Recruitment of damselfishes in One Tree Island lagoon: persistent interannual spatial patterns

The spatial and temporal patterns of distribution of new settlers of 23 species of damselfish (Pomacentridae) within One Tree Island lagoon, southern Great Barrier Reef (GBR) were measured for 3 summers to assess the persistence of spatial patterns of recruitment. Overall recruitment was 3 times higher in 1993/1994 than 1994/1995, and 1.5 times higher than 1999. In general, recruitment decreased towards the lagoon centre, even though habitat availability was not lower there on average, suggesting that most fish settled at outer sites as they were advected from adjacent waters. There was also great variation in numbers of recruits among outer sites. Patterns of recruitment to continuous reef and patch reef habitats also differed among species, suggesting habitat selection at this broad level. For example, Pomacentrus nagasakiensis was primarily found on patch reefs, while P. moluccensis was largely found on continuous reef. One site (Shark Alley) received the highest number of recruits of most species during the study, and this pattern has been observed in studies since 1975. Despite interannual variability in abundance of potential settlers and differences in the habitat preferences of some species, therefore, some sites on the reef can receive relatively high numbers of settlers over decadal time scales. This consistency of spatial pattern may be due to local topography and oceanography at Shark Alley, which appear to favour the input of potential settlers. The availability of live coral may also be important, but species which showed no preferences for live cover also recruited at high levels at this site. The attributes of Shark Alley were compared with those at other sites. Overall, sites that clustered on the basis of oceanographic and habitat features also had similar recruitment, suggesting that these features may be useful in predicting recruitment hotspots on reefs elsewhere.