Open Oceans: Pelagic Ecosystems II. Global scale patterns of pelagic productivity.
Indirect effects of coastal hypoxia on planktivore habitat: implications for pelagic food webs and...
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Transcript of 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