Water hardness, stream size, and A.E. Boycott: A New River reminiscence

Just across the Blue Ridge, where the high meadows lay,

And the galax spreads through the new mown hay,

There's a rusty iron bridge, 'cross a shady ravine

Where the hard road ends and turns to clay [1].

The New River is the second-oldest river in the world, just a bit younger than the Nile.  I have heard that assertion stated so often and so forcefully that it must be so.  Born on the slopes of North Carolina’s Grandfather Mountain (G, down below), the New River first flows rather improbably to the northeast, through high meadows parallel to the Blue Ridge, into the Commonwealth of Virginia.  Then, quite astoundingly, the river shifts its course northwest, orthogonal to the Appalachian Mountains, near the little city of Blacksburg (B), and cuts a deep notch through the Allegheny Plateau, diagonally across West Virginia to The Ohio.  The earliest explorers of the American interior named its lower half the Kanawha River, never imagining that the New River and the Kanawha River might connect through those hundreds of miles of rugged terrain.

New River at Grandview

My mother was born and raised in the little town of Floyd, Virginia, perched on the New River plateau, looking down over the Blue Ridge (M).  And my father was born and raised in Rock Castle Gorge, deep in the Blue Ridge down below (F).  Many were the sparkling summers I spent rocking on my grandmother’s porch, many were the spring times I fished the chilly creeks for trout, many the falls I hunted the dark forests for squirrels.

 

With a suitcase in his hand

There the lonesome boy stands

Gazing at the river sliding by beneath his feet,

But the dark water springs from the black rocks and flows

Out of sight where the twisted laurel grows.

 

So, I matriculated at Virginia Tech, the University of Blacksburg, in the fall of 1973.  And I have shared with this readership quite a few anecdotes about my education in those hallowed halls [2], especially highlighting the impact of my mentor, Dr. E. F. (Fred) Benfield.  Longtime readers might remember that, even as I was finding a seat in my freshman biology class, plans were well advanced to construct a double-dam pump-storage facility on the upper New River at the Virginia / North Carolina border, which would have sunk 100 miles of the world’s second-oldest river into inky blackness and inundated thousands of square miles of lovely farmland.  And the Virginia Tech Center for Environmental Studies had been contracted to prepare the Environmental Impact Statement [3].

 

And so it was that I, a mere sophomore of age 19, found myself checking out boots, buckets and nets from the storeroom of the Virginia Tech Center for Environmental Studies, pulling the keys to a pickup truck from the pegboard, and driving off into the high meadows of the upper New River for my first systematic survey of a freshwater molluscan fauna [4].  And in my undergraduate research thesis, defended in May of 1977, I reported a modest 6 species of unionid mussels, 4 species of pisiidid clams, 4 species of prosobranch snails, and 6 species of pulmonate snails from 87 sites sampled across the drainage in ten counties of southern Virginia and northwestern North Carolina [5].

 

It materialized that those 20 species of freshwater mollusks were not all evenly distributed across my ten-county study area.  Even to my young and untrained eye, patterns manifest themselves.  And the most striking pattern was closely correlated with the underlying geology of the upper New River basin.  Which sent me to the library, looking for clues.

The geology of the New River Valley of Virginia

I do not remember the day or the hour I first discovered the wonderful 1936 work of A. E. Boycott [6], but I do remember the impact.  Boycott’s 70-page review was a thing of beauty; so complete, so rigorous, so bubbling over with cheerful facts about the biology of the creatures we both obviously loved that 20 years later, I patterned an entire book after it [7].  And in retrospect, may have produced but a pale imitation.

 

So Boycott, after reviewing the general biology and local habitats of the 62 species of freshwater mollusks inhabiting the Island of Great Britain, turned to “The relevant qualities of the habitats.”  Item (b) in his list of eight relevant qualities was “lime,” and item (c)  was “reaction,” by which he meant pH, which (he hastened to point out) was essentially the same thing as lime [8].

 

Boycott went on to classify (and map) the 62 British species as 25 “soft-water” species (“all those which we can find in soft water without surprise”) and 30 species “calciphile or calcicole in the sense that they are habitually found in hard water [9].”  He could not identify any British species as “calcifuge,” i.e., restricted to soft water.  Thus, overall molluscan diversity increased in the hard waters, as the 30 calciphiles were added to the 25 softwater species in the richer environments.

 

Well, that explains a lot right here in the good old USA, I thought to myself.  From its North Carolina origin through the first (roughly) hundred miles of its journey, the New River runs through ancient metamorphic rocks such as gneiss and schist, remaining quite soft.  But about halfway to its hard left turn at Blacksburg, the New enters a region of limestone and dolomite, and the water hardens up.  The distribution of most of the unionids and a couple of the gastropods (Pleurocera shenandoa, Physa gyrina) seemed to be restricted below that invisible barrier, as though they were, in Boycott’s terminology, “calciphile.”

 

But there was a second obvious factor in the distribution of the upper New River mollusk fauna, and Boycott had that one covered as well.  Item (d) of Boycott’s eight “relevant qualities” was “Size and Volume.  The larger units of water are liable to contain the more Mollusca.”  And indeed, most of the unionid mussel species were confined to the main New River, apparently unable to inhabit the smaller tributaries.  That also seemed true for Campeloma decisum.

Dillon & Benfield [16]

That’s pretty much where I dropped the shovel for my 1977 undergraduate thesis and sat down in front of the typewriter.  Each of my four subheadings under Results and Discussion – Unionidae, Sphaeriidae, Prosobranch Gastropods, and Pulmonate Gastropods – had a section entitled “Effect of Hardness” and a section entitled “Effect of Stream Size.”  All four subheadings also had a section entitled “Effect of perturbation” or “Effect of (artificial) enrichment.”  This was the 1970s, after all, I had to get pollution in there somehow.  I defended in May, got married in June, and moved to Philadelphia in July.

 

Ah, but.  Hidden deep inside my thesis was the germ of an idea.  Under the “Unionidae” subheading was also a brief section entitled “Interaction of factors.”  And there I speculated, at the age of 21, “Perhaps hardness and stream size interact in some manner so that a large stream can support Elliptio dilatata even though its hardness may be low, and a small stream can support mussels if it has high hardness.”  That hardness x stream size interaction was also obvious in the pulmonate snails.  About the origin of the phenomenon, at my young age, I would not hazard a guess.

 

Past the coal-tipple towns in the cold December rain

Into Charleston runs the New River train,

Where the hillsides are brown, and the broad valleys stained

By a hundred thousand lives of work and pain.

 

Ecology at The University of Pennsylvania and ecology at Virginia Tech are as different as Philadelphia and Blacksburg.  At Penn, I found the intellectual focus entirely upon the interactions among organisms, not the interactions between organisms and their environment.  Density dependence was the key, density-independence a quaint anachronism.  I remember vividly the argument made by the chairman of my graduate committee, Bob Ricklefs.  “A population without density-dependent control will either go extinct, or cover the world ass-deep.”  Since freshwater gastropods exist [10], and we are not ass-deep in them, they must be under density-dependent control.  Food availability or predation might certainly qualify as potential controls for their distribution, perhaps, certainly not the availability of calcium to build their shells.

 

Robert MacArthur’s theory of island biogeography was also still very much en vogue at Penn in the late 1970s, with its focus on island size.  And somewhere during my first year of graduate training, it dawned on me that both the size of a stream and the hardness of its water might affect its productivity.  And that the quantity of food might be controlling freshwater mollusk distributions in the upper New River, neither the calcium nor the stream size directly.

 

And so, at age 22, I hazarded a guess.  In July of 1978 I drove back down I-95/I-81 south from Philadelphia into those high meadows of the Upper New River where I had spent the summers of my youth, with beakers, cylinders, burettes, bottles of indicators and a 0.02 N sulfuric acid titrant carefully stowed behind the hatch of my 1973 Pinto.  I revisited and re-sampled every one of those 87 sites I had collected in the years previous, this time taking a streamside measurement of alkalinity, more reliable than pH, much easier to measure than calcium or overall hardness.  And this time I estimated a rank abundance for each of the five New River pulmonate snails (excluding limpets, which were omnipresent): Physa acuta, Physa gyrina, Lymnaea humilis, Lymnaea columella, and Helisoma anceps [11].

Dillon & Benfield [16]

I found pulmonate snails at 26 of the 87 sites, marked letters A – Z in the map above.  Confirming and deepening my undergraduate results, pulmonates were common and widespread in the main New River and most of its tributaries downstream from where the river entered the limestone/dolomite zone.  Above that zone, however, pulmonates were generally found only in the main river itself.

 

I summed the rank abundances of the five species into an overall measure of pulmonate abundance for each site.  And I calculated the Kendall rank correlation between pulmonate abundance, alkalinity, stream drainage area and (here’s the key!) the alkalinity x drainage area interaction.  The correlation with interaction (0.35**) was greater than either alkalinity or drainage area alone.

 

OK, one last thing.  Notice in the table above that alkalinity and drainage area were negatively correlated.  I guess that’s not too surprising – a little creek running through a limestone valley can get much harder than a big river, buffered as it is by its large catchment.  This gave me the idea of a nonparametric partial correlation coefficient, analogous to (parametric) partial correlation – a correlation between two variables holding a third variable constant.

Dillon & Benfield [16]

So, I invented nonparametric partial correlation [14].  The table above shows that the Kendall rank correlation between abundance and interaction remains high, even if alkalinity is partialled out (0.31) or if drainage area is partialled out (0.27).  The primary phenomenon is the interaction – the increased productivity that both water hardness and stream size promote – not the calcium nor the stream size directly.

 

When the paper by Dillon & Benfield [16] finally reached publication in 1982, I honestly thought I would become famous.  Brilliant young scientist invents novel statistical technique to answer a fundamental question of freshwater biology!  Alas, no.

 

In a tar-paper shack out of town across the track

Stands an old used-up man trying to call something back

But his old memories fade like the city in the haze

And his days have flowed together like the rain

 

And the dark water springs from the black rocks and flows

Out of sight where the twisted laurel grows

 

Notes:

 

[1] The lovely and haunting lyrics interleaved with this month’s essay come from a song entitled “Twisted Laurel” by The Red Clay Ramblers, one of the greatest bands of the postmodern era.  Some good music is still being made today, but for mysterious reasons has fallen out of fashion with the popular multitude.  Exactly the same could be said for science.

 

[2] A small sample of previous essays in which I have reminisced about my undergraduate experiences at Virginia Tech and traced their subsequent influence on my scientific career:

• To Identify a Physa, 1975 [6May14]
• Pleurocera shenandoa n.sp. [11Mar19]
• Interpopulation gene flow: King Arthur’s lesson [7Sept21]
• Growing up with periwinkles [6Apr23]

[3] For more about APCO’s Blue Ridge Project and its ultimate fate, see:

• Woodard, R. S., Jr. (2006) The Appalachian Power Company along the New River: The defeat of the Blue Ridge Project in historical perspective.  M.A. Thesis, Virginia Tech, Blacksburg.  139 pp. [pdf]

 [4] We never change.  Fifty years later, I am still doing exactly the same thing.

 

[5] Dillon, R.T., Jr (1977) Factors in the distributional ecology of upper New River mollusks (Va/NC).  Undergraduate research thesis, Virginia Tech. [pdf]

 

[6] Boycott, A.E. (1936) The habitats of freshwater molluscs in Britain.  Journal of Animal Ecology 5: 118 – 186.

 

[7] Dillon, R.T., Jr. (2000) The Ecology of Freshwater Molluscs. Cambridge University Press.  509 pp.

 

[8] Boycott verbatim: “Broadly speaking, for the natural waters of this country the reactions run parallel with the quantities of calcium.”

 

[9] Boycott did not categorize 7 of the 62 British species because he felt that his data were insufficient.

 

[10] OK, I realize that I have touched a controversial point.  The vast majority of my colleagues today, including (quite likely) most of the handful of you who will ever read this footnote, believe, as an article of faith, that freshwater gastropod populations are indeed going extinct.  Possibly that every living creature on this earth, except cockroaches, mosquitos, thee and me, is going extinct?  And I will grant you all that the vast majority of all species that have ever lived have, indeed, gone extinct.  That is evolution.  That is not a crisis; that is not even bad.  That is normal.

 

[11] Back in 1978, I was still using George Te’s [12] identifications for the Physa, so Physa acuta = “hendersoni” and Physa gyrina = “pomilia.”  I identified the Lymnaea humilis as “Fossaria obrussa” [13] and used “Pseudosuccinea” as the genus for columella.  Science advances.

 

[12] For the complete story, see:

• To identify a Physa, 1971 [8Apr14]
• To identify a Physa, 1975 [6May14]
• To identify a Physa, 1978 [12June14]
• To identify a Physa, 1989 [3Oct18]
• To identify a Physa, 2000 [6Dec18]

[13] For the complete story, see:

• The American Galba and The French Connection [7June21]
• The American Galba: Sex, Wrecks, and Multiplex [22June21]
• Exactly 3ish American Galba [6July21]

[14] I was unable, however, to offer any statistical inference on my newly-invented Kendall partial rank correlation coefficients.  I was experimenting with Monte Carlo techniques at the time [15], and (in retrospect) should have done so.   Then I would have become famous.  Surely.

 

[15] Dillon, R.T., Jr. (1981) Patterns in the morphology and distribution of gastropods in Oneida Lake, New York, detected using computer-generated null hypotheses. American Naturalist 118: 83-101.  [pdf]

 

[16] Dillon, R.T. and E. F. Benfield (1982) Distribution of pulmonate snails in the New River of Virginia and North Carolina, U.S.A.: Interaction between alkalinity and stream drainage area. Freshwater Biology 12: 179-186. [pdf]

The freshwater gastropods of Georgia Gulf drainages

We here in South Carolina think of Georgia as our younger brother, now outgrown us.  The colony to our immediate south was founded in 1732 to protect us from Spaniards, and in that function, at least, has been largely successful.  Our port cities, Charleston and Savannah, have grown up as sisters.  Our capital cities, Atlanta and Columbia, were both burned by Sherman.  We take turns beating Alabama for national championships.  Georgia grows more onions; we grow more peaches.

But if there is any honor of which our younger brother boasts that we here in South Carolina might envy, it is topographic diversity.  From North Georgia arise real mountains, the southern terminus of the ancient Appalachians.  And from those mountains are born rivers flowing in four directions through six USEPA Level III Ecoregions: north to the Tennessee/Ohio, west to the Alabama/Mobile Basin, south to the Gulf and east to the Atlantic.  The luxuriant aquatic biodiversity of Georgia more than compensates for any shortfall it might suffer in production of cannable fruit.

FWGGA v1.0, release 26Mar07

The Freshwater Gastropods of Georgia (FWGGA) web resource debuted online (at our old cofc.edu address) way back in 2007 with a survey of the Atlantic drainages of Georgia only, approximately 45% of the state.  Our database at that time comprised 845 records of 37 species.  It was migrated (as v2.0) to its present address in 2010, and saw minor upgrades (with additional data and fresh maps) in 2013 (v2.1) and 2024 (v2.2).  So as of last month, the FWGGA website v2.2 reported 960 records of 41 species and subspecies.  But that was for the Atlantic drainages alone.

Speaking now for myself and my coauthors Martin Kohl, Will Reeves, and Tim Stewart, today we are pleased to announce Version 3.0 of the FWGGA web resource, now expanded to include the Gulf drainages of Georgia, extending through 11 counties of the Florida panhandle between the Apalachicola and Suwanee Rivers.  Our database has grown to 1,608 records, documenting 56 species and subspecies of freshwater gastropods in the 85% of Georgia now covered.  Check it out today!

[FWGGA v3.0]

 

Most of our new records were gleaned from the extensive and well-curated mollusk collection held by the University of Florida Museum of Natural History in Gainesville.  Our initial search of the FLMNH online database returned 577 freshwater gastropod records from the Gulf drainages of Georgia and 495 from the 11 Florida counties downstream, for a total of 1,074 records in our enlarged study area.  Simple duplicates – records differing only by date or method of preservation, for example – were removed.  The records were then screened by three primary criteria: (1) dated since 1955, (2) locality data of sufficient quality to be plottable, and (3) habitat not brackish, as far as could be determined.

 

That last requirement turned out to be surprisingly restrictive.  Dr. Fred G. Thompson, who was the senior curator of mollusks at the FLMNH for 50 years, specialized in the hydrobioid snails.  And the museum cabinets that survive him in Gainesville to this day are packed with teensy-little vials full of teensy-weensier little gastropods, collected across every square foot of the Sunshine State, curated with great care.

 

FWGGA v3.0, release 19May25

The hydrobioid snails – especially the cochliopids – are famous for their adaptation to varying salinity.  Ultimately, however, we found it necessary to eliminate Heleobops, Onobops, and Littoridinops monroensis/palustris from our survey, because we could not find any records of any of these inhabiting entirely fresh waters in the area under study here.  That last omission was especially surprising, because Littoridinops monroensis was described from the (entirely fresh) upper St. Johns River system on the Atlantic side of Florida [1].  But this is the Freshwater Gastropods of North America Project, not the brackish, and we must draw a line somewhere, even if our study organisms do not.

So.  This past February I printed the resulting list of 454 panhandle Florida + 255 Gulf Georgia = 709 FLMNH records on a clipboard and made an appointment with our good friend and colleague John Slapcinsky, the collection manager way down south in Gainesville.  And we must take a moment to thank, from the bottom of our hearts, our buddy John for his infinite patience, great good humor, and skillful manipulation of the local parking authority hosting us during our most recent sojourn on his sprawling campus.  All identifications were verified, or (if the corresponding museum lot could not be located), deleted.

All qualified, verified lots of freshwater gastropods from our GA/FL Gulf drainage study area were then georeferenced and plotted.  As a rule of thumb, the FWGNA requires that no pair of records for a single species be collected from the same body of water any closer than 5 km.  Removal of the older record from all such near-duplicate pairs yielded a total of 257 Florida + 230 Georgia = 487 unique, modern, verified, georeferenced FLMNH freshwater gastropod records from the Gulf drainages of our two-state study area.  These were added to the 392 older Atlantic-drainage records, to yield the total of 879 FLMNH records analyzed in FWGGA version 3.0.

 

The additional 161 records newly reported in the FWGGA expansion were almost entirely collected by RTD using simple untimed searches 2003 - 2025, specifically targeting freshwater gastropod habitat [2].  Ultimately our survey covered approximately 645 discrete sample sites, located across the Atlantic and Gulf drainages of Georgia, extending through the 11 counties of the Florida panhandle between the Apalachicola and the Suwanee.  See the map above.  No “absence stations” are shown.  If freshwater gastropods were not collected at a site, then no record resulted. 

Marstonia castor UF22178

Our entire 1,608 record database is available (as an excel spreadsheet) from yours truly upon request.

The list of 56 species and subspecies of freshwater snails we have documented from our study area omits Marstonia castor, described by Thompson in 1977 as endemic to Cedar Creek in Crisp County, Ga [3].  Although the FLMNH collection also includes more recently-collected lots of M. castor from Swift Creek (Crisp Co) and Mercer Mill Ck (Worth Co), our 2023 efforts to locate a viable population anywhere in the region were unsuccessful.  The FWS listed M. castor as extinct in 2017, and we concur.

Combining subspecies for analysis, the freshwater gastropod fauna of the region under study here reduces to 53 species: 35 prosobranchs and 18 pulmonates.  Of the pulmonates, three are extralimital or introduced: Biomphalaria, Promenetus, and Physa gyrina. Helisoma scalare is Floridian.  The remaining 14 pulmonate species are all common throughout the southeastern United States, in some cases stratified by ecoregion: Physa carolinae and Helisoma trivolvis (for example) restricted to the coastal plain, Ferrissia rivularis in the piedmont and mountains.

 

A Gradual Transition

More biogeographic signal is apparent in the prosobranchs.  Of the 35 prosobranch species we identified in our study area, 10 are unique to the Gulf drainages, 10 are unique to the Atlantic drainages, and 15 are shared across the state of Georgia broadly.  This observation does not support the hypothesis advanced by Thompson & Hershler [4] that “with the exception of Lyogyrus and two species of Viviparus,” the prosobranch faunas of the Atlantic and Gulf drainages of Georgia “have no species in common.”  Rather, the distributions of the freshwater gastropods of Georgia apparently reflect a gradual transition or blending between the faunas of Atlantic drainages to the east, Alabama/Coosa drainages to the west, and Florida to the south.

 

The DFS Zone

Our modern survey has, however, corroborated the 1991 observations of Thompson & Hershler [4] that the drainage basins of the Satilla and the St. Marys Rivers of the Atlantic drainage, plus the upper portions of the Suwannee and Ochlockonee River systems of the Gulf drainage, are virtually “devoid of freshwater snails.”  The striking absence of sample sites in that region clearly evident on the map above is not due to a lack of effort on our part.  We travelled that area extensively, donning boots and searching keenly, ultimately returning with no freshwater gastropod observations to report.  We here refer to that region as the “DFS Zone,” for “devoid of freshwater snails.”

 

Citing evidence from the paleontological results of Aldrich [5], Thompson and Hershler suggested that the DFS Zone had a rich freshwater gastropod fauna in the Pleistocene, similar to that of surrounding regions today, and attributed the depauperization of the modern fauna to “water chemistry factors” recent in their origin.  We ourselves are hesitant to generalize the fresh/brackish Pleistocene malacofauna catalogued by Aldrich from the lower Satilla across the entire DFS Zone.  But the hypotheses that Thompson & Hershler advanced regarding the influence of bedrock and soil type on water chemistry, and the influence of water chemistry upon freshwater gastropod distributions, are well supported [6].

To live and die in Dixie...

The Satilla, the St Marys, the upper Suwanee and the upper Ochlockonee drainages in South Georgia are underlain by Cretaceous gravels and sands, yielding soft, acidic, low-carbonate surface waters to which freshwater gastropod populations are often poorly adapted.  And to the inhospitable water chemistry of this region, we would hasten to add the inhospitable water physics.  Silt.

 

Clench & Turner [7] suggested that “the greatest source of damage” to the freshwater mollusk fauna of the Georgia Gulf drainages “seems to be land erosion and consequent silting of the rivers.”  For over a century, most of the state was intensively farmed for cotton, stream bank to stream bank.  Harding and colleagues [8] reported that the best predictor of current macroinvertebrate diversity in East Tennessee river systems is not present land use, but rather land use prior to 1950.  We suggest that the intensive burdens of silt that have been carried, and that continue to be carried, by the rivers of South Georgia, together with the softness, acidity, and poor buffering capacity of the regional surface waters, account for the phenomenon we here describe as the DFS Zone.

Although relatively minor in areal extent, the expansion of FWGNA coverage to include this diverse little drip of North American freshwater nevertheless resulted in the addition of 9 new gastropod species and subspecies to the 136 previously included in our coverage, bringing our continental total to 145.  Come visit us again, for the first time!

 

Notes:

 

[1] Von Frauenfeld, G. R. (1863) Verhandel. Kais. Konig. Zool. Botan. Ges. Wein 13: 1023.

 

[2] Dillon, R.T., Jr. 2006. Freshwater Gastropoda. pp 251 - 259 In The Mollusks, A Guide to their Study, Collection, and Preservation. Sturm, Pearce, & Valdes (eds.) American Malacological Society, Los Angeles & Pittsburgh.

 

[3] Thompson, F.G. (1977) The hydrobiid snail genus Marstonia.  Bulletin of the Florida State Museum, Biological Sciences 21: 113 – 158.

 

[4] Thompson, F.G. & R.H. Hershler. 1991. Two new hydrobiid snails (Amnicolinae) from Florida and Georgia, with a discussion of the biogeography of freshwater gastropods of South Georgia streams. Malac. Rev. 24:55-72.

 

[5] Aldrich, T.H. (1911) Notes on some Pliocene fossils from Georgia with descriptions of new species.  Nautilus 24: 131 – 132, 138 – 140.

 

[6] For a review of the effects of calcium concentration and related water chemical variables on the distribution of freshwater gastropods, see pages 326 – 338 in:

• Dillon, R.T. Jr (2000) The Ecology of Freshwater Molluscs.  Cambridge University Press. 509 pp.

[7] Clench, W.J. & R.D. Turner. 1956. Freshwater mollusks of Alabama, Georgia, and Florida from the Escambia to the Suwannee River. Bull. Fl. State Mus., Biol. Sci. 1:95-239.

 

[8] Harding, J.S., E.F. Benfield, P.V. Bolstad, G.S. Helfman and E.B.D. Jones (1998) Stream biodiversity: The ghost of land use past. Proceedings of the National Academy of Sciences 95: 14843 - 14847.

Potamopyrgus, water hardness, and the Gatorade hypothesis

Volume 28(1) of Freshwater Mollusk Biology and Conservation hit the newsstands a couple weeks ago with the unwelcome news that populations of the invasive New Zealand mudsnail, Potamopyrgus antipodarum, have been discovered in two small tributaries of the Monongahela River in Allegheny County, Pennsylvania [1].  These are the first records of Potamopyrgus in the Ohio drainage.

For as many seasons as I have been watching Invasive Species Baseball from the grandstands, the Commonwealth of Pennsylvania has been a perennial contender for the MVA (Most Vigilant Agency) award.  The Pennsylvania Natural Heritage Program iMapInvasives web-based system is peerless, or almost so [2], anywhere in The East.  And in addition to maintaining the state’s elaborate citizen-friendly tool for online reporting, Ms. Amy Jewitt and her iMapInvasives staff post email alerts, publish a newsletter and a blog, sponsor workshops and webinars, and recently even produced a 44-minute, documentary-style film.

Rarely does a month go by that I don’t hear from Amy.  And I’ve also developed longstanding correspondence relationships with Steven Means of the PADEP and Sean Hartzell of the Pennsylvania Fish and Boat Commission (PFBC), who anchors the scientific side of the enterprise [3]. And more often than not, the subject line of all this correspondence with all these colleagues features the abbreviation “NZMS,” New Zealand mudsnail.

Peters Creek, Allegheny Co, PA

So, when one of my clerks dumped the morning mailbag onto the sorting table in my office back on June 26, 2023, I was not surprised to find a cordial message from my good buddy Sean.  And attached to his message was the usual quota of jpeg images of Potamopyrgus, including the one reproduced above.

But although the news that Sean relayed in his 26June23 message was not surprising, I don’t suppose, it was anything but routine.  Three days previous, a PFBC colleague, Mr. Mike Depew, had collected the gastropod sample depicted on those jpegs from a pair of small direct tributaries of the Monongahela River just upstream from Pittsburgh – Peters Creek and Turtle Creek.  Rats.  The first records of Potamopyrgus in an interior drainage of the Eastern United States [4].

My loyal readership will be quite familiar with Potamopyrgus from many previous posts on this blog; occasional visitors are invited to hit the “Invasive species” label at right for a review.  The first Atlantic drainage NZMS population was reported in a mid-Pennsylvania tributary of the Susquehanna River back in 2013 [19Nov13], with reports from Maryland [13June18] and New Jersey [9July18] following rapidly.

In their newly-published note [1], Sean, Mike, and three additional PFBC colleagues have done an excellent job reviewing the ten-year history of this recent Eastern U.S. range expansion, contributing a very nice map of the current distribution of Potamopyrgus across The Keystone State.  Quoting the authors, “both Peters Creek and Turtle Creek contain sections managed as stocked trout fisheries with public fishing access.”  They suggest that this most recent range expansion likely comes “via angling gear from previously invaded sites.”  We concur.

But returning to June of 2023.  In his original message to me, Sean called my attention to the pitting on the shells of the little snails in his jpegs (clearly visible in the figure at the top of this essay), which he “hadn’t seen in Potamopyrgus antipodarum before.”  I agreed that such pitting is unusual, and we swapped a couple additional emails on the topic.  Quoting myself:

The short answer to your question about shell pitting would be, “soft water.”  Presumably Peter’s Creek and Turtle Creek have lower concentrations of calcium, right?  So anywhere the outer proteinaceous periostracum of the shell gets nicked a little bit, the calcium carbonate core of the shell is exposed to dissolution, forming a pit.

That said.  If you’d like to re-write the paragraph above, and scratch out “soft water,” and substitute “Low pH” or “low alkalinity” or “low carbonate” or “Low buffering capacity” or maybe even overall “low conductivity,” it would all be just as true [5].

My 26June23 hypothesis, however, turned out to be unsupportable.  Even as I was offering it, Sean and his PADEP colleague Matthew Shank were embarking on an extensive, statewide study on the relationship between water chemistry and Potamopyrgus invasion that would find the hardness of Peters and Turtle Creeks perfectly suitable.

The Hartzell & Shank paper, published online "early view" last fall and February in hard copy [6], correlated NZMS presence/absence at 443 sites in Pennsylvania to 57 water chemical parameters, including (of course) all those hardness-related variables I had suggested in 2023.  They plotted their 71 present observations (red) and 372 absent observations (blue) on the simplified geological map of Pennsylvania reproduced below.  The relationship between successful Potamopyrgus invasion and the presence of limestone and dolomite in the drainage is striking, am I right?

From Hartzell & Shank [6]

And indeed, the Hartzell & Shank map does show a pair of red “present” dots in the west corresponding to Peters Creek and Turtle Creek [7], indicating limestone in their drainages as well.  Quoting Sean from our more recent (14Apr25) correspondence:

“Although the area has been (mostly historically) impacted by mining, the pH and conductivity samples we had on file for those streams were not reflective of soft water. Additionally, the statewide water chemistry suitability analyses that my colleague Matthew Shank and I worked on more recently . . . suggests that the two respective HUC12s that the snails were found in contain various highly suitable chemical parameters for this species.”

So what, then, might have been the cause of the shell pitting in the original 2023 samples of Potamopyrgus from Peters and Turtle Creeks?  Again, quoting my good buddy Sean, from our 14Apr25 correspondence:

“When Mike (Depew) sampled these streams (both on the same date) and upon finding the P. antipodarum, he realized he neglected to pack any containers to bring snails back to the lab and so upon improvising, he placed them in half-empty Gatorade bottles that he had on hand. As a result, the snails were submerged in Gatorade for about 24 hours before they were transferred to distilled water. From my understanding, Gatorade is quite acidic (a quick Google search indicates a pH of 2.9 to 3.6 depending on the exact flavor purchased) and so this is likely the cause of the pitting observed in the snails.”

Flavor not being among the 57 parameters analyzed by Hartzell & Shank, however, I fear that we shall never have a conclusive answer to this particular mystery.

 

Notes

 

[1] Hartzell, S.M., M.A. Depew, D. Byington, L. Hartman, and R. Pletcher (2025) Collections of the invasive New Zealand mudsnail, Potamopyrgus antipodarum (J.E. Gray, 1843) in the Ohio River basin.  Freshwater Mollusk Biology and Conservation 28: 22 – 25.

[2] To be fair, both New York and Maine also participate in NatureServe's iMapInvasives Network.  But I don't know any of those dedicated folks way up there.  

 

[3] Recent publications from our good friend Sean:

• Hartzell, S.M. and N. Macelko. 2022. Range expansion of the invasive New Zealand Mudsnail (Potamopyrgus antipodarum) in the Susquehanna and Delaware River Basins of Pennsylvania.  Journal of the Pennsylvania Academy of Science 96: 36 - 45.
• Hartzell, S.M. and J.R. Frederick. 2023. First records of the invasive New Zealand mudsnail (Potamopyrgus antipodarum) in the Potomac River Basin.  Northeastern Naturalist 30 (1): N13 - N16.

[4] The USGS Nonindigenous Aquatic Species database does show quite a few records in Wisconsin tributaries of the Rock River, which I think of as being midwestern.

 

[5] I reviewed the subject of environmental calcium as a factor in freshwater gastropod distribution at great length in Chapter 8 of my book, pp 326 - 338:

• Dillon, R.T., Jr. (2000) The Ecology of Freshwater Molluscs.  Cambridge University Press.  509 pp.

[6] Hartzell, S.M. and M.K. Shank. 2025.  Chemical variables predicting colonization risk of the invasive New Zealand mudsnail (Potamopyrgus antipodarum) in Pennsylvania's flowing waters.  Hydrobiologia 852: 645 - 658. https://doi.org/10.1007/s10750-024-05711-2.

 

[7] At the earlier date of the publication of their water quality paper, Hartzell & Shank listed their observations of Potamopyrgus in drainages of The Ohio as “Hartzell et al. unpublished data.”

Lymnaea (Galba) bulimoides and the NCBI GenDump, with lecture notes on the scientific method

Looking back over my essays of the last two months [13Feb25, 11Mar25], as well as my essay of February a year ago [13Feb24], I feel as though my efforts to review the historical and technical background behind my Oregon field trip for L. bulimoides last summer have been largely successful.  But there is a human context as well, to which I fear I have given short shrift.

My faithful readership will (I trust) remember our old friend Dr. Phillippe Jarne of the French National Centre for Scientific Research (CEFE-CNRS) in Montpellier [1], yes?  It was Philippe who introduced me electronically to Dr. Pilar (Pili) Alda back in 2017, when she was working as a postdoc in the laboratory of Dr. Sylvie Hurtrez-Bousses at the Universite’ de Montpellier.  Pili was the lead author on both our (2018) multiplex PCR paper on Galba [3] and that huge (2021) molecular phylogenetic review of the subgenus Galba worldwide [4].  She is currently at CONICET-CERZOS, the Argentinian National Research Agency in Bahia Blanca.

So, I have long harbored suspicions about the lymnaeid fauna of Western North America.  Those suspicions compounded when I began working with Bruce Stephen on the Freshwater Gastropods of the Great Plains project in 2020, expecting to find Lymnaea (Galba) bulimoides in that region, finding  L. cubensis/viator and L. cockerelli but nothing that matched Isaac Lea’s 1840 bulimoides types from Oregon [5] whatsoever.  I promoted my suspicions to the status of an hypothesis in a pair of essays posted on this blog in February [13Feb24] and March [12Mar24] of last year, ultimately concluding that while “huge international teams” have published “mountains of research” on the evolutionary relationships among all the other hosts of Fasciola worldwide, here in the USA we have “zero authentic DNA sequences” for any population of our own L. bulimoides.

Lymnaea (Galba) of the American West [6]

Shortly after that, I began swapping emails with Philippe and Pili.  And over the course of the following months, from mid-March to early May of last year, a miniature online symposium developed on evolutionary relationships among the Galba populations of the western USA, ultimately growing to include Patrice David (CEFE-CNRS), Jean-Pierre Pointier (Universite de Perpignan), and Sam Loker and Martina Laidemitt of the University of New Mexico.  I confess that the main item on my agenda [7] was to find somebody else – anybody else – to fly out to Oregon and collect us a bona fide, gold-seal sample of L. bulimoides.  But ultimately, I found myself volunteering.  And Pili already had plans to return to Montpellier in September, and volunteered to do the sequencing and analysis.

And so it came to pass that my wife and I boarded Delta Flight 954 bound for Portland on July 31, 2024, to return, five days later [8], defeated and humiliated by a basommatophoran pulmonate.  See my essays of February[13Feb25] and March [11Mar25] for a painful recounting.  But tucked into my shirt pocket were those N = 2 individual L. bulimoides that Ms. Courtney Hendrickson had preserved from Gahr Pond in the spring of 2023.  And those I forwarded onward to Philippe and Pili in August.

And in early November, Pili sent us her results.  She sequenced the same four genes that we had analyzed in our 2021 collaboration: the mitochondrial CO1 and 16S, and the nuclear ITS1 and ITS2.   And her results looked like a phylogenetic shotgun blast.

For some reason I always look at CO1 first, and the closest CO1 match to our two Gahr Pond bulimoides anywhere in GenBank was 90 – 91% to Galba cousini from Ecuador.  That strikingly low similarity with anything else supported my primary hypothesis, that all DNA sequences previously deposited into GenBank as “bulimoides” were spurious [13Feb24].  The result did not support my speculation (based on shell morphology) that South American L. cousini might be conspecific with North American L. bulimoides – 10% CO1 divergence is very significant in pulmonate phylogenetics [9].  But it left me with a fig leaf.  The evolutionary relationship between bulimoides and cousini appeared to be closer than any other.

Pili’s 16S mtDNA results also supported my primary hypothesis.  Our pair of Gahr Pond 16S sequences were around 96% similar to maybe 50 – 60 sequences already deposited in GenBank, including truncatula and “humilis” from the former Soviet Republic of Georgia, Brazilian “truncatula,” Japanese “pacifica,” junk from everywhere.  Simply no bona fide matches.

One of Pili’s ITS1 sequences was too short to be informative, but the other was wildly unique – no match closer than 82% in all of GenBank.

Our Gahr Pond ITS2 results, by striking contrast, did hit close matches to a pair of sequences already in GenBank, uploaded in 2020 by the English researchers A. J. Saadi and colleagues in connection with a molecular phylogenetic study of the freshwater pulmonates [10].  Working from their laboratory at the University of Nottingham, Saadi et al. sequenced 4000 nucleotides from the rRNA gene cluster of 39 individual snails, including part of the 5.8S gene, the complete ITS2 region, and almost the entire 28S gene.  They missed the ITS1 region (just upstream from 5.8S) and didn’t touch the mitochondria at all.

The closest of the close matches to our Gahr Pond bulimoides was 98.2% to a sequence from a snail that Saadi and colleagues identified as “Polyrhtis apicina,” but was subsequently emended to Stagnicola or “Ladislavella” apicina, with collection location unknown and collector unknown.  Absolute garbage.  Sometimes I think the NCBI should rename its GenBank to GenDump.

The Willamette Valley of Oregon

But the other close match, 97.6%, was to a sequence from a snail that Saadi identified as “Bakerilymnaea bulimoides (= Fossaria bulimoides),” subsequently listed in GenBank as Galba bulimoides [11], from “Corner of Alvadore Road, Lane County, OR, USA” with the collector identified as our old buddy Dwight Taylor [13].

The corners of Alvadore Road – there are two of them about 500 m apart, actually – are just 40 km south of the Bellfountain Road site I had targeted back in August as the ideal type locality for Lymnaea (Galba) bulimoides.  How a sample of bona fide L. bulimoides, correctly identified with good locality data, found its way from Dwight Taylor’s 1970s-era collection bucket into the buzzing thermal cyclers of Nottingham, England, I cannot imagine.

So, my hypothesis was confirmed, with an asterisk.  In my post of [13Feb24] I had written:

“Meanwhile here in the USA, the richest country on earth, the leader of the free world, we have zero authentic sequences for any population of our own Lymnaea (Galba) bulimoides, known to be an important host of livestock fluke across the Pacific Northwest since 1929.”

That turned out to be sort-of true, but I should have footnoted, “except two rRNA sequences contributed by Saadi et al, one of which was misidentified and utterly useless.”  All the other (really rather few) sequences labelled bulimoides in GenBank were spurious, most notably the 16S/CO1 pair from Oklahoma uploaded by Remigio [14, 15] that caused Correa [16] and Alda [4] and me myself a sinner [7Aug12] to hypothesize that bulimoides might be a junior synonym of cubensis/viator.

I taught freshman biology at the College of Charleston for many years, although I was never any good at it, to judge from student evaluations, which were the only criterion that mattered when the time came for my own annual evaluation.  And the first lecture of the semester, which most of the students missed, because they were all still standing in line at registration or lost on campus, was “The Nature of Science, and The Science of Nature.”  I kicked it off with a blanket statement that this was to be the most important lecture of the semester, and the material I intended to review was so complex and so other-worldly and so difficult to grasp that even most professional scientists never figure it out in our entire careers.

Science is the construction of testable hypotheses about the natural world.  The process by which science moves forward is called “the scientific method.”  But please do not confuse the product with the process.  It is entirely possible to use the scientific method to determine (for example) what color box of detergent is most attractive to housewives shopping in the grocery store.  Just because some guy is wearing a white lab coat, conducting experiments and collecting data in a systematic fashion, does not mean that he is a scientist.  The subject matter must be the natural world.

The scientific method begins with a question, like “What is Lymnaea bulimoides?” [13Feb24]  Then, good scientists do library research – a lot of it – which together with experience and intuition from a fundamental understanding of the foundations of their discipline, enable them to precisely frame a testable hypothesis about the natural world, like “there is not a worker in the field today – not malacologist, nor parasitologist, nor veterinarian, nor guardian of the public health – who could identify a bona fide Lymnaea (Galba) bulimoides if it bit him on the boot toe” [13Feb25].

Then comes the gathering of data to test that hypothesis, such the expedition to Oregon and subsequent DNA sequencing I have now spent three blog posts detailing.  Then data analysis – GenBank fishing in our case – and conclusion.  Hypothesis true.

The Scientific Method [17]

As I delivered my lecture I was, of course, scrawling the steps of the scientific method on the chalkboard in some grossly graphic fashion.  I would then suddenly turn to my students and assert that in actual practice, most of what passes for science of the present day is done backwards.  Huge research groups and agencies – I usually mentioned NASA, for example – typically begin with data collection, then try to find an hypothesis within those data somehow, and then finally, maybe, go to the library to see if anybody had published anything on an hypothesis like theirs before.

It has now gotten to the point, I used to wag my finger at my half-empty lecture hall of freshmen, that my colleagues often segregate science conducted according to the diagram I have outlined on the chalkboard as “hypothesis-driven research.”  But if your research is not driven by a precisely-framed, rigorously-testable hypothesis about the natural world, you are not doing science, you are just screwing around with test tubes.

Now turning to you, my present readership. The construction of a gene tree is not and cannot be the beginning of a research effort!  You cannot derive an hypothesis from a gene tree.  The only appropriate application for a gene tree is to test an hypothesis that you have clearly stated a priori on the basis of library research, field experience, and biological intuition.

We do not need any more DNA sequences from random freshwater gastropods shoveled into the NCBI GenDump.  We do not need any more odd-lot molecular phylogenies of random freshwater gastropod genera or families – we don’t understand the ones we’ve got now.  We do not need more data; we do not need more analysis.  What we need are more precisely-framed, rigorously-testable hypotheses.  Which can only come from a thorough education in evolutionary science, a firm understanding of the biology of the remarkable creatures to which we have dedicated our careers, rigorous scholarship and field experience, lots of all of it.

So finally, returning to our research program on Lymnaea (Galba) bulimoides.  We have proceeded in orderly fashion from question to hypothesis to data to analysis to conclusion.  But there remains yet one final box in the flow chart I used to scrawl on the blackboard in front of my doe-eyed freshmen – a box that the International Bulimoides Study Team has not as yet checked.  And there will be a fourth essay in this series, eventually.  But next month we are moving on to other topics.  So, stay tuned.

Notes

[1] See the brief bio and cute little 2012 photo of Philippe and his postdoc Patrice David [2] in:

• The American Galba and The French Connection [7June21]

[2] Patrice would subsequently rocket to malacological stardom by discovering:

• Cytoplasmic male sterility in Physa! [9June22]
• Cytoplasmic male sterility in the Physa of the Snake River [7Aug24]

[3] Alda, Pilar, M. Lounnas, A. Vázquez, R. Ayaqui, M. Calvopiña, M. Celi-Erazo, R. T. Dillon, P. Jarne, E. Loker, F. Pareja, J. Muzzio-Aroca, A. Nárvaez, O. Noya, L. Robles, R. Rodríguez-Hidalgo, N. Uribe, P. David, J-P. Pointier, & S. Hurtrez-Boussès (2018). A new multiplex PCR assay to distinguish among three cryptic Galba species, intermediate hosts of Fasciola hepatica.  Veterinary Parasitology 251: 101-105. [html] [pdf].  For a review, see:

• The American Galba: Sex, Wrecks, and Multiplex [22June21]

[4] Alda, Pilar, M. Lounnas, A.Vázquez, R. Ayaqui, M. Calvopiña, M. Celi-Erazo, R.T. Dillon Jr., L. González Ramírez,  E. Loker, J. Muzzio-Aroca, A. Nárvaez, O. Noya, A. Pereira, L. Robles, R. Rodríguez-Hidalgo, N. Uribe, P. David, P. Jarne, J-P. Pointier, & S. Hurtrez-Boussès (2021) Systematics and geographical distribution of Galba species, a group of cryptic and world-wide freshwater snails.  Molecular Phylogenetics and Evolution 157: 107035. [pdf] [html].  For a review, see:

• Exactly 3ish American Galba [6July21] 

[5] Isaac Lea initially described Lymnaea bulimoides in brief Latinate form in 1841, with more complete English description in 1844:

• Lea, I (1841) On fresh water and land shells (continued).  Proceedings of the American Philosophical Society 2(17): 30 – 34.
• Lea, I. (1844/46) Continuation of Mr. Lea’s paper on fresh water and land shells.  Transactions of the American Philosophical Society 9(1): 1 – 31.

[6] Lymnaea humilis from Bellingham, Washington, L. bulimoides from Alvadore Road, L. viator from Alda et al. [4], L. cockerelli from Bosque del Apache, NM.  Thanks to Will Reeves for the first, and photo credits to J-P. Pointier for the last three.

 

[7] Actually, the evolutionary relationships of the mysterious “Bosque del Apache” population from New Mexico may have been a topic of greater discussion than Lymnaea bulimoides.  Originally identified as Galba cubensis in the gigantic 2021 paper we had all coauthored with Pili [4], molecular data kicked the Bosque del Apache population out as specifically separate.  Ultimately the research I reported in my essay of [12Mar24], together with the shell morphology, convinced the entire working group that “Galba sp Bosque del Apache” must have been Lymnaea (Galba) cockerelli.  Grist, perhaps, for a future post.

 

[8] My exceptionally keen-eyed readership might note that my essays of February and March covered three days only.  Shary and I toured the Oregon Coast on Aug 3, and the Columbia Gorge on Aug 4.  It was the least I could do for her.  She was very patient with me.

 

[9] As a rule of thumb, a CO1 sequence divergence of 5% or more suggests speciation in the freshwater pulmonates.  For my rationale, see:

• The Lymnaeidae 2012: stagnalis yardstick [4June12] 

[10] Saadi, A.J., A. Davison and C.M Wade (2020) Molecular phylogeny of freshwater snails and limpets (Panpulmonata: Hygrophila)  Zoological Journal of the Linnean Society 190: 518 – 531.

 

[11] Here, writ in flickering pixels on the face of an obscure blog, is the Embarrassment of International Malacology.  Six generic names – Stagnicola, Ladislavella, Polyrytis, Bakerilymnaea, Fossaria, and Galba – for a single biological species that ought never to have been split from Lamarck’s (1799) Lymnaea [12].  Please stop making up ridiculous names for random subsets of mollusks, everybody!  You make us look like a bunch of clueless hacks.  Which we are.  But must we broadcast that sad fact to the world?

 

[12] For a bracing splash of 1951 common sense in the rouged face of 21st century systematic malacology, see

• The Classification of the Lymnaeidae [28Dec06].

[13] My faithful readership will certainly remember Dwight Taylor as the author of the great Snake River Physa scandal [12Mar08, 14May24, 11June24].  Early in his career he (correctly) recognized the specific status of Lymnaea cockerelli [12Mar24] and (cavalierly) detonated the genus Helisoma [11Apr08].

 

[14] Remigio, E.A. and Hebert, P.D. (2003) Testing the utility of partial COI sequences for phylogenetic estimates of gastropod relationships.  Molecular Phylogenetics and Evolution 29 (3): 641-647.

 

[15] Remigio, E.A. (2002) Molecular phylogenetic relationships in the aquatic snail genus Lymnaea, the intermediate host of the causative agent of fascioliasis: insights from broader taxon sampling, Parasitol. Res. 88 (7), 687-696.

 

[16] Correa, A.C., J.S. Escobar, O. Noya, L.E. Velasquez, C. Gonzalez-Ramirez, S. Hurtrez-Bousses & J-P. Pointier (2011)  Morphological and molecular characterization of Neotropic Lymnaeidae (Gastropoda: Lymnaeoidea), vectors of fasciolosis.  Infection, Genetics and Evolution 11: 1978-1988.  I reviewed that paper in my post:

• The Lymnaeidae 2012: Fossarine Football [7Aug12]

[17] Graphic from The Biologos Forum.