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Not so fast: promoting invasive species to enhance multifunctionality in a native ecosystem requires strong(er) scrutiny

Sotka, E. E., Byers, J. E.
Biological invasions 2019 v.21 no.1 pp. 19-25
Gracilaria, ecological invasion, ecosystem engineers, ecosystems, estuaries, field experimentation, habitats, invasive species, landscapes, macroalgae, North Carolina
Since at least the 1980s, ecologists have argued that restoring ecosystem functioning in highly degraded areas is the “acid test” for ecological understanding (Bradshaw 1987). Ecosystem engineers and foundational species are often considered pivotal in the restoration of degraded areas (Suding et al. 2004; Byers et al. 2006), as by definition, they “engineer” biotic structure that serves as habitat. For decades, ecologists have debated when and where we may promote non-native engineers instead of native engineers for restoration. Entering into this long-standing debate, Ramus et al. (2017) reported the results from a field experiment in North Carolina with the Japanese seaweed Gracilaria vermiculophylla and concluded that this and other invasive engineering species should more frequently be considered as candidate species to restore ecosystem function of degraded habitats. Here, we argue that it is premature to suggest we understand the effects of the non-native Gracilaria on the native estuarine system well enough to promote this invader as a lynchpin of restoration efforts. Our argument is fourfold: (1) The net ecosystem effects of Gracilaria remain unknown because Ramus et al. overstated or did not examine the ability of the invasive seaweed to perform key services. (2) The conclusion of enhanced multifunctionality is highly dependent on several subjective, poorly justified decisions regarding the treatment of variables. (3) Contrary to the claim by Ramus et al., the mudflats where Gracilaria resides are not a barren sedimentary landscape without its presence. Finally, (4) Ramus et al. rely on a well-worn “strawman” approach that ignores decades of ecological research. No doubt, there are systems in which non-native engineers benefit local ecosystem functioning, but any recommendation to use a non-native in such a capacity should require careful and thorough evaluation.