Diadema antillarum, frequently referred to as the long-spined black sea urchin, is a common herbivorous echinoid that can be found in almost all marine habitats within their native range. (Ogden & Carpenter, 1987). They serve as a keystone grazer by preferentially feeding on algae that can overgrow and kill coral (Jeremy & Kaufmann, 1987). Between 1983 and 1984 a mass mortality event swept through D. antillarum populations, which caused a phase shift from coral-dominated to algal-dominated on many reefs throughout the Caribbean (Weil et al., 2005). This analysis sought to understand the occurrence of Diadema antillarum within national parks served by the South Florida/Caribbean Inventory and Monitoring Network (SFCN) division of the National Park Service (NPS) from 2008 to 2018. SFCN began monitoring urchins in 2008 in conjunction with the development of their benthic coral monitoring protocol. The abundances of D. antillarum are monitored along each transect at which coral monitoring takes place. Individuals are visually counted within a 2-meter swath of the targeted coral transect and recorded on the datasheet (Miller et al., 2017). Abundance counts inside the Research National Area (RNA) in Dry Tortugas National Park (DRTO) were compared, and occurrence data were compared between Biscayne National Park and Dry Tortugas National Park in Florida and Buck Island Reef National Monument, Salt River National Historical Park and Ecological Preserve, and Virgin Islands National Park in the United States Virgin Islands. Occurrence was highest at two subsites outside the RNA in DRTO, followed by two index sites in Biscayne National Park. Due to a high number of observations with zero urchins at many sites, the data were transformed using a negative binomial regression and delta lognormal transformation (Lo et al., 1992; Maunder & Punt 2004). The combined delta lognormal index determined that the probability of presence was the same between the zones inside the RNA and outside the RNA, but the abundance when present was different. When expanded to analyze urchins between Florida and Caribbean parks, the combined delta lognormal index again determined that the probability of presence was the same between the two regions, but the abundance when present was different. Weak correlations were found with depth and percent coral cover using Spearman’s rank coefficient and Kendall’s Tau correlation tests, but no firm trends could be determined. The delta lognormal index indicated that the urchins are unaffected by the presence of the RNA, and are faring similarly in national parks located in both Florida and the Caribbean. Abundance counts indicated that D. antillarum are recovering very slowly, if at all, within Florida and Caribbean national parks. Close monitoring of this keystone species should continue to search for clues as to why they have not recovered within these national parks.
Hyduk, Thomas, "Occurrence of Diadema Antillarum in South Florida and Caribbean National Parks from 2008-2018" (2018). Internship Reports (Restricted). 328.
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