Accelerated reef ecosystem collapse following population explosion of a pivotal range-extender
Dr Scott Ling1, Dr John Keane1
1Institute For Marine & Antarctic Studies, Hobart, Australia
This presentation will detail the results of a recent coast-wide resurvey of the range-extending sea urchin (Centrostephanus rodgersii) and its’ overgrazing impact on Tasmanian reefs relative to baselines established in 2001. Since the first positive identification of an individual C. rodgersii on the coast of Tasmania in 1978, the population has now reached ~20 million individuals. Diver re-survey of baseline sites in eastern Tasmania revealed an increase in average density from 1,495 to 2,623 urchins per hectare (an increase of 1.75 times) over the past 15 years. The coverage of barren grounds, as assessed using towed underwater video, has increased from 3.4% to 15.2% of eastern Tasmanian reefs (an increase of 4.5 times). Increases in both density of C. rodgersii and the accelerated increase in collapse of kelp beds were both greatest on boulder-dominated reef between 18 to 30 m depth. Re-confirming baseline findings, commercial quantities of lucrative abalone and rock lobster are absent from the impoverished barren grounds. Management of the ongoing collapse of kelp beds must be proactive given the observed hysteresis of overgrazing, i.e. ‘an ounce of prevention is demonstrably worth a ton of cure’. Importantly, reefs approaching the critical tipping-point of overgrazing have been identified and the race for tactical intervention is now on before it becomes too late. Conversely, for reefs already collapsed to extensive barren grounds, massive upscaling of yet to be trialed mitigation efforts will be required if natural kelp bed cover, productivity and the broader ecosystem is to be recoverable.
Biography:
Dr Scott Ling is a marine ecologist from Tasmania (Australia) who spent much of his youth as an avid fisherman and naturalist on the island’s east coast. Over his lifetime he has directly observed, documented and revealed the mechanisms of major ecological change on this temperate reef system – which has been driven by the cascading interplay of ecological overfishing and sustained ocean warming.
Scott’s work as an sub-tidal experimental field ecologist has broadly focused on determining the effects of human stressors on reef ecosystems including climate change, fishing, pollution and the introduction of invasive species. Central to his interests is the interaction of these multiple human-stressors and ultimately the dynamics of ecosystem collapse and recovery and/ or the emergence of novel ‘futuristic’ regimes.
Today Scott will reveal further understanding of the unfolding ecological crisis that has occurred in Tasmania due to species-redistribution in a hot-spot of marine climate change.