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 colors, 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 color sensor can make an initial identification of its chlorophyll pigment, and therefore its species and toxicity.
Photo credit: ESA