Phytoplankton bloom in the Bay of Biscay, satellite image. North is at top. Water is blue, vegetation is green and cloud cover is white. Phytoplankton are photosynthetic microscopic algae. The bright green colour in the bloom (centre) is caused by chlorophyll and sediment. The light blue colour is caused by the presence of coccolithophores, a group of phytoplankton that produce a calcerous shell around themselves. Image obtained on May 16 2004 by the Aqua satellite.