Abstract:  A dramatic, undesirable and persistent phase-shift among marine landscapes is observable on temperate rocky reefs as a result of sea urchin overgrazing. In this presentation, I will detail the key findings from over a decade of research on the ongoing threat of urchin overgrazing in eastern Tasmania – a threat driven by the interaction of climate change and ecological overfishing of urchin predators. Importantly, urchin overgrazing on this coastline demonstrates a discontinuous ‘catastrophic’ phase-shift and I will present results from a range of field-surveys, plus small and large-scale experiments (utilizing no-take Marine Reserves plus translocations of large predators) to show that ‘an ounce of prevention is worth a ton of cure’ for managing urchin barrens in Tasmania.

Generality of this phase-shift dynamic will then be explored for urchin grazing systems on rocky reefs across the world by compiling available survey and experimental data. From this collaborative research effort, a globally-coherent pattern emerges with urchin overgrazing broadly defined as a catastrophic phase-shift with hysteresis effect of approx. 1 order of magnitude in urchin biomass between critical overgrazing versus kelp recovery thresholds.

Importantly, as demonstrated in Tasmania and elsewhere, human-derived stressors can act to erode resilience of productive kelp beds while strengthen resilience of impoverished urchin barrens, thus exacerbating the risk, spatial extent and irreversibility of an unwanted phase-shift for temperate reefs.

Biography: Dr. Scott Ling is a postdoctoral Research Associate in Marine Ecology working with Prof. Craig Johnson at the Institute for Marine & Antarctic Studies (IMAS), University of Tasmania where he also completed a BSc Hons (first-class) and PhD in Marine Ecology. His research experience spans a broad range of temperate marine ecological investigations with a strong focus on in situ sub-tidal surveys and experimental manipulations spanning > 1500 research dives over the past 15 years.  Much of his research has centred on investigating the effects of increasing, but ostensibly manageable, human stressors on temperate marine ecosystems such as fishing, climate change, increasing urbanisation and the introduction of invasive species. Central to his research interest is the identification of alternative ecosystem states and processes influencing shift to less desirable states, particularly those proving surprisingly difficult to reverse.