P3.56 Friday, Jan. 6 Sea Urchin Foraging: Impacts in Coral Recruits WALTERS, L*; TURNER, T; PAUL, V; KUFFNER, I; Univ. of Central Florida; Univ. of the Virgin Islands; Smithsonian, Ft. Pierce; USGS firstname.lastname@example.org
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 hypothesize 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, US Virgin Islands, Diadema abundance in shallow waters has greatly increased in recent years, making this a perfect location for studying juvenile coral-algal-Diadema interactions. We have previously run 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 found that sometimes Dictyota significantly reduced coral recruitment. Here we show the results of complementary trials in which we examined the survival of coral spat on tiles when placed in contact with these macroalgae with and without Diadema. Survival of corals on tiles, algal consumption and algal fragmentation were checked after 14 hr (overnight). Additionally, we ensured Diadema was actually contacting the tile surfaces by counting Diadema encounter incidences (scrapes, shallow and deep punctures) with each algal species on tiles covered with plasticene after 14 hr. Only Dictyota menstrualis had an impact and coral spat mortality was greatest when in contact with both Dictyota and foraging Diadema. Hence, even the positive impacts associated with the return of Diadema may be reduced in the presence of certain species of algae.