The macrofaunal community of Ecklonia radiata holdfasts: Variation associated with sediment regime,sponge cover and depth

Abstract The relationship among the Ecklonia radiata holdfast macrofaunal community, sediment content and sponge cover was evaluated for data collected over a four year period at Coffs Harbour, mid-north coast, New South Wales. While several taxa demonstrated significant relationships with these factors, the correlations explained a maximum of 24% of the variation in the data and explanatory power was consequently low. Differences in the composition of the holdfast community were also evaluated at two depths (2m and 6m) at two sites in a mensurative field experiment conducted in summer and winter 1991. The results of both ANOVA and non-parametric multivariate statistical analyses (MDS, ANOSIM, SIMPER) indicated that there were consistent, significant differences between depths over the two sample times. Although some common species demonstrated significant associations with one depth, small differences in the abundance of a large number of species were primarily responsible for the overall differences in community structure between depths. Sediment content and holdfast age were both significantly greater in samples collected from 6 m which may account for some of the depth-related faunistic differences. However, the overall differences between depths are probably related to unmeasured factors such as turbulence due to wave action and holdfast morphology which covary with depth. The results highlight the enormous variability associated with the Ecklonia radiata holdfast macrofaunal community and the consequent necessity to consider as many factors as possible in comparative studies of community structure.