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| Date: | Fri, 3 Dec 1999 01:27:32 EST |
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Ross and others:
Please read the attached ASCII file regarding zebra mussels in the
Mississippi River system.
Marian E Havlik
Malacological Consultants
1603 MIssissippi Street
La Crosse, Wisconsin 54601-4969
[log in to unmask]
Phone/Fax: 608.782.7958
<HTML><PRE>Re: Zebra mussels:
I live in the middle of the best unionid fauna in the Mississippi River system. No unionid species has gone extinct (to date) in the Mississippi from zebra mussels, no unionid species is known to be in imminent danger of extinction. It's true the impacts are there (1-300+ zebra mussels attached to many living unionids). The Mississippi River is quite different from Lake Erie, so no one really knows what to expect in the long run.
One nearby Mississippi River area (that has declining diversity) had declining diversity before zebra mussels were in the Mississippi (1991); decline is probably due to increased commercial navigation in that area--unionids at this site have a double whammy. In Sept 1999 I looked at a nearby area that we studied extensively in 1997; in several hours we found 21 species---not too bad for effort expended.
Zebra mussels are not directly killing mussels by "suffocating" them. What is probably happening is that the native fauna is getting "less to eat" in some (but not all) areas. Eventually this will lead to reproductive problems which I see as the greatest danger.
The potential is there for severe impacts to the native unionids, but to date I have not seen this. I spent 8 wks in 1996, 13 wks in 1997, and lessor amounts of time in 1998 & 1999, on the Mississippi River. To my surprise I did not see unusual numbers of fresh-dead unios. In 1996 we found 27 species at 1 site (<1000 m2) including some very rare species. In 1997 we found 32 species (4 had not been found alive by anyone for ~20 yrs).
In the past 5 yrs researchers have documented 37 species (of a historic~50) in the Mississippi River mainstem. There are ~6 other species living in immediate tributaries within 100 mi of the Miss. River. Only 2 historic species can currently be considered extinct (but they live in nearby areas); their extinction occurred long before zebra mussels were an issue (after Locks & Dams were put in, in early 20th century, habitat changed then. The remaining species are extralimital, small stream species that were . rarely found in the mainstem. Please see my abstracts in Triannual Unionid Report (#10,11,13, 14,15):
http://www.inhs.uiuc.edu/cbd/collections/mollusk_links/TUR/TOC.html
(Kevin Cumming's site)
I'm very concerned about some things that apparently have not been addressed by any researcher, such as how much do zebra mussels take sperm and glochidia out of the water column? Down the road this could be a very big problem.
There is a reported mussel density decrease in one major Mississippi River tributary that is also a Wild and Scenic River (river only has a few zebra mussels, no zebra mussels live where decrease took place). What is the reason for those changes?
Basically, the unionid fauna exists in the Mississippi River only above the mouth of the Ohio River, so zebra mussels will not impact unionids in the lower Mississippi River delta because no unionids have lived there for years.
Marian E Havlik
Malacological Consultants
1603 Mississippi Street
La Crosse, Wisconsin 54601-4969 USA
[log in to unmask]
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