Diadema antillarium populations in Bonaire: is there evidence of over- or under population?
The sea urchin Diadema antillarum is an important herbivore in coral reef ecosystems of the Caribbean. The Caribbean is still recovering from a 1983 mass mortality event that decimated D. antillarum throughout the Caribbean, reducing populations to <3% of former levels (Lessios et al. 2001). By feeding on algae, D. antillarum helps prevent excessive algal growth and is beneficial to juvenile corals (Edmunds and Carpenter 2001). The urchin die off may have precipitated a phase shift in coral reef communities in the Caribbean from coral to algal dominated ecosystems. However, at high densities D. antillarum can have a negative effect, reducing the number of coral recruits (Sammarco 1980; Mumby et al. 2006)
In light of the potential of ecosystem level consequences of D. antillarum population; the purpose of this study was to document the densities in Bonaire to determine if they are over or underpopulated. The range of D. antillarum expected in an area at equilibrium was found to be equal to or greater than 1 m-2 and less than 16 m-2 (Mumby et al. 2006). Using transects, the densities of D. antillarum were counted on the leeward side of Bonaire, Netherlands Antilles at 20 sites. Urchins were found to be extremely patchy and underpopulated (< 1 urchin m-2) for all but one site. Karpata’s population of D. antillarum was within the normal parameters (1< x < 16 urchins m-2). No sites sampled had densities that would indicate overpopulation of D. antillarum (> 16 urchins m-2).