Scales of similarity in soft sediment epibenthic assemblages: implications for marine protected area design

Remote videography was used to investigate relationships between biological similarity and distance in Moreton Bay, Australia at site (1 km) and local (10 km) scales, and for separate biotic groups. Numerical analysis using Mantels tests to compare distance and similarity matrices showed that at both scales there was a negative correlation between similarity and distance, in that sites further apart were less similar than sites close together. The relationship, although significant (p <0.001), was quite weak (R²=5%) at the site-scale, with no significant (ANOVA with Tukeys pairwise comparisons, p >0.05) decline in similarity up to distances of 2.1–2.6 km. At the local-scale, between-site similarity was high (mean Bray-Curtis similarity >30% for 4th root transformed data) at scales of 10 km or less, and declined markedly with increasing distance. Scales of similarity for different broad taxonomic and functional groups within Moreton Bay were broadly consistent between groups and with the complete dataset. There was evidence of patchiness in the distributions of seagrass and anthozoans at scales less than 16 km. In other biotic groups there was an essentially monotonic decline in similarity with distance. The study showed that the spatial classification approach to habitat mapping is valid in this case, and that site spacing of less than 10 km is necessary to capture important components of biological similarity. Site spacing of less than 2.5 km does not appear to be warranted to capture additional components of biological similarity at the scales studied.Communicated by G.F. Humphrey, Sydney