Patterns in sponge (Porifera) assemblages on temperate coastal reefs off Sydney, Australia

Abstract

Pattern and process in deep-water macrobenthic assemblages have largely been inferred from the study of such assemblages on shaded artificial structures in relatively shallow water. This paper examines patterns in the diversity and abundance of sponges to a depth of 50 m on coastal reefs off Sydney, Australia. Photo-quadrats were used to provide estimates of the species richness and percentage cover of sponges on three reefs. Sponge morphotype (i.e. encrusting or massive) was also recorded. Within-reef variation was examined by nesting three sites within each reef at each of three depths; replicate photo-quadrats (0.45 m², n = 5) were taken at each site. In addition, a remotely operated vehicle was used to collect voucher specimens. Over 50 species of sponge were identified, many of which have never been described. In general, sponge richness increased with depth, as did the number of erect or massive forms. In contrast, cover decreased with depth, particularly for encrusting sponges. Univariate and multivariate analyses revealed considerable small-scale spatial and temporal variation in sponge distribution and abundance. A significant positive relationship between richness and cover was also apparent. In general, there were greater temporal changes in the patterns of abundance for the shallow reef assemblages at 20 m, relative to those at 30 m and 50 m.