In contrast, newly introduced species probably enhance ecosystem functioning via identity effects where the influence of the invader is much greater than expected based on its relative abundance in the assemblage (Ruesink et al. 2006). Also, we expect high-diversity assemblages to enhance the predictability of respiration and light-use efficiency response of assemblages. Macroalgal assemblages (64 cm2) were created from natural boulders Angiogenesis inhibitor collected at Praia Norte (Viana do Castelo, Portugal; 41°41′ 48″ N, 08°51′ 11″ W; see Arenas et al. 2009 for a full description of the collection

site and boulder type). Using synthetic assemblages of macroalgae, we manipulated functional diversity by creating assemblages with different numbers of functional groups. Macroalgae were grouped into functional groups following Arenas et al. (2006), and three morpho-functional groups were selected: (a) encrusting coralline species, e.g., Lithophyllum incrustans; (b) turf-forming species from the genus Corallina and (c) subcanopy species, e.g., Chondrus crispus

and Mastocarpus stellatus. selleck compound These species are common in macroalgal assemblages from intertidal rock pools in northern Portugal (Arenas et al. 2009). Synthetic assemblages consisted of 12 × 17 × 1 cm PVC plates with 16 pieces of rock surrounded by 1 cm PVC pieces for support and protection. Boulders were cut into 2 × 2 × 2 cm rock pieces and were attached to PVC plates using fast setting underwater cement and screws. Individual rock pieces represented one functional group characterized by a percent cover greater than 50%, or in the case of subcanopy species, the presence of one or more adult individuals. A total of 60 plates were built: 12 plates of only bare-rock, 36 plates with only one functional group (12 plates per group), and 12 plates with three functional groups. In the last case, the spatial distribution of the three functional groups within plates was random. Synthetic macroalgal assemblages were then subjected to an artificial invasion by the brown canopy-forming macroalga S. muticum. This was accomplished

by collecting fertile individuals of S. muticum with receptacles bearing exuded propagules from the field MG-132 cost and transporting them to the laboratory where they were rinsed with freshwater to eliminate grazers. Fertile S. muticum was then placed floating over the assemblages in tanks of ~300 L of seawater. To assure different biomass of the invader in the final assemblage composition, propagule pressure was manipulated by suspending a different biomass of fertile individuals of S. muticum over the macroalgal assemblages (High density ≈ 25 kg; Low density ≈ 13 kg; Control – none). Control assemblages were used to assess natural assemblage composition in the field. A total of 20 macroalgal assemblages of combined functional diversity treatments (n = 4) were randomly assigned to each propagule pressure treatment (i.e.