Ecological kinetics in a turbulent sea
Bacteria have a vital influence on marine ecosystems by consuming dissolved organic matter and making it available to species at higher trophic levels. Bacteria encounter organic matter as an intricate, dynamic landscape of patches, pulses, and filaments, which they navigate using chemotaxis. Despite this, experimental and theoretical studies of chemotaxis are largely restricted to simplified, artificial environments. We developed new mathematical theory to predict the behavior of bacterial populations in dynamic nutrient environments. To evaluate this theory, we engineered a new experimental setup that allowed us to study chemotactic responses of the marine bacterium Vibrio ordalii in the laboratory, in resource landscapes with prescribed spatial and temporal variability.
By combining mathematical and computational models with data from chemotaxis experiments, we show how a single pulse of resources induces a predictable response from the population of bacteria in the surrounding medium. We argue that turbulent mixing generates such pulses on the spatial and temporal scales relevant to bacterial chemotaxis in the ocean, and that these pulses may serve as the basic ecological units of interaction between chemotactic bacteria and the dissolved organic matter that supports them. This joint theoretical-empirical approach facilitates the systematic study of the foraging dynamics of species that are essential in oceanic nutrient cycling.