Oral Presentation Australian Freshwater Sciences Society Conference 2024

Slow recovery of stream invertebrates on subantarctic Macquarie Island after eradication of rabbits (112432)

Richard Marchant 1
  1. Museum of Victoria, MELBOURNE, VIC, Australia

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 (over 15 sites) 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. Thirteen of the original 15 sites sampled in 1992 were resampled in 2016 to determine the extent to which the invertebrate communities had changed after rabbit removal. Five kick samples were taken at each site, as in previous surveys. 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. Recovery of steam invertebrate communities appeared to be slow, possibly because few refuges were available. Lakes on the island may provide refuges for some of the fauna. Minor changes in climate and water quality did not influence recovery. Stream invertebrate communities could take a decade or more to recover. It is impossible to say whether composition will revert to that present in 1992 or whether a different composition will prevail. No long-term data exist for streams on isolated oceanic islands that would enable prediction of events after disturbance.