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The recent collapse of predatory sunflower sea stars ( Pycnopodia helianthoides ) owing to sea star wasting disease (SSWD) is hypothesized to have contributed to proliferation of sea urchin barrens and losses of kelp forests on the North American west coast. We used experiments and a model to test whether restored Pycnopodia populations may help recover kelp forests through their consumption of nutritionally poor purple sea urchins ( Strongylocentrotus purpuratus ) typical of barrens. Pycnopodia consumed 0.68 S. purpuratus d −1 , and our model and sensitivity analysis shows that the magnitude of recent Pycnopodia declines is consistent with urchin proliferation after modest sea urchin recruitment, and even small Pycnopodia recoveries could generally lead to lower densities of sea urchins that are consistent with kelp-urchin coexistence. Pycnopodia seem unable to chemically distinguish starved from fed urchins and indeed have higher predation rates on starved urchins owing to shorter handling times. These results highlight the importance of Pycnopodia in regulating purple sea urchin populations and maintaining healthy kelp forests through top-down control. The recovery of this important predator to densities commonly found prior to SSWD, whether through natural means or human-assisted reintroductions, may therefore be a key step in kelp forest restoration at ecologically significant scales.
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This content will become publicly available on January 2, 2026
Abalone recruitment patterns before and after sea urchin barrens formation in northern California: incorporating climate change
Understanding the recruitment dynamics of invertebrates in kelp forests is critical to informing climate-ready restoration. Here we examine abalone and sea urchin recruitment (3–20 mm in size) patterns in northern California across a period of drastic change. Annual surveys were conducted before, during and after the MHW (2014–2016), the loss of a major predatory sea star (2012–2016) and the collapse of a bull kelp forest in 2014. Divers surveyed artificial reef recruitment modules (n = 12) over 20 years in an area that once supported dense bull kelp, Nereocystis leutkeana, forests and the world's largest recreational abalone fishery. From 2016 to 2022, we tracked the decline of red abalone, Haliotis rufescens, recruitment and the rise of purple sea urchin, Strongylocentrotus purpuratus, recruitment. Adult densities of purple sea urchins increased as did newly settled sea urchins (<3 mm), while adult and newly settled red abalone declined. Eight years after the kelp forest collapse, red abalone recruitment remained low and sea urchin recruitment continued to increase. Recruitment patterns can inform both abalone restoration targets and sea urchin dynamics as part of a more holistic kelp forest recovery plan that is responsive to climate change drivers.
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- Award ID(s):
- 2023664
- PAR ID:
- 10566129
- Editor(s):
- Alfaro, Andrea C; Ragg, Norman; Venter, Leonie
- Publisher / Repository:
- Taylor and Francis
- Date Published:
- Journal Name:
- New Zealand Journal of Marine and Freshwater Research
- Edition / Version:
- 1
- Volume:
- 59
- Issue:
- 1
- ISSN:
- 0028-8330
- Page Range / eLocation ID:
- 283 to 299
- Subject(s) / Keyword(s):
- Climate change conservation Haliotis kelp forest recruitment modules recovery restoration Strongylocentrotus
- Format(s):
- Medium: X Size: 2MB Other: pdfA
- Size(s):
- 2MB
- Sponsoring Org:
- National Science Foundation
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