Abstract Summary
The die-off of the long-spined sea urchin (Diadema antillarum) in the early 1980s is a well-studied event in the Caribbean. The loss of this important herbivore lead to significant increases in algal abundance, and consequently, coral reef degradation. Recently, D. antillarum populations have been increasing throughout the Caribbean basin. The potential effects of the return of this species on coral recruitment, however, remain unclear. While the return of D. antillarum is expected to increase the availability of suitable habitat for settling larvae and young settlers, dense urchin populations may also cause high settler mortality due to incidental grazing. On Curaçao, early algal community succession and subsequent coral recruitment are currently studied on ceramic tiles that were deployed on June 1st 2018 in areas where populations of D. antillarum are naturally recovering (≥ 1 urchin m-2), and in areas where they are virtually absent. In August 2018, settling larvae of the critically endangered coral species Acropora palmata will be exposed to tiles harboring these algal communities to track their settlement success. The tiles harboring settlers will be returned to their original location so their long-term survival and growth can be monitored. At present, two-month-old algal communities grown in the presence of dense urchin populations comprise 1.6 times more CCA and 2.1 times less turf algae compared to tiles conditioned in areas where D. antillarum are absent, confirming the role of D. antillarum in aiding the formation of benthic communities beneficial to recruiting corals. We thus expect D. antillarum to promote A. palmata settlement. If the latter hypothesis is confirmed, restoration techniques using sexually reared Caribbean corals may be significantly improved by conditioning and outplanting artificial settlement substrates in areas where D. antillarum is naturally occurring or recovering.
