The extensive sponge mortalities observed in Florida Bay during the 1990s have been linked by some researchers to recent blooms of the planktonic cyanobacterium, Synechococcus spp. However, a direct causal link between these phenomena has yet to be firmly established. This study
examined the relationship between the cyanobacterium, Synechococcus spp., and the function and survival of three sponge species, Biemna spp., Halichondria melanadocia, and Spheciospongia vesparia (loggerhead sponges), found in Florida Bay. Two hypotheses were tested:
(1) The presence of bloom concentrations of Synechococcus 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 Synechococcus under varying laboratory conditions and their filtration and water transport rates were measured. All sponge species tested were able to filter 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 for H. melanadocia, and 0.069 ml ml−1 for S. vesparia. Repeated and multiple day (i.e.,
up to 5 d) exposures to bloom concentrations of Synechococcus did not lead to rapid mortality or significantly diminished filtration capabilities in S. vesparia. These results are discussed within the broader context of other scenarios by which cyanobacterial blooms may effect
the survival of sponges, e.g., alternate ecophysiological conditions and longer exposure periods.
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