Engineering or food? mechanisms of facilitation by a habitat‐forming invasive seaweed

Abstract

Abstract. Nonnative species that form novel habitats strongly affect ecosystem processes. The effects of these ecosystem engineers can be both positive and negative but the mechanisms behind their effects are not well described. In this study we determined the relative importance of three main mechanisms by which invasive ecosystem engineers can facilitate native fauna. The engineer may provide new physical structure that reduces harsh abiotic conditions or gives refuge from predation (both engineering mechanisms), or provide a new profitable food resource (a trophic mechanism). The invasive seaweed Gracilaria vermiculophylla is a novel addition to estuarine intertidal mudflats of the southeastern United States. The epifaunal amphipod Gammarus mucronatus is up to 100 times more abundant on Gracilaria-invaded mudflats compared to uninvaded mudflats. Feeding assays, a survivorship experiment and stable isotope analysis demonstrated that Gammarus consumes little Gracilaria and cannot survive on Gracilaria alone. However, the structural engineering effects of Gracilaria greatly enhanced the survivorship of Gammarus in the presence of predators during high tide and when exposed to harsh abiotic conditions during low tide. Our results demonstrate that invasive ecosystem engineers can dramatically affect the distribution and abundance of native species by providing a novel protective structure.

Co-occurring morphologically distinct algae support a diverse associated fauna in the intertidal zone of Araçá Bay, Brazil

“…Turfs intricate canopy can retain water and ameliorate conditions during periods of air exposure (Bertness et al 1999), enhancing the survivorship of G. mucronatus during low tides (Wright et al 2014). During high tides, G. mucronatus on algal turf, similar to the studied here, were less prone to be detected by predators (Wright et al 2014). We believe that such algal attributes would work for most of the groups found on the algal turf in Araçá Bay, representing then a suitable refuge from biotic and abiotic pressures.…”

“…In shores from the Northwestern Atlantic Ocean, patches of Gracilaria vermiculophylla (Papenfuss 1967) are effective shelters for the amphipod Gammarus mucronatus (Say 1818) regarding both desiccation and predation risks (Wright et al 2014). Turfs intricate canopy can retain water and ameliorate conditions during periods of air exposure (Bertness et al 1999), enhancing the survivorship of G. mucronatus during low tides (Wright et al 2014). During high tides, G. mucronatus on algal turf, similar to the studied here, were less prone to be detected by predators (Wright et al 2014).…”

Beyond the border: Effects of an expanding algal habitat on the fauna of neighbouring habitats

“…Impacts on fauna are also evident due to the addition of habitat forming organisms e exotic species that have spread beyond their natural range (Crooks, 2002;Gribben et al, 2013;Wright and Gribben, 2008) and the range expansions of species native to a region (Carey et al, 2012;Sorte et al, 2010). These range expansions have mostly negative effects on co-occurring habitat formers due to competition for space and resources (Thomsen et al, 2014), but can benefit associated fauna due to the provision of higher quality food or refuge (e.g., Neira et al, 2005;Wright et al, 2014) or modifications of the abiotic environments (e.g., Gribben et al, 2013;Gribben and Wright, 2006). Whilst many of these studies describe differences in associated fauna among habitat-formers, or in contrast to unvegetated areas, few studies have considered how the spatial configuration or connectivity among habitats may contribute to observed faunal changes.…”

The influence of species, density, and diversity of macroalgal aggregations on microphytobenthic settlement

“…, Wright et al. ). As a result, changes in macroalgal communities may have a significant influence on the diversity and abundance of macroalgae‐associated organisms (Wilson et al.…”