Phytoplankton populations frequently encounter conditions that do not permit cell proliferation e.g. nutrient limitation. Investigation of aging cultures of the cyanobacterium S. elongatus serves to unravel strategies of cell survival as well as cell-death in non-growing cultures. We revealed adaptive plasticity of cell morphology, which is dictated by ambient nutrient status. Additionally, we demonstrated that collapsing aging cultures of S. elongatus produce toxic compounds that effectively kill a large variety of phytoplankton species (see “Our Projects” for details).