Meeting Abstract
Invasive species commonly alter community structure within invaded habitats. We investigated the effects of an invasive red alga, Gracilaria vermiculophylla, on epifaunal and infaunal communities in the coastal bays of Virginia. Native to the Western Pacific, G. vermiculophylla has represented 90% or more of all macroalgal biomass in these habitats since at least 2003. Epifaunal communities on G. vermiculophylla show lower taxon richness and total abundance compared to the most abundant native alga, Ulva. Yet, at the same time, infaunal communities under mats of G. vermiculophylla show greater species diversity compared to unvegetated areas, possibly because G. vermiculophylla offers refuge from predation. This may suggest that epifaunal and infaunal communities respond differently to the invasion of G. vermiculophylla. Worryingly, G. vermiculophylla has displayed the ability to seasonally form thick, continuous mats in these habitats, which have historically lacked algal mats. Within these seasonal mats, the native polychaete Diopatra cuprea has exhibited elevated mortality rates, possibly associated with a reduced oxic layer. This suggests that G. vermiculophylla may initially facilitate infaunal communities, but extensive mat formation may negatively impact infauna. Understanding (i) how widespread G. vermiculophylla mats are becoming, (ii) what underlying factors cause the differences in epifaunal and infaunal community responses to G. vermiculophylla, and (iii) the causal link (if any) between G. vermiculophylla and D. cuprea mortality are important questions for future work.
