These swellings keep the frond afloat. Seaweeds belong to the brown, red, and green algae groups. Most brown algae prefer cold water, where they may grow extremely large. Brown algae called gulfweeds prefer warm water. Gulfweeds grow in large, floating masses over an area of the North Atlantic Ocean known as the Sargasso Sea.
Most red algae are small and delicate, with a feathery appearance.
They prefer warm water, and they are particularly abundant in tropical and subtropical seas. Green algae grow in both warm and cold seas. The greatest variety is found in shallow tropical waters. Most of these seaweeds are small. The name seaweed incorrectly implies that these organisms have little value.