Biophysical Interactions in Phytoplankton

Abstract

The aim of this chapter is to introduce the main concepts of biophysical interactions between phytoplankton and the physical water environment of lakes. The physical environment inhabited by phytoplankton has a profound effect on the shape and size of the organisms and their behavior. While most research focusses on this physical control of mixing on phytoplankton, less commonly considered is the role that phytoplankton play in shaping the physical conditions in lakes that they experience such as the light climate and the generation of convective mixing. The vertical dimension of lakes can represent enormous gradients in the resources required by phytoplankton to grow and replicate. Mixing induced by wind energy, thermal convection and inflows also varies across this vertical dimension. These gradients are dynamic and shift in time. A range of physical mixing processes such as convection, wind mixing and seiching can also result in horizontal multi-scale patchiness in phytoplankton ranging from < 1 m to > 1 km. Patchiness and patch formation is determined both by the type and strength of physical forcing impacting a lake and by the characteristics of the phytoplankton community, such as the motility and buoyancy of species, which interact to determine horizontal and vertical positions of patches. Patch formation has implications for biogeochemical processing in lakes. The observation of biophysical interactions in-situ has been enhanced in recent years by the more widespread adoption of sensing technologies that enable both physical and biological variation at shorter timescales and larger spatial scales to be captured. Biophysical interactions in phytoplankton occur across multiple time and space scales. The physical environment experienced by phytoplankton both shapes and is shaped by their presence affecting species selection, community succession, heat absorption and mixing. These interactions have implications for how we can use lakes and the ecosystem services that they provide.