Data from: Habitat formation prevails over predation in influencing fouling communities

Coastal human-made structures, such as marinas and harbours, are expanding
worldwide. Species assemblages described from these artificial habitats
are novel relative to natural reefs, particularly in terms of the
abundance of non-indigenous species (NIS). Although these fouling
assemblages are clearly distinctive, the ecosystem functioning and species
interactions taking place there are little understood. For instance, large
predators may influence the fouling community development either directly
(feeding on sessile fauna) or indirectly (feeding on small predators
associated with these assemblages). In addition, by providing refuges,
habitat complexity may modify the outcome of species interactions and the
extent of biotic resistance (e.g. by increasing the abundance of
niche-specific competitors and predators of NIS). Using experimental
settlement panels deployed in the field for 2.5 months, we tested the
influence of predation (i.e. caging experiment), artificial structural
complexity (i.e. mimics of turf-forming species), and their interactions
(i.e. refuge effects) on the development of sessile and mobile fauna in
two marinas. In addition, we tested the role of biotic complexity –
arising from the habitat-forming species that grew on the panels during
the trial – on the richness and abundance of mobile fauna. The effect of
predation and artificial habitat complexity was negligible, regardless of
assemblage status (i.e. native, cryptogenic and non-indigenous).
Conversely, habitat-forming species and associated epibionts, responsible
for biotic complexity, had a significant effect on mobile invertebrates
(richness, abundance and community structure). In particular, the richness
and abundance of mobile NIS were positively affected by biotic complexity,
with site-dependent relationships. Altogether, our results indicate that
biotic complexity prevails over artificial habitat complexity in
determining the distribution of mobile species under low predation
pressure. Facilitation of native and non-native species thus seems to act
upon diversity and community development: this process deserves further
consideration in models of biotic resistance to invasion in urban marine
habitats.