Spatial Distribution of the Infaunal Benthos of Hong Kong

Abstract

Five replicate Smith-McIntyre grab samples were collected at 200 stations around Hong Kong. The total of 1000 samples comprised 10,142 specimens belonging to 139 animal species; mean density was 101.4 individuals m-2, and mean wet weight 35.2 g m-2. Agglomerative hierarchical classification was used to delineate 5 station groups; these were related to environmental parameters by multiple discriminant analysis. Four station groups were separated along a salinity gradient extending from the Pearl River estuary in the west to more oceanic waters in the east. The 5th group was associated with coarser sediments in scoured tidal channels; it had the lowest diversity value and the highest numbers and biomass. The other 4 groups were highly diverse, biologically accommodated communities, despite the fact that Hong Kong has an annual temperature range from 15 to 30.degree. C, and bottom salinity may fall to 6.3 .permill. S in western waters when the Pearl River is in spate in summer. It is argued that biological interactions, involving keystone species, may have a controlling influence on community structure and diversity, and must be taken into account when infaunal communities are compared. In 4 of the station groups, low biomass may be partially accounted for by the preponderance of silt, a sediment difficult to colonize. Communities could be named after the 3 most dominant species in each group, but this would serve little purpose since fidelity was low. Although central Hong Kong receives very large quantities of untreated sewage, its effects were not evident in the benthos; this is attributed to dispersion by strong tidal currents.