Bacterial response to labile dissolved organic matter increases associated with marine discontinuities

Abstract

Selected oligotrophic or low-nutrient (LN) bacteria were used in laboratory studies to measure the amounts of available or labile dissolved organic carbon (DOC) in waters collected from various locations and depths in the central and northeastern Pacific Ocean. Two parameters, bacterial specific growth rates and maximum cell densities, were examined as indicators of DOC availability in unsupplemented seawater samples. Maximum growth rates of LN bacteria were 0.1-0.3 h-1 regardless of sample location. Growth rates were slightly depressed due to anthropogenic inputs such as chlorine or metals. The range of specific growth rates measured for the test bacteria is considerably less (approximately 3-fold) than that for maximum cell density (approximately three orders of magnitude). Highest levels of labile DOC (as determined by maximum cell densities attained) were observed in waters collected from interfaces or discontinuities such as surface films, thermocline and oxygen minima waters, chlorophyll maxima and ammonium regeneration zones, benthic boundary layers, sediment/water interface and sediment trap supernatants. We estimate labile DOC pools of < 1% to approximately 45% of the total measured DOC. © 1987.