The Aldabra banded snail (Rachistia aldabrae), last seen alive in 1997, has been driven to extinction by reduced rainfall associated with climate change, according to new research.
Justin Gerlach of the Nature Protection Trust of Seychelles collated data from 16 invertebrate collections, made between 1895 and 2006, to examine changes in the abundance, distribution and demography of the only known population of the snail. Because no live snails were found in surveys after 1997, there were two specific searches for R. aldabrae in 2005 and 2006, which only found shells that were at least five years old.
The Aldabra atoll is one of the least disturbed places on Earth. However, regional rainfall has decreased and prolonged dry periods have increased since the late twentieth century. Juvenile snails were more susceptible to desiccation than adults, with all young perishing in prolonged dry spells. The demographic population change from juvenile loss strongly correlates with reduced rainfall and dry periods.
R. aldabrae now has the unfortunate distinction of being one of the few species whose extinction can be attributed directly to climate change, rather than indirect effects such as habitat change. Gerlach believes that further species surveys on the atoll will likely show the impact of reduced rainfall on biodiversity.
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Wilkinson, R. Snail sayonara. Nature Clim Change 1, 50 (2007). https://doi.org/10.1038/climate.2007.43