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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 Octobe r 2001. Hong Kong: Hong Kong University Press , 2003. MARINE OLIGOCHAETE ASSEMBLAGES I N A HONG KON G MANGROVE AND ADJACENT FORESHORE SANDFLAT , WITH A DESCRIPTION O F A NEW SPECIE S H. Zhou The Swire Institute o f Marine Science and Department o f Ecology an d Biodiversity , The University o f Hong Kong, Hong Kong* and Christer Erseu s Department of Invertebrate Zoology, Swedish Museum of Natural History , Box 50007, S-104 0 5 Stockholm, Swede n ABSTRACT This study reports upon preliminary results obtained during the course of a quantitative study of marine oligochaete assemblages associated with different habita t types and tidal elevations at the Ting Kok mangrove, New Territories, Hong Kong. Triplicate samples, each with a surface area of 18.45 cm2 , were obtained from twelve stations encompassing the mangrove , it s seawar d edg e an d th e foreshor e sandfla t alon g fou r transect s perpendicular t o the shore. A total of 1,08 2 individual s representing eleven specie s of oligochaetes wa s extracte d fro m th e meiofauna l samples . Representative s o f thre e species (two Tubificidae, one Enchytraeidae) previously unreported from the Hong Kong area were recognized. One of them, Ainudrilus semicapillatus sp . nov., is described in the presen t paper . Fauna l densitie s range d fro m 0 to 53,87 4 individuals-nr 2 , wit h a n average of > 16,000 individuals-m-2 . Species patterns showed a clear-cut differentiatio n between mangrov e an d non-mangrov e habitats , but als o a patchy distributio n withi n the sam e habitat, suggestin g habita t preferences an d microhabitat partitionin g amon g the meiofaunal oligochaet e species . Present address: College of Life Science , Ocean University o f Qingdao, 5 Yushan Road, 266003, Qingdao, China. 122 H.ZHOU &C . ERSEUS INTRODUCTION Marine an d brackis h wate r sediment s ar e inhabite d b y a rich an d abundan t faun a o f marine oligochaetes, mostly composed o f microscopic, i.e., either meiofaunal o r small macrofaunal, species . Durin g macro - an d meiofauna l investigations , oligochaete s ar e often perceived as difficult t o identify an d treated merely as a single taxon, 'Oligochaeta ' (Erseus 1994) . I n suc h cases , quantitativ e samplin g o f eithe r macrobentho s o r meiobenthos ca n only yield figures o f total oligochaete density an d biomass. In mangrove sediments , oligochaete s ofte n constitut e a n important componen t o f the infauna , an d thei r taxonom y an d specie s diversit y hav e been reviewe d b y Erseu s (2002). Yet, the apparent lack of ecological information o n oligochaetes in this habitat world-wide would render an y evaluation o f their functioning i n the mangrove system s a matter of speculation . Hong Kong and its surroundings in southern China harbour a diverse fauna of marine and brackish-water oligochaetes. To date, a total of 71 species has been recorded fro m this area (Erseus 1984 ; 1990a ; 1992a , b; 1997a) ; their ecology, however, has receive d relatively littl e attention (Sundber g et al. 1992 ; Erseus and Diaz 1997) . This i s th e firs t quantitativ e stud y o f meiofauna l oligochaet e assemblage s i n a mangrove habitat in Hong Kong. Oligochaetes were recovered from meiofaunal sample s obtained fro m a mangrove-fringed tida l flat a t Ting Kok , New Territories b y th e firs t author. Thi s investigatio n aime d a t providin g baselin e informatio n o n oligochaet e densities an d specie s distributiona l pattern s i n a mangrove-relate d benthi c system . Species preferences fo r differen t habitat s i n relation t o mangrove vegetatio n an d tida l elevation were assessed by comparing mangrove-vegetated an d non-vegetated habitats, while allowing for an evaluation of within-habitat variation. Two species of Tubificida e and on e belonging t o th e Enchytraeidae , al l previously unreporte d fro m Hon g Kong , were recognized in the material. One of them, a new species...

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