Zoological Studies

Variations in Intertidal Assemblages and Zonation Patterns between Vertical Artificial Seawalls and Natural Rocky Shores: A Case Study from Victoria Harbour, Hong Kong

Nelson W.Y. Lam, Richard Huang, and Benny K.K. Chan (2009) Development of coastal cities often results in destruction of natural coastlines, which are consequently replaced by artificial coastal urban structures, commonly including smoothly surfaced vertical seawalls.  Artificial seawalls can create novel habitats which may affect the diversity, abundances, and distribution patterns of intertidal assemblages.  In the present study, the intertidal assemblages on 3 vertical artificial seawalls and 3 natural rocky shores were studied in Victoria Harbour, Hong Kong.  Both artificial seawalls and natural rocky shores shared similar assemblages of common species, but the species abundance and percentage cover of certain taxa differed between the 2 habitat types.  Artificial seawalls supported a greater abundance of the chiton Acanthopleura japonica and greater percentage coverage of the oyster Saccostrea cucullata and barnacle Amphibalanus (= Balanus) amphitrite.  In contrast, a greater abundance of the false limpet Siphonaria laciniosa and a greater percentage cover of the barnacle Tetraclita squamosa occurred on natural rocky shores.  Some species were found exclusively on only one of the habitats.  The green mussel Perna viridus, tube worms Hydriodes spp., and sea squirt Styela sp. were only found on artificial seawalls, while the black mussel Septifer virgatus was exclusively recorded on natural rocky shores.  Artificial seawalls had different zonation patterns compared to natural rocky shores.  The barnacle Tetraclita squamosa and chiton Acanthopleura japonica were commonly low on natural rocky shores but they became abundant on the mid-shore of artificial seawalls.  Differences in zonation patterns of species could be due to the vertical orientation of artificial seawalls leading to different temperature and humidity profiles compared to natural rocky shores.  Spatial variability of the assemblage structure at the scale of tens of meters was greater on natural rocky shores than on artificial seawalls.  Greater horizontal spatial variation in species assemblages on natural rocky shores may be associated with greater habitat diversity (e.g., rock pools, crevices, and vertical and horizontal surfaces) on natural shores than on smooth vertical seawalls.