Structural complexity of macroalgae influences epifaunal assemblages associated with native and invasive species

• Epifaunal assemblages associated with native and invasive macroalgae.
• Macroalga complexity shaping epifaunal assemblages.
• Good correlation of macroalga structural complexity with epifaunal assemblages.
• Invasive macroalga differed in structural complexity from native species.
• Invasive macroalga harboured distinct epifaunal assemblages to native species.

Habitat structure is a primary factor determining the organism distribution. Here, two native and one invasive macroalgal species, apparently different in morphology, were sampled to examine the effects of habitat complexity on the abundance (N), taxon richness (S) and structure of their associated epifaunal assemblages by means of univariate and multivariate techniques. Dry weight and fractal measures were used as proxies of habitat quantity and habitat architecture respectively. Results revealed significant differences in the complexity and in N, S and the structure of epifaunal assemblages among macroalgae and significant correlations between complexity and epifauna. Results suggested that, beside the effect of habitat quantity, the habitat architecture also seems to play a significant role in shaping epifaunal assemblages. Complexity of the studied invasive macroalga significantly differed from that of native species and hosted also different assemblages. Therefore, our findings suggest that invasive macroalgae, if structurally different from native species, induce changes in the associated epifauna.