36 years after the species\u27 mass-mortality: Diadema antillarum test sizes, population densities, and substrate preferences in three Guna Yala reefs near Wichub Wala Island

In January 1983, a waterborne pathogen beginning near the Atlantic Panama Canal entrance caused history\u27s largest recorded marine animal die-off, wiping out 95-99% of Diadema antillarum populations throughout the Caribbean. D. antillarum, the long-spined sea urchin, is a keystone herbivore in coral reefs and its decreased densities have caused many reefs to suffer macroalgal phase shifts. Modest recovery of this species has been documented in some Caribbean locations, but reefs in Guna Yala, Panama continued to experience population decline. This study investigates density, test size, and substrate preferences of D. antillarum in three shallow coral reef areas to update the species\u27 recovery in Guna Yala. Over the total 1,080 m2 of reef surveyed, D. antillarum was present at a mean density of 0.11 individuals m-2. This is only 3.03% of the 1982 pre-mortality density for the area, but is a slight recovery from the 2015 density of 0.03 individuals m-2. This study was the first to document test sizes in Guna Yala in 24 years and did so at novel reef sites. Test sizes ranged from 8-62.5 mm with a mean of 38.85 mm, and the presence of 6 juveniles (test size\u3c2 cm) indicates a level of recruitment. Out of the total 119 urchins counted, 94 individuals were located under dead coral skeletons covered in algae. There were no significant relationships (p\u3c0.05) between urchin test sizes and the type of substrate they resided on (within live coral, under live coral, under dead coral, or under rocks), suggesting that a factor other than size determines where D. antillarum are located within a reef, and that D. antillarum in Guna Yala could potentially aid in phase shift reduction due to their exhibited preference for algae-covered surfaces. This study demonstrated consistent average densities, test sizes, and substrate preferences between the three sites, indicating that the different sites are experiencing similar population recovery phenomena despite their varying observed characterizations. The consistent results between sites bode well for this study\u27s representation of D. antillarum\u27s current status in Guna Yala reefs