Phytoplankton bloom off South Africa
The vibrant blue colors visible in this image are caused by phytoplankton blooms. Phytoplankton are tiny, microscopic plants that form the base of the food web in marine ecosystems. Phytoplankton are consumed by zooplankton, or microscopic animals, which in turn are eaten by variety of fish, whales, and birds. Blooms are fed by the upwelling of nutrients; currents deep beneath the ocean surface reach the coastline and are forced to the surface carrying minerals such as iron with them. Phytoplankton are poised to rapidly exploit this temporary resource, growing very rapidly under such conditions. However, as nutrients are depleted, the blooms die and decay. The blooms can harm fish directly by clogging their gills and by the release of toxins, as well as indirectly through oxygen depletion.