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Sea lions and algae bloom

Facts for Prelims (FFP)

Source: TH

 Context: A recent outbreak of algae bloom – commonly known as red tide – has sickened and killed an unknown number of sea lions and dolphins off the coast of California, US.


Sea lions (IUCN Status – Endangered):

  • They are pinnipeds characterised by external ear flaps, long fore flippers, the ability to walk on all fours, short and thick hair and a big chest and belly.
  • Their range extends from the subarctic to tropical waters of the global ocean in both the Northern and Southern Hemispheres, except the northern Atlantic Ocean.


Algal bloom/red tides:

  • An algal bloom is a term used for the excessive growth of algae over a water body causing discolouration of the water body.
    • Blooms can proliferate because of human causes such as climate change and an excess of nitrates washed out to sea.
  • Red tide is the red colouration of seawater due to the presence of dinoflagellate Gonyaulax.



  • Algal blooms cause the production of a neurotoxin called domoic acid and result in the death of fish and other aquatic organisms.
  • Small fish consume the toxin and pass it up the food chain. Humans are unaffected unless they eat infected shellfish.