Mrs Emily McLaren1, Dr Brigitte Sommer, Professor Maria Byrne
1The University Of Sydney, Camperdown, Australia
The biogeographic transition zone on the southeast coast of Australia is characterised by dynamic and mixed ecological communities. The composition of these communities is mediated by the East Australian Current (EAC), a western boundary current that flows poleward ~50km offshore from the coral sea, creating a gradient from tropical to temperate waters. Sea urchins are important herbivores, impacting the ecological dynamics of habitat formers like coral and kelp. We determined the population size structures and densities of four prolific sea urchin species (Centrostephanus rodgersii, Tripneustes kermadecensis, Diadema savignyi and Phyllacanthus parvispinus) from 2010 to 2019 spanning 28.196 – 30.948S. Centrostephanus rodgersii was the largest and most stable population of urchin across the decade, averaging densities from 3.2m-2 in 2010 to 2.92 m-2 in 2019 with no indications of recruitment. Conversely, the population of T. kermadecensis was marked by a dramatic decline in population density from 0.36m-2 in 2010 to 0.025m-2 in 2016, and displayed no signals of recruitment or recovery in 2019. Diadema savignyi displayed a similar pattern; densities decreased significantly from 0.025m-2 in 2010, to 0.018m-2 in 2016, while P. parvispinus showed no change in size, structure, or density over time. We also found a strong positive relationship between latitude and the density of all species; density increased significantly from ~0 m-2 at low latitudes to ~6m-2 at high latitudes. These findings highlight the contrasting population dynamics of different sea urchin species in the biogeographic transition zone of southeast Australia, and the need for long-term studies to understand the demography of these important herbivores.
Presentation Slides – Emily Mclaren
Biography:
I am a PhD candidate at the University of Sydney interested in the biology and ecology of echinoderms in the biogographic transiton zone of NSW.
