Ecosystem collapse on a sub-Antarctic island

Sub-Antarctic Macquarie Island has been the location of a rapid ecosystem collapse in its most dominant vegetation assemblage, the Macquarie Island alpine mosaic, beginning around 2008 and continuing today. An ecosystem engineer and endemic, keystone species, the cushion plant, Azorella macquariensis (Apiaceae), and associated bryophyte species have undergone sudden and widespread dieback. Additional species, particularly the megaherb daisy, Pleurophyllum hookeri (Asteraceae), are currently also showing widespread mortality. Initially, water stress linked to long-term changes in climate appeared to be the primary pressure causing dieback, with a secondary putative pathogen emerging. However, over the last 10 years there has been a shift in fundamental ecosystem processes with the pathogenic system appearing to be the current predominant cause of dieback. This change suggests that a threshold has been crossed into a new operating state. Furthermore, an ecosystem regime shift with two clear new states (grassland and bare ground) appears to be emerging with the loss of the ecosystem engineering species from many areas of fellfield. Modelling suggests that cold refugia may allow current elements to survive into the future, but as interstitial species, rather than as dominants present at the start of the twenty-first century. This ecosystem presents a potential exemplar for climate change response in patchy, resource-concentrated ecosystems elsewhere. In particular, showing how interactions change in response to climate change and how longer-term consequences may emerge following short-term effects.