Durvillaea

The common name for Durvillaea is southern bull kelp. This is often shortened to bull kelp, which can generate confusion with the North Pacific kelp species Nereocystis luetkeana. ==Description==

'' showing the 'honeycomb' structure of the blades Durvillaea species are dioecious. Based on the concentration of pigments in thalli, males and females of D. antarctica do not significantly differ in colouration. In contrast, species as D. willana lack such 'honeycomb' tissue and are non-buoyant, preventing the individuals from moving long distances. ==Ecology==

Durvillaea bull kelp grow within intertidal and shallow subtidal areas, typically on rocky wave-exposed coastal sites. Intertidal species can grow at the uppermost limit of the intertidal zone if there is sufficient wave wash. Species can withstand a high level of disturbance from wave action, Research on the bacteria associated with Durvillaea indicates that local environmental conditions shape external microbiome diversity significantly. Further research suggests that the diversity of bacterial microbiomes associated with D. antarctica is influenced by the density and connectivity of the host kelp populations. Onithochiton neglectus, Durvillaea individuals can detach from substrates, particularly during storms. Once detached, buoyant species such as D. antarctica and D. poha can float as rafts, and can travel vast distances at sea, driven by ocean currents. Rafts of Kelp-associated invertebrates inside holdfasts and external epiphytes can be transported by rafting individuals, potentially leading to long-distance dispersal and a significant impact upon the population genetic structure of the invertebrate species. Rafts of D. antarctica currently reach Antarctica, Rafts of Durvillaea can be colonised by the goose barnacles Lepas australis and L. pectinata. Beachcast, decomposing bull-kelp is colonised and consumed by a wide variety of invertebrates including sandhoppers Bellorchestia quoyana, and kelp flies Chaetocoelopa littoralis. Other seaweeds including Gelidium lingulatum, G. rex, Corallina officinalis var. chilensis, and Lessonia spicata also grow as epiphytes in the holdfasts of D. antarctica. Rafting on D. antarctica appears to have influenced the dispersal and phylogeography of these non-buoyant species. In New Zealand, Durvillaea fronds can also be infected by the obligate red algal epiphyte Pyrophyllon subtumens (J. Agardh ex R.M. Laing) W.A. Nelson 2003. Fronds of D. antarctica can be infected by an endophytic, phaeophycean algal parasite Herpodiscus durvillaeae (Lindauer) G.R. South. Fronds can also be infected by Maullinia, a genus of intracellular, protistan parasites. Based on genetic evidence, both H. durvillaeae and Maullinia have probably been dispersed across the Southern Hemisphere via rafting bull kelp. Environmental stressors Increased temperatures and heatwaves, increased sedimentation, and invasive species (such as Undaria pinnatifida) are sources of physiological stress and disturbance for members of the genus. A marine heatwave in the summer of 2017/18 appears to have caused the local extinction of multiple Durvillaea species at Pile Bay, on the Banks Peninsula. Once the kelp was extirpated, the invasive kelp Undaria pinnatifida recruited in high densities. ==Disturbance from earthquake uplift==

Earthquake uplift that raises the intertidal zone by as little as 1.5 metres can cause Durvillaea bull kelp to die off in large numbers. Increased sedimentation following landslides caused by earthquakes is also detrimental. Intertidal species of Durvillaea can be used to estimate earthquake uplift height, with comparable results to traditional methods such as lidar. This uplift caused large scale die offs of D. antarctica and dramatically affected the intertidal community. New Zealand Akatore Duvillaea bull kelp diversity appears to have been affected by uplift along the Akatore fault zone. Phylogeographic analyses using mitochondrial COX1 sequence data and genotyping by sequencing data for thousands of anonymous nuclear loci, indicate that a historic uplift event (800 – 1400 years before present) along the fault zone and subsequent recolonisation, has left a lasting impact upon the genetic diversity of the intertidal species D. antarctica and D. poha, but not on the subtidal species D. willana. Aerial drone imaging two years after the earthquake indicated that Durvillaea abundance remained low on reefs with significant uplift, but it revealed offshore refuge populations less frequently detected by field researchers. A genetic analysis indicated that some of the Durvillaea that subsequently reached the affected coastline (i.e. potential colonists) came from areas >1,200 kilometres away. Specifically, the analysis showed that disturbed bull kelp populations supported higher functional, taxonomic and phylogenetic microbial beta diversity than non-disturbed populations. Independently, based on LiDAR mapping and field observations, geologists have discovered a zone of uplifted rocky coastline at the same location. This range expansion coincides with areas affected by tectonic uplift and landslides caused by historic earthquakes, including the 1855 Wairarapa earthquake. Notably, two spatial-genomic sectors of D. antarctica were identified on Turakirae Head, which received the greatest degree of uplift (2 – 6 m). Phylogeographic modelling indicated that bull kelp that survived moderate uplift in the Wellington region (≤2 m) likely recolonised Turakirae Head via two parallel, eastward colonisation events - resulting in the two observed units of population structure. The hierarchical phylogeographic variation observed in the study provided non-experimental evidence of parapatric sectoring (see Founder takes all) as a result of natural disturbance, over a timescale observable to humans (i.e. <200 years). It has been hypothesised that gaps in the current geographic range of D. willana around Wellington and the Wairarapa may have been caused by local extinction following historic earthquake uplift events such as the 1855 Wairarapa earthquake. However, uplift along the Akatore fault zone does not appear to have significantly affected the genetic diversity of D. willana in that region. The interpretation of this genetic result for Akatore was that earthquake uplift is likely insufficient to cause the complete extirpation of subtidal kelp species such as D. willana. ==Species and distribution==

There are currently eight recognised species within the genus, and the type species is D. antarctica. All species are restricted to the Southern Hemisphere and many taxa are endemic to particular coastlines or subantarctic islands. • Durvillaea amatheiae X.A. Weber, G.J. Edgar, S.C. Banks, J.M. Waters & C.I. Fraser, 2017, endemic to southeast Australia. endemic to the Chatham Islands. • Durvillaea willana Lindauer, 1949, endemic to New Zealand. ==Evolution==

Time-calibrated phylogenetic trees using mixtures of mitochondrial and nuclear DNA markers have estimated that Durvillaea diverged from other brown algae approximately 20 to 60 million years ago. Given the modern distribution of extant Durvillaea species throughout the Southern Ocean, it has been suggested that the distribution may reflect vicariance following the break-up of Gondwana 40 to 50 million years ago, but this distribution can also be explained by the long-distance dispersal of buoyant Durvillaea lineages throughout the Southern Ocean. Based on molecular phylogenetic research, non-buoyancy is not necessarily the ancestral state for the genus, and non-buoyant lineages could have still been transported across the ocean when attached to rafts of different species of buoyant algae. A phylogeny focused on the genus, based on four genes (COI, rbcL, 28S and 18S) indicates the evolutionary relationships shown in the cladogram below. Notably, additional unclassified lineages were estimated within D. antarctica. Mitochondrial introgression has been observed between two species, where some individuals with nuclear DNA of D. poha exhibited mitochondrial DNA belonging to D. antarctica. }} }} ==Use of Durvillaea species==

Australia D. potatorum was used extensively for clothing and tools by Aboriginal Tasmanians, with uses including material for shoes and bags to transport freshwater and food. Currently, D. potatorum is collected as beach wrack from King Island, where it is then dried as chips and sent to Scotland for phycocolloid extraction. Chile D. antarctica and D. incurvata have been used in Chilean cuisine for salads and stews, predominantly by the Mapuche indigenous people who refer to it as ' or . The same species is also called '' (': lake, and ': weed), and hulte''' in Quechua. The kelp harvest, complemented with shellfish gathering, supports artisanal fishing communities in Chile. are especially associated with Ngāi Tahu and are often used to carry and store muttonbird () chicks. People living in coastal Otago and Southland have also traditionally carved bouncing balls, including cricket balls, out of the solid stipes of Durvillaea. ==References==