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Habitats

Wave action decreases noticeably from outer to inner coast. The more sheltered the shore, the more fine sediments can be deposited. This leads to the formation of a spectrum of soft shores, ranging from sandy shores to mudflats.

Similar to the organisms living in other intertidal habitats, the composition and abundance of soft-shore organisms vary with respect to the degree of wave exposure (i.e. shore types) and the duration of submersion (i.e. shore levels). Soft shores are a three-dimensional habitat, where organisms live not only on the surface but also inside the substratum. Regardless of where organisms live, they have to face a set of challenges. Living on the shore surface allows organisms to search for food or mates easily, but they also face a higher risk of water loss and heat stress during low tides. These organisms are also more susceptible to wave dislodgement and predation during high tides. In contrast, organisms living within the substratum are less susceptible to wave action, predation and desiccation, but they may struggle to obtain food and oxygen for survival, as well as find mates for reproduction.

Soft shore organisms can be categorised into three groups by their ways of habitation: surface dwellers (epifauna), burrowers (infauna) and temporary burrowers. The surface dwellers are mostly snails, whereas the burrowers are mostly bivalves and worms. The temporary burrowers, which act as either surface dwellers or burrowers, depending on the phase of tidal cycle, are mainly crabs capable of digging burrows.

In Hong Kong, mudflats are mostly located in Deep Bay and Inner Tolo, whereas the soft shores with coarser sediments (e.g. sandy shores) are scattered all over Hong Kong. A number of soft shores in Hong Kong are key nursery grounds and shelters for ecologically or commercially important species, including many species of global conservation concern (e.g. Black-faced Spoonbill, Green Turtle and horseshoe crabs).

Soft Shore at Shui HauMud snails (<em>Batillaria</em> spp.) are common surface dwellers of local soft shores. You can often see the trails they leave as they move on the shore surface to feed on organic matter.Ribbed Venus Clam (<em>Gafrarium pectinatum</em>) is one of the most common bivalves living on sandy shores. It is a burrower, which extends its siphons to filter plankton and organic matters during high tides.<em>Coecella</em> sp. is a filter feeder found on sandy shores. Soldier Crab (<em>Mictyris brevidactylus</em>) is one of the few crab species that does not only walk sideways.  When the tide is falling, they emerge from the burrows and often march around feeding in a large number on the shore, which gives them the common name. <em>Siphonosoma cumanense</em> is a burrower commonly found in the low-shore zone of local soft shores.Innkeeper Worm (<em>Ochetostoma erythrogrammon</em>) is another common burrower found on local soft shores. It lives in a U-shaped burrow, and it has a transparent and extendable proboscis that allows it to feed on the organic matter on the shore surface.  Horseshoe crabs breed on soft shores, and their juveniles also live on soft shores.

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