Tuesday, June 5, 2007
537

Invasion and Production of New Zealand Mudsnails in the Colorado River, Glen Canyon, AZ

Kathrine E. Behn1, Wyatt F. Cross1, Robert O. Hall1, Emma J. Rosi-Marshall2, and Theodore A. Kennedy3. (1) Zoology & Physiology, University of Wyoming, Laramie, WY 82071, (2) Biology, Loyola University Chicago, Chicago, IL 60626, (3) USGS Grand Canyon Monitoring and Research Center, Flagstaff, AZ 86001

New Zealand mudsnails (NZMS) have invaded many rivers in the Western U.S., yet little is known about their production and capacity to sequester carbon. We examined size-specific growth rates, biomass, and secondary production of mudsnails in the Glen Canyon reach of the Colorado River. We measured in situ growth rates using cages, and compared our estimates with those from other systems. Instantaneous growth rates ranged from 0.001 to 0.023 day-1, and significantly declined with body size (r2 = 0.55, p<0.001). Growth rates were ~3 times lower than those measured in warmer Yellowstone rivers, but faster than rates measured in their native habitats in New Zealand. These moderate growth rates are likely due to temperatures (average ~11 deg C) that are warmer than New Zealand and colder than geothermal Yellowstone rivers. Since 1995, biomass of mudsnails has increased from 0 to ~15 g m-2, which represents an increase in production from 0 to ~44 g m-2 y-1 (quantified using the instantaneous growth method).  In this tailwater ecosystem, which has stable temperatures throughout the year due to hypolimnetic releases, NZMS have high production and may sequester a large portion of the potential energy otherwise available for higher trophic levels.    

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