Slow recovery of stream invertebrates on subantarctic Macquarie Island after eradication of introduced rabbits and regrowth of vegetation

Abstract

Context Streams on subantarctic Macquarie Island were first sampled for freshwater invertebrates in 1992 when rabbit numbers were low. Then an average 11.6 taxa per site were recorded. Between 2000 and 2011, vegetation was overgrazed as rabbit numbers increased. In 2008 and 2010, 7.4–8.4 taxa per site were recorded, abundance of most taxa had decreased and greatest compositional changes occurred at sites exposed to moderate or severe vegetation damage. Rabbits were eradicated in 2011 and substantial regrowth of vegetation was evident by 2016. Aims Sites were resampled in 2016 to determine the extent to which the invertebrate communities had changed after rabbit removal. Methods In all, 13 of the original 15 sites sampled in 1992 were resampled. Five kick samples were taken at each site. Key results Mean taxon richness (8.2 taxa per site) and community composition at individual sites remained, in 2016, very similar to that recorded in 2008 and 2010 when the island was heavily grazed. Conclusions Recovery of stream invertebrate communities appeared to be slow, possibly because few refuges were available. Minor changes in climate and water quality did not influence recovery. Implications Stream invertebrate communities could take a decade or more to recover.