Latitudinal variation in patterns of colonisation of cryptic calcareous marine organisms

Few studies of fouling communities have directly compared colonisation patterns over wide geographical scales in similar community types. In this study, the recruitment and early growth of calcareous cryptic fouling organisms were examined on settlement panels at 2 tropical and 2 subtropical locations at varying distances from the mainland in eastern Australia. Species diversity and cover on the settlement panels after 6 mo were higher at the subtropical inshore site than at any of the offshore or tropical sites. Classification of the sites by multivariate cluster analysis and ordination showed clear distinctions between inshore and offshore sites, while sites separated by approximately 14 degrees of latitude were less clearly distinguished. Inshore/offshore variation in the physical environment, especially turbidity and eutrophication, and the effects of longshore currents in the regions are possible explanations for these patterns. There was a significantly higher weight of calcified material at the subtropical inshore site than at the other 3 sites, attributable to higher cover of both bryozoans and barnacles; these taxa are likely to make a significant contribution to community calcification rates in subtropical coral communities. Competition for space with encrusting species is proposed as a potential mechanism limiting coral recruitment in coastal subtropical eastern Australia.