Iversen K, Primicerio R, Larsen A, Egge JK, Peters F, Guadayol O, Jacobsen A, Havskum H, Marasse C
Turbulence, Food web, Bacteria, phytoplankton, nutrient addition, mesocosm, Bergen, Espegrend, Norway, 2.6 m3
Small-scale turbulence affects the pelagic food web and energy flow in marine systemsand the impact is related to nutrient conditions and the assemblage of organismspresent. We generated five levels of turbulence (2*1029 to 1*1024 W kg21) in landbasedmesocosms (volume 2.6 m3) with and without additional nutrients (31:16:1Si:N:P mM) to asses the effect of small-scale turbulence on the lower part of thepelagic food web under different nutrient conditions. The ecological influence ofnutrients and small-scale turbulence on lower trophic levels was quantified usingmultivariate statistics (RDA), where nutrients accounted for 31.8% of the observed biologicalvariation, while 7.2% of the variation was explained by small-scale turbulenceand its interaction with nutrients. Chlorophyll a, primary production rates, bacterialproduction rates and diatom and dinoflagellate abundance were positively correlatedto turbulence, regardless of nutrient conditions. Abundance of autotrophic flagellates,total phytoplankton and bacteria were positively correlated to turbulence only whennutrients were added. Impact of small-scale turbulence was related to nutrient conditions,with implications for oligotrophic and eutrophic situations. The effect on communitylevel was also different compared to single species level. Microbial processesdrive biogeochemical cycles, and nutrient-controlled effects of small-scale turbulenceon such processes are relevant to foresee altered carbon flow in marine systems.