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The north-western Australian Kimberley is one of fifteen Australian biodiversity hotspots. 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 1980s, the islands’ biota has attracted little attention. The fragile environment of the Kimberley suffers from human impacts, such as via the introduction of cattle, weeds and fire. These factors have contributed to a wave of extinctions among medium-sized mammals, but whether invertebrates are also affected has escaped our attention. Additional disturbances relating to tourism, aquaculture, oil and gas exploration, and the invasion of cane toads are expected to occur in the near future.
With the mainland facing various impacts, the offshore islands have attracted the attention of conservationists because, to date, they have remained relatively protected from the above threats. 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 found in the region. One of the most exciting outcomes of the Kimberley Island Survey has been the discovery, by Dr Frank Koehler, of huge diversity among land snails, many of which are new to science.
What did we do?
Twenty-two of the largest islands in the Kimberley were selected to survey. We focused on groups that are at particular risk from the threats outlined above: mammals, reptiles, frogs, land snails and plants.
The islands were explored using 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. We collected specimens found under rocks and among leaf litter. Back in the Australian Museum, we sorted 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 particular islands, meaning they occur nowhere else. To understand how they evolved, we probably have to look back 5–10 million years, 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 this process of fragmentation has created an exceptional diversity — while forest patches became refuges to their very own species assemblages that contain up to 12 species from different genera. Similar processes have occurred in other groups of animals as well creating the Kimberley biodiversity hotspot.
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, and each island supports a unique suite of species. But many hundreds of islands remain unstudied suggesting that a huge number of species still await discovery.
What does this tell us?
Because literally every forest patch is inhabited by unique snail species, even locally restricted disturbances are devastating and likely to lead to species extinctions. The Kimberley Island Survey has underpinned the importance of the Kimberley as biodiversity hotspot.