New Zealand mud snails Utah inventories

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New Zealand mud snails Utah inventories
digestibility
www.usu.edu/buglab
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Past activities Broad-scale inventories Site
level population dynamics Present
Activities Site-level habitat preferences Pre-
and post-invasion invertebrate assemblage
changes Targeted inventories Assimilation by
rainbow trout Foodweb dynamics
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Maps courtesy of Dan Gustafson, Montana State
University
2001
lt2000
2002
2003
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Maps courtesy of Dan Gustafson, Montana State
University
2001
2005
as of April 2005
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Utah Survey Results, 2000 - 2004
Absent
Present
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• Current locations in Utah and vicinity
• Regulated rivers
• High quality trout fisheries
• Close to a major road
• Close to another NZMS site
• Disturbed simple ecosystems

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Site Level Population Dynamics Green River -
NZMS the only Hydrobiid snail Bear River NZMS
co-occur with native Hydrobiid, Pyrgulopsis
pilsbrayana
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Green River downstream from Flaming Gorge
Dam Seasonal samples from September 2001 to
present
9
700
Green River at Little Hole
600
500
400
Density (number m-2)
300
200
100
0
Jan
Apr
Jul
Oct
Jan
Apr
Jul
Oct
Jan
Apr
Jul
Oct
Jan
Apr
Jul
2002
2004
2005
2003
Date
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Bear River near Preston, Idaho Monthly samples
from September 2002 to May 2004
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Bear River near Preston, Idaho
Date
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Green River
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Polecat Creek, Wyoming, June 2003
250000
200000
150000
Density (number m-2)
100000
50000
0
Riffles
Other habitats
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• Digestibility assimilation experiment I
• C N stable isotope enrichment study
• Step 1 Enrich algae with C13 and N15 labeled
  fertilizer
• Step 2 Introduce amphipods (Hyalella azteca) and
  New Zealand mud snails into enriched aquaria
• Step 3 Mark individual fish with pit tags
• Step 4 Randomly assign fish to 4 feeding
  treatments
• Purina fish chow
• NZMS natural
• NZMS enriched
• Hyalella azteca enriched
• Step 5 Feed fish twice per day, weigh fish each
  week
• Step 6 Analyze fish muscle tissue for C13 and
  N15

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Experiment I, enriched isotope uptake
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Experiment I, enriched isotope uptake by fish
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Experiment I, enriched isotopes
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• Experiment II, Unlimited food and space
• 2 Feeding Treatments, evaluate growth
• NZMS, densities ca. 130,000 m2
• Scuds, unlimited, replenished weekly

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Experiment II, unlimited food space Food
switched after 108 213 days
140
Food switched on days 108 and 213
120
Group A
Group B
NZMS
100
80
NZMS
60
Hyalella azteca
Relative change in weight from initial weight ()
40
Hyalella azteca
20
0
-20
Hyalella azteca
NZMS
-40
0
30
60
90
120
150
180
210
240
270
300
Days
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Given essentially unlimited food space over 3
months
On average Fish fed scuds gained about 1 of
their body weight per day Fish fed NZMS lost
0.2 of their body weight per day
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Fate of 914 snails passing through the trouts
digestive tract
Dead, 42
Empty, 15
Alive, 43
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Foodweb dynamics
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Somewhat preliminary, but interesting data
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Green River Downstream from Flaming Gorge Dam
Food Web
20
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brown trout, n 135
mountain whitefish, n 29
rainbow trout, n 139
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salmonid eggs, n 13
d 15N ()
sculpin, n 19
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invert predators, n 12
invert scuds, n 6
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New Zealand mud snails, n 11
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invert herbivores, n 22
Aquatic vegetation, n 12
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-32
-31
-30
-29
-28
-27
-26
-25
-24
d 13C ()
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Green River Downstream from Flaming Gorge Dam
Food Web
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Thanks to all who assisted over the years BugLab
Eric Billman, Kris Buelow, Greta Burkart,
Brooke Bushman, Warren Collier, Nathan
Etherington, Tarita Harju, Krista Keuster, Ben
Kuhns, Greg Parry, Kaori Sasakura, Matt Tagg,
Erin Thompson, Andree Walker, Tom Wauters, Chris
Webster and many, many others Don Archer, Steve
Brayton, Roger Schneidervin Jeff Kershner Ted
Angradi Talk available at www.usu.edu/buglab