Standard Presentation and Poster Presentation Australian Marine Sciences Association Annual Meeting 2023

Urchin diet and rates of predation on tethered urchins are not determined by macroalgae cover (#232)

Jeremy Day 1
  1. School of Environmental and Life Sciences, University Of Newcastle, Newcastle, NSW, Australia

Controlling macroalgal grazing by sea urchins has long been of interest in marine ecology. When urchins overgraze macroalgae, they are thought to become impoverished due to their main food (macroalgae) no longer being abundant. An impoverished state for urchins is reflected by low gonad yield. Additionally, macroalgal forests are considered to harbour an abundance of urchin predators that provide protection of these habitats from overgrazing. Theoretically, this means that urchins in macroalgal-limited habitats provide low roe-yields and experience low predation, while urchins in dense macroalgae have higher roe-yields and experience higher predation because predators are more abundant. We tested this by (1) dissecting Centrostephanus rodgersii collected in barrens and macroalgae habitats within five locations (n=100 urchins) for gut contents and gonad analysis, (2) undertaking tethering experiments in barrens-mosaic and macroalgal habitats with C. rodgersii and Heliocidaris erythrogramma (n=96 urchins) within four locations along the New South Wales coast. C. rodgersii in both habitats had a diverse diet and comparable roe yield, and there was no habitat difference in predation of tethered urchins. This suggests that urchins are not always impoverished in the absence of macroalgae and that macroalgal cover does not translate to higher rates of predation on tethered urchins.