Community-Level and Species-Specific Associations between Phytoplankton and Particle-Associated Vibrio Species in Delaware's Inland Bays

Vibrio species are an abundant and diverse group of bacteria that form associations with phytoplankton. Correlations betweenVibrio and phytoplankton abundance have been noted, suggesting that growth is enhanced during algal blooms or that association with phytoplankton provides a refuge from predation. Here, we investigated relationships between particle-associatedVibrio spp. and phytoplankton in Delaware's inland bays (DIB). The relative abundances of particle-associatedVibrio spp. and algal classes that form blooms in DIB (dinoflagellates, diatoms, and raphidophytes) were determined using quantitative PCR. The results demonstrated a significant correlation between particle-associatedVibrio abundance and phytoplankton, with higher correlations to diatoms and raphidophytes than to dinoflagellates. Species-specific associations were examined during a mixed bloom ofHeterosigma akashiwo andFibrocapsa japonica (Raphidophyceae) and indicated a significant positive correlation for particle-associatedVibrio abundance withH. akashiwo but a negative correlation withF. japonica . Changes inVibrio assemblages during the bloom were evaluated using automated ribosomal intergenic spacer analysis (ARISA), which revealed significant differences between each size fraction but no significant change inVibrio assemblages over the course of the bloom. Microzooplankton grazing experiments showed that losses of particle-associatedVibrio spp. may be offset by increased growth in theVibrio population. Moreover, analysis ofVibrio assemblages by ARISA also indicated an increase in the relative abundance for specific members of theVibrio community despite higher grazing pressure on the particle-associated population as a whole. The results of this investigation demonstrate links between phytoplankton andVibrio that may lead to predictions of potential health risks and inform future management practices in this region.