This contribution reviews the nonlinear
stochastic properties of turbulent velocity and passive scalar
intermittent fluctuations in Eulerian and Lagrangian turbulence.
These properties are illustrated with original data sets of (i)
velocity fluctuations collected in the field and in the
laboratory, and (ii) temperature, salinity and in vivo
fluorescence (a proxy of phytoplankton biomass, i.e. unicelled
vegetals passively advected by turbulence) sampled from highly
turbulent coastal waters. The strength of three of the most
popular models describing intermittent fluctuations (the
lognormal, log-Lévy and log-Poisson models) to fit the
distribution of in vivo fluorescence has subsequently been
critically assessed. A theoretical formulation for the stochastic
properties of biologically active scalars is also provided and
validated. Finally, the potential effect of the intermittent
properties of turbulent velocity fluctuations on processes
relevant to the life of plankton organisms are theoretically
investigated. It is shown that the intermittent nature of
microscale turbulence may result in (i) a decrease in the rate of
nutrient fluxes towards non-motile phytoplankton cells (6-62 %),
(ii) a decrease in the physical coagulation of phytoplankton cells
(25-48 %) and in the subsequent phytoplankton aggregate volumes
(22-41 %), and (iii) a decrease of the turbulence contribution to
predator-prey encounter rates (25-50 %).