Factors driving the biogeographic distribution of two temperate Australian damselfishes and ramifications for range shifts

The distribution and abundance of marine organisms is determined by interactions among numerous abiotic and biotic factors that operate across multiple spatial scales. This study focused on 2 endemic temperate damselfishes Parma microlepis and P. unifasciata, which have a similar ecology but only partially overlapping (~3° of latitude) biogeographical and depth ranges. The synergistic effects of temperature, competition and habitat use on patterns of abundance, distribution and growth were investigated using a combination of mensurative and manipulative field and laboratory experiments. Evidence suggests that the current ranges of both species are driven largely by latitudinal and depth variations in habitat types and not by thermal regimes. P. microlepis was shown to be a slower-growing, long-lived species (to 37 yr) that appears to be specialised in using urchin-grazed barrens. In contrast, P. unifasciata is a shorter-lived species (to 12 yr) and more of a habitat generalist. Where the ranges of these 2 species overlap, competitive interactions appear to drive patterns of habitat use, with P. microlepis potentially excluding P. unifasciata from urchin-grazed barrens habitat. Mesocosm laboratory experiments indicated that the outcome of competitive interactions between these 2 species is temperature-dependent, with P. microlepis dominance increasing at higher temperatures. This study clarifies the important role of habitat in determining latitudinal ranges of these 2 species. It also highlights the need to consider temperature-dependent behavioural interactions to properly understand future potential shifts in species ranges that may result from global climate change.