Factors Influencing the Settling of the Principal Marine Fouling Organisms in Sydney Harbour

Abstract

The macrofouling organisms most commonly encountered during intermittent plate exposures in Sydney Harbour over 10 years (1947-57) comprised a barnacle (mainly Balanus (Balanus) amphitrite var. cirratus Darwin), several serpulids and bryozoans (Hydroides norvegica Gunnerus, Spirorbis sp.; Bugula neritina L., Bugula avicularia L., Watersipora cucullata (Busk)), a mussel (Mytilus planulatus Lamarck), and an oyster (Crassostrea commercialis Iredale & Roughley). With the exception of the mussel, settlement was heaviest during the summer months. Surface water temperatures averaged from about 15°C in midwinter to 24º in midsummer and were over 20°C for 6 months of the year. Two cases where freshwater dilution apparently affected biological populations are recorded. The effects of colour, surface texture, depth, aspect, and horizontal distance on settling were investigated using paired series of plates. The results were treated statistically and compared with those reported by others. It is suggested that during antifouling raft tests at this locality the control plates for any group of experimental plates need to be placed at the same site, same depth, facing the same way, and 5-10 ft apart horizontally. Providing the most common macrofouling organisma settling at the station were considered as a whole, this arrangement seemed to give a reasonably accurate assessment of their settling intensity at the test site.