The largest marine algae are kelp species, which include bull kelp (Durvillaea antarctica), which can reach over 20 metres (66 ft) long and is thought to be the strongest kelp in the world. As many as 47 individual plants can live on 1 square metre (10.8 sq ft), and they can grow at 60 centimetres (24 in) a day. Kelp that is broken off its anchor provides a valuable food source for many animals, as well as providing a method of oceanic dispersal for animals such as invertebrates to travel across the Southern Ocean by riding floating kelp.[34]