The macrofaunal community of Ecklonia radiata holdfasts: Description of the faunal assemblage and variation associated with differences in holdfast volume

We describe the structure of the macrofaunal community inhabiting holdfasts of the kelp Ecklonia radiata sampled over a 4 year period on the mid-north coast of New South Wales, Australia. Both the physical and biological structures of the holdfast are described. Analyses focused on the relationships between holdfast volume and a range of summary community statistics (number of species, total abundance, total biomass) as well as the description of successional patterns with increasing holdfast size for the common species, higher taxa and trophic groups. The holdfast habitat supports a diverse faunal community that was dominated by polychaete worms and amphipod crustaceans, which together accounted for 78% of the total number of organisms sampled. Many of the species present have a much wider distribution in both intertidal and sublittoral marine habitats. Successional patterns within the holdfast were from a community dominated by small worms with a predominance of deposit-feeding strategies to one with a greater representation of amphipods with omnivorous feeding strategies. There was also a trend to increasing mean size of individuals with increasing holdfast size, which may be attributable to either growth of individuals over time or physical limitations (smaller spaces) in smaller holdfasts. The analysis of differences in spatial patterns for summary statistics of the community structure (species number, number of individuals, faunal density) suggested that small-scale variability (sites within locations) was more important than larger scale variability (between locations) and that the most easterly sites at each location supported the highest species count and number of individuals.