High Quality Content by WIKIPEDIA articles! The spring bloom is a strong increase in phytoplankton abundance (i.e. stock) that typically occurs in the early spring and lasts until late spring or early summer. This seasonal event is characteristic of temperate North Atlantic, sub-polar, and coastal waters. The magnitude, spatial extent and duration of a bloom depends on a variety of environmental conditions, such as light availability, nutrients, temperature, and stratification of the water column. The initial phytoplankton stock size is also important.