Do urban structures influence local abundance and diversity of subtidal epibiota? A case study from Sydney Harbour, Australia

In an age when human modification of natural substrata is increasingly cite d as an agent of population decline and extinction, understanding the role of artificial surfaces as surrogate habitats for natural surfaces is critic al. It has been predicted that the addition of new habitats to an area can lead to increases in species abundance and diversity. We tested this hypoth esis by contrasting assemblages of subtidal epibiota on natural reef and si x common urban surfaces in Sydney Harbour, Australia. All surfaces were in shallow water and consisted of rocky reef, sandstone (brick) retaining wall s, fibreglass and concrete pontoons, concrete pilings and wooden pilings wi th bark and stripped of bark. Assemblages of epibiota on sandstone surfaces (natural rocky reefs and sandstone retaining walls) differed from non-sand stone surfaces. The major distinguishing features of sandstone surfaces wer e the large cover of coralline algae and small number of taxa. Assemblages on pilings and pontoons were most different from those on sandstone surface s and relatively similar to each other. There were, however, some differenc es which seemed to be consistent with features such as type of surface (con crete vs wood) and arrangement of surface (floating pontoons vs fixed pilin gs). We suggest that artificial structures may increase the abundance and d iversity of subtidal epibiota in the shallow areas of an estuary, but are n ot surrogate surfaces for epibiotic assemblages that occur on nearby natura l rock. It would appear that urbanisation of estuarine habitats has consequ ences for the identity, diversity and abundance of subtidal epibiota. (C) 1 999 Elsevier Science Ltd. All rights reserved.