The role of shallow water sponges in mediating water quality in the Florida Keys, Florida (USA)
Abstract
Sponges are important to benthic-pelagic coupling in marine ecosystems via their role in re-mineralizing dissolved organic nutrients and filtration of particulate and microbial material from the water column. This is especially so in shallow water and poorly flushed environments where the ratio of sponge biomass to water volume is highest. Such is the case in shallow, hard-bottom habitats surrounding the Florida Keys (Florida, USA), where over 60 species of primarily high microbial abundance (HMA) sponges dominate the animal biomass. We examined the feeding of the five most abundant inshore HMA sponge species in this region, focusing on their filtration of bloom-forming microalgae, aqueous nutrients, and dosed human-associated bacteria (E. coli) measured through their retention efficiencies, removal capacities, and clearance rates. Due to high variation, filtration of all bacterioplankton combined was largely non-significant across species. However, high nucleic acid bacteria and Picoeukaryotes were filtered at rates 3-5-fold greater (respectively) compared to controls. Significant species-specific effects were observed in the removal of nitrates, nitrites, total nitrogen, total phosphorus, and dissolved organic carbon compared to controls. This study confirms the reliance of HMA sponges on dissolved nutrients and carbon, whereas their retention of bacterioplankton was idiosyncratic among sponge species and type of microbe. The HMA sponges we tested had significant effects on water chemistry, which again varied among species. With respect to the potential use of sponges as a restoration tool for improving water quality, our results suggest that alteration of specific water quality constituents may be possible through the selective use of various sponge species in restoration.