Does epibiosis facilitate the invasion success of marine benthic invertebrates?

The theoretical understanding of invasion success is linked to a variety of drivers including enemy release, facilitation, and competitive ability. Within the marine environment, any bare solid substrate is quickly colonised making “free” space for settlement a limited resource. Consequently, the living surfaces of many species are subjected to the constant threat from overgrowth and/or epibiosis. Epibiosis presents a mechanism that eliminates the need to find bare space while increasing overgrowth success by settling on competitors. The ability of non-indigenous species (NIS) to see and use more types of space as “free” space may confer a competitive advantage to these species and requires greater investigation. As such the basis of this thesis is to explore epibiosis in NIS and native marine community assemblages. Theoretically, native species have co-evolved defence mechanisms against epibiosis, whereas they are naïve against epibiosis by NIS (and vice versa). Epibiosis is common, however a systematic review revealed a lack of information comparing native and NIS interactions, especially where the outcome of epibiosis was mortality. The pattern of epibiosis was examined within naturally assembled communities to understand native:NIS epibiotic interactions. Recruitment phenology was contrasted with settlement preferences and epibiotic pressures of both native and introduced species in communities of varying ages in northern Tasmania. Native species were found to have more interactions than expected with natives than with NIS. In contrast, NIS demonstrated no significant preferences between NIS, native and bare substrates: Thus, they see all space as available, compared to native species that show a preference for type of space to settle upon. Building on this, ex situ manipulative experiments were used to examine pairwise interactions controlling for propagule pressure, propagule arrival time and environmental factors hypothesised in the literature to influence recruitment and subsequent settlement success. The experimental outcomes demonstrate that native species experience greater epibiotic settlement by both native and NIS, whereas NIS were relatively free of epibiotic load. The multiple lines of evidence used in this dissertation have illustrated fundamental differences between marine native species and marine NIS, reinforcing the view that NIS are opportunistic settlers using a greater suite of substrates as available space than native species. Moreover, given that epibiosis generally comes at a cost to basibionts, a reduced epibiotic load on NIS compared to native competitors, infers a competitive advantage to NIS