indirect effects of coastal hypoxia on planktivore habitat: implications for pelagic food webs and...

Indirect effects of coastal hypoxia on planktivore habitat: implications for pelagic

food webs and fisheries

Stuart Ludsin, Stephen Brandt & Doran Mason National Oceanic & Atmospheric AdministrationGreat Lakes Environmental Research Laboratory

Chris Rae & Hongyan ZhangSchool of Natural Resources

University of Michigan

Mike Roman, Bill Boicourt, Dave Kimmel & Krista HozyashHorn Point LaboratoryUniversity of Maryland

Xinsheng ZhangNational Oceanic & Atmospheric Administration

OAA-JHT, Cooperative Oxford Laboratory

• Hypoxia is common to many systems– Freshwater & marine– Especially prevalent in coastal systems

• Causes of hypoxia are generally understood– Nutrient pollution (cultural eutrophication)

• e.g. Gulf of Mexico, Chesapeake Bay

• Ecological consequences are less understood– Especially for pelagic organisms

General BackgroundGeneral Background

• Research objectives – Understand hypoxia’s effects on food webs

• emphasis on pelagic food webs

– Benefit resource management efforts• Should agencies care about hypoxia?

– Seek generalities in processes & responses• Comparative systems approach

– Chesapeake Bay– Northern Gulf of Mexico– Lake Erie

Hypoxia Research Program

‘50s ‘60s ‘70s ‘80s ‘90s

Hypoxic(< 2 mg/l)

Anoxic(< 0.2 mg/l)

12

10

8

6

4

2

0

Vo

lum

e x

10

9 m

3 Chesapeake Bay(Hagy 2002)

ChesapeakeBay

NY

PA

WV

VA

DEMD

Focus on Chesapeake BayExplore how hypoxia might be indirectly influencing

Chesapeake Bay’s pelagic food web

PiscivorousPiscivorousFishFish

ZooplanktivorousZooplanktivorousFishFish

ZooplanktonZooplankton

Bay anchovyBay anchovy

(www.njscuba.net)(www.njscuba.net)

StripedStripedbassbass

Acartia tonsaAcartia tonsa(copepod)(copepod)(www.zp-online.net)(www.zp-online.net)

Chesapeake Bay Pelagic Food Chain

95% offish biomass

(www.trophybassonly.com)(www.trophybassonly.com)

Baywide

Year

1960 1970 1980 1990 2000

Strip

ed b

ass harvest

(metric to

ns)

0

1000

2000

3000

4000

Bay

anc

hovy

abu

ndan

ce(#

indi

vs/h

aul)

0

2

4

6

8

• Conventional wisdom striped bass predation to blame

Baywide

Year

1960 1970 1980 1990 2000

Bay

anc

hovy

abu

ndan

ce(#

indi

vs/h

aul)

0

2

4

6

8

Stripedbass

Sources:Bay anchovy: Maryland DNR; striped bass: NMFS

Chesapeake Bay Trends• Bay anchovy record low levels

PoorrecruitmentBay

anchovy

Hyp

oxi

cvo

lum

e(x

109 m

3 )

4

8

12

• Is predation only to blame?

Baywide

Year

1960 1970 1980 1990 2000

Strip

ed b

ass harvest

(metric to

ns)

0

1000

2000

3000

4000

Bay

anc

hovy

abu

ndan

ce(#

indi

vs/h

aul)

0

2

4

6

8

StripedbassBay

anchovy

Sources:Bay anchovy: Maryland DNR; Striped bass: NMFS; Oxygen: Hagy et al. (2004)

Chesapeake Bay Trends

- High levels of both predator & prey before 1975

Reduce access to bottom during day increase predation risk

- striped bass are visual predators

Hypothesis 1

Pycnocline

DayDayBay

anchovy

Chesapeake Bay Hypotheses

CoolDark

Warm

HypoxicHypoxicDayDay

Stripedbass

Chesapeake Bay HypothesesHypothesis 2

DayDayBay

anchovy

HypoxicHypoxic

DayDay

ZP

NormoxicNormoxic

Ho 2: Hypoxia reduces access to prey poor growth conditions

- zooplankton use hypoxic zone, perhaps as a refuge

• East-west transects sampled while underway- 1996, 1997, 2000

- summer (hypoxic period)

Chesapeake Bay Example

R/V Cape Henlopen

www.ocean.udel.edu

• Dissolved oxygenDissolved oxygen• ZooplanktonZooplankton• TemperatureTemperature• Chlorophyll Chlorophyll aa

FishFishBiomassBiomass

Chesapeake Bay Field Program

0

20

40

0

5

10

De

pth

(m

)

Longitude (degrees)-37 -36.96

Summer 1996

DO(mg/l)

Longitude (degrees)

DO(mg/l)

0

5

10

Summer 2000

DO(mg/l)

Ludsin et al.(in review)

Increased Predation RiskHo 1: Reduce access to bottom during day predation risk

- striped bass are visual predators

Longitude (degrees)

Fish(dB)Fish(dB)

0

20

40

Longitude (degrees)

-37 -36.96

-100

-50

Lat. 1 Day

Fish(dB)

-100

-50

0

20

40

0

20

40

De

pth

(m

)

-76.20 -76.15

Lat. 18 Day

-76.20 -76.15

Longitude (degrees)

-37 -36.96

De

pth

(m

)

Longitude (degrees)

0

10

20

30

40

-76.20 -76.15 -76.48 -76.44

Oxygen (mg/l)

0 5 10 Lateral 18

Ludsin et al. (in review)Ludsin et al. (in review)

ZP (mg/l)

0 2 4

0

10

20

30

40

Lateral 20

Ho 2: Hypoxia reduces access to prey poor growth conditions

- zooplankton use hypoxic zone, perhaps as a refuge

Hypoxia as a Refuge

-76.20 -76.15 -76.48 -76.44

Longitude (degrees)

De

pth

(m

)

Summer2000

Summer2000

Ludsin et al.Ludsin et al.(in review)(in review)

Hypoxiccells

(< 3 mg/l)

Normoxiccells

(> 3 mg/l)

Hypoxia as a RefugeHo 2: Hypoxia reduces access to prey poor growth conditions

- zooplankton use hypoxic zone, perhaps as a refuge

Median ZP biomass(mg/L)

0.0 0.5 1.0

La

tera

l tr

an

se

ct

& y

ea

r 131517

12131617

101822

2000

1997

1996

• Spatially-explicit bioenergetics modeling approach

• Bay anchovy growth rate potential (GRP) (Brandt et al. 1992)- Expected growth response, given habitat conditions- Good measure of habitat quality

Longitude

Depth

Bottom

• Create equal-sized cells- 50 m x 1 m x 1 m

• Run bioenergetics model in each cell

- Parameters from Lou and Brandt (1993)

Ludsin et al. (in review)

Habitat Quality ModelingHypoxia reduces access to prey poor growth conditions

Fish (dB)

<-80 -60 -40

ZP (ml/mm3)

0 2 4

Oxygen (ml/l)

0 5 10

Temp. (ºC)

15 25

GRP (g/g/d)

0 0.04 0.08

De

pth

(m

)

0

20

40

-76.20 -76.15Longitude (degrees)

20

40

20

40

20

40

20

40

-76.48 -76.44

Lateral 18 Lateral 20

Ludsin et al.Ludsin et al.(in review)(in review)

Summer2000

• Hypoxia reduces access to zooplankton prey Hypoxia reduces access to zooplankton prey poor growth poor growth

• Hypoxia can indirectly influence pelagic organisms

Conclusions

• Alter distributions & behavior– Diel vertical migration behavior disrupted– Zooplankton using hypoxic zone (perhaps as a refuge)

• A likely role in declining bay anchovy recruitment

• Hypoxia also may influence top predator dynamics(Costantini, Ludsin et al. in review)

- increased benthos in diets- reduced growth rate- increased disease

Pending Chesapeake Bay funding

• “Comparative Evaluation of Hypoxia’s Effects on the Living

Resources of Coastal Ecosystems”

- NOAA-CSCOR Program, 2007-2011

Future Research

• More comprehensive approach

- improved field design (address behavior better)

- diet & growth work

- experimentation

- rigorous modeling (behavioral to ecosystem)

• Test hypotheses, test model predictions

• Compare Chesapeake Bay, Gulf of Mexico & Lake Erie

Funding SupportFunding Support

National Science Foundation

NOAA Ecofore Program

Longitude

Depth

Bottom

Habitat Quality Modeling

dB/dt = C – (R + E + U)

Bioenergetics Modeling Framework(Kitchell et al. 1977, Hanson et al. 1997)

B = bay anchovy biomass C = consumptiont = time R = respiration + SDAE = egestion U = excretion

Fish Mass

Oxygen

Temperature

ZP prey Growth Rate(dB/dt)

Oxygen

TemperatureZooplankton

Fish Mass

Habitat Quality Modeling

Growth Rate(dB/dt)

Gro

wth

ra

te (

g·g·d

-1)

Temperature (˚ C)

Bay anchovyZP biomass = 1.75 mg/l Fish mass = 1.75 g

Oxygen (mg/l)

Ludsin et al.Ludsin et al.(in review)(in review)

Positive

Negative