Macquarie Island invertebrate monitoring
The Macquarie Island Pest Eradication Project (MIPEP) was the most ambitious island eradication program to date, ridding a remote and species-rich island of immensely damaging pest rabbits and rodents. In 2014, the eradication was declared a success. Already, expeditioners and tourists are witnessing the island’s vegetation recovery with Macquarie Island cabbage (Stilbocarpa polaris) and tussock grasses (Poa foliosa and smaller Poa cookii) recolonising the slopes. However, exactly what we expect to see, or what we want to see in the ecosystem’s recovery remains largely unknown. Justine Shaw from The University of Queensland is leading a large Australian Antarctic Science project assessing post-eradication ecosystem recovery on Macquarie Island. The project is in partnership with DPIPWE and involves researchers from Monash University, the Institute for Marine and Antarctic Studies (IMAS), the University of Tasmania (UTAS), and the University of Melbourne. One element of the project is to collate historic biological data (pre eradication) of a range of taxa including macro-invertebrates and then compare it to newly acquired data, post eradication. The project will explore changes in abundance, distribution, diversity and community structure. It aims to understand ecosystem processes and recovery mechanisms. Invertebrates are thought to be a key indicator of ecosystem recovery as they were a major prey item of mice, and strongly influenced by vegetation cover. They are particularly important for soil nutrient cycling, plant pollination, a food source for kelp gulls, and play a major role in the ecosystem
This season we implemented the first stage of an island-wide macro-invertebrate monitoring program. My work involved re-establishing 10 historical invertebrate monitoring sites in the north of the island and the setting up of 10 new sites in the southern half of the island. The new sites were selected on the basis of aspect, vegetation type, altitude and what region of the island they occurred in. Five different vegetation communities were sampled – feldmark (plateau), lower coastal slopes dominated by Stilbocarpa polaris (Macquarie Island cabbage), tall grassland (tussock) dominated by Poa foliosa, short grasslands (including Deschampsia, Festuca, Agrostis, Luzula, Uncinia), and herb field dominated by Pleurophyllum hookerii. At each site, temperature was logged and five pitfalls traps installed along a trap line. These traps collect invertebrates present in the vegetation and leaf litter. Additional sampling involved sweep netting the vegetation, manual searching of litter, and a 20 minute count for otherwise potentially un-trappable invertebrates such as worms, slugs, snails and moths.
Approximately 500 samples were gathered in six weeks of sampling. To give us an understanding of how invertebrates change seasonally from summer through to autumn, willing and wonderful volunteers Jacque, Jane, Karen, Paul, Rowena, Kim and Marcus will continue pitfall trapping at eight of the 20 sites for the months of January, February and March. Temperature loggers will remain at each site to give us an annual temperature profile at each site.
On a personal level, having previously been a dog handler on the pest eradication program in its first year, I am moved by the vegetation recovery about the island four years on. When I first laid eyes on Macquarie Island in 2010, many of slopes and had been reduced to short grasslands, bare dirt and slips. Now as I walk around I finally see all that she can be and the recovery is still in its infancy! Anecdotally, expeditioners have all noted a resurgence in invertebrates, particularly spiders which helpfully festoon the cold porches and the huts and keep us company in the shower! It will be fascinating to watch the ecosystem keep evolving.