Filtration of the bloom-forming cyanobacteria Synechococcus by three sponge species from Florida Bay, USA

The extensive sponge mortalities observed in Florida Bay during the 1990s h ave been linked by some researchers to recent blooms of the planktonic cyan obacterium, Synechococcus spp. However, a direct causal link between these phenomena has yet to be firmly established. This study examined the relatio nship between the cyanobacterium, Synechococcus spp., and the function and survival of three sponge species, Biemna spp., Halichondria melanadocia, an d Spheciospongia vesparia (loggerhead sponges), found in Florida Bay. Two h ypotheses were tested: (1)The presence of bloom concentrations of Synechoco ccus diminish the filtration efficiency of sponges, potentially leading to food resource limitation and (2) bloom concentrations of Synechococcus are associated with the death of sponges over short time scales. To test these hypotheses sponges were exposed to both natural and laboratory-cultured Syn echococcus under varying laboratory conditions and their filtration and wat er transport rates were measured. All sponge species tested were able to fi lter Synechococcus. Water transport rates were similar to those reported in the literature for other sponges. Mean transport rates were 0.221 ml ml(-1 ) s(-1) for Biemna, 0.080 ml ml(-1) s(-1) for H. melanadocia, and 0.069 ml ml(-1) s(-1) for S. vesparia. Repeated and multiple day (i.e., up to 5 d) e xposures to bloom concentrations of Synechococcus did not lead to rapid mor tality or significantly diminished filtration capabilities in S. vesparia. These results are discussed within the broader context of other scenarios b y which cyanobacterial blooms may effect the survival of sponges, e.g., alt ernate ecophysiological conditions and longer exposure periods.