>  Littorina littorea has almost certainly inhabited North America for a much
>  longer period than is generally understood, or accepted; certainly since
>  long before Europeans arrived on this continent.
>
>  For just one of many pieces of evidence in support of this statement, see:
>
>  Wares, John P., Deena S. Goldwater, Bo Y. Kong, and Clifford W. Cunningham.
>  2002. "Refuting a controversial case of human-mediated marine species
>  introduction" Ecological Letters 5:577-584.
>

Although that was the conclusion of that paper, I'm not convinced that they could truly rule out the possibility that the North American populations derive from multiple introductions from Europe, from populations not all sampled by their study.  For that matter, the source populations could be extinct, e.g. if a European harbor with L. littorea in the 1000-1800 or so range later lost its population to pollution or habitat modification.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa

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