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The marine soft‐sediment benthic communities of Hong Kong: a comparison of submarine cave and open habitats

In October 2002, staff from the Swire Institute of Marine Science (SWIMS), the University of Hong Kong, and the Natural History Museum (NHM), London, mounted a joint expedition to study submarine caves (zawns) off the eastern coast of Hong Kong, to test hypotheses that they may support either endemic or unusual communities, or they may act as refugia for such taxa. The present paper analyses the sedimentary macroinfaunal communities from that survey. Sampling was by hand‐coring undertaken by SCUBA divers. Muddy‐sand habitats within two caves were sampled in comparison with four control sites outside the caves, one of heterogeneous muddy sand, one of clean sand and two of fine mud; the samples were sieved across a 0.5 mm mesh. Sedimentary granulometry, water temperature, pH and dissolved oxygen were also measured. The benthic community within the caves showed a higher density and diversity than most of those described from non‐cave sediments in Hong Kong waters. The community was distinct from that found at the control sites, partly owing to sediment granulometry differences. Thirty‐three species were found only in the caves, some of which are known from elsewhere in non‐cave habitats; six species are, to date, only known from these caves. It is concluded that the cave habitat conditions offer a stable and sheltered habitat which allows the development of a distinct community, although not representing an endemic fauna, as well as being a refuge for species under threat from anthropogenic or natural stresses outside the caves.