Correlates of Environmental Variables with Patterns in the Distribution and Abundance of Two Anemonefishes (Pomacentridae: Amphiprion) on an Eastern Australian Sub-tropical Reef System

Abstract

The relationship between characteristics of the reef environment and variations in the distribution and abundance of the anemonefishes Amphiprion akindynos and A. latezonatus was investigated at North Solitary Island, a sub-tropical rocky reef system on the east coast of Australia. During the summers of 1994 and 1995, fish densities and host sea-anemone cover were assessed on replicate 25 m transects at sites where host sea-anemones form semi-contiguous mats throughout the 6–21 m depth range. Multiple regression analyses indicated that environmental variables accounted for 65–71% and 61–80% of the variations in the number of A. akindynos and A. latezonatus among-sites, respectively. Among-habitat comparisons indicated that A. latezonatus densities were positively correlated with depth (r=0.45–0.90), whereas A. akindynos showed no consistent depth-related abundance patterns. Poor correlations (p>0.05) between the densities of each species on transect lines suggested that present-day competition was unlikely to determine the preference of A. latezonatus for deeper depths. Correlations between host sea-anemone cover and fish densities at the within-habitat (depth) scale were comparatively stronger than correlations at among-habitats in both species. These results suggest that among-habitat comparisons can confound finer scale fish-habitat associations within habitat (depth) zones. Evidence suggests that while sea-anemone cover does, to an extent, regulate the local ecology of anemonefishes, other factors are also likely to interact to limit their densities.