Diversity At A Glance (pdf)

This column aims to introduce interesting species of Hong Kong flora and fauna that might be encountered during fieldwork. Distinctive physical characteristics and some interesting ecological facts are included for each example. If you wish to contribute to this column, or have any comments or suggestions, please contact eitherJacqueline Weir (jesweir@hkusua.hku.hk) or Sukh Mantel (skmantel@hkusua.hku.hk)

	'The six common Bauhinia species in Hong Kong'
	'Siphonaria japonica'
	'Chinese three-striped box turtle Cuora trifasciata in Hong Kong: possibly the last viable wild population in the world'

"Siphonaria japonica"

by Wallis K.S. Chan

The Siphonariidae is the most primitive family of limpets, known as basommatophoran pulmonate limpets (Hyman, 1967). They are known as false limpets due to the presence of a secondary gill which lies within the mantle cavity. To accommodate the opening of this so-called "lung" the shells of these animals are slightly asymmetric.

Three species of Siphonaria (Sowerby, 1824) have been recorded on Hong Kong shores: Siphonaria atra Quoy and Gaimard, 1833; Siphonaria sirius Pilsbry, 1894 and Siphonaria japonica Donovan, 1834. Siphonaria sirius and S. atra are sometimes very difficult to tell apart and recently were proposed (based on electrophoresis and morphological analysis) to be ecomorphs of the same species, Siphonaria laciniosa (Slingsby et al., 2000).

Siphonaria japonica is relatively small (10 – 25 mm, Morton and Morton, 1983; Liu, 1994), and is easy to distinguish from the other Siphonaria species on Hong Kong shores due to its distinctive shell morphology; with numerous ribs at regular intervals radiating around the shell. Siphonaria japonica generally occurs from mid to low shore on sheltered to semi-exposed shores, such as Butterfly Beach, Cafeteria Old, Angler’s Beach, Wu Kwai Sha, Clear Water Bay, Wah Fu, Middle Bay and South Bay.

Siphonaria japonica can live up to one year, growing rapidly during the winter and breeding and recruiting in winter. They lay yellow gelatinous egg ribbons on the mid-low shore or in rock pools. Their egg capsules are ellipsoid and early development is rapid, releasing veligers (one of their larval stages) after seven days at 21°C. These limpets disappear from the shore completely by May at most sites (after a life span of ~ 8 months). At some sites, which are north facing, (such as Wu Kwai Sha) they can survive for a year, perhaps due to the shores’ aspect that protects the limpets from summer heat stress.

Siphonaria japonica is a grazer and the most abundant food items in its diet are cyanobacteria. The availability and species composition of this food supply, however, varies greatly around Hong Kong and has important implications for growth and reproduction. In my study, most population parameters were positively correlated with abundance of filamentous cyanobacteria (Phormidium spp., Lyngbya and Oscillatoria spp.), whilst negative correlations were found with Kyrtuthrix maculans, Hildenbrandia rubra and diatoms. Shores with a high standing crop of filamentous cyanobacteria were mostly found on the west coast, and supported faster growing individuals which laid more, larger egg masses, as compared to shores on the east coast which lacked these cyanobacteria.