Shallow soft-sediment habitats are under threat and degraded by intense coastal urbanisation, pollution, overfishing and direct habitat loss. These habitats are concentrated near sources of sediment supply, i.e. estuaries, which bear the grunt of the most drastic environmental change among all marine habitats.

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Globally, ecosystems such as mangrove forests are considered amongst the most endangered ecosystems of the world. This challenge is particularly strong in burgeoning East Asia.

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The soft-sediment habitats of Hong Kong, as part of the megalopolis of the Pearl River delta supporting >65 million inhabitants, face particularly immense pressures that threaten their functionality. As part of the Pearl River estuary, the Mai Po Marshes-inner Deep Bay ecosystem, especially, is threatened by sustained eutrophication (i.e. nutrient enrichment) and other pollution, as well as disturbances related to urbanisation, all potentially compromising its conservation value.

Coastal environments in Hong Kong are affected by the Pearl River estuary, particularly in the western waters of Hong Kong. Freshwater outflow from the Pearl River containing a high level of sediment and nutrient content are beneficial to the marine lives inhabited in estuarine environments, by providing a nursery ground with plenty of food (planktonic organisms). Deep Bay is one of the largest estuaries in Hong Kong receiving freshwater outflow from the Pearl and Shenzhen Rivers.

Being exposed to ocean swells driven by the easterly monsoons, the Hong Kong Eastern coastline, in contrast, is minimally influenced by the Pearl River. This condition does not favour the growth and development of mangroves, which inhabit soft bottom shores. There are limited estuarine environments in the eastern parts of Hong Kong. Where mangroves occur, for instance, at Lai Chi Wo and Kei Ling Ha, these communities develop because of the presence of small local rivers and streams.

Miscellaneous soft shore habitats could be found in Hong Kong, such as sandflats, mangrove forest, mudflats, tidal flats and seagrass beds. These habitats may be found in areas like Deep Bay and Sai Kung. The following are some recommended sites worthy of your further exploration.

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To spot the sites on Google Map, refer to http://www.nature.edu.hk/field_sites

Lai Chi Wo

Situated at the North-Eastern part of Hong Kong, Lai Chi Wo is within the areas of Plover Cove Country Park and Double Haven Marine Park. Here you find one of the largest mangrove habitats in Eastern Hong Kong. You can also find other soft-bottom habitats, such as mudflats and seagrass beds (the rare intertidal seagrass Zostera japonica), at Lai Chi Wo.

Lai Chi Wo is known for its unique Hakka culture, a Site of Special Scientific Interest (designated in 1979), and a part of the Hong Kong UNESCO Global Geoparks.

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Accessibility
It is relatively inaccessible. Apart from a 2-hour hike from Wu Kau Tang, you may reach Lai Chi Wo by ferry at a limited schedule.

Ferry service (Saturdays, Sundays and Public Holidays only)

• Ma Liu Shui ↔ Lai Chi Wo

Kowloon Motor Bus (KMB) Bus Routes*

• 275R Tai Po Market Station ↔ Wu Kau Tang (Sundays and Public Holidays only)

Green Minibus Bus (GMB) Routes*

• 20R Tai Po Market Station ↔ Wu Kau Tang

*Remarks: It takes around 2 hours to hike from Wu Kau Tang to Lai Chi Wo.

Biodiversity values

• The largest trees of the true mangrove, Heritiera littoralis, occur at Lai Chi Wo. This mangrove tree can grow up to 15 meters in height. You can also find a characteristic giant species of the mangrove associate Derris trifoliata at Lai Chi Wo.

• Kandelia obovata is common at Lai Chi Wo.

• The rare local seagrass, Zostera japonica, serve as the food and habitat for crabs and shrimps, etc.

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Human intervention

Disturbances:​

• Situated in a remote location, Lai Chi Wo does not suffer from severe human disturbance. However, marine debris do wash up onto the shore of Lai Chi Wo, which may hinder the growth of flora and fauna.

• The increase in the number of visitors may adversely affect the habitats there. For instance, visitors may step on the unique species for photo taking without supervision, causing significant damage.

Sheung Pak Nai

Photo taken by Yan Ping Loo

Sheung Pak Nai is located at North-Western New Territories. This site comprises of soft and deep muddy substratum, particularly in the foreshore areas. Local aquaculturists have long worked at aquaculture ponds and oyster farms in Pak Nai. Sheung Pak Nai is designated as part of the Pak Nai Site of Special Scientific Interest.

Accessibility
The site is accessible with minibus.

New Territories Green Minibus (GMB) Route

• No.33 Yuen Long (Tai Fung Street) ↔ Ha Pak Nai

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Biodiversity values

• Uncommon seagrass species, Halophila ovalis and H. becarrii, have been recorded. Their current status is, however, unknown.

• A record indicated that the true mangrove species Kandelia obovata was planted in the 1980s by local farmers in attempt to protect their fishponds from erosion.

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Human intervention
Disturbances:

• Spilling of fuel oil nearby by illegal smugglers happened in the late 1990s. The smugglers discharged oil from their fishing boats or merchant ships into the sea to escape prosecution by the Marine Police.

• Leakage of polluted water from the West New Territories Landfill was recorded in 2018. Pak Nai was one of the affected areas.

• Recreational facilities, including rental caravans and farms, are next to the site.

Rehabilitation:

• Environmental NGOs, such as Green Power and The Nature Conservancy, have initiated educational campaigns for the protection of Pak Nai.

• For instance, Green Power’s “The Cordgrass Removal Action” gathers public effort to halt the growth of the invasive Cordgrass (Spartina alterniflora) and to rehabilitate the habitats at Pak Nai.

• The Nature Conservancy launched the permanent Hong Kong Oyster Reefs Exhibition Project to advocate the conservation value of oyster reefs.