pearl Pool
As the sea inundated low lying areas following the ice age, marine life including corals colonised the inshore waters. There were oysters, too, and these became the focus of a pearl gathering industry, which began during the Southern Han kingdom (917-971 AD). Mirs Bay was one of the kingdom’s main pearl producing areas – pearl oysters were so abundant that it was known as the “Pearl Pool”.
Pearl gathering was dangerous work. Divers attached themselves to ropes with weights, and dropped from small boats to the shallow seabed to search for oysters. Mortality rates were so high that after the succeeding Song emperor gained control of the area from 971, he banned pearl diving. But in 1114 the ban was lifted, and officials again obtained pearls on behalf of their rulers. Double Haven was a collecting area for pearls, which were then carried west along a route guarded by forts – eventually reaching a garrison at Tuen Mun, before being transported to Guangzhou.
The pearl oyster beds were eventually so depleted that most pearl harvesting ceased by the mid-17th century. But even in 1898, when the New Territories were leased to Britain for 99 years, there were still pearl fisheries in Tolo Harbour.
A Challenging Area to Settle; and Deforestation
Some of the soldiers who guarded the pearl route may have been among the first people to establish villages in the northeast New Territories. This hilly region proved a challenging area to settle: although Hong Kong’s lowland plains became rice farming areas from the 11th century, it seems villages including Lai Chi Wo were established within the last 400 years, as Hakka farmers moved in. Villages sometimes grouped together; Lai Chi Wo became one of seven villages in the Hing Chun Yeuk, which collaborated on projects that included building barriers across small estuaries, so creating more flat land for rice fields, as well as fish and shrimp ponds.
According to the history of Lai Chi Wo, the hills above were barren when the village was first established. Perhaps this was because the original forests had been cleared to supply timber and fuel for villages in nearby lowlands, as well as for forts and soldiers along the pearl route, and for boat building. Though villages established fung shui woods, the remaining hillside came under further, sustained pressure as autumn fires were lit to create ash that was carried downhill after rains, fertilising fields. Burning hillside vegetation also allowed grass to grow, so cattle could graze – and would have reduced potential hiding places for some dangerous animals, such as South China Tigers Pantheris tigris amoyensis, which were last recorded in Hong Kong in 1947.
Demand for timber and fuel soared when Japan occupied Hong Kong during the Second World War, increasing pressure on already sparse woodland. Even some trees in fung shui woods were felled.
No longer facing such intense pressures from cutting and burning, and helped by protection within the country park, the vegetation is recovering, with even some areas that had become almost badlands now supporting scrub and secondary woodland. The mainland northeast New Territories is home to good populations of animals such as Wild Boar Sus scrofa and Red Muntjac (Barking Deer) Muntiacus muntjak – the muntjac even occurring on Crescent Island.
Lai Chi Wo is the main village on mainland coast of Double Haven. During its heyday, there were up to a hundred households here. It’s named after the many lychee trees the villagers once cultivated, though they switched to more profitable mandarins in the 1960s and 1970s. Bandits sometimes arrived to steal from Lai Chi Wo, and the villagers bought cannons, which they fired using homemade gunpowder.
There were fishing communities including Kat O on northwest Crooked Island, and on nearby Ap Chau.
But it’s hard making a living from farming and fishing here, and Double Haven’s population has sharply declined since the 1970s.
The Islands of Double Haven
There are three main islands around Double Haven: Crooked Island, Crescent Island, and Double Island. Take a boat out into the haven, and these plus the mainland appear to surround you – from several angles, the channels leading in and out aren’t visible, so it can appear you are in a landlocked lagoon that’s ringed by green hills.
Of the Double Haven islands proper, only Crooked Island has settlements – at Kat O Fishermen’s Village and nearby, though there is an Outward Bound base on the south coast of Double Island. Smaller islets here and close by include Ap Chau (Robinson Island), where there is also a small village.
Crooked Island (Kat O Chau)
In its heyday, Crooked Island was home to a Hakka fishing community. Hakka people reportedly settled here in the Qing dynasty, and named the place Kat O – Kat Bay – after the word kat for prosperity, or for Mandarin trees that were perhaps then grown here. To the British, it became Crooked Island because of its quirky shape, with spindly headlands thrusting east, southeast and southwest from its slender centre.
The settlements are in the northwest of the island, which offered some shelter from the worst storms, as well as relatively flat land for buildings and fields. The population is said to have reached around 4000, but today there may be only around a hundred residents, many of them living in the Kat O Fishermen’s Village. This village is typical of fishing communities along the South China coast, with densely packed small houses along a rough grid of narrow streets. There are also simple wooden buildings, built on stilts above the sandy beach. Boats are moored in the shallow water, and there are small fish farms.
South of the fishermen’s village is a pier, and beyond this a fine Tin Hau temple, built in 1763, and recently renovated. There’s a fig tree by the shore in front of the temple. Known as the Lovers’ Tree, it seems well suited to this oddly shaped island, as its main trunk is initially horizontal, curling upwards to spread branches with abundant leaves.
There are abandoned fields south of the temple, with paths leading by two hexagonal wells. Beyond the fields, the island is hilly, and now overgrown with shrubs and small trees. Like the northeast peninsula, this wilder, southern part of Crooked Island is within Plover Cove Country Park. There are rough trails, including to the top of 120-metre Wong Fong Shan – an almost conical hill that is among the most distinctive landmarks around Double Haven.
Crescent Island (Ngo Mei Chau)
As its English name suggests, Crescent Island is crescent-shaped: on a map, it’s like a crab claw that’s open to the north. Within the crescent there is a good beach, and just offshore, the shallow waters around Wu Pai – a cluster of rocks above the tideline – there is excellent snorkelling over corals.
Double Island (Wong Wan Chau)
The English name of Double Island likely also stems from its shape – it’s like two islands joined together by a narrow isthmus, and forms a broad arc around the southeast of Double Haven. Along the east coast is a cove with a pleasant beach, at the mouth of a creek. Hills rise above the creek, including Wong Wan Pak Teng – which at 154 metres is the highest peak of the Double Haven islands.
Hung Shek Mun (Red Rock Channel)
Between Double Island and the mainland is a narrow gap known as Hung Shek Mun (Red Rock Channel). Though it’s the narrowest, shallowest route into Double Haven by boat, it’s perhaps also the most interesting, partly because the rocks along the tideline are indeed distinctly red – they’re sandstones, belonging to the Cretaceous red beds.
The Six Treasures of Double Haven – and Sombrero Islands
As so often with Chinese landscapes, some imaginative people have looked around Double Haven, and come up with various ideas for items that various features resemble. These include the “Six Treasures” of Double Haven: Wong Fong Shan of Crooked Island, which looks like a parasol, and below which the islet of Pak Ka Chau is said to resemble a brush rack. Should a gigantic calligrapher arrive, he or she could also find a pen – Pak Sha Tau Tsui, a sharp point of white sand at the southwest tip of Crooked Island – as well an ink slab formed from almost level rock outcrops. For paper, the giant could write on the smooth surface of the sea within Double Haven. And once the calligraphy is done, there’s a rocky islet that looks like a royal seal.
Pak Ka Chau is among the islets here that are of the form known as sombrero islands, so named as their profiles resemble the wide rimmed Mexican hats known as sombreros. These are formed of tuff, which are susceptible to weathering by salty water. Waves splash the rock, and salt crystals grow within it, causing the rock to weaken. Over time, the rock disintegrates, and storm waves wash away the debris – resulting in a rock platform above the high tide level, with the shrinking core of the islet in the middle of it.
Partly as Double Haven is usually sheltered, this is the only place in Hong Kong with sombrero islands.
Ap Chau (Robinson Island, or Duck Island)
Ap Chau is tiny – just 500 metres long, and under 100 metres wide – yet, in its sheltered location near the mouth of Starling Inlet, it has a small village along its west coast. There’s a church, as residents here are Christians – though, as elsewhere, the population has plummeted in recent decades.
A fine sea arch, known as the Duck’s Eye, leads through the low, northernmost headland. It’s cut through talus, a sedimentary rock with chunks of dark volcanic rock set in red sandy material, which probably formed as rubble from eroding volcanoes fell into a desert basin. The duck’s head shape of Ap Chau is best seen from the north: at this angle, it rather appears that a duck’s bill stretches from in front of the eyes towards the sea.
The Mainland Coastline Including Lai Chi Wo
Villages dot the coastline, sited at the mouths of streams, especially where there was some relatively flat land. Most are now deserted, their buildings maybe just ruins. Lai Chi Wo, the main village here – it was the region’s former cultural centre – is still relatively intact. With several well-maintained buildings including temples, as well as a superb fung shui wood and large mangroves, it makes an excellent destination for a hike.
Other surviving villages that are worth visiting include two hamlets at Sam A Tsuen, along trails south of Lai Chi Wo. There are two hostels here, with small restaurants that make fine places to halt for refreshments.
This area also boasts secluded stretches of coastline, wooded valleys, and hillsides rising to the area’s main peak – 416-metre Tiu Tang Lung – and to the line of hills that soar above the north shore of Plover Cove Reservoir.
Grand Trees at Lai Chi Wo
Lai Chi Wo boasts one of the best fung shui woods in Hong Kong. Over 100 plant species have been recorded here, including the Incense Tree Aquilaria sinensis, and uncommon plants such as Langkok Fig Ficus langkokensis and Golden-leaved Tree Chrysophyllum lanceolatum. The upper part of the wood was included in Plover Cove Country Park, and in 2005 the lower section of wood became a Special Area, managed by the Agriculture, Fisheries and Conservation Department for conservation and education purposes.
The wood is also notable for some grand old trees. Four trees at Lai Chi Wo are included in the government’s Register of Rare and Valuable Trees (526 trees were registered by August 2004).
One of these trees is known as the Five-fingered Camphor, at the southwest corner of the village. This large Camphor Tree Cinnamomum camphora is so named as it formerly had five trunks that grew from ground level. During the Japanese occupation in the 1940s, Japanese soldiers threatened to chop down the whole tree – perhaps to reduce cover for guerrillas, but villagers rallied to the tree’s defence, and one trunk was felled instead. Even with four “fingers”, this tree is impressive: at the base, its diameter is over 3 metres, and the crown spreads some 29 metres.
Nearby is an Autumn Maple – or Javanese Bishopwood – Bischofia javanica, which is 23 metres high and has a trunk more than 2.5 metres in diameter. The roots of a Chinese Banyan Ficus microcarpa have formed a lattice around the maple. The banyan is growing in classic strangler fig fashion; its roots are competing for nutrients and water. If out-competed by the banyan, the Autumn Maple will die, and rot away to leave the banyan.
At the northwest corner of the village is another Autumn Maple. This one is called the Hollow Tree, as its inside has rotted away, leaving an empty space big enough for a person to fit inside, with a gaping hole through the bark. It’s over 100 years old, and 18 metres tall, with branches spreading 15 metres at its crown.
The fourth of the “rare and valuable” trees is just below and east of the village. It’s a Chinese Banyan that’s 18 metres tall and over 100 years old, and is a marvellous example of a Hong Kong village banyan tree.
Lai Chi Wo Mangroves and Sea-grass
Near the banyan is a small wood that’s like a fragment of primeval forest. The trees here are Coastal Heritiera – or Looking-glass Mangrove – Heritiera littoralis. But while Hong Kong’s other mangrove trees are small, these are big trees, with substantial buttress roots for support. The trees are hung with the thick stems of a climber, White-flowered Derris Derris alboruba. Some of these stems are 20-30 centimetres across, and this climber is over 100 years old.
There’s also a stand of typical Hong Kong mangroves. Including Heritiera, all Hong Kong’s eight species of true mangroves are found at Lai Chi Wo.
On the tidal mudflats beyond the mangroves, there is a bed of Japanese Eel Grass Zostera japonica.This is a kind of sea-grass – flowering plants (angiosperms) that have developed methods for flowering and pollination underwater.
Both mangroves and sea-grass are important habitats for marine life, such as juvenile fish including sharks. They also help stabilise mudflats, and protect coastlines against storm damage.
The Coral Triangle – and Yan Chau Tong Marine Park
Double Haven is at the western edge of a region that marine biologist P.O. Ang has dubbed the “coral triangle”; Tung Ping Chau is at the eastern corner, and the southern corner is at Hoi Ha Wan on the Sai Kung Peninsula. As the name suggests, this area is home to a diverse marine life, including corals. Most of the 84 species of stony corals recorded to date in Hong Kong can be found here, in oceanic waters away from the influence of the Pearl River. However, as stony corals grow best in warm water, and Hong Kong has relatively cool winters, with sea temperatures sometimes falling to 15ºC, corals here don’t form major reefs.
Remarkably given it is so small, Hong Kong has over 10 percent of the world’s stony coral species. The mix of species is unique: although many are widely found across tropical areas of the Indo-Pacific (which includes the Indian and Pacific oceans), there are some species that are normally restricted to only parts of this region – such as Alveopora gigas from Australia and Papua New Guinea in the south, and Acropora japonica from Japan in the north.
Thanks to the cool winters, Hong Kong is also home to other more northern (temperate) marine life, such as the marine macro-algae that are commonly known as seaweeds. Growing mainly in winter, these compete for sunlight, and may prevent corals becoming established in places that may be otherwise suitable.
A host of other marine animals and plants includes species that are dependent on corals for food and shelter.
Man’s Influence: Damage, and Conservation
Though Mirs Bay is far less polluted than waters around western Hong Kong, the marine environment is not pristine. As the surrounding land was deforested, especially in the last few centuries, silt from increased erosion would have boosted turbidity, perhaps restricting growth of corals, even smothering some.
The pearl harvesting industry devastated oyster beds. Corals and seashells were harvested for the lime industry. More recently, corals hare reportedly been collected for ornamental purposes, such as decorating aquariums. These could be additional reasons – on top of the cooler winters – that branching corals are scarce in Hong Kong, even though they dominate coral communities in the South Pacific.
Pollution has killed some corals, and may explain why it’s now hard to find corals below six metres, yet during the early 1980s corals could be found at depths to 10 metres and more in Mirs Bay and Tolo Channel. Over-fishing has reduced fish stocks: eight species of grouper were considered fairly abundant around 1970, yet most are rare today. Fishing techniques such as trawling damage undersea habitats.
However, some measures have been taken to protect the marine environment here. These include the establishment of the 680-hectare Yan Chau Tong Marine Park – covering the southern area of Double Haven, plus the bay in front of Lai Chi Wo. Commercial fishing is among activities that are banned here.
The Agriculture, Fisheries and Conservation Department has also deployed artificial reefs, at sites including Double Haven. Formed of unwanted items such as old boats and clusters of used tyres, these “reefs” become structures that can attract fish and other creatures, and deter bottom trawling as nets may snag and tear. Fish have indeed begun aggregating and breeding at the artificial reefs – especially snapper, grunt and sea bream.
Hard (Stony) and Soft Corals
The stony corals (or hard corals) are colonies of anemone-like creatures – the individuals of which are polyps – which grow in protective limestone skeletons, often together with symbiotic algae. The algae are characteristic of the reef-building corals – and as they require light for photosynthesis, these corals are restricted to shallow water with ample sunlight.
Hong Kong is the only place in the world where brain corals in the genus Platygyra are relatively abundant and often large. Named because their surface patterns resemble the convolutions of a brain, these corals can form castle-like structures up to two metres high. These “castles” are among the most distinctive features of the local coral communities, helping to create bizarre underwater landscapes.
Another of the common corals in this area is Favia speciosa, which also forms massive colonies, though these lack the turrets of Platygyra. Also, because each polyp is surrounded by a skeletal wall rather than sharing with neighbours, the surfaces have honeycomb rather than brain-like patterns. The finger corals Porites lutea and P. lobata may also form small mounds, though as the polyp cavities are smaller, their surfaces appear smoother.
The Crusty Star Coral Leptastrea purpurea is also common here, though easily overlooked as it grows across rock surfaces. Lithophyllon undulatum may also grow as an encrusting coral, and as overlapping plates.
Fish
Over 580 species of fish have been recorded in Hong Kong’s coral communities since 1846. Although this is a high total, there is an overall paucity of fish, especially large and adult fish. This was clearly revealed during a study in 1997 and 1998, which estimated the average mass of fish per cubic metre over the best coral areas was among the lowest ever recorded in the Indo-Pacific: the figure of 20-30 grams was around a tenth of that reported from Australia’s Great Barrier Reef.
Some of the fish feed on corals. Beautifully patterned butterfly fish, with elongated mouths looking ready to kiss, nibble on polyps. Parrotfish, named for their parrot-like beaks, can bite off small chunks of coral, as well as graze on algae.
Various species of wrasses are among the commonest and most colourful fish in the coral communities, feeding on animals including bivalves and crabs. Coral Trout Plectropomus leopardus are scarce, but also colourful, usually red to greenish brown, with a multitude of blue dots.
Orange-and-black striped Clark’s Clownfish Amphiprion clarkii – looking straight from the movie Finding Nemo – live together with their host anemones Entacmaea quadricolor. Skin secretions protect them from the anemones’ stings, while these in turn help keep the clownfish safe by deterring predators, and the anemones get scraps of food from clownfish meals.
Groupers are among the predators here, lurking in crevices and lunging at prey. Moray eels likewise have their hideouts, from which they grab small fish. Sleek, fast Barracuda Syphraena sp. are top-level predators of the open water that hunt in packs.
Scorpion fish prefer to lie in wait, relying on their cryptic patterns and outlandish to appear unlike living creatures, so unwary animals swim too close and – gulp! – are promptly eaten. The spines of their fins are equipped with poison, for defence: the stings are intensely painful to humans, and can cause nausea and even paralysis.
Sea urchins, shellfish and nudibranchs among host of invertebrates
The invertebrates in coral communities also include species that can harm humans, such as the Black-spined Urchin Diadema setosum. This has long, sharp spines it can point towards shadows as predators approach, and are equipped with a toxin. Despite these spines, on typical Indo-Pacific reefs these urchins typically hide from predatory fish by day, and feed at night. Here in Hong Kong, however, they are readily seen in daytime – perhaps because a formerly common urchin predator, Black-spot Tuskfish, Choerodon schoenleinii, has been over-fished and is now rare, and lost from our commercial fishery, as it was among the most expensive reef fish.
The Textile Cone Conus textile and Blue-ringed Octopus Haploclaena maculosa have potent venom that is primarily for killing prey, though can be used in self-defence. The Textile Cone hunts animals such as small fish, firing a “harpoon” to inject them with a toxin that paralyses and kills them. Blue-ringed Octopuses use a very similar venom – and though the body is only the size of a golf ball, each has enough venom to kill 26 human adults within minutes. They chiefly prey on crabs and shrimps, and usually blend into their surroundings – though if danger threatens, pigments make their blue rings conspicuous and so warn: Danger – stay away.
Mantis Shrimps Gonodactylus falcatus have claws that can strike with blinding speed. This species belongs to the group of mantis shrimps which have club-like claws and are dubbed “smashers” for their ability to bash through thick bivalve shells, or even smash fingers or thumbs of careless divers. In the UK, a four-inch long mantis shrimp broke the quarter-inch glass of an aquarium – and was named “Tyson” after boxer Mike Tyson.
Many other creatures have equally successful, but less spectacular, ways of feeding. A wide variety of worms live here, some boring into the coral. Members of one group of worms, the brittle stars, may have five whip-like arms, which they use to move around, and to feed on detritus and smaller animals. Sponges remain fixed in place, pumping water through their bodies to filter plankton. Barnacles are among other filter feeders.
Jellyfish drift through the water, catching plankton with stinging tentacles. Though most species are not strong enough to harm people, a few can cause paralysis.
On the seabed, crabs scuttle about to find prey, and scavenge. Some snails (gastropods) graze on algae; one of them – Magilus seriatus – feeds exclusively on Favia corals, ingesting food particles in the mucus surrounding polyps.
Nudibranchs are carnivorous sea slugs (shell-less snails), and may be strikingly patterned. Some have cryptic camouflage, but others are so brightly coloured they are sometimes known as the butterflies of the ocean. Some of them feed on hydroids, and can do so without triggering their stinging nematocysts – instead transferring them to tentacles where they retain their stinging power, and so help deter any creatures that might otherwise make a meal of them.
