cerithidea californica ilyanassa obsoleta nutrient loading ... · animal-nutrient invasion dynamics...

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

Global Increase in Nitrogen

Effects of Eutrophication

Threats to Coastal Ecosystems

Global Increase in Invasions

Conceptual Framework

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)

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, &parasite behavior

(food web impacts)

http://library.thinkquest.org/04oct/01590/pollution/culturaleutroph.jpg


http://www.marietta.edu/~biol/biomes/images/mangroves/florida_eutrophication_7536.jpg

http://cache.eb.com/eb/image?id=90452&rendTypeId=4

• 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)


– 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

Would we expect the effects of nutrients to propagate up to higher trophic levels?

Animal-Nutrient Invasion Dynamics

Atlantic mud snail Ilyanassa obsoleta

Talk Outline

• Conceptual framework for research

• Introduction to system in San Francisco Bay

• Nutrient-invasion experiments

• 2007 results & conclusions

• 2008 preliminary results

• Future Directions

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

Robert’s Landing - >

San

Francisco Bay, CA

Inspiration

Photo Credit: J.T. Carlton

Ilyanassa obsoleta Cerithidea californica

Omnivore/Deposit Feeder Herbivore / Deposit Feeder

Introduced 1907 Native

30 mm

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)

Can nutrients alter competitive

dynamics between native and invasive

consumers in a marine system?

Cyanobacteria

IlyanassaCerithidea

DiatomsO2

Trophic Dynamics

MUD

NUTRIENTS

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

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

Experimental DesignFactor I = Snail Density (7) Factor 2 = Nutrients (2)

No Cage Control

0 Density Cage

0 Invasive 50 Native


No Nutrient Additions

Nutrient Additions




C

L

H

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)

Field Experiment 2007

2 nutrient events4,800 snails96 cages

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

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

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

**

*

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)

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

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

Expectation for the invasive snail:nutrients diatoms cyanobacteria growth mortality

Outcome for the invasive snail:nutrients diatoms cyanobacteria growth mortality

N/A

Expectation for the native snail:nutrients diatoms cyanobacteria growth mortality

Outcome for the native snail:nutrients diatoms cyanobacteria growth mortality

N/A

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?

Nutrient effects may be habitat-dependent

Nutrients increase food qualityand ameliorate stressful conditions

in nutrient-limited systems

Original Habitat Preferences

N

I

I

N

N = Native I = Invasive

Spartina eradication opened new habitat

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

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

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

Field Experiment 2008

5 nutrient events9,600 snails168 cages

2008 Results to DateDiverse microalgal community

Modified habitat use

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?)

Global Increase in Nitrogen


Threats to Coastal Ecosystems


Conceptual Framework

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

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

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!!!

Winter sunset in San Francisco Bay

QUESTIONS?

cerithidea californica ilyanassa obsoleta nutrient loading ... · animal-nutrient invasion dynamics...

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