Durvillaea

Beachcast D. antarctica at St Kilda Beach, Dunedin

Holdfasts of D. antarctica and other species are often inhabited by a diverse array of epifaunal and infaunal invertebrates, many of which burrow into and graze on the kelp.[4][5] In New Zealand, species that inhabit Durvillaea include the sea-star Anasterias suteri, crustaceans such as Parawaldeckia kidderi, P. karaka,[5] and the gribbles Limnoria segnis[5] and L. stephenseni, as well as the molluscs Cantharidus roseus, Onchidella marginata,[19] Onithochiton neglectus,[20][5] and Sypharochiton sinclairi,[16][17][18] and the spider Desis marina.[21][22]

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.[6][7] 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.[6][7] Environmental factors such as temperature, solar radiation and surface winds (all of which vary with latitude) affect buoyancy of southern bull kelp rafts and their rate of travel.[6] Rafts of D. antarctica are more likely to disperse offshore if individuals detach during outgoing tides during autumn and winter.[23] Rafts of 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.[16][17][18][19][20]

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,[24] 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.[25] Rafting on D. antarctica appears to have influenced the dispersal and phylogeography of these non-buoyant species.[25][26] 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.[27][28]

Fronds of D. antarctica can be infected by an endophytic, phaeophycean algal parasite Herpodiscus durvillaeae (Lindauer) G.R. South.[29][30] Fronds can also be infected Maullinia, a genus of intracellular, protistan parasites.[31][32][33] Based on genetic evidence, both H. durvillaeae and Maullinia have likely been dispersed across the Southern Hemisphere via rafting bull kelp.[30][31][33][34]

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.[35]

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.[36] Once the kelp was extirpated, the invasive kelp Undaria pinnatifida recruited in high densities.[36]

The 2010 Chile earthquake caused significant coastal uplift (~0.2 to 3.1 m), particularly around the Gulf of Arauco, Santa María Island and the Bay of Concepción.[40] This uplift caused large scale die offs of D. antarctica and dramatically affected the intertidal community.[40] The damage to infrastructure and ecological disturbance caused by the earthquake was assessed to be particularly damaging for seaweed gatherers and cochayuyo harvest.[41]

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.[14][42] Such a genetic impact may support the founder takes all hypothesis.[14][42] Further genetic analysis has revealed that the population structure of two epifaunal species, the gribble L. segnis and the chiton O. neglectus, closely matches the pattern observed in the intertidal host species of Durvillaea along the Akatore fault zone.[5] However, no matching pattern was observed for another epifaunal species, the amphipod P. karaka, most likely because this species has better swimming potential and can rely upon other host seaweeds.[5]

A substantial die off of Durvillaea bull kelp occurred along the Kaikoura coastline following the 2016 Kaikoura earthquake, which caused uplift up to 6 metres.[15][4][37][38][39] The loss of Durvillaea kelp caused ecological disturbance, significantly affecting the biodiversity of the local intertidal community.[37][38] 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.[43] Areas 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.[39]

The D. antarctica sampled from Rarangi, near Blenheim in Marlborough has been found to be genetically distinct from nearby geographic populations, and the kelp is most closely related to D. antarctica populations sampled over 300 km to the south on Banks Peninsula.[44] Independently, based on LiDAR mapping and field observations, geologists have discovered a zone of uplifted rocky coastline at the same location.[44] By combining the above genomic and geological evidence, researchers have hypothesised that a small section of coastline at Rarangi was uplifted by one of four major earthquakes between 6000 and 2000 years ago, which was sufficient in height and sudden enough to extirpate the original population of D. antarctica.[44] Under this hypothesis, the present-day population was founded by rafts of kelp that were not related to the nearby geographic populations, leading the to current genetically distinct population present at Rarangi.[44]

Based on genetic data, the predominantly southern-restricted species D. poha appears to have undergone a recent range expansion into the North Island, as it can be found at low frequencies along the Wellington coastline.[45] This range expansion coincides with areas affected by tectonic uplift and landslides caused by historic earthquakes, including the 1855 Wairarapa earthquake.[45] The removal of D. antarctica and formation of new coastline by such tectonic disturbance likely provided an ecological opportunity for D. poha to successfully colonise coastline north of the Cook Strait.[45]

A genetic study of D. antarctica identified distinct units of population structure across the uplift zone of the 1855 Wairarapa earthquake.[46] Notably, two spatial-genomic sectors of D. antarctica were identified on Turakirae Head, which received the greatest degree of uplift (2 – 6 m).[46] 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.[46] 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).[46]

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.[13] However, uplift along the Akatore fault zone does not appear to have significantly affected the genetic diversity of D. willana in that region.[14] 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.[14]

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.[54][55] 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.[56]

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 collofe or kollof.[3][57] The same species is also called cochayuyo (cocha: lake, and yuyo: weed), and hulte in Quechua.[3][41][58] The kelp harvest, complemented with shellfish gathering, supports artisanal fishing communities in Chile.[58] Exclusive harvest rights are designated using coves or caletas, and the income for fishers (and their unions) often depends upon the sale of cochayuyo.[58]

Māori use D. antarctica (rimurapa) 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.[59][60][61] Pōhā are especially associated with Ngāi Tahu and are often used to carry and store muttonbird (tītī) chicks.[59][60] The Ngai Tahu Claims Settlement Act 1998 protects Durvillaea bull kelp from commercial harvesting within the tribe's traditional seaweed-gathering areas.[62]

People living in coastal Otago and Southland have also traditionally carved bouncing balls, including cricket balls, out of the solid stipes of Durvillaea.[63][64]