Effects of turbulence on bacterial growth mediated through food web interactions

Abstract

We performed laboratory experiments with natural seawater communities of the Northwestern Mediterranean to test whether turbulence could affect bacterial abundance and activity. There was no direct effect of turbulence on bacteria when they were uncoupled from the remainder of the microbial community. In the presence of the microbial community, bacteria showed higher activity and maintained high abundances for a longer time under turbulence than in still water Thus, turbulence sufficiently altered some microbial component or process in the water samples that indirectly affected bacteria. The population dynamics of bacteria and pigmented eukaryotes suggests that, under turbulence, there is a community grazing shift from smaller to larger prey sizes. This shift can be explained in terms of the advantage to protozoan predators which are able to prey on larger and more nutritious cells when the encounter rates with these cells are increased through the shear present under turbulence. The result is a higher control on phytoplankton and a relaxation of grazing on bacteria. Hence. episodic high turbulence events in coastal systems could accelerate nutrient recycling.

Dynamic forcing of coastal plankton by nutrient imbalances and match-mismatch between nutrients and turbulence

“…We know from previous studies that bacteria show insignificant sedimentation, thus the positive response to turbulence may be due to either increased availability of large dissolved molecules and colloids, or shifts in the grazing pressure of phagotrophic flagellates (Peters et al 1998, Malits et al 2004.…”

Analysis of wind events in a coastal area: a tool for assessing turbulence variability for studies on plankton

“…For example, usually the first element to respond positively to turbulence in laboratory experiments is phytoplankton, particularly diatoms. Then bacteria increase because of the released DOM but also because of changes in the structure of the food web (Peters et al, 1998), and organic matter enters the microbial food web. The duration of the turbulent event in this situation is critical, since it can determine the fate of the organic matter produced, which can either sediment out of the system or go up the food web to higher trophic levels.…”

Effects of turbulence on TEP dynamics under contrasting nutrient conditions: implications for aggregation and sedimentation processes

“…To date most studies have focused on the role of turbulence on biological processes, such as planktonic production and respiration , zooplankton feeding (e.g. Caparroy et al 1998), microzooplankton feeding (Dolan et al 2003, Havskum et al 2005, osmotrophic plankton and bacterial growth (Peters et al 1998, Maltis et al 2004). All these processes affect the dynamics of the particles suspended within, and exported from, the water column, but their net effect on production of non-living particulate matter is difficult to predict.…”