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Perspectives on Marine Environment Change in Hong Kong and Southern China, 1977-2001 (ed . B. Morton). Proceedings o f a n Internationa l Worksho p Reunio n Conference, Hon g Kong 21-26 October 2001. Hong Kong: Hong Kong University Press , 2003. EFFECTS O F LONG-TERM ANTHROPOGENI C PERTURBATIONS O N THREE SUBTIDAL EPIBENTHI C MOLLUSCAN COMMUNITIE S I N HONG KON G K.F. Leung Environmental Protection Department , The Government o f the Hong Kong Special Administrative Region , 28/F, Southorn Centre , 13 0 Hennessy Road , Wan Chai, Hong Kong and Brian Morto n The Swire Institute of Marine Science and Department of Ecology an d Biodiversity , The University o f Hong Kong, Hong Kong ABSTRACT This paper presents the results of the 1992 , 1995, 1998 and 2001 benthic trawl surveys carried ou t i n th e water s o f Hon g Kong . It aime d a t identifying an y tempora l and/o r spatial changes in three subtidal epibenthic molluscan communities in the northwestern, southeastern an d easter n sector s o f Hon g Kong' s territoria l waters . Eac h secto r i s characterized no t onl y b y differen t hydrographi c regime s bu t als o intensitie s an d frequencies o f anthropogeni c perturbations , particularl y fishin g b y botto m gears , eutrophication, reclamation, sediment dredging and dumping. Non-parametric analyse s were performed t o identify an d compare any such changes. The composition o f the three molluscan assemblage s showe d different degree s of change i n relation t o externa l factor s ove r th e period betwee n 199 2 an d 2001 . These modifications wer e characterized by more or less rapid and abrupt replacements, in terms of species richness, density and diversity, of distinct families of Bivalvia and Gastropoda, but the amplitude and resilience of these were different between sites. A common featur e shared by the three surveyed sectors in response to anthropogenic impacts was, however, the structure of their resident communities which are now dominated by generalist, ofte n scavenging and deposit feeding gastropod s and a suite of highly tolerant bivalves, with respect t o physica l impact s an d periodi c anoxia . Th e result s obtaine d fo r mollusca n communities in 1992, 1995, 1998 and 2001, suggest that the single-most important factor driving long-term changes in them is fishing b y bottom gears. 656 K.F. LEUNG & B. MORTON INTRODUCTION The area of Hong Kong' s territoria l water s and, thus, seabed is some 165 6 km2 and is subjected t o intens e developmenta l stres s fro m a huma n populatio n i n 200 1 o f 6. 7 million. The pressure of urbanization has dramatically increased the levels of domestic sewage and industrial wastes that are discharged into the coastal waters of Hong Kong. Recent extensiv e reclamation , marin e dredgin g an d spoi l dumpin g activitie s hav e aggravated the pollution problem and disturbed and destroyed marine habitats and life. Morton (1996a) provided a map of all the various activities that take place in Hong Kong's waters, ranging from recreational pursuits to effluent discharge s from factories , sewage outfall s an d marine dumpin g o f uncontaminated an d contaminated sediments . There are also impacts from fishing, notably bottom trawling and, since 1992 , extensive dredging fo r reclamation . T o date , mor e tha n 6 0 km2 o f land , o r som e 20 % of Hon g Kong's shoreline , has been reclaimed fo r urba n and port development an d is ongoing. The first study of Hong Kong's seabed was by Shin (1982) and Shin and Thompson (1982) who showed a relatively uniform distribution of both sediment and macrobenthos. Subsequent research focussed o n Tolo Harbour, following an initial survey of its seabed in 1977 by Horikoshi and Thompson (1980). At three year intervals, thereafter, i n 1980, 1983, 1986 and 1989, the harbour's seabed was resurveyed with respect to crabs (Cheung 1990; Davi e 1992; Lam 1992) , fishe s (A.W.Y . Leun g 1992 , 1997a) , prawn s (Leun g 1992) an d mollusc s (Taylo r 1982 , 1992 ; Taylo r an d Shi n 1990) . Th e benthi c invertebrates o f Tol o Harbou r an d Mir s Ba y wer e reviewe...

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