Supplement 1 (A) PERMANOVA results from the analysis of differences between months and species at Aramoana in February/March 2012 and December 2012 (Table S1), pair-wise test among seaweed species (Table S2), and MDS plots of ordination of epifaunal composition by time (Fig. S1) and seaweed species (Fig. S2)

The role of dominant species is of central importance in ecology. Such species play a key role in ecosystem structure, stability and function, regulating resource allocation across trophic levels and overall ecosystem productivity. Although ecological interactions between dominant and subordinate species are often considered to influence the latter negatively, the presence of dominant species can also be beneficial. These species commonly act as ecosystem engineers and enhance biodiversity by creating habitat for other species. Along rocky coastlines, dominant species are often sessile suspension-feeding organisms that can monopolize all available substrata. This is particularly noticeable in intertidal and shallow subtidal habitats where the number of species that achieve ecological dominance is limited. Here, we review the ecological and evolutionary mechanisms that facilitate dominance along rocky coastlines. We then focus on a prominent example, the members of the Pyura stolonifera species complex (Tunicata), which are an emerging model system for studying ecological dominance. These ascidians achieve the highest biomass levels ever reported in rocky intertidal habitats and, when invasive, can fundamentally transform entire ecosystems. Finally, we discuss conservation implications and conclude with directions for future research.

Food webs on sandy beaches rely heavily on spatial subsidies of macroalgae and other detritus. Invasive macroalgal species are modifying many ecosystems worldwide, so the potential exists for them to alter the quantity and quality of food available to sandy beach consumers. We evaluated the suitability of the invasive kelp Undaria pinnatifida as a food for the talitrid amphipod Bellorchestia quoyana, an abundant consumer on sandy beaches in southern New Zealand. U. pinnatifida had similar gross nutritional and biomechanical properties to the three native macroalgal species (the kelps Macrocystis pyrifera and Durvillaea antarctica, and the green Ulva spp.). B. quoyana consumed U. pinnatifida at similar or higher rates than the native kelps in laboratory feeding assays (choice and no-choice assays with fresh tissues, and choice assays with tissue reconstituted into agar foods to remove structural properties). Our results indicate that U. pinnatifida is a usable alternative food source for B. quoyana and could, therefore, contribute to the local sandy beach food web. Understanding the role that invasive macroalgae play as a food source for beach consumers is essential to better comprehend how they may affect these subsidy-dependent ecosystems

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