Evidence for sedimenting particles as the origin of the microbial community in a coastal marine sediment

The origin of the microbial community in a coastal marine sediment was investigated by examining the physical, chemical, and microbial characteristics of the sedimenting particles in Halifax Harbor, Canada. Particles were collected using particle interceptor traps placed on the sediment surface. The measured rate of particle accumulation compared to the sediment accumulation rate indicates that over 85 % of the dry weight of the particles is removed (including resuspension) or solubilized before deposition as sediment. Active decomposition is facilitated by the large microbial community present. The particles are heavily colonized by both bacteria (109 gl ) and protozoa (106 g' ) before they reach the sediment such that the microbial communities of the sinking particles and sediment-water interface are nearly indistinguishable. The particles and sediment are also similar with respect to community growth rates and carbon, nitrogen, and ATP content. Artificial sediment cores inserted into the sediment and left in place for 1 yr were colonized only to a depth of 4 cm. The data indicate that an extensive microbial community is already established on particles before they become sediment and that in situ sediment colonization is not necessary for the establishment of the sediment microbial community.