Meeting Abstract

P3.7  Jan. 6  Foraging by the long-spined sea urchin Diadema antillarium: are unconsumed algal fragments perpetuating algal dominance on coral reefs? WALTERS, L*; TURNER, T; PARISH, E; SACKS, P; Univ. of Central Florida, Orlando; Univ. of the Virgin Islands, St. Thomas; Univ. of the Virgin Islands, St. Thomas; Univ. of Central Florida, Orlando ljwalter@pegasus.cc.ucf.edu

Scientists and resource managers have hypothesized that the return of the keystone herbivore Diadema antillarium to Carribean coral reefs will dramatically reduce algal biomass and enable corals to once again dominate these systems. On reefs in St. Thomas, USVI we are beginning to address this question by testing urchin foraging preferences and following the fate of unconsumed algal fragments. Many genera of macroalgae (e.g. Dictyota, Halimeda, Caulerpa) are known to asexually propagate via vegetative fragmentation. If large numbers of fragments of these macroalgae are created by Diadema, then algal biomass may actually increase rather than decrease on reefs. We have tested a range of species of macroalgae with urchins (test diameter: 4-7 cm) starved for 48 h. In 12-h trials, no fragments of any algal species were generated in running seawater chambers without urchins (controls) and urchins created no/few fragments of Dictyosphaeria cavernosa, Acanthophora spicifera, Laurencia papillosa and Padina sanctae-crucis. Alternatively, individual urchins created up to 54 fragments of Dictyota menstrualis, 28 fragments of Halimeda opuntia, and 11 fragments of Caulerpa sertularioides (primarily blades). Survival and attachment of these fragments was 56%, 4%, and 45%, respectively. Our results suggest that Diadema may be able to increase algal biomass on reefs; we plan to continue our trials to look at urchins starved for longer time periods and when multiple urchins compete for limited food.