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The magnitude of the Great Lakes. 95,000 square miles of water surface area Drinking Water for 40 Million People 10,000 miles of coastline. 20% of World’s Surface Freshwater. Cover Continental US with 9.5’ of water!. Lake Superior. 150 m. 60 m. Lake Huron. 85 m. Lake Michigan.

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Presentation Transcript
slide1

The magnitudeof theGreat Lakes

95,000 square miles of water surface area

Drinking Water for 40 Million People

10,000 miles of coastline

20% of World’s Surface Freshwater

Cover Continental US with 9.5’ of water!

slide2

Lake Superior

150 m

60 m

Lake

Huron

85 m

Lake Michigan

Lake Ontario

86 m

Mean Depths

Lake Erie

19 m

slide3

HOW DO GREAT LAKES COMPARE ON GLOBAL BASIS??

3 of the largest freshwater lakes

#1 SA #3 in Volume

#3 SA #6 Volume

#4 SA #5 Volume

#12 SA #11 Volume

#9 SA #16 Volume

slide4

LAKE MICHIGAN UNDER SIEGE:

DREISSENID MUSSELS FLEXING THEIR MUSCLES

The ‘New’ Lower Food-web

COLLABORATORS:

Steve Pothoven- NOAA

Tom Nalepa- NOAA

Hank Vanderploeg-NOAA

Mike McCormick-NOAA

Don Scavia- UM

*

*

take home message
TAKE HOME MESSAGE
  • Accidental oligotrophication of Great Lakes
  • Historic changes in lower food-web and water column properties. Lake Michigan (and Lake Huron) now looks like Lake Superior and clearest it has been in since white man arrived.
  • Principal cause of these changes are filtering activities of Dreissenid mussels-(Quagga)

Benthification of Lake Michigan Food-Web

Most planktonic carbon ending up in mussels on bottom that is not readily

consumed by fish

slide7

BOTTOM OF LAKE MICHIGAN (east coast)

POST 30m

POST 40m

PRE DREISSENIDS

QUAGGA MUSSELS AT 110 M

slide8

Zebra Mussel

Quagga Mussel

D. rostriformis bugensis

D. polymorpha

Intake Siphon

  • Competitive Advantages
  • Cold water adapted
  • Ability to live on soft substrates

>900 Trillion Dreissenids

in Lake Michigan (99% Quaggas)

slide9

Annual Temperature Cycle

in Lake Michigan (no ice-monomictic)

WINTER/SPRING

FALL

SUMMER

Mixing

Late stratification

Mid Stratification

Jan. 1- end May

Early June-mid Sept.

Mid Sept.- Jan. 1

slide11

IMPORTANT NATIVE GROUPS

Phytoplankton 0.001- 0.1 mm

(floating algae)

Diatoms

ZOOPLANKTON 1mm

(planktonic invertebrates)

Copepods

Cladocerans

Daphnia

Benthic Invertebrates 10mm

Historically major fish food

Mysis relicta

Oppossum shrimp

Diporeia

Amphipod, scud

slide12

Pelagic Primary Productivity Trends (mgC/m2/d)

Tremendous decrease in spring 2007/08 (70%)

Annual decrease ca. 30%

More similar to Lake Superior- 200-400 mg/m2/d

slide13

Phytoplankton biomass measured as chlorophyll a

Large decrease in spring isothermal period 2007/08 (66%)

slide14

Phytoplankton Compositional Changes in 2007/08

Spring Diatoms

Spring diatoms decreased

significantly–especially large net diatoms

Spring BGs

Cyanobacteria (BGs) did not decrease (only group)

Low absolute abundance in 1980s and 1990s but now

similar to diatoms

slide15

WHY LARGE CHANGES IN 2007/08?

Large Populations of Dreissenid mussels became

established after 1983/87 and 1995/98 samplings

slide16
Only time of year Dreissenid filtering is linked to entire water column (monomictic period)

WHY BIG CHANGES IN SPRING??

.

.

Isothermal mixing

slide17

LESS PHYTOPLANKTON - LARGE INCREASE IN WATER CLARITY

In 2010 Secchi disk transparency as high as 32 m off Frankfort

lake michigan seasonal si utilization indicator of diatom production
Lake Michigan Seasonal Si Utilization(Indicator of Diatom Production)

Spring

Drawdown

Summer

Closed symbols, northern basin

Open symbols, southern basin

EPA_GLNPO data

mi hu silica drawdown becoming like lake superior
MI/HU Silica Drawdown Becoming likeLake Superior

Michigan

Huron

Superior

Closed symbols, northern basin

Open symbols, southern basin

EPA_GLNPO data

slide20

IMPORTANT NATIVE GROUPS

Diatoms

Phytoplankton 0.001- 0.1 mm

(floating algae)

ZOOPLANKTON 1mm

(planktonic invertebrates)

Copepods

Cladocerans

Daphnia

Benthic Invertebrates 10mm

Historically major fish food

Mysis relicta

Oppossum shrimp

Diporeia

Amphipod, scud

slide21

Total zooplankton: 2007 and 2008 very low

Most of total zooplankton biomass consists of

calanoid copepods in 2007 and 2009! Similar

to Lake Superior in abundance and composition

slide22

Native Zooplankton Declines-food availability and predation

Less food available (phytoplankton) –

linked to Dreissenid mussels (after 2004/05)

Increased invertebrate predation: Bythotrephes and mussel predation

(resting eggs)

slide23

IMPORTANT NATIVE GROUPS

Phytoplankton 0.001- 0.1 mm

(floating algae)

Diatoms

ZOOPLANKTON 1mm

(planktonic invertebrates)

Cladocerans

Daphnia

Copepods

Benthic Invertebrates

Historically major fish food

Mysis relicta

Oppossum shrimp

Diporeia

Amphipod, scud

slide24

Benthic food-web shift

Wet Weight Biomass in Lake Michigan (g m-2)

423 g is shell

The Problem With Shells:

1) No nutritional value to fish

2) Energetic cost for fish to handle and pass

3) Energetic cost for mussel to produce

Bottom Line: Mussels are an energy sink

historic changes to lower food web
Historic Changes to Lower Food-Web
  • Phytoplankton-70% decrease in spring (diatom),

30% annual decrease

  • Zooplankton- 2 out of 3 dominant groups decrease abundance
  • Benthic Invertebrate- Diporeia decline (94%)

Mysis decline(50%)

  • Exceptionally clear water and low phosphorus offshore
  • Dreissena mussels populations exploding (dominant invertebrate biomass in lake)
  • Invasive invertebrate predators abundant
take home message1
TAKE HOME MESSAGE
  • Accidental oligotrophication of Great Lakes
  • Historic changes in lower food-web and water column. Lake Michigan (and Lake Huron) now looks like Lake Superior and probably clearest it has been since white man arrived.
  • Principal cause of these changes are filtering activities of Dreissenid mussels-(Quagga)

Benthification of Lake Michigan Food-Web

Most planktonic carbon ending up in mussels on bottom that is not readily

consumed by fish

slide27

Management in Post-Dreissenid Period

  • Oligotrophication of Lake Michigan and Great Lakes
  • -Meet IJC target P loads and concentrations (50%)
  • -Offshore region of Lake Michigan now like Lake Superior

2. New Nearshore Problems- Large mussels populations nuisance algae

NEW SPATIAL AND TEMPORAL MANAGEMENT GOALS

3. Collapse and impairment of key commercial and recreational fisheries

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