The common name for Durvillaea is southern bull kelp, although this is often shortened to bull kelp, which can generate confusion with the North Pacific kelp species Nereocystis luetkeana. The genus is named after French explorerJules Dumont d'Urville.
Description
Durvillaea species are characterised by their prolific growth and plastic morphology. Two species, D. antarctica and D. poha are buoyant due to a honeycomb-like structure in the fronds of the kelp that holds air. When these species detach from the seabed, this buoyancy allows for plants to drift for substantial distances, permitting long distance dispersal. In contrast, species as D. willana lack such 'honeycomb' tissue and are non-buoyant, preventing the plants from moving long distances.
Ecology
Durvillaea bull kelp grow within intertidal and shallow subtidal areas, typically on rocky wave-exposed coastal sites. D. antarctica and D. poha are intertidal, whereas D. willana is subtidal. 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, although storms can remove plants from substrates.
Epifauna and rafting
Holdfasts of D. antarctica and other species 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 sea-star Anasterias suteri, crustaceans Parawaldeckia kidderi, P. karaka, Limnoria segnis and L. stephenseni, and the molluscsCantharidus roseus, Onchidella marginata, Onithochiton neglectus, and Sypharochiton sinclairi. Specimens of Durvillaea 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. Kelp-associated invertebrates can be transported inside of drifting kelp holdfasts, potentially leading to long-distance dispersal and a significant impact upon the population genetic structure of the invertebrate species.
Environmental stressors
Increased temperatures and heatwaves, increased sedimentation, and invasive species 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
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. Once an area is cleared of Durvillaea following an uplift event, the bull kelp that re-colonises the area can potentially originate from genetically distinct populations far outside the uplift zone, spread via long distance-dispersal. Intertidal species of Durvillaea can be used to estimate earthquake uplift height, with comparable results to traditional methods such as lidar. However, since Durvillaea holdfasts often grow at the uppermost limit of the intertidal zone, these uplift estimates are slightly less accurate compared to measures derived from other intertidal kelp such as Carpophyllum maschalocarpum.
Chile
The 2010 Chile earthquake caused significant coastal uplift, particularly around the Gulf of Arauco, Santa María Island and the Bay of Concepción. This uplift caused large scale die offs of D. antarctica and dramatically affected the intertidal community. The damage to infrastructure and ecological disturbance caused by the earthquake was assessed to be particularly damaging for seaweed gatherers and cochayuyo harvest.
New Zealand
Akatore
Duvillaea bull kelp diversity appears to have been affected by uplift along the Akatore fault zone. Phylogeographic analyses using mitochondrialCOX1 sequence data and genotyping by sequencing data for thousands of anonymous nuclear loci, indicate that a historic uplift event along the fault zone and subsequent recolonisation, has left a lasting impact upon the genetic diversity of the of the intertidal species D. antarctica and D. poha, but not on the subtidal species D. willana. Such a genetic impact may support the founder takes all hypothesis.
A substantial die off of Durvillaea bull kelp occurred along the Kaikōura coastline following the 2016 Kaikōura earthquake, which caused uplift up to 6 metres. The loss of Durvillaea kelp caused ecological disturbance, significantly affecting the biodiversity of the local intertidal community. Genetic analysis indicated that some of the Durvillaea that subsequently reached the affected coastline came from areas >1,200 kilometres away.
Wellington and the Wairarapa
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, which suggests that earthquake uplift may be insufficient to cause the complete extirpation of this subtidal species.
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 potatorumAreschoug, endemic to southeast Australia.
Durvillaea willanaLindauer, 1949, endemic to New Zealand.
Evolution
A time-calibrated phylogeny of Durvillaea based on four mitochondrial and nuclear DNAmarkers indicates the evolutionary relationships shown in the cladogram below. Notably, additional unclassified lineages were estimated within 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 extraction.
Chile
D. antarctica and D. incurvata have been used in Chilean cuisine for salads and stews, predominantly by the Mapucheindigenous people who refer to it as collofe or kollof. The same species is also called cochayuyo, and hulte in Quechua. The kelp harvest, complemented with shellfish gathering, supports artisanal fishing communities in Chile. Exclusive harvest rights are designated using coves or caletas, and the income for fishers often depends upon the sale of cochayuyo.
New Zealand
use D. antarctica and D. poha to make traditional pōhā bags, which are used to transport 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 chicks. The Ngai Tahu Claims Settlement Act 1998 protects Durvillaea bull kelp from commercial harvesting within the tribe’s traditional seaweed-gathering areas.
