Resumen de Influence of turbulence variability on osmotrophic plankton dynamics in a coastal area
Turbulence affects plankton at very different levels and scales. The study of this topic has been mainly based on the assessment of effects of constant levels of turbulence, particularly through experimental studies, and little is known about the influence of intermittent patterns. The aim of the present thesis is to address how the variability in forcing factors, especially turbulence, affects the dynamics of coastal plankton communities. To do so the distribution of wind events as a proxy of the variability of turbulent energy input in a coastal zone, has been first studied. Turbulent forcing derived from wind in the Catalan coast is shown to have a large spatial and temporal variability. An empirical model has been developed which allows predicting the distribution of wind events with an ecologically relevant intensity. An assessment of the statistical distribution of turbulence in the Catalan coast is given.
In chapter 2 the actual turbulence levels achieved in the laboratory set-ups used for experimental research are measured. These analyses have been extended to a range of different set-ups frequently used in experimental studies of plankton and turbulence, including different oscillating-grid systems and orbital shakers with common laboratory containers. In the case of oscillating grid systems, measurements have shown that turbulence is isotropic, and homogeneously distributed within cylindrical containers as long as the stroke length is comparable to the water column height. Away from the grid oscillation dissipations decay nonlinearly. Turbulence can be trustfully estimated using theoretical considerations about the energy entered into the system by the oscillating grid. A list of drag coefficients for different grids inferred from turbulence measurements is provided.
In order to identify the variability in the responses of the planktonic community to realistic episodes of turbulence, two complementary approaches have been developed: a time series analysi
