P. Greenslade and R. Farrow, XCS Consulting for The Department of the Environment, Water, Heritage and the Arts, June 2008.

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Executive summary

Major Findings in relation to management

1. A major change in composition of the invertebrate fauna on North East Herald (NEH) has occurred since the last monitoring event in 1997. The most significant is a change in the dominant ant species present resulting in habitat change in an important ecological community, the Pisonia forest. Our fieldwork also suggests that the Guinea ant, Tetramorium bicarinatum, is a key driver of these communities and can act as a surrogate in indicating reductions in epigaeic (active above the ground) invertebrates on these islands. These results indicate a need for ongoing monitoring of ants and strict quarantine controls applied for Magdelaine Island.
2. There are differences in species composition and/or abundance between the two island groups, Coringa and Magdelaine and the Heralds. These differences are in ant species composition and relative abundance and not related to vegetational differences, indicating a need to prevent transfer of organisms between island groups.
3. Some species that normally occur only in marine littoral habitats on larger landmasses are found inland away from the beach habitat on these islands, illustrating the process of colonisation of newly emerged land.
4. Many new taxa were recorded from the 2007 collections compared to previous collections and some species collected in 1995 and 1997 on NEH were not found in spite of more comprehensive sampling in 2007. These results support the hypothesis of repeated wind-borne invasions of many species that persist for varying periods depending on resources available and a relatively rapid turnover of species on these islands.
5. Up to 20 species of parasitic Hymenoptera were found, indicating a healthy and diverse range of species parasitic on Lepidoptera, Orthoptera, Hemiptera and other groups. The relative abundance and diversity of micro-Hymenoptera wasp parasitoids on the Heralds suggests that parasite-induced mortality may help stabilise the populations of at least some of the resident host species, for example, the grasshopper Aiolopus thalassinus and some of the moths, emphasising that the introduction of more parasitoids is not indicated.
6. Some non-vagile soil taxa, vulnerable to desiccation and intolerant of immersion in salt water, have colonised some habitats on NEH and South West Herald (SWH). In addition, one wingless beetle was discovered on SWH that had not been previously recorded anywhere in the Coral Sea. Dispersal of these organisms may be during extreme weather events as they are otherwise not mobile.
7. Major differences in invertebrate composition were found between the four common vegetation types on all four islands sampled in 2007, illustrating that a range of ecosystems allows a higher diversity of invertebrates to find niches to colonise.
8. The moisture content of the ground layer had a major influence on composition and abundance of invertebrate fauna at the period visited, which was the dry season, suggesting that a lower rainfall would threaten the survival of these humid-loving faunas.
9. The total terrestrial invertebrate fauna of NEH and SWH is probably about 150 species. Although island endemism is probably non-existent, a few species appear to be restricted to the Coral Sea Island Territory (CSIT), indicating that some elements of the fauna have a high conservation value because of their rarity.
10. The resilience of terrestrial ecosystems, especially decomposer organisms, depends on high numbers of nesting seabirds providing nutrients to maintain a diverse and abundant invertebrate fauna, emphasising that a holistic approach to adaptive management of these islands should be adopted.