Lake Superior’s Lower
Trophic Levels
Mary Balcer
University of Wisconsin – Superior
Presented at Making a Great Lake Superior Conference
Fisheries and Aquatic Ecology Section
October 2007
Contributors
Great Lakes National
Program Office
University of WI Superior
David Rockwell
Mary Balcer
Kurt Schmude
Travis Mangan
Steve Hagedorn
Heidi Schaeffer
Heidi Saillard
Mid-Continent
Ecology Division
Jack Kelly
Peder Yurista
Fisheries Management Goal
Maintain Balance Between
Density of Predators and Prey
Components of Food Web
Physical
Features
Temperature
Light
Predators
Salmonids
Phytoplankton
Crustacean
Zooplankton
Cladocerans
Copepods
Planktivorous
Forage Fish
Nutrients
Phosphorus
Benthos
Diporeia
Limiting Factors in Lake Superior
Cold Water temperatures
Spring Water Temperatures
4
Temperature (C)
3.5
3
2.5
2
1.5
1
0.5
0
2001
2002
2003
2004
Superior
2005
2006
Spring Water Temperatures
4.5
Temperature (C)
4
3.5
3
2.5
2
1.5
1
0.5
0
2001
2002
2003
Superior
2004
Michigan
2005
Huron
2006
Summer Water Temperatures
Temperature (C)
25
20
15
10
5
0
2001
2002
2003
2004
Superior Offshore
2005
2006
Nearshore
Summer Water Temperatures
Temperature (C)
25
20
15
10
5
0
2001
2002
Superior
2003
2004
Huron
2005
Michigan
2006
Limiting Factors in Lake Superior
Cold water temperatures
Low Levels of Nutrients
Effects on Food Web
Physical
Features
Temperature
Light
Predators
Salmonids
Phytoplankton
Crustacean
Zooplankton
Cladocerans
Copepods
Planktivorous
Forage Fish
Nutrients
Phosphorus
Benthos
Diporeia
Effects on Food Web
Physical
Features
Temperature
Light
Predators
Salmonids
Phytoplankton
Nutrients
Phosphorus
Crustacean
Zooplankton
Cladocerans
Copepods
Benthos
Diporeia
Planktivorous
Forage Fish
Spring Phosphorus Levels
7
Total P (ug P/L)
6
5
4
3
2
1
0
2001
2002
2003
Superior
2004
2005
Spring Phosphorus Levels
7
Total P(ug/L)
6
5
4
3
2
1
0
2001
2002
Superior
2003
Huron
2004
2005
Michigan
Limiting Factors
Cold Water temperatures
Low Levels of Nutrients
Lead to lower primary productivity
Chlrophyll a (ug/L)
Spring Chlorophyll
2
1.5
1
0.5
0
2001
2002
Huron
2003
2004
Superior
2005
Michigan
2006
Lake Superior Chlorophyll
Chlorophyll (ug/L)
2
1.5
1
0.5
0
2001
2002
2003
summer
2004
spring
2005
2006
Phytoplankton Community
Structure
Chlorophyll concentrations don’t show
complexity of phytoplankton communities
Distinct differences in phytoplankton
species composition and biomass in Great
Lakes each year
8
7
6
5
Relative abundance (%)
4
3
2
1
0
0
20
40
60
80
100
120
140
0
20
40
60
80
100
120
140
3
2
1
0
Total phosphorus concentration (µg/L)
Euan Reavie
Spring Phytoplankton Biomass from Integrated Samples
Phytoplankton
Community
80,000
70,000
Biomass (ug/m3)
60,000
50,000
40,000
30,000
20,000
10,000
0
2001
2002
2003
2004
Superior
Centric Diatoms
Cryptophytes
Pennate Diatoms
Cyanophytes
Chlorophytes
Dinoflagellates
Chrysophytes
Others
Spring Phytoplankton Biomass
Total Biomass (ug/m3)
250,000
200,000
150,000
100,000
50,000
0
2001
2002
Superior
2003
2004
Michigan
Huron
Phytoplankton Community
Summer Phytoplankton Biomass from Integrated Samples
350,000
Biomass (ug/m3)
300,000
250,000
200,000
150,000
100,000
50,000
0
2001
2002
2003
2004
Superior
Centric Diatoms
Cryptophytes
Pennate Diatoms
Cyanophytes
Chlorophytes
Dinoflagellates
Chrysophytes
Others
Zooplankton community
Depends on phytoplankton abundance
and species composition
Certain types of zooplankton are important
food for fish
Relative size of common zooplankton
Cladocerans
Cyclopoid Copepods
Calanoid Copepods
Relative size of common zooplankton
Cladocerans
Cyclopoid Copepods
Diporeia
Calanoid Copepods
Mysis
Opossum shrimp
GLERL photo gallery
Community Composition
Spring Zooplankton Density
1,400
1,200
3
Density (#/m )
1,000
800
600
400
200
0
2001
Daphnia
Adult Cyclopoids
2002
2003
Bosminids
Immature Calanoids
2004
Other Cladocerans
Adult Calanoids
2005
2006
Immature Cyclopoids
Density (#/m3)
Spring Zooplankton Density
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
2001
2002
2003
SUPERIOR
2004
MICHIGAN
2005
HURON
2006
Lake Superior - Spring 2001
1000
3
Biomass (ug/m )
1200
800
Adult Calanoids
Imm Calanoids
Adult Cyclopoids
Imm Cyclopoids
600
400
200
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
0
Length (mm)
Summer Zooplankton Density
5,000
4,500
Density (#/m 3)
4,000
Adult Calanoids
Imm Calanoids
Adult Cyclopoids
Imm Cyclopoids
Other Cladocerans
Bosminids
Daphnia
3,500
3,000
2,500
2,000
1,500
1,000
500
0
2001 2002 2003 2004 2005 2006
Summer Zooplankton Density
Density (#/m3)
25,000
20,000
15,000
10,000
5,000
0
2001
2002
Superior
2003
2004
Michigan
2005
Huron
2006
Lake Superior - Summer 2001
2000
Adult Calanoids
Imm Calanoids
Adult Cyclopoids
Imm Cyclopoids
Other Cladocerans
Bosminids
Daphnia
1500
1000
500
Length (mm)
3.3
3
2.7
2.4
2.1
1.8
1.5
1.2
0.9
0.6
0.3
0
0
Biomass (ug/m 3)
2500
Lake Superior - Summer 2006
2500
3
Biomass (ug/m )
2000
Adult Calanoids
Imm Calanoids
Adult Cyclopoids
Imm Cyclopoids
Other Cladocerans
Bosminids
Daphnia
1500
1000
500
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
3
3.2
3.4
0
Length (mm)
Nearshore Zooplankton Summer 2005
30,000
Density (#/m3)
25,000
Ad Calanoids
imm cal
ad Cyc
imm cyc
bytho
other cla
daphnia
bosminid
20,000
15,000
10,000
5,000
SN95
SN127
SN143
SN103
SN07
SN147
SN159
SN35
SN19
SN99
SN29
SN109
SN102
SN135
SN13
SN145
SN81
SN101
SN33
SN129
SN17
SN97
0
Threats to Lower Food Web
Introduction of non
non--native species
Competitors
Predators
Invertebrate Predators
Bythotrephes and Cercopagis
Invertebrate predators would select
smaller or slower prey - cladocerans
Changes in Food Web
Physical
Features
Temperature
Light
Predators
Salmonids
Phytoplankton
Crustacean
Zooplankton
Cladocerans
Copepods
Bythotrephes
Cercopagis
Forage Fish
Coregonids
Nutrients
Phosphorus
Benthos
Diporeia
Dreissenid mussels
Zebra and quagga mussels
Filter algae and small zooplankton
Change flow of nutrients to offshore
regions of lakes
Changes in Food Web
Physical
Features
Temperature
Light
Predators
Salmonids
Phytoplankton
Crustacean
Zooplankton
Cladocerans
Copepods
Forage Fish
Coregonids
Nutrients
Phosphorus
Benthos
Diporeia
Dreissenid
mussels
Diporeia Abundance
Lake Superior Diporeia - Moderate depths
2000
1800
Density (#/m2)
1600
1400
1200
1000
800
600
400
200
0
97
98
99
00
01
02
03
04
05
06
Diporeia
Abundance
Diporeia
Abundance
# m-2
Lake Superior Diporeia Density at Deep Stations
2000
1800
1600
1400
1200
1000
800
600
400
200
0
97
98
99
00
01
02
Year
03
04
05
06
Summary
Lake Superior is an oligotrophic lake
Cool temperatures and low nutrients limit
primary production
Chlorophyll and phytoplankton
concentrations are lower than in other
Great Lakes
Lake Superior’s phytoplankton community
is quite diverse
Summary
Offshore zooplankton density and biomass
are lower than in other Great Lakes
Communities are dominated by large
calanoid copepods which prefer cold water
A few cladocerans appear in summer
NearNear-shore zooplankton populations are
more variable in density and composition
Summary
Offshore Diporeia density is low
Abundance is greater at moderate depths
These regions can serve as nursery areas
for fish
Summary
Low abundance of nonnon-native predatory
cladocerans
Dreissenid mussels are not established in
open lake
Lake Superior’s lower food web is not
showing the major changes in composition
that are occurring in the other Great Lakes