Meeting Abstract

P1.38  Sunday, Jan. 4  Coral-Algal-Urchin Interactions in Caribbean Waters WALTERS, LJ*; TURNER, T; KUFFNER, IB; PAUL, VJ; RITSON-WILLIAMS, R; GRABLOW, K; SETTAR, C; RIVERA, G; HICKEY, TD; Univ. of Central Florida; Univ. of the Virgin Islands; US Geological Service; Smithsonian Inst.; Smithsonian Inst.; Univ. of Central Florida; Univ. of the Virgin Islands; Univ. of the Virgin Islands ljwalter@pegasus.cc.ucf.edu

The die-off of the long-spined black sea urchin Diadema antillarum in Caribbean waters in the 1980s coincided with a dramatic increase in macroalgal biomass on coral reefs. Scientists and resource managers have hypothesized that the return of this keystone herbivore will drastically reduce current algal biomass and enable corals to once again dominate. On reefs in St. Thomas, United States Virgin Islands, Diadema abundance in shallow waters has greatly increased in recent years. We are beginning to address the impact of their recovery by: 1) running in-situ, recruitment assays with larvae of the hard coral Porites astreoides and dominant macroalgal species (Dictyota menstrualis, Lobophora variegata, Acanthophora spicifera, Halimeda opuntia) and 2) looking at survival of coral spat on tiles when placed in contact with these same macroalgae with and without Diadema present. Tiles from the different treatments and appropriate controls were checked after 14 hr (overnight) and at the end of 6 days. While coral recruitment was significantly impacted by some tested species of macroalgae (D. menstrualis), any negative effects associated with the macroalgae, predation or accidental damage was minimal when Diadema was able forage over the tiles with attached coral spat. Thus, it appears that, at their present densities, Diadema is not detrimental to the survival of this common hard coral species. Our data support the hypothesis that Diadema facilitates coral recruitment by removing chemically active species of macroalgae.