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The Marine Flora and Fauna ofHong Kong and Southern China IV (ed. B. Morton). Proceedings of the Eighth International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 2-20 April 1995. Hong Kong: Hong Kong University Press, 1997. MUCUS PRODUCTION BY SPECIES OF SIPHONARIA (MOLLUSCA: GASTROPODA: PULMONATA) IN HONG KONG Mark S. Davies Ecology Centre, University of Sunderland, Sunderland, SRI 3SD, UK and Gray A. Williams Department of Ecology and Biodiversity and The Swire Institute of Marine Science, The University of Hong Kong, Hong Kong ABSTRACT Mucus production by species of Siphonaria from Hong Kong was investigated by comparing it in stationary and mobile individuals. Mucus produced by stationary animals was collected by forceps and razor blade after attachment to glass in air for 10 minutes. Mucus produced by mobile animals crawling on glass in air was removed by razor blade. Whilst Siphonaria japonica is established as a distinct species, there is confusion over the status of Siphonaria atra and Siphonaria sirius, as they may be ecomorphs of Siphonaria laciniosa. We, accordingly, analysed data from S. atra and S. sirius separately and then pooled the data to analyse S. laciniosa. For stationary S. japonica, no relationships were apparent between mucus produced and either flesh dry weight, shell dry weight, whole dry weight, shell length or foot area. For S. atra, S. sirius and S. laciniosa, however, all these relationships were significant with the exception of the relationship between mucus production and foot area for S. sirius. Where comparisons could be made, there were no significant differences between relationships for S. atra and S. sirius (ANCOYA). For mobile S. sirius and, thus, S. laciniosa, no relationships were apparent between mucus produced per unit distance travelled and any measurement of body size. Mucus production per unit distance travelled did, however, show some significant relationships with morphological characters for S. japonica and S. atra. Mucus production scaled differently between these two species in terms of whole animal dry weight and foot area, S. japonica secreting more than S. atra. Most derived slopes between mucus production in either stationary or mobile animals showed some degree of positive allometry, i.e., the larger the limpet the proportionately more mucus it 304 M..S. DAVIES & G.A. WILLIAMS produced. Estimates of energy export as locomotory mucus from shores were derived: S. atra, 0.55-128 J·day-I depending on animal size; S. japonica, 0.59-169 J·day-I. Morphometric comparisons between the species revealed significantly different relationships between flesh dry weight and shell dry weight for S. atra and S. sirius but relationships between flesh dry weight and foot area were not significantly different. S. japonica, however, showed differences in both of these relationships to S. atra, S. sirius and S. iaciniosa. INTRODUCTION Most gastropod molluscs use mucus as a coupler between foot and substratum during locomotion. Despite its obvious functional importance, mucus remains to be studied in most marine gastropods and all previous work has been restricted to prosobranchs. Mucus production by limpets has also been shown to be energetically important (Davies and Williams 1995), placing a significant drain on consumed energy, ranging from 2332 % in temperate species (Davies et ai. 1990). In this paper, we examine mucus production in species of Siphonaria from Cape d'Aguilar, Hong Kong. Three Siphonaria species, Siphonaria atra Quoy and Gaimard, Siphonaria sirius Pilsbry and Siphonaria japonica Donovan, occur on Hong Kong shores (Morton and Morton 1983; Liu 1994), although there is considerable confusion over the taxonomic status of S. atra and S. sirius as some authors consider the two to be synonymous and ecomorphs of Siphonaria iaciniosa L. (Christiaens 1980). These species, or forms, occur over a range of exposures from sheltered to exposed shores, S. japonica being more tolerant of reduced salinities (Morton and Morton 1983). S. sirius and S. atra occur at similar tidal levels (+0.6-1.2 m C.D., optimum height - +1.0 m C.D., Williams 1993; Harper 1996) and at higher shore levels they tend to occur in rock pools. These species have a patchy distribution, but can reach densities as high as 33·m-2 in the case of S. atra and 15·m-2 for S. sirius at Cape d'Aguilar, although both species can reach much higher densities in rock pools (Harper 1996). The zonation patterns of these two species seems to be consistent between monsoons, probably a result of either living low on the shore or in rock pools...

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