Corrao, Norah Myers

Darby, Philip

Pomory, Christopher

English

Aquatic Commons

Nitrate Impacts on Florida Apple 
Snail (Pomacea paludosa) 
Survival and Growth
Norah Myers Corrao, Philip Darby, 
and Christopher Pomory
University of West Florida 
Department of Biology
Pensacola, FL
Prompting for Study
• Decreased limpkin 
use at Wakulla
• Low snail density?
Predator-Snail Relationship
1
3
5
7
9
11
13
15
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
N
u
m
b
e
r
 
o
f
 
S
n
a
i
l
 
K
i
t
e
s
Mean No. Snails/m2
Other Predators …
Are Elevated Nitrates Impacting Snails?
• Field component 
(2002)
• Lab component 
(2003)
Environmental Levels
• Florida Springs Report (2000)
– 0.03 ppm Steinhatchee Rise
– 4.20 ppm Fanning Spring
Nitrate Toxicity
• Little literature available on freshwater 
snails
– sodium nitrate v. ammonium nitrate
– > 2.2 for Hydropsyche occidentalis v. 2316 
ppm for Penaeus monodon
• Often not toxic at environmental levels
Field Study - Hypothesis
• Snail density decreases with elevated 
nitrate
Field Study - Site Description
• First 
magnitude 
springs:
– Jackson Blue
– Wakulla
– Wacissa
– Rainbow
– Ichnetucknee
– Alexander
Field Study - Data Collection
• 1-m2 throw trap
• 50 per spring
– Dip net …
– Capture 
probability …
Field Study - Statistical Analysis
• Negative binomial
• Generalized Linear Models (GENMOD)
– Snail density between springs
• Correlation analysis
– Mean snail density
– Nitrate levels
Field Survey - Results
 
0.0 
0.5 
1.0 
1.5 
2.0 
2.5 
3.0 
3.5 
4.0 
4.5 
5.0 
5.5 
6.0 
Alex Waci Ichn Waku Rain Blue 
Snails/
m 2 
0.04 
0.41 
0.83 
1.3 
3.1 
No Snails
0.99 
p = -0.4
Critical value 
at α = 0.05 is     
-0.81
Lab Hypotheses
• Little effect on survival at ecologically 
relevant levels (0-25 ppm)
– adults
– juveniles
• No suppression of growth at these levels
– juveniles
Methods - Collection
• Snails and eggs from 
Wacissa River, 
Jefferson County
Methods - Holding and Maintenance
• Protocol development
– Water quality
– Water temperature
– Feeding schedule
– Light conditions
– Hatching setup
Methods - Experimental Design
Adult 
Survival
Juvenile 
Survival
Juvenile 
Growth
96-h LC50 14-d EC50
* 3 replicates of each;
2 trials of each
0, 125, 250, 
500, 1000 
ppm
0, 250, 500, 
750, 1000 
ppm
Methods - Experimental Design
• Water changes
• Water sampling
– Nitrate (ion 
chromatography)
– Ammonia
– pH
– Temperature
– Dissolved oxygen
– hardness
Methods - Statistical Analysis
• LC50: regression of percent survival on 
nitrate concentration
– target 30-70%
• EC50: regression of percent growth on 
nitrate concentration
Results - Survival
• Rangefinders: 0-1000 ppm
• High survivorship of both adults and juveniles 
(77-100%) = no LC50
Results - Growth, Trial 1
Percentage Change in Length, Growth Trial 1
y = -0.048x + 73.193
R2 = 0.7889
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
nitrate concentration (ppm)
p
e
r
c
e
n
t
a
g
e
 
g
r
o
w
t
h
 
(
t
r
a
n
s
f
o
r
m
e
d
)
EC50 = 587.35 ppm
Results - Growth, Trial 2
Percentage Change in Length, Growth Trial 2
y = -0.0524x + 77.365
R2 = 0.8746
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
nitrate concentration (ppm)
p
e
r
c
e
n
t
a
g
e
 
g
r
o
w
t
h
 
(
t
r
a
n
s
f
o
r
m
e
d
)
EC50 = 617.65 ppm
Discussion/Conclusions
• No effect on survival in the lab
• Growth affected at environmentally 
irrelevant levels
Jackson Blue Springs, FL
circa. 1990
Density in 2002: 0.02 snails/m2
… But Snails Have Declined
Vegetation Survey - Jackson Blue
• Filamentous 
algae
• Chemical 
treatment of 
hydrilla
Discussion/Conclusions
• If not nitrate toxicity, then …
• Changes in habitat structure?
Prairie
v.
slough
Habitat Structure Can Be Critical!
P rairie-Slo ugh A djusted A pple Snail densit ies
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
M
e
a
n
 
N
u
m
b
e
r
 
S
n
a
i
l
s
/
m
2
No Snai ls
WCA1 WCA3
Sit e B Sit e C Sit e D Sit e 1 Sit e 11 Sit e 2 Sit e 3
Slough     Pr ai r ie Slough     Pr ai r ie Slough     Pr ai r ie Slough     Pr ai r ie Slough     Pr ai r ie Slough     Pr ai r ieSlough     Pr ai r ie
adjusted for p-hat
Slough
Prairie
Invasion of the Exotics …
• Sediment structure?
Hydrilla Displaces Other Plants
• Vallisneria
v. Hydrilla?
• Forage base?
Treatment of Exotics
• Chemical
– Acute and/or chronic direct effects?
– Indirect effects such as …
Destruction of Emergents
Gee, I hope this 
vegetation 
doesn’t fall over
… And/Or Forage Base
Manual Removal
• Removing 
vegetation …
– snails?
– cover?
Repopulation Issues
• Apple snails are an 
annual species!
Annual Post Reproductive Die Off
FEB       MAR         APR        MAY         JUN          JUL   AUG
0.00
0.20
0.40
0.60
0.80
1.00
0.0
1.0
2.0
3.0
4.0
5.0
6.0
1995 Field
1996 Lab
1996 Clusters
s
u
r
v
i
v
a
l
c
l
u
s
t
e
r
s
/
5
 
m
Further Investigations?
• Snail habitat preferences in the springs?
• Exotic plant management
– Direct?
– Indirect?
• Repopulation potential
Project Support
• Florida Department of 
Environmental Protection
• University of West Florida
• Center for Environmental 
Diagnostics and 
Bioremediation (CEDB)
Acknowledgements
• Laura Morse and Dana Bryan
• CEDB staff
• DEP Parks Staff: Sam Cole, Wesley Jones, Scott 
Savery and Pete Sleszynski
• Lab support: Michael Corrao, Kathy Ferrozi, 
Nancy Glass, Jim Hammond, Michael Huggins, 
Laksiri Karunaratne, Sara LaPorte, Allyson 
Mille, Rachael Poston and Alex Ren
Thanks!


Nitrate Impacts on Florida Apple

Snail (Pomacea paludosa)

Survival and Growth

http://aquaticcommons.org/806/1/Applesnail.pdf

Nitrate Impacts on Florida Apple Snail (Pomacea paludosa) Survival and Growth

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