Thursday, August 28, 2008

The Slender Walker Snail

Kansas is often thought of as a very dry state, a prairie state. Compared to my experiences in Wisconsin, Michigan and Indiana, this is true. That doesn’t mean there aren’t some unique and wonderful wetlands and streams in Kansas that contain unique wildlife. Take for instance the Muscotah Marsh. Located in Atchison County, the marsh is an artesian wetland. Meaning, water is literally coming up out of the ground to create the marsh. I use the name “Muscotah Marsh” to imply a significant sized wetland, but in reality, this is just a tiny little area (Muscotah is the name of the nearest town).

Apart from being the only artesian marsh I’m aware of it Kansas (I’m sure there are more), the marsh is notable for being the home to the only population of slender walker snails in the state (Pomatiopsis lapidaria). Apparently this snail occurs commonly in the eastern U.S. (Pratt 1935), but only isolated population are known from the Kansas-Oklahoma/Great Plains region. However, Liechti (1984) described them as having a spotty occurrence even in the Eastern U.S.

This population of snails is interesting not just because it is so isolated, but because it is so abundant where found. Liechti (1984) found them in densities of 1,255 individuals per square meter (in raised portions of the marsh). Dundee (1957) found a single female could lay 42 eggs after a single mating and all of them would hatch.

Although the Marsh has actually been the subject of research for over a hundred years (see summary in Liechti 1984), there’s been essentially no research done on the site or the snail since the previously mentioned Liechti (1984) paper. In fact, I spoke with Paul on Tuesday about the site, and he wasn’t aware of anyone even visiting the site since he did the paper. In 2003, William Layher submitted a Recovery Plan for the species to KDWP, which was subsequently signed and approved, but this was simply a recounting of other studies. There’s no indicate a new site visit was made, or that the author had even seen the site.

The recovery plan is interesting in its own right. Right now the species is listed as endangered. In order to move from Endangered to Threatened, all that KDWP needs to do is buy or put the land into a conservation easement (the Marsh is currently privately owned). Why this hasn’t been done is beyond me, since getting a species downlisted is the whole point of having a T&E program.

The next part of the recovery plan is the difficult part:

P. lapidaria should be introduced to five sites in various regions of the state. Introductions should be monitored. If the species proliferates and become established in three new locales and persists for five years, the species could be downlisted [from Threatened] to SINC [species in need of conservation] status as events that may impact on site would not affect other sites. If populations continue to flourish for ten years, the species could be removed from all lists.

-- Layher, W.G. 2003. Kansas Recovery Plan for the Slender Walker Snail, Pomatiopsis lapidaria (Say) in Kansas.

This is tough, because introducing species outside of their range is a tricky prospect. Non-indigenous species have turned invasive all over the world. I doubt the Slender Walker Snail poses much threat as an invasive, but what we don’t understand about how species become invasive could fill several books (and has). Probably the entire reason we know as much as we do about the snail is due to its status as a potential intermediate host for Schistosoma japonicum, the human blood fluke, which causes schistosomiasis. The U.S. realized this (and other) species needed to be studied as potential vectors after WWII when soldiers in areas known to contain the fluke started returning state-side.

As I discussed previously, I think many peripheral populations should be conserved, and I think that’s true here too. However, I’m not so confident about introducing them outside their range. Any thoughts?

Sometime before winter, I plan on heading up to try and visit the Muscotah Marsh and see the Slender Walker Snail for myself. I'll be sure to publish pics when/if I get permission to get on-site.

Dundee, D.S. 1957. Aspects of the biology of Pomatiopsis lapidaria (Say). Misc. Publ. Mus. Zool., Univ. Michigan No. 100:1-37.

Liechti, P.M. 1984. Population study of Pomatiopsis lapidaria (Say), a small amphibious snail of endangered status in Kansas. Kansas Biological Survey (KU No. 5054-705). 18 pp.

Pratt, H.S. 1935. A manual of the common invertebrate animals, exclusive of insects. P. Blakiston’s Son and Co., Inc. Philadelphia. Pp. 616-625.


William Layher said...

In 2005 we conducted field investigations at the site of slender walker snail occurrence in Kansas.

We compared populations of snail density in different areas of the marsh.

We also visited 47 other wetland sites from Gary county north easterly to the north east corner of Kansas and found no other populations.

The site was also visited prior to the recovery plan.

Ask KDWP for “Investigations into the Status of the Slender Walker Snail, Pomatiopsis lapidaria (Say) in Kansas” by William G. Layher, Ph.D. for more information pertaining to the study.

William Layher said...

Gary should read Geary County.