Cerithidea californica Ilyanassa obsoleta Nutrient loading ... · Animal-Nutrient Invasion Dynamics...
Transcript of Cerithidea californica Ilyanassa obsoleta Nutrient loading ... · Animal-Nutrient Invasion Dynamics...
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Nutrient loading & benthic
native-invasive species dynamics
Romberg Tiburon Center Seminar Series5 November 2008
Heidi W. Weiskel & Edwin D. Grosholz
University of California, DavisRomberg Tiburon Center (adopted)
Cerithidea californica Ilyanassa obsoleta
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Global Increase in Nitrogen
Effects of Eutrophication
Threats to Coastal Ecosystems
Global Increase in Invasions
Conceptual Framework
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Global Increase in NitrogenHowarth et al. 1996
The substantial nitrogen increase has “caused changes in the composition and functioning of estuarine and nearshore ecosystems, and contributed to long-term declines in coastal marine fisheries.”(Vitousek et al. 1997)
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Nitrogen a Concern in Marine Systems
• N-limited
• Change algal &
plant community
• Can create
hypoxic (<2 mg O2/L)
or anoxic (<0 mg O2/L)
zones
• Change herbivore, predator, ¶site behavior
(food web impacts)
http://library.thinkquest.org/04oct/01590/pollution/culturaleutroph.jpg
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Effects of Eutrophication
http://www.marietta.edu/~biol/biomes/images/mangroves/florida_eutrophication_7536.jpg
http://cache.eb.com/eb/image?id=90452&rendTypeId=4
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• As trade increases, biological invasions are
increasing in both terrestrial and aquatic
ecosystems (Levine & D’Antonio 2003)
• “One of the five most critical environmental
issues facing the ocean’s marine life” (NRC 1995)
Global Increase in Invasions
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– Nutrients can facilitate invasion success(Pennings et al. 2005, Tyler et al. 2007)
• increase productivity
• increase biomass, even with increased herbivory
– Invasive plants can edge out their competitors(Ehrenfeld 2003, Fargione et al. 2003, Levine et al. 2003)
• capable of fixing nitrogen
• partition nutrient resources
Plant Nutrient-Invasion Dynamics
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Would we expect the effects of nutrients to propagate up to higher trophic levels?
Animal-Nutrient Invasion Dynamics
Atlantic mud snail Ilyanassa obsoleta
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Talk Outline
• Conceptual framework for research
• Introduction to system in San Francisco Bay
• Nutrient-invasion experiments
• 2007 results & conclusions
• 2008 preliminary results
• Future Directions
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Estuaries highly invaded compared to outer coast (Wasson et al. 2005)
Cohen & Carlton 1998
Estuaries disproportionately vulnerable to nutrient
pollution & eutrophication (Bricker et al. 1999, Anderson et al. 2002)
Cloern 2001
SAN FRANCISCO BAYInvasions Nutrients
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Robert’s Landing - >
San
Francisco Bay, CA
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Inspiration
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Photo Credit: J.T. Carlton
Ilyanassa obsoleta Cerithidea californica
Omnivore/Deposit Feeder Herbivore / Deposit Feeder
Introduced 1907 Native
30 mm
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Previous Studies
• Northern CA work:
invasive successfully
competes with &
disturbs the native (Race 1982)
• Southern CA work:
native does not
influence microalgae
but is negatively
affected by nutrients(Armitage & Fong 2004)
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Can nutrients alter competitive
dynamics between native and invasive
consumers in a marine system?
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Cyanobacteria
IlyanassaCerithidea
DiatomsO2
Trophic Dynamics
MUD
NUTRIENTS
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Objectives
• Test the direct effects of nutrients on consumers
• Investigate the impacts of nutrients on the competitive dynamics between native & invasive consumers
• Further our understanding of the effects of nutrients in invaded, eutrophic intertidal systems
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Hypotheses1) The invasive snail will be POSITIVELY affected by nutrients
Nutrients Diatoms Cyanobacteria Growth Mortality
2) The native snail will be NEGATIVELY affected by nutrients
Nutrients Diatoms Cyanobacteria Growth Mortality
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Experimental DesignFactor I = Snail Density (7) Factor 2 = Nutrients (2)
No Cage Control
0 Density Cage
0 Invasive 50 Native
50 Invasive 0 Native
No Nutrient Additions
Nutrient Additions
0 Invasive 100 Native
100 Invasive 0 Native
50 Invasive 50 Native
C
L
H
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Response Variables
Snail populations– Growth– Mortality
Microalgal community– Composition (HPLC)– Density (Microscopy & chl a)
Habitat characteristics– Organic matter– Grain size– Carbon-nitrogen ratios– Stable isotopes– Nutrients (ammonium)
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Field Experiment 2007
2 nutrient events4,800 snails96 cages
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Nutrients Influence the Effects of Grazing
by the Invasive Snail
0
100
200
300
400
500
NoSnails
Native
Open M
udBoth
Spp
Inva
sive
Snail Treatment
Fu
co
xa
nth
in l
ev
els
(u
nc
on
ve
rte
d)
Fertilized
Unfertilized
NS NS
No
Cage
p < 0.05p = 0.07
p = 0.09
= 50 Invasive snails
= 50 Native snails
No
Snails
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Nutrients Influence the Effects of Grazing
by the Invasive Snail
0
100
200
300
400
500
NoSnails
Native
Open M
udBoth
Spp
Inva
sive
Snail Treatment
Fu
co
xa
nth
in l
ev
els
(u
nc
on
ve
rte
d)
Fertilized
Unfertilized
NS
No
Cage
p < 0.05
= 50 Invasive snails
= 50 Native snails
No
Snails
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Growth Increases With Nutrients
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Low
Nat
ive
Hig
hNat
ive
BothN
ativ
e
Low
Inva
sive
Hig
hInv
asiv
eBot
hInv
asiv
e
Density Treatments
Gro
wth
(m
m)
Fertilized
Unfertilized
* p < 0.0001 Fert/Unfertacross all density treatments
NATIVE
**
*
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p = NS Fert/Unfertacross all density treatments
No Growth Increase With Nutrients
INVASIVE
Density Treatments
Fertilized
Unfertilized
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
Gro
wth
(m
m)
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Nutrients Reduce Mortality At High Snail
Density
0
10
20
30
40
50
60
Low
Den
_Nat
ive
Hig
hDen
_Nat
ive
Both_
Nat
ive
Low
Den
_Inv
asH
ighD
en_I
nvas
Both_
Inva
s
Density Treatments
Perc
en
t M
ort
ali
ty (
%)
Fertilized
Unfertilized
**
NATIVE
**
** p < 0.005 Fert/Unfertacross all density treatments
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Nutrients Reduce Mortality At High Snail
Density
0
10
20
30
40
50
60
Low
Den
_Nat
ive
Hig
hDen
_Nat
ive
Both_
Nat
ive
Low
Den
_Inv
asH
ighD
en_I
nvas
Both_
Inva
s
Density Treatments
Perc
en
t M
ort
ali
ty (
%)
Fertilized
Unfertilized
INVASIVE
**
** p < 0.005 Fert/Unfertacross all density treatments
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Expectation for the invasive snail:nutrients diatoms cyanobacteria growth mortality
Outcome for the invasive snail:nutrients diatoms cyanobacteria growth mortality
N/A
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Expectation for the native snail:nutrients diatoms cyanobacteria growth mortality
Outcome for the native snail:nutrients diatoms cyanobacteria growth mortality
N/A
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2007 Conclusions
The invasive snail negatively affects the native snail � resource competition
Nutrients increase growth & reduce mortality in the native snail & reduce mortality in the invasive snail
� nutrients ameliorate stressful conditions
SF Bay benthic habitats can be nutrient-limited
� contrary to existing paradigm
Native response to nutrients is positive & strong
� Other factors?
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Nutrient effects may be habitat-dependent
Nutrients increase food qualityand ameliorate stressful conditions
in nutrient-limited systems
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Original Habitat Preferences
N
I
I
N
N = Native I = Invasive
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Spartina eradication opened new habitat
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Both Species Found at Higher Densities in Transition Zone
0
20
40
60
80
100
120
140
160
180
Low Mudflat High Marsh Transition Zone
Habitat
Nu
mb
er
of
Sn
ail
s (
pe
r s
q m
)
Invasive
Native
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0
2
4
6
8
10
12
14
16
18
High Low Outfall
Tidal Elevation
Invasive
Native
Sediment
Stable Isotope Analysis Reveals Differences
between Species & Habitats
NS * * = p < 0.05
between species
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Predation Pressure• Lab trials with invasive green crab Carcinus
• Field anecdotal evidence
– Low marsh cages only
Snail Mortality from Carcinus Predation
0
50
100
Ilyanassa Cerithidea
Snail Species
Pe
rce
nt
Mo
rta
lity
Percent Mortality
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Field Experiment 2008
5 nutrient events9,600 snails168 cages
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2008 Results to DateDiverse microalgal community
Modified habitat use
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General Conclusions
• The overall effects of nutrients are habitat-dependent– Increase edible microalgal biomass and quality (higher N)– Facilitate competitive advantage for toxic cyanobacteria
• The overall effects of invaders are negative– Invasive snail outcompetes native snail (within trophic levels)
– Invasive crab preys on native snail only (between trophic levels)
• Nutrient effects on invaders vary
– Ameliorate effects of invaders in nutrient-limited systems (2007)
– Exacerbate effects of invaders in nutrient-replete systems (2008?)
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Global Increase in Nitrogen
Effects of Eutrophication
Threats to Coastal Ecosystems
Global Increase in Invasions
Conceptual Framework
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Future Steps• Test results with other species
– New snail invader Batillaria attramentaria
• Test results in other systems with different nutrient limitations– Cuba
– Southeast USA
• Introduce climate change into these study systems: How will increasing pCO2 and T interact with nutrients and invaders?– Productivity– Herbivory
– Predation
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Special Thanks to Everyone at
RTC!!!• Dennis
• Chahn
• Brita
• Toby
• Kathy
• Jonathon
• Wim
• Sarah
• Tomoko
• Jaime
• Lara
• Anne
• Toni
• Raman
• Ed
• Chris B
• Dave
• Steph
• Gwen
• Lindsay
• Matt
• Chris R
• Chela
• Al
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Acknowledgements• Advisor
Ted Grosholz
• Funding
• Lab Space & Equipment
• Volunteers & AssistantsChristy Bowles, Bryan Bugler, Andy Chang, Katie Faulkner, Stephanie Kiriakoplos, Stephen Lau, Sarah Lewis, Alice Lemeux, Nathan Mineo, April Ridlon, Gwen Santos, Jeffrey Waters, Betsy Wells, & Christine Whitcraft
APRIL!!!
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Winter sunset in San Francisco Bay
QUESTIONS?