Research

A. Lemke, M. Lunau, O. Dellwig, M. Simon

Tidal dynamics affect the growth and substrate uptake of particle-associated and free-living bacterial communities

Tidally affected coastal ecosystems with a high load of suspended particulate matter (SPM) exhibit high activities of heterotrophic bacteria and often are net-heterotrophic. Despite this general significance of heterotrophic bacteria in these ecosystems surprisingly little is known about their growth and substrate uptake dynamics and relationship to the tidally induced spatio-temporal variations of SPM and dissolved organic substrates. Therefore, we studied the abundance, biomass production (BP) and amino acid (AA) turnover and uptake of free-living (FL) and SPM-associated bacteria together with substrate dynamics (amino acids, DOC) during tidal cycles at various seasonal situations in the German Wadden Sea. The results show pronounced spatio-temporal variations of BP and AA turnover and uptake within tidal cycles as well as seasonally, indicating that hydrodynamics, besides substrate availability, strongly affect bacterial BP, AA turnover and uptake. The relative partitioning of FL and SPM-associated bacteria also varied, but mainly seasonally. Hydrodynamics appear to be more important in controlling bacterial decomposition processes in tidal flat ecosystems than previously assumed.