A species of freshwater snail previously considered likely to be extinct was rediscovered during a survey at yingina/Great Lake in January this year.
The discovery of Beddomeia tumida, a tiny freshwater snail measuring around 4mm, was made as part of ongoing conservation monitoring of the lake by Entura (an arm of Hydro Tasmania) and identified with the help of aquatic mollusc expert Dr Karen Richards, Senior Zoologist (Threatened Species) with NRE Tas.
As Tasmania’s only freshwater malacologist, Dr Richards says she has been involved with Hydro-funded surveys since 2013, undertaking additional research in a personal capacity in 2016, when water levels in the Great Lake had dropped significantly.
Entura were initially conducting a population survey for another previously thought to be extinct snail species, the Great Lake giant freshwater limpet (Ancylastrum cumingianus) which was rediscovered in 2015, present in trout gut contents. Fun fact – at 12mm the giant freshwater limpet is actually smaller than the only other species of limpet (Ancylastrum irvinae – reaching a massive 20mm) found in the lake!
Late last year, researchers returned to survey the lake using 100 old roof tiles attached to ropes and buoys. The tiles were dropped between 2 and 10 metres to the lake floor at six locations, in the hope they would be colonised by bottom-dwelling species.
When the tiles were retrieved earlier this year, they were found to host both species of limpets, with Ancylastrum cumingianus in low abundance, as well as evidence of limpet egg masses attached to some tiles. Subsequent surveys recorded the first evidence of Beddomeia tumida, with three individuals located.
“There were a few shells found in the 1970s, but this is the first finding of a live specimen in a very long time,” says Dr Richards. “It’s fantastic to know that the species is still existing, and especially to know that they exist at depth because we had no idea how deep they went.”
Beddomeia tumida is listed as ‘endangered’ under the Tasmanian Threatened Species Protection Act 1995, and ‘critically endangered but possibly extinct’ on the International Union for Conservation of Nature’s red list. The elusive snail has so far only been found at one location, a site off Brandum on the western shore of the lake. No live snail has been seen or recorded in the area since before damming of the lake in 1916, making this a significant find.
The snail is a member of the Tateidae (formerly Hydrobiidae) family of freshwater snails – a small, cryptic species that can be difficult to tell apart from other Beddomeia. This find provides us with the first opportunity to complete the taxonomic description of the species, something which has remained incomplete until now.
“There are 74 identifying characteristics of the Beddomeia tumida. Six of these are based on the shell, and everything else is internal. The original shell specimens came from a dried snail, so this is the first time we have been able to look at the species’ internal structure to really dissect and describe it,” says Dr Richards.
Unlike many other snails which are hermaphrodite, Tateidae snails are single-sex, with separate males and females – which limits their ability to reproduce, since they are rare and occur in large waterbodies. They are also relatively long-lived and lay few eggs. Beddomeia tumida is the only still water-dwelling species in the genus recorded.
“When we look at all of these factors, together with the fact that they are only present in one small area of the lake, we can see why they are vulnerable to extinction,” says Dr Richards.
Beddomeia tumida on tile (Credit - Kevin Macfarlane, Entura)