Temporal attachment dynamics by distinct bacterial taxa during a dinoflagellate bloom

Abstract

Limited quantitative information exists on the physical interaction between specific taxa of heterotrophic bacteria and phytoplankton in pelagic aquatic environments. Using catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), we quantified bacterial attach- ment to the cells of the dinoflagellate Lingulodinium polyedrum in 39 surface samples collected during a natural bloom in summer 2005 off the coast of La Jolla, California, USA. Using a ribosomal RNA based tunable array with Luminex® bead technology, we also quantified the relative abun- dances of 11 particle-associated bacterial taxa during this time, including 8 members of the Bac- teroidetes division. Bacterial colonization of dinoflagellate cells was generally low (mean <2 bacteria alga -1 ) but increased during the days preceding bloom decline events. This indicates that physical associations, and thus potentially physiological interactions among bacteria and dinoflagellates, changed over the course of the algal bloom cycle. The 11 detected bacterial taxa exhibited diverse patterns of colonization over time, suggesting that they mediated different types of interactions with the dinoflagellates. Some bacterial types were only detected during the early bloom phase, others peaked in abundance during peaks in algal numbers, and still others peaked following bloom decline events. Our data linking the temporal succession of different bacterial colonizers to algal bloom dynamics exemplify the idea that microscale, species-specific interactions between bacteria and pro- tists can result in large-scale ecosystem level changes that can impact phytoplankton community structure in the coastal ocean.