| Summary: | The Diadema antillarum population in the Florida Keys has not recovered since the Caribbean-wide mass mortality event of the early 1980s. Concomitantly, coral reefs have degraded to the point that there has been a loss of habitat complexity and thus of refuge from predation, possibly creating a bottleneck to the recovery of D. antillarum. With interest rising in using D. antillarum in coral reef ecosystem restoration, we initiated this study to investigate some factors that may limit the survival of D. antillarum. First, we conducted a field experiment to determine whether D. antillarum survival was size-specific by tethering urchins from four size classes (test diameters: 21–30 mm, 31–40 mm, 41–50 mm, and ≥51 mm) on a degraded, offshore reef. We found that size did not offer any protection against predation as there was no difference in survival among size classes. Next, we tethered another set of urchins, approximately 60 mm in test diameter, at the same location but provided half with artificial shelter in the form of halved terracotta flowerpots. We found that urchins that were provided artificial shelter had significantly higher survival than those that did not have access to artificial shelter. Finally, because certain behaviors in D. antillarum are density-dependent, we conducted a laboratory experiment to evaluate whether D. antillarum sheltering behavior was also density dependent. This experiment showed that sheltering behavior decreased significantly as stocking density increased. Our results indicate that restoration practitioners must be cognizant of and facilitate urchin behaviors that maximize survival (e.g., shelter use) and, more importantly, that successful restoration of D. antillarum in Florida will require that suitable refuge be available, either in the form of overhead cover provided by highly rugose reef habitat or by enhancing degraded habitat with artificial shelter. Thus, we suggest that incorporating artificial shelter into the dual-pronged approach of simultaneous urchin and coral restoration may facilitate the recovery of Florida’s reefs.
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