Species invasion and the ecology of rocky subtidal communities

As ecologists and students of the ocean, we have become increasingly aware that coastal ecosystems have been profoundly altered, relative to their naturally evolved state, by the activity of humans. Among the most urgent concerns is the introduction of new species into marine communities, that then expand rapidly to replace native species. These human-mediated biological invasions can result in pronounced changes in habitat and ecosystem structure and function, often with dire ecologic and economic consequences. The community of seaweeds, invertebrates and fish that inhabit the rocky seabed of Atlantic Canada provides a striking example of a heavily impacted ecosystem. Historically, this community has alternated between two ecological states dependent on the abundance of a key herbivore, the sea urchin: kelp beds where urchins are rare and barrens where urchins dominate the seascape and seaweeds are absent. Cyclical alternations between these states are driven by sporadic outbreaks of a disease that kills urchins. Amid this backdrop of perturbation and instability, synergistic interactions between recently introduced species have shifted the ecosystem towards a novel community state dominated by an invasive Asian seaweed. The objective of our research is to understand the biological and environmental processes that regulate transitions between ecosystem states or determine their persistence. In particular, we will investigate the effects of invasive species on ecosystem structure and function using a range of experimental and observational approaches to examine species interactions, construct food webs, and develop predictive mathematical models that are needed for intelligent management of this increasingly perturbed ecosystem.