Trends in Lake Michigan’s Food-web
Steven Pothoven
Data from T. Nalepa
Data from T. Nalepa
50
40
30
20
10
40
30
20
10
0
0
1997
1999
2001
2003
2005
2007
2009
1997
2011
Year
50
2001
30
20
10
1997
1999
2001
2003
Year
2005
2007
2009
2011
2007
2009
2011
2005
2007
2009
2011
40
30
20
10
0
0
2005
> 90 m
)
Shell-free Biomass (g/m
40
2003
Year
2
)
1999
50
31-50 m
2
Shell-free Biomass (g/m
51-90 m
2
16-30 m
Shell-free Biomass (g/m
Shell-free Biomass (g/m
2
)
Quagga
Zebra
)
50
1997
1999
2001
2003
Year
Quagga biomass stabilizing/decreasing in nearshore; continues to increase offshore
Data from T. Nalepa (UM)
Secchi (m)
20
15
Spring-offshore
10
5
0
1985-89
1995-98
2007-10
Increased water clarity—
secchi depth up to 32 m in northern Lake Michigan
Chlorophyll a (mg/m3)
4
Offshore-Spring Chlorophyll a
3
2
1
0
1983-1987
1995-1998
2007-2011
The loss of the spring phytoplankton bloom—
especially diatoms
0
1
Chlorophyll a (mg/m3)
2
3
4
0
Spring isothermal period
Depth (m)
20
40
60
80
100
In the spring, mussels in the offshore are
“connected” to the entire water column
5
Temperature (°C)
0
5
10
15
20
25
0
20
40
60
Depth (m)
80
100
120
Chlorophyll a (mg/m3)
0
1
2
3
0
4
5
6
July 1995
20
40
Deep chlorophyll layer
60
80
100
120
Nepheloid
7
Mean early summer DCL (Area > 2 mg/m3)
Offshore -110 m
Integrated DCL Chl a (mg/m2)
90
80
70
60
50
40
30
20
10
0
1980
1985
1990
1995
2000
2005
2010
2015
Summer chlorophyll profile
Chlorophyll a (mg/m3)
0
1
2
3
4
0
5
6
7
July 2011
Depth (m)
20
Smaller DCL
40
60
80
No nepheloid
100
Less spring bloom material settling
Nearshore-Offshore transport disrupted by nearshore mussels
Typical Zebra Mussel Shallow Water Impact in 1990sSaginaw Bay, Lake Huron
SAGINAW BAY
RETENTION OF NUTRIENTS NEARSHOREmore algae (Cha et al. 2011)
28% of mapped nearshore habitat
in Lake Michigan is occupied by
Cladophora or other SAV
From Shuchman et al. 2013
Nearshore and Offshore are different environments
Increasing temp and zoopl; decreasing chl
(temperature, chl, zooplankton)
Decreasing temperature and chl
10
Spring 2007-2012 total phosphorus
Muskegon
TP (mg/m3)
9
8
7
6
5
4
3
2
1
0
15
45
Depth (m)
110
500
Spring 2007-2012 total phosphorus
Muskegon
TP (mg/m2)
450
400
350
300
250
200
150
100
50
0
15
45
Depth (m)
110
Spring 2007-2012 chlorophyll
Muskegon
2.5
Chl a (mg/m2)
2.0
1.5
1.0
0.5
0.0
15
45
Depth (m)
110
Mean annual zooplankton abundance 2007-2012
Muskegon
Biomass (mg/m3)
25
20
Other
Daphnia galeata
15
Bosmina
10
Limnocalanus
Diaptomid
5
cyclopoid
0
M15
M45
M110
Depth (m)
Reflective of an oligotrophic community
Mean annual zooplankton abundance 2007-2012
Muskegon
Biomass (mg/m2)
2500
2000
Other
Daphnia galeata
1500
Bosmina
1000
Limnocalanus
Diaptomid
500
cyclopoid
0
M15
M45
Depth (m)
M110
Zooplankton community differences nearshore-offshore
CLADOCERANS (fleas)
Bosmina –small bodied, nearshore
Daphnia –large bodied, offshore
Cercopagis –small bodied, nearshore
Bythotrephes –large bodied, offshore
Cubic feet/sec
Muskegon River Discharge (below Croton; USGS data)
7000
6000
5000
4000
3000
2000
1000
0
2007-2012
2013
1
2
3
4
5
6
Month
7
8
9
10 11 12
Total phosphorus - Nearshore Muskegon
30
25
April
20
15
TP (mg/m3)
10
5
0
30
25
20
15
10
5
0
May
10
8
Chlorophyll - Nearshore Muskegon
April
chl a (mg/m3)
6
4
2
0
10
8
6
4
2
0
May
Total phosphorus - Nearshore Muskegon
40
TP (mg/m3)
35
30
25
20
2010
15
2013
10
5
0
0
50
100
150
200
Day of Year
250
300
350
Total phosphorus Muskegon 15 m
40
TP (mg/m3)
35
30
25
2010
20
1996
15
2013
10
1972
5
0
0
50
100
150
200
Day of Year
250
300
350
chl a (mg/m3)
Chlorophyll – Nearshore Muskegon
9
8
7
6
5
4
3
2
1
0
2010
2013
0
50
100
150
200
Day of Year
250
300
350
Chlorophyll – Nearshore Muskegon
chl a (mg/m3)
12
10
8
2010
6
1996
2013
4
1972
2
0
0
50
100
150
200
Day of Year
250
300
350
TP (mg/m3)
200
Historical comparison - spring
Grand Haven- Muskegon river mouths
Total phosphorus
150
100
50
0
chl a (mg/m3)
25
Chlorophyll
20
15
10
5
0
1972
1996
Grand Haven
1996
1972
Muskegon
Spring zooplankton community assemblage analysis
More variable within a year than between years
A few things to consider….
The nearshore and offshore are different, but connected
Can P be reduced enough to eliminate nearshore water
quality issues but still support the offshore pelagic food web?
Is removal of P by mussels temporary or permanent?