Durvillaea antarctica
Durvillaea antarctica, also known as and , is a large, robust species of southern bull kelp found on the coasts of Chile, southern New Zealand, and Macquarie Island. "D. antarctica", an alga, does not have air bladders, but floats due to a unique honeycomb structure within the alga's blades, which also helps the kelp avoid being damaged by the strong waves. Taxonomy. The species was first described in 1822, as "Fucus antarcticus", and revised in 1892 as "Durvillaea antarctica". The genus name "Durvillaea" was given in memory of the French explorer Jules Dumont d'Urville, while the Latin derived  epithet refers to antarctic. In 2012, a taxonomic revision led to the recognition of a new species, "Durvillaea poha", based on genetic, morphological and ecological evidence, which was previously recognised as the 'cape' lineage of "Durvillaea antarctica". "D. poha" is the only other species in the genus to share the honeycombed structure and buoyancy of "D. antarctica." "D. poha" occurs only in southern New Zealand and on subantarctic islands (including Snares and Auckland Islands), whereas "D. antarctica" has a wider distribution, and is found around New Zealand, Chile and other subantarctic islands. In southern New Zealand, "D. poha" and "D.  antarctica" can be found growing together, although "D. poha" normally grows higher up or further back on the rock platforms, or in more sheltered bays, where wave force is weaker. "D. poha" generally has wider fronds than "D. antarctica", and can appear more 'orange' across the frond area. Mitochondrial introgression has been observed between the two species, where some plants in Wellington exhibited the nuclear DNA of "D. poha" but also mitochondrial DNA belonging to "D. antarctica". Further diversity, with additional unclassified lineages have been identified within the species. Description. The blades of "Durvillaea antarctica" are green to golden brown  with a leathery texture. The honeycomb structure of the blade gives strength and buoyancy. This novel structure is thought to be responsible for the wide distribution of this genus, as the kelp is able to float when its holdfast fails. It can colonise other coastlines in this manner, and has been shown to carry communities of invertebrates across vast ocean distances from one shore to another. Specimens of "D. antarctica" have been found to float for up to 210 days, during which time high wind speeds transport kelp rafts up to 10,000 km. Environmental factors such as temperature, solar radiation  and surface winds (all of which vary with latitude) affect buoyancy of rafts and their rate of travel. Rafts of "D. antarctica" are more likely to disperse offshore if plants detach during outgoing tides during autumn and winter. It is thought that this 'rafting' with "Durvillaea antarctica" and other floating seaweeds allowed a wide range of species to recolonise sub-Antarctic shores scoured clean by ice during the last Ice Age. The holdfast of "D. antarctica" is large and is very difficult to remove. "D. antarctica" has to resist forces equivalent to 1100 km/h on land. The holdfast failing  is usually the result of worms and molluscs which feed on the tissue because of the sheltered habitat it creates. It is also common for its host rock to be broken off without the holdfast losing its grip, with this contributing significantly to erosion in some areas. Recruitment rates of this species is very low, therefore the ecological impact of harvesting this species is too great. Life cycle. "Durvillaea antarctica" reproduces sexually by producing egg and sperm that are released into the water. Eggs and sperm are produced on specific sites of the frond. A large individual can produce 100  million eggs in twelve hours. The season when reproduction occurs varies with location, but is generally during winter months. Distribution. "Durvillaea antarctica" has a circumpolar distribution between the latitudes of 29°S and 55°S, found in Chile, southern New Zealand, and Macquarie Island. The type locality is Cape Horn, Chile. It is found on exposed shores, especially in the northern parts of its range, and attaches itself with a strong holdfast. Epifauna, parasites and rafting. Holdfasts of "D. antarctica" are often inhabited by a diverse array of epifaunal invertebrates, many of which burrow into and graze on  the kelp. In New Zealand, epifaunal species include the crustaceans "Parawaldeckia kidderi", "P. karaka" and "Limnoria stephenseni", and the molluscs "Cantharidus roseus", "Onchidella marginata", "Onithochiton neglectus", and "Sypharochiton sinclairi". The intertidal spider "Desis marina" also inhabits the holdfasts of "D. antarctica". Plants of "D. antarctica" can from detach substrates, particularly during storms. The kelp floats as a raft and can travel vast distances at sea, driven by ocean currents. Kelp-associated invertebrates can be transported inside of drifting holdfasts, potentially leading to long-distance dispersal and a significant impact upon the population genetic structure of those species. Fronds of "D.  antarctica" can be infected by an endophytic, phaeophycean algal parasite "Herpodiscus durvillaeae" . Fronds can also be infected "Maullinia", a genus of intracellular, protistan parasites. Based on genetic evidence, both "H. durvillaeae" and "Maullinia" have likely been dispersed across the Southern Hemisphere via rafting bull kelp. Human use. Chilean culture. Use in cuisine. Stems and holdfasts of "D. antarctica" and "D. incurvata" are harvested from the coast of Chile and is used in Chilean cuisine for various recipes, including salads and stews. In Quechua the species is called: (': lake, and ': weed), and "hulte". The Mapuche indigenous people refer to it as  ' or '. Expression. The expression "remojar el cochayuyo" (literally: to soak the cochayuyo) is used in Chilean Spanish to refer to sexual intercourse. The expression derives from the fact that harvested "D. antarctica" is preserved by being sun-dried and then softened by soaking in a dish of water. Māori culture. Along with "D. poha", blades of "D. antarctica" are used to make traditional pōhā bags, which are used to carry and store food and fresh water, to propagate live shellfish, and to make clothing and equipment for sports. Pōhā are especially associated with Ngāi Tahu and are often used to  carry and store muttonbird (tītī) chicks. The species is called in Māori.