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

Abstract

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 0.8μm occupied 75-78% of the total populations in sediments. Mean cell volume of bacteria in sediments (0.159μm3) was about twice as large as that in seawater (0.088μm3). There was no remarkable variation in bacterial mean volumes in sediments with season, depth and locality. Bacteria in sediments ranged from 6.2 to 29.2×108 cells·cm-3 in number and from 8.0 to 40.5μgC·cm-3 in biomass. Abundance of bacteria over the top 20cm sediments varied between 2.22 and 3.76gC·m-2. Viable bacteria enumerated by MPN method ranged from 0.2×107cm-3 in deeper sediments to 12.9×107cm-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 0.66-2.72×106ml-1 and 4.81-21.05μgC·l-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.