Hidden deep inside last month’s big release of the new “Freshwater Gastropods of Mid-Atlantic States” web resource was at least one item of unwelcome news. A population of the New Zealand Mud Snail, Potamopyrgus antipodarum, has been discovered in Spring Creek, a small tributary of the Susquehanna River in Centre County, PA. This is the first record of Potamopyrgus from a US Atlantic drainage.
I wrote “F. nickliniana teensy and weird” on line #415 of the spreadsheet I carried that day on my clipboard. In retrospect, I’m surprised that I remember anything at all about any particular vial among the thousands I have examined over the last 18 months. But I don’t think any of those (hundreds?) of tiny little gastropods contained in vial #415 was much over 1 mm standard shell length. I don’t remember any individuals that looked like legitimate adults. But surely a sample containing hundreds of individuals couldn't be comprised entirely of juveniles, could it? In retrospect, my eyes were not prepared to see what they were looking at.
So six months later, our good friend Steve Means of the PADEP sent me an email inquiry with “New Zealand Mud Snail in Spring Creek, Centre County” on the subject line. And the jpegs attached to his email (one of which is inserted above) clearly depicted adult Potamopyrgus antipodarum in the 4-5 mm range, collected this most recent summer at WQN415. Oops! A bit red-faced, I added P. antipodarum as species #41 to the Mid-Atlantic photo gallery, and composed species page #87 for the FWGNA site .
Potamopyrgus is a notorious invader, making its first North American appearance in Idaho’s Snake River back in 1987. Populations spread to Montana in 1995, Oregon and California in 1997, and as far as Arizona in 2002 . Most of the western populations seem to be associated with trout fishing, and it has been speculated that their spread has been facilitated either by untidy anglers, or by gut passage in the fish themselves.
Meanwhile back East, populations of Potamopyrgus were first reported in Lake Ontario in 1991, Lake Superior in 2001, and Lake Erie in 2005 . The eastern populations seem more associated with commercial shipping, the implication being that they might represent a separate introduction via bilge water. And recent research has indeed confirmed that the eastern and western populations represent genetically distinct clones .
. I understand from Steve that the hatchery does not import trout into its facility, from the West or anywhere else, and that recent benthic surveys show lower densities of Potamopyrgus at the hatchery, increasing downstream toward WQN415. This strongly suggests that the source of the introduction has not been the fish, but the fishermen.
Might some transcontinental angler have carried a sticky creel or muddy set of boots all the way from Montana to Pennsylvania? Or is the Spring Creek population a fresh introduction of the eastern clone, which has heretofore seemed primarily associated with commercial shipping ? I understand that our colleagues Ed Levri of Penn State Altoona and Mark Dybdahl of Washington State University are working on this question as we speak.
Meanwhile, the Pennsylvania Fish and Boat Commission has issued the press release available from the link below:
- PFBC Issues Alert to Contain Invasive Species in Centre County [pdf]
 For a broad review of the general biology, life history, ecology and systematics of the New Zealand Mud Snail, see the FWGNA species page...
 ...or the USGS Nonindigenous species database:
 See “Invaders Great and Small” [19Sept08]
 From the Aquatic Nuisance Species Taskforce:
- National Management and Control Plan for the New Zealand Mudsnail [pdf]
 Although populations of the Great Lakes clone typically seem to reach maximum abundances at depths of 4 meters and below, recent surveys have uncovered populations in two small streams in western New York state, draining into Lake Ontario perhaps 300 km north of Spring Creek. See Levri, Colledge, Bilka & Smith (2012) The distribution of the invasive New Zealand mud snail in streams in the Lake Ontario and Lake Erie watersheds. BioInvasions Records 1: 215-219.
 Here’s a very nice interactive map from the PFBC: