A Holocene Snail Fauna in the Middle Snake River Sub-Basin, Southern Idaho, U.S.a.

Authors: Bowler Peter, Terrence Frest

Year: 2018

Abstract

Comprehensive lists of the modern native and non-native mollusk fauna in the Middle Snake River Sub-Basin were compiled over two decades ago (Bowler and Frest, 1991; Bowler, 1992; Frest and Bowler, 1993; Frest and Johannes, 1993). Subfossils recovered from sand, basalt cobble, and Melon Gravel substrates at the confluence of the Malad and the Snake Rivers reveal a diversity of species present as a holocene fauna. The collection site is above the present elevations of both rivers and its sediments were deposited after the Bonneville Flood approximately 14,500 years ago. Fourteen native taxa were identified and two of these species are currently Federally listed as Threatened (Taylorconcha serpenticola, Hannan, 2016; Bogan, 2000) or Endangered Species (Physa natricina Taylor, endangered throughout its distribution; Rabot/U.S. Fish and Wildlife Service, January 22, 2018). Several species no longer occur in either river at the confluence. Subsequently introduced non-native mollusks present near the site include the New Zealand Mudsnail (Potamopyrgus antipodarum, which appeared in the Middle Snake River in ca. 1986 (Bowler, 1991) and is abundant in the Snake and Malad Rivers), Ferrisia rivularis (Malad River), and Corbicula fluminea (Snake River at the mouth of the Malad River).