Mechanisms of stability of urchin-dominated barrens in southeastern Newfoundland

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Two central questions in ecology are (1) how can assemblages of different species occur side by side, as distinct community states; and (2) what factors and processes trigger transitions from one state to another (phase shifts) and stabilize each state. The shallow rocky subtidal zone in southeastern Newfoundland (SEN) exhibits two community states presumably dependent on the abundance of a key herbivore, the green sea urchin: kelp beds where urchins are rare; and barrens where urchins dominate and only a few grazing-resistant seaweeds grow. Contrary to many regions in eastern Canada, barrens in SEN predominate and appear to be stable at decadal scales, with infrequent recolonization by kelp. Limited understanding of interactions between biological and environmental factors that govern phase shifts, and the stability of the barrens and kelp states in SEN, limits our predictive capacity as scientists and managers. Consequences of phase shifts (or lack thereof) for commercial species of finfish, urchins, and lobsters, which use kelp beds as habitat, food, and nursery areas, and could form the basis of lucrative fisheries as they do in other regions of eastern Canada, are unknown. My proposed research is aimed at understanding interactions between biological and environmental factors and processes that govern phase shifts and the apparent stability of the barrens state in SEN, while developing models that aid in predicting changes in species abundance and phase shifts under varying environmental conditions. My students and I will: (1) quantify the dynamics of destructive urchin grazing and thresholds for phase shifts, (2) measure effects of two grazing-resistant seaweeds on the ability of community states to return to equilibrium, and (3) model phase shifts and explore effects of ocean warming and acidification on strength of kelp-urchin interactions. We will use a diverse blend of complementary methods from observational studies of dynamic processes, to rigorous hypothesis testing in field and laboratory settings, to mathematical modeling. Our studies will yield one of the most detailed and comprehensive investigations of the causes and consequences of stability and productivity in cold marine benthic ecosystems. They will be transformative with respect to our understanding of the ecology of cold-temperate reefs in the face of a changing ocean climate. The proposed work combines discovery-driven and applied research that will contribute to understanding and anticipating ecosystem changes in a largely unstudied and increasingly perturbed region of Canada. It will create a productive research training environment for many graduate and undergraduate students, and provide government and industry stakeholders and scientists with novel data and predictive tools to support policy decisions.