Ecological status and conservation value of soft shore habitats in Hong Kong

香港軟灘生境的生態狀況及保育價值

Student thesis: Master's Thesis

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Author(s)

  • Koon Keung TAI

Detail(s)

Awarding Institution
Supervisors/Advisors
Award date3 Oct 2005

Abstract

Soft shores, i.e., sandy and/or muddy intertidal flats, are distinct habitats which provide refuges for a diversity of fauna. However, in Hong Kong such habitats are under risk, since soft shores are generally the first coastal areas that would be reclaimed for urban development. A territory-wide survey of 40 soft shores was conducted once in the summer and another in the winter in 2000-2002 in order to assess their ecological status and conservation value. On each shore, three zones: upper, middle and lower, were divided according to the tidal level. Within each zone, 10 quadrat samples (25 x 25 cm) and core samples (8 cm diameter, 20 cm length) were collected randomly and in total, 30 quadrat and 30 core samples were collected per shore for analysis of epifaunal and infaunal communities. Additional core sediments were taken in each zone for determination of particle size distribution and total organic content for physiochemical comparisons. A total of 107 ha of soft shore habitats were surveyed in this study, with a collection of 2,400 quadrat and 2,400 core samples for faunal analysis, and 720 core samples for physicochemical analyses. In addition, data on crab fauna on 17 shores and fish fry surveys in inshore waters at 18 shores were collected. The physical environment of the survey soft shores showed a distinct separation based on their degree of exposure to wave actions and sediment characteristics. The mean median diameter of sediment of very-protected shores ranged from 2.09 to 4.45φ and total organic carbon content from 0.73 to 1.86%. For protected shores, mean median diameter of sediment ranged from -0.26 to 2.47φ and total organic content varied from 0.19 to 0.61%. For exposed and very exposed shores, the mean median diameter of sediment particle size ranged from -1.00 to 2.38φ and total organic carbon content from 0.03 to 0.48%. In total, 70,195 specimens belonging to 305 species were collected from all the shores investigated. Of these, 124 species were molluscs, 77 crustaceans, 56 polychaetes, 39 fish and 9 other animal groups. For epifaunal communities recorded from the quadrat sampling, molluscs were the most abundant group (63.4%), followed by polychaetes (22.7%) and crustaceans (11.5%); while for infaunal communities sampled from the sediment cores, polychaetes (52.7%) were the most dominant group, followed by molluscs (29.3%) and crustaceans (14.2%). In addition, a total of 37 species of crabs were recorded on the shores with the dominance of the fiddler crab Uca lactea, Buddhist crab Tmethypocoelis ceratophora and mangrove swimming crab Thalamita crenata. For fish fry surveys, a total of 40 species of fish and invertebrates were obtained with the dominance of the pony fish Leiognathus brevirostris and crimson seabream Evynnis cardinalis, and juveniles of the Akiami paste shrimp Acetes japonicus, particularly in inshore waters of the soft shores on southwest of Hong Kong. Multivariate analysis on both epifaunal and infaunal communities showed that three shore groups could be delineated mostly owing on their extent of exposure to wave actions, similar to the observations from the shore sediment characteristics. The first group ‘very-protected shores’ composed of five shores which had an average density of 554.9 ind m-2 shore-1. For this shore group, the dominant animal group was polycheates, comprising mainly nereidids, nephtyids and capitellids. The second group‘protected shores’ consisted of 14 shores which had an average density of 666.3 ind m-2 shore-1. Gastropods were the most dominant fauna on these shores, with representatives including the mud snails Batillaria spp. and Cerithidea spp., and ‘necklace’ shell Clithon oualaniensis. The third group ‘exposed to very exposed shores’ composed of 19 shores with an average density 146.5 ind m-2 shore-1. Representative species in this shore group included amphipods Phoxocephalus sp. and Platorchesia platensis, and isopod Excirolana japonica. Results of multivariate statistics also showed no significant difference in the shore community structure between the summer and winter seasons. However, marked zonation was evident between the lower and upper tidal zones, with the lower zone having the highest animal diversity and abundance than the upper zone. Conservation value of individual shore was ranked using a habitat scoring system which comprised the following criteria: naturalness, habitat diversity, size, non-recreatability, degree of disturbance, species diversity and rarity. The assessment of ranking of shores according to these criteria was based on the results of the present survey, landuse and population data from relevant government reports, and findings from previous shore studies. From the results of such ranking and further consideration on the community structure of the shores, a total of 6 shores were deemed important in terms of conservation value and maintenance of a diversity of soft shore habitats in Hong Kong. These encompassed the sandy shore at Tong Fuk Miu Wan on Lantau Island, the protected shore at Yung Shue O in Tolo Channel, the mudflats in Deep Bay, including Tsim Bei Tsui and Hang Hau, and the exposed sandy shores at Long Ke Wan and Tai Long Tai Wan in the Sai Kung Peninsula. The habitat and biodiversity characteristics of these shores were highlighted and recommendations on soft shores conservation in Hong Kong were discussed.

    Research areas

  • Seashore ecology, Hong Kong, Coastal ecology, China