Project Summary for 2005–17B: Barrel Sponges on Florida Reefs: Reproduction, Mortality and Bleaching
The Caribbean barrel sponge, Xestospongia muta, is a large and common member of the Florida coral reef community at depths greater than 12 m. Despite its prominence, high biomass and importance to habitat complexity, very little is know about the basic biology of this massive sponge, including rates of mortality and recruitment, reproduction, growth and age. This species has been observed to bleach, much like reef corals, with some subsequent mortality. Additional threats to this species include monofilament fishing line debris, which can cleanly slice through sponges in high–flow environments.
The PI requests facilities support in the form of dayboat and laboratory use at the Key Largo site of NURP, and a small amount of student salary and travel funds to continue long–term studies of X. muta, and to continue NSF co–sponsored investigations of the chemical ecology of Caribbean sponges. With past NURC support, the PI and his students have established 12 permanent circular transects (16 m diameter), containing over 450 marked individual X. muta, for twice-yearly missions to monitor sponge mortality, recruitment, bleaching, growth, and damage by debris. Past NURC awards have also supported a survey of the chemical and structural antipredatory defenses of 71 species of sponges from reef, mangrove, and grassbed habitats, with the determination that predation by sponge–eating fish greatly affects the distribution and abundance of sponges on reefs. Defensive metabolites from several sponge species have been isolated and identified, and intraspecific variability in chemical defense has been explored for several species. Based on the results to date, the following objectives are proposed for the next two years of research:
Coral reefs are generally perceived to be in decline around the world, with a variety of possible explanations. Bleaching of reef corals may be a consequence of steadily rising sea temperatures due to global climate change; this proposal will test this and an alternate hypothesis for bleaching of a coral reef sponge. Alternative hypotheses for loss of coral cover include those of “indirect effects”: loss of spongivorous reef fishes may alter the ecology of reef sponges to permit the growth of otherwise cryptic species, some of which may more effectively compete for space with corals. The proposed study will advance our understanding of the complex relationships between benthic invertebrates, their predators and their competitors in coral reef environments. This proposal will also continue a long-term demographic study of a prominent and important coral reef sponge that, like reef–building corals, is susceptible to bleaching.
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