Response of the microbial community to coral spawning in lagoon and reef flat environments of Hawaii, USA

The response of the microbial community to coral spawning was investigated over a period of 18 mo, from January 2006 to July 2007, in reef flat and lagoon environments of a subtropical embayment (Kaneohe Bay, Oahu, Hawaii, USA). The composition of the bacterioplankton community was characterized using terminal restriction fragment length polymorphism (T-RFLP) analysis of bacterial small-subunit (SSU) ribosomal RNA genes in parallel with measurements of microbial cell abundances, bacterial production via H-3-leucine incorporation, and seawater biochemical parameters. We observed a variable bacterioplankton community structure and 2- to 3-fold changes in the cellular abundance of microorganisms, concentrations of chlorophyll a, and rates of bacterial carbon production at both sites during non-spawning conditions. While shifts in the structure of the bacterioplankton community were evident for both environments following coral spawning, microbial abundances and rates of bacterial production remained largely unchanged from pre-spawning levels. Thus, it appeared that only a small fraction of the microbial community responded to the presence of coral-produced organic matter. Differences in the composition of the bacterioplankton community, cellular abundances of microorganisms, and rates of bacterial production were evident between the lagoon and reef flat sites during non-spawning conditions, probably signifying the importance of the surface flow regime for coastal reef microbial communities. Our observations indicate that the Kaneohe Bay microbial community may be more significantly affected by physical mixing processes than by organic matter loading from coral spawning.