Mr Tristan Graham1, Dr Rebecca Morris1, Dr Elisabeth Strain1,2, Dr Paul Carnell3, Dr Fletcher Warren-Myers4, Prof Stephen Swearer1
1National Centre for Coasts and Climate (NCCC), School of BioSciences, University of Melbourne, Parkville, Australia, 2Institute for Marine and Antarctic Sciences (IMAS), University of Tasmania, Hobart, Australia, 3School of Live and Environmental Science, Centre for Integrative Ecology, Deakin University, Burwood, Australia, 4School of BioSciences, University of Melbourne, Parkville, Australia
Overgrazing by urchins is a key driver of kelp loss on temperate rocky reefs and results in the formation of alternative stable states with poorer ecological service provision. Understanding the status and relationships between reef state (vegetated vs. bare) and urchins is essential for informing targeted management actions such as urchin harvesting or culling. We examined the current distribution of macroalgal cover (including kelp) and reef state, urchin density, and roe quality in Port Phillip Bay, Australia, and compared these metrics to a baseline study from 2002. We also explored the potential for environmental variables (i.e., bathymetric derivatives, lidar reflectance, and spectral wave model outputs) to predict reef state. Clear differences were observed in reef state among regions, with all subsites near the bay opening identified as vegetated. Across the entire bay only a single subsite was dominated by kelp, and more than half the subsites were bare. Urchin density varied greatly by region, consistent with the previous survey, however, densities had increased since that survey, most notably in the north of the bay. The relationship between reef state and urchin density was consistent with hysteresis. These findings suggest reefs within Port Phillip Bay are mostly in a degraded state and are subject to increasing grazing pressure from urchins. A flow chart for reef management is presented, taking into consideration reef state, urchin density, and roe quality to determine which interventions are most likely to provide the greatest benefit.
Presentation Slides – Tristan Graham
Biography:
Tristan is a PhD candidate at the National Centre for Coasts and Climate (NCCC) at the University of Melbourne. His thesis is focuses on the restoration of native kelp Ecklonia radiata with a number of experiments carried out in Port Phillip Bay, Victoria. He explores the use of artificial kelp mimics, transplanting of juvenile kelp, the natural recruitment of kelp on rocky reefs, and the relationship between urchins and reef state. The latter work is presented at this symposium.
