The distribution and abundance of macro-invertebrates in the major vegetation communities of Marion Island and the impact of alien species

• Main Author: Hanel, Christine
• Other Authors: Chown, Steven Loudon
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: University of Pretoria 2013
• Subjects: Marion Island; Macro-invertebrates; UCTD; Antarctic; Antarc*
• Online Access: http://hdl.handle.net/2263/29482; http://upetd.up.ac.za/thesis/available/etd-11152010-105242/

In this study macro-invertebrates were sampled quantitatively in 10 lowland vegetation communities on Marion Island over a one-year period commencing in May 1996 as part of a larger investigation into the distribution, abundance and species energy use of invertebrates across an altitudinal transect on Marion Island. The data collected for this particular study were used to investigate the habitat specificity and seasonality of the macro-invertebrates, as well as the impact of alien species on the local community. As part of the latter study a watching brief for alien species was kept throughout the field year and the alien species list was updated accordingly. The quantitative data were also used to compare changes in the density and biomass of selected macro-invertebrate species between 1976/77 and 1996/97 by reworking the data on macro-invertebrates collected by Alan Burger in 1976/77 during the course of his work on the Lesser Sheathbill. In the current study it was found that the majority of the macro-invertebrate species are not particularly habitat specific. Rather, they generally prefer either moist mire habitats, or the more well-drained non-mire vegetation complexes. In addition, many of the species had pronounced peaks in abundance in a given season (winter, summer, autumn and spring peaks were recorded), although this seasonality varied between species and between habitats for a given species. Although this finding does not support previous generalizations concerning an absence of seasonality in sub-Antarctic invertebrates, it does show that sub-Antarctic invertebrates, like their Antarctic counterparts, may have extremely flexible life history strategies. Limnophyes minimus was found to be one of the most abundant alien species on the island, and reached high densities in most of the plant communities sampled, with the highest density being recorded in the Cotula plumosa biotically influenced community (annual mean of 4365 individuals.m-2 ) and the lowest in the Crassula moschata salt spray community ...