Influences of the Loggerhead Sponge (spheciospongia Vesparium) and the Vase Sponge (ircinia Campana) on Nearshore Hard-bottom Community Development in the Florida Keys

INFLUENCES OF THE LOGGERHEAD SPONGE (SPHECIOSPONGIA VESPARIUM) AND THE VASE SPONGE (IRCINIA CAMPANA) ON NEARSHORE HARDBOTTOM COMMUNITY DEVELOPMENT IN THE FLORIDA KEYS Scott Donahue Old Dominion University, 2008 Director: Dr. Mark J. Butler IV Sponges, octocorals, and stony corals are the dominant sessile fauna within shallow, hard-bottom communities in the Florida Keys, FL (USA). The sponge component of these communities is not well studied and has been cyclically decimated from as early as 1844, most recently in south-central Florida Bay in 1991 and 1992, in apparent association with phytoplankton blooms. The purpose of this research was to examine ways in which sponges may contribute to the maintenance of hard-bottom communities. Specifically, I investigated: 1) the effect of sponges and physical structures on local sea floor scouring and thus the potential for maintenance of hard-bottom; 2) the growth and survival of sponge transplants inside and outside of areas historically susceptible to sponge die offs; and 3) the influence of sponges and physical structures on the recruitment of hard-bottom fauna onto artificial substrates. Sponges induce turbulent flow and increase scouring of the benthos immediately adjacent to them under both high and low-flow conditions. In general, the effect of large sponges on scouring was slightly greater than that of similar sized boulders. Loggerhead sponge and Vase sponge transplants grew better in the region subjected to recent sponge die offs than they did elsewhere, including the sites from which they originated. Settlement patterns of invertebrates around sponges could not be quantified as designed due to experimental failure. However, periodic observations of settlement plates revealed a gradual succession from a monotypic stand of red macroalgae (Laurencia sp.) after one year, to a mix of red and green macroalgae, one sponge species (Chondrilla sp.), and small corals (probably Siderastrea radians) by the third year. Furthermore, known spongivorous macroinvertebrates sheltered under the settlement plates and their presence may have altered hard-bottom community development. The results of this study show that sponges can thrive in areas previously impacted by sponge mass mortalities if they can successfully recolonize those areas. Once an area is colonized, sponges may contribute to the persistence of hard-bottom habitat by enhancing local benthic scouring and thus precluding sedimentation and succession to seagrass.