Restoration of the Long-spined Sea Urchin, Diadema antillarum, to Caribbean Coral Reefs

Bodmer, Max David Vincent (2019). Restoration of the Long-spined Sea Urchin, Diadema antillarum, to Caribbean Coral Reefs. PhD thesis The Open University.



Coral reefs are among the most valuable and threatened ecosystems on Earth. Lower species diversity, and subsequently reduced resilience, make Caribbean reefs especially vulnerable to anthropogenic stressors. Overfishing and disease have reduced Caribbean herbivore abundances and their associated compensatory dynamics, leading to a 53% decrease in scleractinian coral cover since the 1970s. The long-spined sea urchin, Diadema antillarum, is an important Caribbean herbivore, and its functional extinction in the early 1980s, coupled with a subsequent lack of recovery, makes its restoration a conservation priority. A combination of in situ ecological surveys and environmental manipulations are coupled with ex situ experimental studies to aid D. antillarum restoration efforts. The thesis begins by assessing the relative impacts of fish and urchin grazing on the structure and diversity of reef communities and concludes that, whilst reestablishment of D. antillarum ecosystem functions may not represent a long-term conservation solution, it will provide short-term resilience benefits. A lab-based investigation then indicates that D. antillarum will be, at least partially, resistant to predicted future sea surface temperature increases, and observed negative fitness consequences may be mitigated by artificial structures; population restoration is therefore worthwhile in the context of climate change. Exploration of an isolated population boom then identifies a dearth of predation refugia, created by region-wide reef flattening, as the major barrier to recovery, and deployment of experimental artificial reefs demonstrates that augmentation of reef complexity is a viable strategy for increasing population size and reversing phase shifts. Restoration of D. antillarum will undoubtedly contribute to long-term ecosystem persistence, and insights contained within this thesis may help facilitate the difficult transition of Caribbean coral reefs to their future stable state.

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