The north-western Australian Kimberley is one of fifteen biodiversity hotspots in Australia. Its coast boasts an archipelago that comprises several hundred large and thousands of much smaller islands.
While the flora and fauna of the mainland was surveyed in the late 1980’s, the biota of this vast archipelago of off-shore islands has attracted little attention. The fragile environment of the Kimberley suffers from human impact, such as cattle, weeds and fire. These impacts have contributed to a wave of extinctions among medium sized mammals – but whether invertebrates are also affected has so far escaped our attention. The near future is going to see additional disturbances relating to tourism, aquaculture or oil and gas exploration along the coastlines.
With the mainland facing various threats, the offshore islands came into the fore of conservationists because they have remained relatively sheltered from the above mentioned disturbances on the mainland. Therefore, an important objective of the Kimberley Island Survey was to understand whether the islands may function as refuges for the highly endemic flora and fauna. One of the most existing outcomes of the Kimberley Island Survey was the finding of a huge diversity of new land snail species, according to malacologist Frank Koehler.
What did we do?
Twenty-two of the largest islands in the Kimberley were selected for the survey. We focused on groups that are at special risk from threats outlined above – along with the new impact of invading cane toads: Mammals, reptiles, frogs, land snails and plants.
The islands were explored by use of helicopters by teams that included scientists as well as traditional owners as custodians of their country. The survey included an extended visit in the dry season and a shorter stay during the wet. At daytime, my colleagues and collected specimen by lifting rocks and raking under leaf litter. Back in the Australian Museum, I started to sort the material, analysed DNA samples and studied the anatomy of the animals.
What do these snails tell us about the fauna of the Kimberley and its origin?
Most snails were found to be endemic to an island, which means they occur nowhere else. To understand how they evolved, we have to look back into the late Miocene, 5-10 million years ago, when Australia progressively became drier. Rainforests, once covering the entire continent, shrank into tiny patches and animals and plants had to adapt to changing landscapes and conditions. In the snails, shrinking habitats produced remarkable results: Each rainforest patch became habitat for it’s very own species assemblage and up to 12 species from different genera are found in each forest patch. This process of fragmentation has created an exceptionally diversity in the snails and we postulate that similar processes have occurred in other groups of animals as well, which has caused the emergence of the Kimberley as one of Australia’s biodiversity hotspots.
What are your conclusions?
The survey indicates just how little we still know about the distribution of species in this remote area. All of the snail species appear to be absent from the mainland, each island supports a unique suite of species. But many hundred islands have remained unstudied indicating that the a huge number of species remains to be discovered.
What’s that good for?
Because literally every gully inhabits its unique snail species, even locally restricted disturbances are devastating and likely to lead to extinction of species. The Kimberley Island Survey has underpinned the importance of the Kimberley as biodiversity hotspot.