Overview
Kelp are large seaweeds (algae) belonging to the brown algae (class Phaeophyceae) and are classified as the order Laminariales. There are about 300 different genera. Some species can be very long and form kelp forests. Kelp fisheries is a branch of fisheries science which deals with the study of and uses of large seaweeds of the brown algae group that are commonly called kelp. Despite their plant-like appearance, scientists group them not with the terrestrial plants (kingdom Plantae), but instead place them either in kingdom Protista or in kingdom Chromista. Kelp grows in underwater "forests" (kelp forests) in shallow oceans. It requires nutrient-rich water below about 20 °C (68 °F). It is known for its high growth rate - the genera Macrocystis and Nereocystis grow as fast as half a metre a day, ultimately reaching 30 to 80 m. Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.