Marine Plant Facts



  • Plants in the sea can only live in the sunlit surface waters of the ocean, called the photic zone.
  • The photic zone goes down about 100 m.
  • Phytoplankton is a minute, floating, plant-like organisms made from just a single cell.
  • Almost any marine plant which is big enough to be seen with the naked eye is called seaweed.
  • Seaweeds are anchored by holdfasts that look like roots but are really suckers for holding on to rocks.
  • Seaweeds are red, green or brown algae. Red algae are small and fern-like and grow 30-60 m down in tropical seas. Brown algae like giant kelp are big and grow down to about 20 m, mostly in cold water.
  • Some seaweed such as the bladder wrack has gas pockets to help their fronds (leaves) float.
  • The fastest growing plant in the sea is the giant kelp, which can grow 1 m in a single day. Giant kelp can grow up to 60 m long.
  • The Sargasso Sea is a vast area of sea covering 5.2 million square kilometers east of the West Indies. Gulfweed floats so densely here that it looks like green meadows.
  • The Sargasso Sea was discovered by Christopher Columbus in 1492.