Ramus, A. P., Silliman, B. R., Thomsen, M. S., & Long, Z. T. (2017). An invasive foundation species enhances multifunctionality in a coastal ecosystem. Proceedings of the National Academy of Sciences, 114(32), 8580–8585.
The accelerating loss of coastal foundation species impairs the delivery of vital ecosystem services on which nearly half the human population depends. Recognizing how loss of habitat-forming species such as seagrasses and oysters can be offset is therefore essential. This paper demonstrates that in areas where native foundation species are absent, nonnative habitat formers can amplify the production of diverse ecosystem functions that underpin provisioning of services to humans, such as food production. Our findings suggest that in areas where native foundation species have been lost, invasive habitat formers may be considered as a tool to enhance multiple ecosystem functions.
While invasive species often threaten biodiversity and human well-being, their potential to enhance functioning by offsetting the loss of native habitat has rarely been considered. We manipulated the abundance of the nonnative, habitat-forming seaweed Gracilaria vermiculophylla in large plots (25 m2) on southeastern US intertidal landscapes to assess impacts on multiple ecosystem functions underlying coastal ecosystem services. We document that in the absence of native habitat formers, this invasion has an overall positive, density-dependent impact across a diverse set of ecosystem processes (e.g., abundance and richness of nursery taxa, flow attenuation). Manipulation of invader abundance revealed both thresholds and saturations in the provisioning of ecosystem functions. Taken together, these findings call into question the focus of traditional invasion research and management that assumes negative effects of nonnatives, and emphasize the need to consider context-dependence and integrative measurements when assessing the impact of an invader, including density dependence, multifunctionality, and the status of native habitat formers. This work supports discussion of the idea that where native foundation species have been lost, invasive habitat formers may be considered as sources of valuable ecosystem functions.