Perturbing a Marine Food Web: Consequences for Food Web Structure and Trivariate Patterns

It is widely understood that natural and human-induced global changes such as habitat destruction and fragmentation, pollution and global warming could have profound consequences for the biodiversity of ecological communities with an increasing risk of species extinctions and species invasions. Ecological network analyses provide a valuable framework within which to investigate impacts of climate and anthropogenic drivers of change. Even at small spatial scales, real food webs can be large and complex, describing networks of interacting species. Although significant progress has been made in recent years, understanding the mechanisms through which real systems persist in nature remains a significant challenge. Here, we describe a set of new marine benthic food webs and perturb them by suppressing the biomass of a highly connected predator, the spiny seastar, Marthasterias glacialis, The sub-systems of this food web were monitored over a twelve month period after the perturbation was applied. To identify any resulting effects, we combined topological and dynamical approaches by investigating changes in traditional univariate response variables, together with changes in bi- and trivariate food web patterns. We hypothesised that the loss of larger sized predators would have profound impacts on the entire community, however our results suggest that the suppression of M. glacialis, a highly connected predator in these systems has rather weak effects on the remaining community structure. Removing large individuals of this intermediate predator had unanticipated consequences, which may have led to confounding effects, and may explain how the communities remained stable in the face of this perturbation.