Maintenance of chitons on seawalls using crevices on sandstone blocks as habitat in Sydney Harbour, Australia

Intertidal seawalls support different assemblages and fewer species than do natural habitats. One explanation for these patterns may be the lack of some microhabitats on seawalls. Preliminary observations suggested that some features of sandstone seawalls, such as the presence of crevices among blocks, may provide chitons with an important habitat. To test the hypothesis that numbers of the chiton, Sypharochiton pelliserpentis, would be greater in crevices than on exposed surfaces of seawalls, sampling was done on sandstone seawalls in Sydney Harbour. S. pelliserpentis were more abundant in crevices among blocks than on exposed surfaces. Experimental manipulations transplanting chitons to exposed surfaces showed that they were found in greater numbers in crevices where those were available than on exposed surfaces. Chitons transplanted to blocks where crevices had been filled tended to move to non-filled crevices on other blocks. The design of seawalls could easily be improved to offer a better habitat for survival and maintenance of species such as chitons by incorporating crevices and similar features. In an increasingly urbanized world, understanding how to improve the value as habitat of man-made structures will be essential for conserving biodiversity.