Succession of bacterial abundance, activity and temperature adaptation during winter 1996 in parts of the German Wadden Sea and adjacent coastal waters

The development of the microbial community was studied in the northern German Wadden Sea and adjacent parts of the North Sea in three synoptic surveys between 9 February and 8 March 1996. During the study period the abundance of bacteria remained relatively constant, with mean values ranging from 0.7 to 0.8×105 cells cm−3. The mean bacterial activity, measured as thymidine uptake, slightly increased from 11 to 16×10−12 mol thymidine h−1 dm−3, but high rates of up to 70×10−12 mol h−1 dm−3 were also observed within inner tidal basins and near freshwater in-flows. These sites were categorised as having a rapid winter turn-over of organic material. Temperature adaptation was tested in incubations at 2, 12 and 22°C. At the beginning of the study period, only the organisms of the near-shore stations showed highest activity at the lowest temperature, but in the course of the experiment the number of cold-adapted organisms increased steadily. This shift from cold tolerance to cold preference was probably facilitated by the supply of organic material from various sources and indicates the development of the microbial community simultaneously with the onset of the growing season.