A Sponge Mortality Event Associated With a Picocyanobacterial Bloom in a Semi-Enclosed Basin in Central Florida Bay, USA

Abstract Sponges historically dominated the heterotrophic biomass of Florida Bay’s hard-bottom communities, and the ecological services they provide have long been recognized. However, these communities have become degraded over the last several decades, in part, due to periodic cyanobacterial blooms. During August 2013 a detailed assessment of a sponge community across a semi-enclosed basin within central Florida Bay, colloquially known as Mystery Basin, that supported a heathy sponge community was concluded. During September 2013, reduced water visibility and water discoloration — consistent with past picocyanobacterial blooms in Florida Bay — were observed. Satellite imagery confirmed that a cyanobacteria bloom started in early September and ended in December 2013. The sponge community was re-surveyed in early 2014 at a subset of the original survey sites. Of the 21 sponge taxa identified at those sites during 2013, 12 were not observed during the 2014 survey, including three species ( Spheciospongia vesparium , Ircinia felix , Geodia gibberosa ) that collectively accounted for approximately 95% of the pre-bloom sponge biomass. Subsequent surveys conducted during 2015 and 2016 revealed a sponge community dominated by fast-growing weedy species. Of the three formally dominant species, S. vesparium remained absent, and only a few individuals of I. felix and a single individual of G. gibberosa were observed. These results underscore the effects of the cyanobacterial blooms on Florida Bay’s sponge communities, the protracted recolonization period necessary once those communities are affected, and the challenges that assisted sponge restoration efforts will encounter in the face of continued cyanobacterial blooms.