In this Envisat image acquired on 2 December 2011, a phytoplankton bloom swirls a figure-of-8 in the South Atlantic Ocean about 600 km east of the Falkland Islands. Different types and quantities of phytoplankton exhibit different colours, such as the blues and greens in this image. Earth-observing satellites like Envisat can monitor these algal blooms. Once a bloom begins, an ocean colour sensor can make an initial identification of its chlorophyll pigment, and therefore its species and toxicity. [Source: ESA]

Phytoplankton are photosynthesizing microscopic organisms that inhabit the upper sunlit layer of almost all oceans and bodies of fresh water. They are agents for “primary production,” the creation of organic compounds from carbon dioxide dissolved in the water, a process that sustains the aquatic food web.

Phytoplankton account for half of all photosynthetic activity on Earth. Thus phytoplankton are responsible for much of the oxygen present in the Earth’s atmosphere – half of the total amount produced by all plant life. [Source: Wikipedia]