In the past two decades observations of thin phytoplankton layers have become a common occurrence in the coastal ocean. Because of the small size of phytoplankton and their limited mobility, turbulence is thought to have a significant effect on their biodynamics. However, until very recently there has been very limited in situ observations of turbulence within and around thin layers. This book examines and quantifies the nature of turbulent mixing and its influence on the evolution of thin phytoplankton layers. Simultaneous and collocated spatial measurements of turbulence, fine structure, and chlorophyll a fields were made from an Autonomous Underwater Vehicle. Results indicate that thin layers can occur and evolve in both an environment of strong and weak turbulence. Two cases are examined where a thermocline thin layer persisted in strong turbulence. For the first case, the thin layer was embedded within the turbulent field and behaving as a Lagrangian tracer collapsed vertically with the collapse of the turbulent layer. For the second case, vertical diffusion gradually weakened the thin layer as it advected into the experimental site.