Phytoplankton ecology is the study of the relationship of planktonic microscopic algae with the physical, chemical, and biological factors that influence their growth and distribution.  Phytoplankton are primary producers, and comprise the foundation of the oceanic and freshwater food webs.  Phytoplankton exist in numerous shapes and sizes, and thrive in all climates and types of water body.  Most species are benign, and many are readily consumed by wide array of organisms from zooplankton to whales to humans.  However, some species can form nuisance or even toxic blooms that can disrupt food webs, cause fish kills, and harm human beings. While climate, season, and weather exert natural controls over phytoplankton productivity and distribution, nutrient pollution and shipping by humans increasingly influence the distribution and productivity of benign and harmful species alike over the world ocean.