Size Distribution, Number and Biomass of Bacteria in Intertidal Sediments and Seawater of Ohmi Bay, Japan

The size distribution, number and biomass of bacteria in intertidal sediments and seawater of Ohmi Bay were investigated by the image analysis and DAPI direct count technique, in March, July and November, 1983. Bacteria with the equivalent spherical diameter between 0. 5 and 0.81am occupied 75-78% of the total populations in sediments. Mean cell volume of bacteria in sediments (0.159um3) was about twice as large as that in seawater (0.088um3). There was no remarkable variation in bacterial mean volumes in sediments with season, depth and locality. Bacteria in sediments ranged from 6.2 to 29.2x108 cellscm-3 in number and from 8.0 to 40.5 1ugC. cm-3 in biomass. Abundance of bacteria over the top 20 cm sediments varied between 2. 2 and 3.76 gC•m-2. Viable bacteria enumerated by MPN method ranged from 0.2X 10' cm-3 in deeper sediments to 12.9 X 10cm-3 in surface in July. For viable bacteria, plate counts were comparable with MPN counts in sediments. Number and biomass of bacteria in seawater were 0.66-2.72x 106 mland 4. 81-21.05 ugC•1-1, respectively. The amounts of bacteria were three orders of magnitude larger in sediments than seawater; which suggests the quantitative importance of bacteria in intertidal sediments for microbial production and remineralization of loaded organic matter.