Marine Ecology Progress Series
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DOI: https://doi.org/10.3354/meps14952
copiedSize-specific predation on an overgrazing sea urchin reveals dominant role of large predatory fish
ABSTRACT:
Predators can play a key role in structuring ecological communities through top-down control, which may be influenced by size-specific relationships, abundance and richness of predatory guilds. In southeastern Australia, the diadematid sea urchin Centrostephanus rodgersii reaches high abundances, overgrazing kelp and maintaining extensive barrens. Despite its ecological importance, predator identity and size-specific nature of predation on this urchin remain incomplete. Here, we conducted urchin tethering assays with remote underwater videos to identify predators across a full size range of urchins (16-110 mm test diameter). We identified 5 predatory fishes from a total of 94 arrays and 61 predation events from 7 sites in the Sydney region, Australia. The eastern blue groper Achoerodus viridis (Labridae) accounted for 75% of events, and the other 4 predatory fishes accounted for the remainder, which involved small urchins only (≤25 mm test diameter). Overall, predation risk decreased as urchin size increased, while time to predation decreased with predator richness. Smaller urchins were more likely attacked from the aboral side, while larger urchins were flipped and attacked from the oral surface. A. viridis was the only predator observed consuming all urchin sizes. These findings show that predator size and richness are key factors determining the predation pressure on C. rodgersii. As many of these factors have been heavily impacted by historical overfishing, regulating urchin populations through effective predator management may be crucial for sustaining ecosystem services in kelp forests.
KEYWORDS
- Video (m770p083_VS1.mp4)
Video S1. Footage of all urchin predators captured throughout the tethering experiment.
- Video (m770p083_VS2.mp4)
Video S2. A female blue groper can be seen foraging around and completely ignoring the readily available urchin.
- Video (m770p083_VS3.mp4)
Video S3. A male blue groper maneuvers carefully to avoid longspined sea urchins while attacking the test by flipping the urchin over and going straight to an oral attack on the urchin's mouth.
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Jessica Nguyen (Corresponding Author)
- Centre for Marine Science and Innovation, School of Biological, Earth & Environmental Sciences, UNSW Sydney, Kensington, NSW 2052, Australia
Scott Ling (Co-author)
- Institute for Marine & Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia
John Keane (Co-author)
- Institute for Marine & Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, TAS 7001, Australia
Adriana Vergés (Co-author)
- Centre for Marine Science and Innovation, School of Biological, Earth & Environmental Sciences, UNSW Sydney, Kensington, NSW 2052, Australia
Handling Editor:
John N. Griffin, Swansea, UK
Reviewers:
J. E. Caselle and 2 anonymous referees
Acknowledgements:
We thank Clayton Mead, Derrick Cruz, Sam Nolan, Tess Moriarty, Millie Brown, Jade McEwan, Olivier Pastore, Tahnee Chandler, Emmerson Sweeting, Nicole Sroba, Cata Musrri, Mitch Brennan and Suzy Evans for assisting with fieldwork. We thank Eve Slavich at Stats Central UNSW who advised on the statistical analysis of this study. We thank Andrew Niccum, Sergio Torres and Emily Bastow for help housing urchins in the Sydney Institute for Marine Science aquaria. Urchins were collected and deployed under permit P13/0007-2.0, and the experiment within an aquatic reserve was run under permit FP23/78-AR-MPL. This project was funded by ARC projects DP19102030 awarded to A.V. and FT200100949 to S.D.L. and by a WWF Innovate to Regenerate grant to A.V. Finally, we acknowledge that all fieldwork took place on the traditional lands of the Gadigal people of the Eora nation.