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  • /. Moll. Stud. (1994), 60, 431-443 The Malacological Society of London 1994

    DISTRIBUTION AND POPULATION DYNAMICS OF THREEPOPULATIONS OF SIPHONARIA ON ROCKY INTERTIDAL

    SHORES IN HONG KONG

    J .H. LIUThe Swire Marine Laboratory, The University of Hong Kong, Hong Kong

    (Received 17 September 1993; accepted 16 June 1994)

    ABSTRACT

    The pulmonate limpets Siphonaria japonica andSiphonana sirius occur over a wide range of localhabitat types in terms of exposure to wave action andsalinity. This is a study of these two species on threedifferent shore types in Hong Kong, ranging from anextremely exposed, high salinity (32-35%o) shore atCape d'Aguilar to a sheltered, low salinity (1633%o)shore at Tai Lam Chung. Both species are restrictedto the low shore, year round. 5. japonica is a winterbreeder and recruitment occurred between Octoberand January. The recruitment of 5. sirius could not berecognised from the size-frequency histograms. Thealgal standing crop at Tai Lam Chung was higher thanat Wu Kwai Sha during the winter period, i.e., be-tween October and April. Seasonal fluctuations ingrowth rate were recorded for both Siphonariaspecies with the time of fastest growth occurring inwinter. S. japonica grew faster at Tai Lam Chungthan at Wu Kwai Sha. Food availability is thought tobe an important factor affecting growth.

    INTRODUCTION

    Although much work has been done on thepopulation biology of prosobranch limpets (seereview by Branch, 1981), most studies onSiphonaria have focused on activity rhythmsand homing behaviour (Cook, 1969, 1971,1976; Thomas, 1973; Cook & Cook, 1975,1978,1981; Garrity & Levings, 1983; Verderber etal., 1983; Branch & Cherry; 1985; Branch,1988) and competition (Creese & Underwood,1982; Ortega, 1985; Sutherland, 1986; Lasiak &White, 1993). Ortega (1987) studied habitatsegregation and seasonal changes in density ofS. gigas Sowerby and S. maura (Sowerby).Johnson and Black (1982) studied the variationin four polymorphic enzymes of an undescribedspecies of Siphonaria, from a rocky shore atRottnest Island, Western Australia. Little in-formation is, however, available on the popula-tion biology of species of Siphonaria and this ismainly from temperate shores. For example,

    Quinn (1988a, b) has studied the ecology of theintertidal pulmonate limpet S. diemenensisQuoy & Gaimard in terms of population dy-namics and food availability and reproductivepatterns and energetics. The population dy-namics of S. denticulata and S. virgulata havealso been studied by Creese (1981).

    Siphonarid limpets are common on the rockyintertidal shores of Hong Kong but informationon them is restricted to a general study of theiroccurrence and vertical distribution (Morton &Morton, 1983). Three species occur, i.e.,Siphonaria japonica (Donovan, 1834), Sipho-naria sirius (Pilsbry, 1894) and Siphonaria atraQuoy & Gaimard, 1833 (Christiaens, 1980,1982). The present study investigates the distri-bution, abundance and population dynamics ofthe three Siphonaria populations on three HongKong shores at Cape d'Aguilar, Wu Kwai Shaand Tai Lam Chung (Figure 1). Such shoresexperience a variety of hydrographical con-ditions and this study aimed at determining howeach species responded to such differences interms of patterns of recruitment, growth andpopulation dynamics.

    MATERIALS AND METHODS

    Stations and species studied

    Cape d'Aguilar is located on the south-eastern tip ofHong Kong Island. As predominantly easterly windsprevail throughout the year, the shore experiencesheavy wave action and is characterized by near-normal salinities (32-35%o). Wu Kwai Sha, located inthe embayment of Tolo Harbour, is protected fromheavy wave action and experiences salinities of be-tween 28-33%o. Tai Lam Chung is a moderatelysheltered shore located in the western estuarine re-gion of Hong Kong. Fresh water issuing from thePearl River affects salinity, causing it to vary over awide range (16-33%o).

    The substratum at Cape d'Aguilar is a coarse darkgrey tuff. It forms thick massive, beds with no inter-nal stratification (Allen & Stephens, 1971). The

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  • 432 J.H. LIU

    LAW UA BLAND

    D NIHEPtO0

    ETAOLOLAR

    @* WMLAII ISLAND

    POTtKOBOUP

    Figure 1 A map of Hong Kong showing the three study sites.

    shore, in this area, falls gently to the sea formingpools and crevices. The shore substratum whichSiphonaria inhabits at Wu Kwai Sha is granitic rocks(Allen & Stephens, 1971). The shore falls steeply tothe sea and comprises broken granitic rocks withmany crevices. The Sung Kong Granite of Tai LamChung is uniformly coarse-grained (Allen andStephens, 1971) and the shore falls smoothly andgently to the sea.

    Siphonaria japonica occurs mainly on shelteredshores but a few were found at Cape d'Aguilar.Siphonaria sirius tends to be a species of near-normalsalinities, common at both Cape d'Aguilar and WuKwai Sha but, at the latter, not available in sufficientnumbers to be sampled and only a few were found atTai Lam Chung. Siphonaria atra occurs on bothexposed and sheltered shores, i.e., Cape d'Aguilarand Wu Kwai Sha but was present in insufficientnumbers to be sampled. S. atra and 5. sirius from WuKwai Sha were not studied.

    Distribution and abundance

    To investigate the distribution of the limpets, fieldwork was undertaken at Cape d'Aguilar, Wu KwaiSha and Tai Lam Chung (Figure 1) between August1987 and December 1988. The vertical distributionand limpet abundance were assessed using 0.25 m2

    quadrats placed at 1 m intervals down transect lines

    set from Extreme High Water Spring Tide (EHWST)to the waters edge (ELWST). Height (m) of thequadrats above Extreme Low Water Spring Tide(ELWST) were calculated from the profiles obtained.The distribution and abundance of limpets were re-corded monthly in terms of the numbers of limpets.0.25 m~2 along the transect.

    Chlorophyll analysis was used to estimate theabundance of the algal assemblage present at eachsite, i.e., encrusting algae, microalgae and filamen-tous algae. Samples were obtained every threemonths. Usually, six randomly-chosen rock samples,each of about 10 cm2, were chopped from the rockbelow mid tide level (MTL) where the limpets occur-red. Samples were analysed within 24 hours of collec-tion, usually after overnight storage in an air-tightand light-sealed container placed in a refrigerator(4 C). Exposure to strong light and high tempera-tures were also avoided in transit. Chlorophyll wasextracted from each sample using the acetone extrac-tion technique of Parsons et al. (1984).

    Size-frequency histograms

    Limpets were sampled monthly, i.e., from August1987 to March 1989 for Siphonaria sirius at Caped'Aguilar; from August 1987 to December 1988 forSiphonaria japonica at Wu Kwai Sha and fromNovember 1987 to December 1988 for S. japonica at

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  • POPULATION BIOLOGY OF SIPHONARIA 433

    3 20

    10

    15 J_CD

    15 1 0 -szCO

    5-

    0

    jjn

    19871988

    N D J F M1987 1988

    N D

    Figure 9 The estimated mean shell length of each cohort of the population of Siphonaria japonica at Tai LamChung. The number represents the year of birth of each cohort.

    Table 1. The chlorophyll content of rock samplestaken from the three sites, sampled betweenMarch 1988 and March 1989: mean SD chloro-phyll u.. cm"2; n = 6.

    Sites Mar. Jun. Sept. Dec. Mar.1988 1989

    Cape d'Aguilar 3.54 1.56 1.70 2.53 3.87(1.22) (0.68) (0.55) (1.22) (1.56)

    Wu Kwai Sha 3.24 1.30 1.48 2.57 3.16(1.05) (0.65) (0.54) (1.04) (1.07)

    Tai Lam Chung 5.5 0.86 1.08 6.17 6.57(1.19) (0.24) (0.24) (1.38) (1.02)

    The population dynamics of a species can beexpected to differ at sites where different bioticand abiotic environments are encountered. Thegrowth and population dynamics of the samespecies of limpets may also be expected to varyamong different habitats (Sutherland, 1970,1972; Branch, 1975, 1976; Creese, 1980; Work-man, 1983; Fletcher, 1984). Lewis and Bowman

    (1975) stressed the importance of biologicalhabitat upon growth and pointed out thatchanges in the surrounding species compositionwould produce corresponding changes in thelimpet populations. Estimates of growth bySiphonaria japonica indicate that the popula-tion at Tai Lam Chung grew faster than that atWu Kwai Sha (Figure 10).

    On the shore at Wu Kwai Sha, the mostabundant herbivores were Patelloida pygmaea(Dunker), Siphonaria japonica and S. sirius.These three species characterize the middle andlower shore. Other grazing gastropods such asMonodonta labio (Linnaeus) and Nerita albi-cilla Linnaeus were also common on the middleand lower shore. The shore at Tai Lam Chungwas occupied only by 5. japonica, from Novem-ber to April, with other herbivores occurring inlow numbers. Liu (1992) has shown that thesiphonariid radula comprises numerous fineteeth of uniform size, capable of rasping macro-algae but not of scraping into rock. Competi-tion for food may lead to different growth rates

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  • 440 J.H. LIU

    Table 2. Mean air temperature and relativehumidity of Hong Kong between 1987-1989 (Datafrom: Monthly Weather Summary 1987-1989,Royal Observatory, Hong Kong).

    Jan.Feb.Mar.Apr.MayJun.Jul.Aug.Sep.Oct.Nov.Dec.

    1987

    M.A.T.(C)

    17.318.321.321.925.027.528.9

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