Dr. Rob Dillon, Coordinator

Friday, October 16, 2015

To Only Know Invasives

Editor’s Note – This essay was subsequently published as: Dillon, R.T., Jr. (2019d) To Only Know Invasives.  Pp 63 - 71 in The Freshwater Gastropods of North America Volume 4, Essays on Ecology and Biogeography.  FWGNA Press, Charleston.

I’ve never compiled any statistics, but it is my impression that the most common category of inquiry I find delivered to my email inbox on any long-term basis probably bears the modifier “invasive” on the subject line.  Such messages are usually requests for identification of putatively exotic freshwater gastropods, with jpeg images attached.  Sometimes these inquiries come from professional biologists working with agencies, and other times just from ordinary concerned citizens.  I always try to help.

So a couple years ago I receive a variant of the typical email described above, from a NOAA biologist in the Great Lakes area.  The attached jpeg image depicted a couple beach worn shells of the common pleurocerid Pleurocera semicarinata livescens.  And in the body of his message the biologist confessed, amidst other routine background matter, “I really only know the invasives.”  He was quite certain that these freshwater gastropods were not Bithynia, or Bellamya, or Potamopyrgus.  But he didn’t know what they were.

And this struck me as a sad way of looking at the world.  One is reminded of a clinical practitioner who never leaves the hospital – only knowing the sick, never meeting the well. 

But in a larger sense, the existence of a biologist, or an agency, or indeed multiple governmental agencies, who “only know invasives” has become an article of public policy in recent years.  The Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 established a body called the “Aquatic Nuisance Species Task Force,” with representation from 13 federal agencies, which in turn established a National Nonindigenous Aquatic Species Information Center “to collect, analyze, and disseminate information about the presence and distribution of nonindigenous aquatic species and their effects.”  That Center is currently located at the US Geological Survey’s Southeast Ecological Science Center in Gainesville, Florida [1].

The most visible product of the USGS Information Center has been the development of the Nonindigenous Aquatic Species database, which can, under some circumstances, be a useful resource, if you understand its limitations, which are extensive.  Do open this site in a new window and check it out, if you’re not familiar with it already:

The USGS-NAS tracks a staggering 44 species (or categories of species) of freshwater gastropods: 11 ampullariids, 8 viviparids, 3 thiarids, 7 miscellaneous prosobranchs, 7 planorbids, 5 physids, and 3 lymnaeids.  Of this extensive list only 32 are exotic; 12 species or categories are native to North America, but have expanded their ranges so recently or so dramatically, possibly by human agency, as to attract the attention of The Feds.  Current distributions of these 44 species are displayed as good quality dot maps which are zoomable and clickable, to see the underlying records.  Public users are allowed to add records to the database through a process that is not terribly difficult or onerous, which certainly has a downside, but which (on the whole) I think is good.

The site is, however, a taxonomic mess.  It reminds me of my son’s bedroom, when he was nine years old.  Stuff is thrown around everywhere, and it would be very difficult to find anything you might want in there, if (hypothetically) you wanted to find it, and most of the stuff you can see when you pass by the open doorway is just junk, and should be thrown out.

USGS-NAS chinensis
For example, the USGS-NAS collects data on four separate categories of the Asian Mystery Snail: Cipangopaludina japonicaCipangopaludina chinensisCipangopaludina chinensis malleata, and "Cipangopaludina species.”   The most current science suggests, however, that just two species of mystery snail have been introduced to North America, best identified as Bellamya japonica and Bellamya chinensis.  It is very difficult for laymen, or indeed most field biologists, to distinguish japonica from chinensis.  In fact, both of the thumbnail photos of shells adorning the clickboxes for chinensis and japonica on the USGS-NAS website depict chinensis [2].

I really don’t trust the species-level identifications upon which any of the four “Cipangopaludina” maps are based, and would advocate combining all those data into a single map that simply shows “Bellamya species.”   If the mission of the USGS-NAS database is indeed to disseminate information about the “distribution of nonindigenous species and their effects,” B. chinensis and B. japonica are ecologically equivalent [3], and combining them would make sense.

USGS-NAS "japonica"
(not, actually)
The situation is much more complicated in the Ampullariidae, I fear.  It is not entirely clear how many exotic species of Pomacea have been introduced into US waters, but the best hypothesis at this writing is probably four: Pomacea maculata (aka insularum) which is the most common, Pomacea canaliculata (bona fide) which is very similar but more rare, Pomacea diffusa (aka bridgesii) which is smaller and not as voracious, and Pomacea haustorum, which is much larger and rare.  I myself am not sure I could distinguish maculata from canaliculata (bona fide) in the field, although their egg masses are distinctive [4].

So users of the USGS-NAS database will find these four differently-sized pies cut into seven differently-sized pieces: maculata, canaliculata, diffusa, bridesii, haustorum, cumingi, and “Pomacea species.”  Again, I really don’t trust any of the identifications upon which any of the resulting maps are based, and would advocate collapsing the categories ecologically, into “Exotics that do eat macrophytes” (maculata, canaliculata, haustorum, and probably “species”) and “Exotics that do not” (diffusa, bridgesii, and cumingi).

I have similar misgivings about almost all the pulmonate groups.  Lymnaea auricularia can be identified unambiguously, but the distinction between “Planorbella duryi” and “Helisoma species” gives me pause, and just the thought of clicking on some of those physid links scares me to death.  What the heck is exotic “Physella species?”  Some of the things in my 9-year-old son’s bedroom did not warrant close examination.

But to be clear, I am not criticizing the hard-working public servants who are doing their best to administer the USGS Nonindigenous Aquatic Species database.  They are trying to play baseball in a bluegrass jam session, bless their hearts [5].

And the most important feature of the USGS-NAS database is not the maps, but rather the ready
availability of the data upon which the maps are based.  Some of the USGS records are ancient extractions from vague literature reports, while others are rigorously documented and vouchered at major museums.  As long as we users can right-click and judge the quality of the records ourselves, I can’t see how any damage can be done.  And some benefit might certainly be had.

So what fraction of the USGS-NAS data might be useful for the FWGNA project?  And should we move to incorporate it?

At this point I should register a scruple.  The primary goal of the FWGNA project has always been to survey the distribution and abundance of the North American freshwater gastropod fauna, as objectively as possible.  Early on we identified a phenomenon I called “conservation-biased oversampling" [6] which is the (self-defeating) tendency for agencies to conduct surveys directed toward putatively-endangered species.  And I have consistently tried to avoid incorporating data which might reflect such bias in the FWGNA database, albeit with mixed success.

The USGS-NAS database very clearly demonstrates a related phenomenon, which I hereby dub “invasion-biased oversampling.”  I suppose if the USGS ran a parallel site, where biologists might upload data on the native species of freshwater gastropods they found in addition to the nonindigenous species recorded at each site, such a bias would not be a problem.  But they don’t, so it is.

With that dab of balm applied to my tender conscience, last week I spent a few hours fishing around in the USGS-NAS database [7], looking for good-quality freshwater gastropod records that might reasonably be added to the FWGNA.  I focused on the Atlantic-drainage fauna of the nine-state region from Georgia to the New York line, the region with which I am most familiar.  I disqualified the Bellamya (“Cipangopaludina”) records, the Pomacea records, and any weirdo pulmonate records for the reasons outlined above.  This left me with just the four taxa it is harder to mess up: Viviparus, Bithynia, Potamopyrgus, and Melanoides.

USGS-NAS V. georgianus
Well actually, Viviparus is a bit problematic.  The NAS database contains 235 records in total: 227 of Viviparus georgianus, 7 of Viviparus viviparus and 1 of Viviparus subpurpureus.  The distinction between (the putatively native) V. georgianus and (the European) V. viviparus simply is not clear [8], but lumping those two categories and sorting geographically, I was able to extract 10 records.  Three of those records corresponded to populations already in the FWGNA database.  Four referred to Viviparus populations in the Potomac River near Washington, of which I was already aware, but which I have been unable to confirm.  The other three records were from the 1970s, not vouchered or accompanied by sufficient data [9].

The USGS-NAS database also contains (a very similar) 247 records of Bithynia tentaculata, of which 9 fall in our study area.  All nine of these records refer to the Potomac River Bithynia population already well-documented in the FWGNA database.

Although the USGS-NAS database contains a whopping 1,210 records of the New Zealand Mud Snail, Potamopyrgus antipodarium, only one, single record falls within our nine-state study area.  That would be the population in Spring Creek, Centre County (PA) with which we are already quite familiar [10].

Similarly, the 94 records of Melanoides tuberculata in the USGS-NAS database also include but a single observation in our study area.  But it is a good one.  Record #153847 reports a 2001 collection of M. tuberculata in the small coastal town of Southport, NC.  Zooming the USGS map inward shows the collection site at Bonnetts Creek, near the entrance to the “Olde Southport Subdivision.”  And reference to the online database at the North Carolina State Museum shows a lot of 82 Melanoides tuberculata shells collected in Southport on 27Jan06 under catalog number 40541.  Super – can’t beat that.

Although I have seen secondary reports of Melanoides in North Carolina [11], this is the first well-documented, bona fide record of that species I have ever seen north of Florida, east of Texas.  So the
USGS-NAS Melanoides
USGS-NAS database can, at least occasionally, serve for the effective dissemination of “information about the presence and distribution of nonindigenous aquatic species” as it was designed to do, even to such a specialist as myself.

But let me conclude this month’s essay with another anecdote from the old mail bag.  A couple years ago I got an email from a colleague in Europe asking a simple question.  He wanted an estimate of the number of freshwater gastropod species in the US Great Lakes.  I was gratified to be able to answer promptly, and I did.  I said I didn’t know [12].   So my European correspondent wrote me back incredulous, and asked, “Do you mean to tell me that the US Government charges 13 Federal Agencies to record and monitor the latitude, longitude, date and sex of every pallid 5 mm European gastropod that sets foot onto American shores, but spends not one nickel and gives not one rip about any of its own native species whatsoever?”

Yes, I told him that was indeed the case, and suggested that we might either swap faunas, or swap governments, to solve the problem.  That former solution seems to be in the works.


[1] The actual legislative and regulatory history is much more complicated than this.  The 1990 act was amended and expanded by the 1996 “National Invasive Species Act,” and a body called the “National Invasive Species Council” was also created by Executive Order in 1999.  Exactly why the Nonindigenous Aquatic Species database landed in the US Geological Survey, as opposed to the Fish & Wildlife Service, or the USDA Department of Pests and Weeds, or the Coast Guard, or the Corps of Engineers (both of which were explicitly charged in the 1990 act) I have no idea.

[2] I do feel considerable sympathy for our long-suffering civil servants here.   It amazes me how often freshwater mollusk invasions are not single-species efforts, but rather seem to result from conspiracies of multiple species nearly indistinguishable from each other.  The zebra mussel / quagga mussel invasion is a prominent example, of course, as is the situation with the purple-Corbicula and the white-Corbicula.

[3]  Community Consequences of Bellamya Invasion [18Dec09]

[4]  Although the distribution data are vintage 2006, there are excellent illustrations of the various Pomacea species and their egg masses in a colorful PDF flyer available from the Florida Fish & Wildlife Commission:
  • Non-Native Applesnails in Florida [pdf]
[5] Science and Public Policy are not compatible, but they’re not incompatible either.  They’re two entirely different things.  See any of my essays under the menu item “Science and Public Policy” at right above for more.

[6] Toward the Scientific Ranking of Conservation Status – Part III [19Mar12]

[7] I simply blocked and copied from the “Collection Info” page(s) for each species of interest, then pasted into an excel spreadsheet.  I could have gotten a lot more data if I had requested a “custom query” from the NAS staff, but screw it.

[8] The original footnote I posted here in October of 2015 remarked that it seemed possible to me "that all the Viviparus populations that have spread throughout the American North and Midwest in recent decades may be a cryptic invasion of the European V. viviparus."  But I cautioned that "no actual data have been brought to bear on the question as yet."  Some actual data were ultimately published five years later, however, and the cryptic invasion hypothesis was not supported.  See:
  • A Gene Tree for the Worldwide Viviparidae [9Mar21]
[9] These three records from the 1970s got the sticky-note treatment.  I marked the creeks involved with sticky-notes on my Maryland map book.  Next time I’m in the area…

[10] Potamopyrgus in US Atlantic drainages [19Nov13]

[11]  Anderson, T. K. (2004) A review of the United States distribution of Melanoides tubeculatus (Muller, 1774), an exotic freshwater snail.  Ellipsaria 6: 15-18.

[12] This quote comes from Mark Twain’s (1875) Old Times on the Mississippi.  The dialogue between The Captain and the author continues:
“You—you—don’t know?"  The captain mimicked my drawling manner of speech. “What do you know?”
“I—I—nothing, for certain.”
“By the great Caesar’s ghost, you don’t know enough to pilot a cow down a lane.”

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