1. 95,000 square miles of water surface area Drinking Water for 40 Million People 10,000 miles of coastline The magnitude of the Great Lakes Cover Continental US with 9.5’ of water! 20% of World’s Surface Freshwater

2. Lake Superior Lake Huron Lake Ontario Lake Erie Lake Michigan 85 m 60 m 150 m 19 m 86 m Mean Depths

3. #1 SA #3 in Volume HOW DO GREAT LAKES COMPARE ON GLOBAL BASIS?? #3 SA #6 Volume #4 SA #5 Volume #9 SA #16 Volume # 12 SA #11 Volume 3 of the largest freshwater lakes

4. LAKE MICHIGAN UNDER SIEGE: DREISSENID MUSSELS FLEXING THEIR MUSCLES * * COLLABORATORS: Steve Pothoven- NOAA Tom Nalepa- NOAA Hank Vanderploeg-NOAA Mike McCormick-NOAA Don Scavia- UM The ‘New’ Lower Food-web

5. 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

6. Dreissenid Mussels– The principle cause of changes in native food- web Zebra Quagga

7. QUAGGA MUSSELS AT 110 M PRE DREISSENIDS POST 30mPOST 40m BOTTOM OF LAKE MICHIGAN (east coast)

8. D. polymorpha D. rostriformis bugensis Intake Siphon Zebra MusselQuagga Mussel >900 Trillion Dreissenids in Lake Michigan (99% Quaggas) Competitive Advantages -Cold water adapted - Ability to live on soft substrates

9. Mid Stratification SUMMER Annual Temperature Cycle in Lake Michigan (no ice-monomictic) FALL Late stratification WINTER/SPRING Mixing Jan. 1- end MayEarly June-mid Sept.Mid Sept.- Jan. 1

11. ZOOPLANKTON 1mm (planktonic invertebrates) Benthic Invertebrates 10mm Historically major fish food IMPORTANT NATIVE GROUPS Mysis relicta Oppossum shrimp Diporeia Amphipod, scud CopepodsCladocerans Daphnia Phytoplankton 0.001- 0.1 mm (floating algae) Diatoms

12. Pelagic Primary Productivity Trends (mgC/m2/d) Tremendous decrease in spring 2007/08 (70%) More similar to Lake Superior- 200-400 mg/m2/d Annual decrease ca. 30%

13. Phytoplankton biomass measured as chlorophyll a Large decrease in spring isothermal period 2007/08 (66%)

14. Phytoplankton Compositional Changes in 2007/08 Spring diatoms decreased significantly–especially large net diatoms Spring Diatoms Cyanobacteria (BGs) did not decrease (only group) Low absolute abundance in 1980s and 1990s but now similar to diatoms Spring BGs

15. WHY LARGE CHANGES IN 2007/08? Large Populations of Dreissenid mussels became established after 1983/87 and 1995/98 samplings

16. Only time of year Dreissenid filtering is linked to entire water column (monomictic period) WHY BIG CHANGES IN SPRING?? Isothermal mixing..

17. LESS PHYTOPLANKTON - LARGE INCREASE IN WATER CLARITY In 2010 Secchi disk transparency as high as 32 m off Frankfort

18. Lake Michigan Seasonal Si Utilization (Indicator of Diatom Production) Closed symbols, northern basin Open symbols, southern basin Spring Summer Drawdown EPA_GLNPO data

19. MI/HU Silica Drawdown Becoming like Lake Superior Closed symbols, northern basin Open symbols, southern basin Michigan Superior Huron EPA_GLNPO data

20. ZOOPLANKTON 1mm (planktonic invertebrates) Benthic Invertebrates 10mm Historically major fish food IMPORTANT NATIVE GROUPS Mysis relicta Oppossum shrimp Diporeia Amphipod, scud CopepodsCladocerans Daphnia Phytoplankton 0.001- 0.1 mm (floating algae) Diatoms

21. 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

22. 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)

23. ZOOPLANKTON 1mm (planktonic invertebrates) Benthic Invertebrates Historically major fish food IMPORTANT NATIVE GROUPS Mysis relicta Oppossum shrimp Diporeia Amphipod, scud Copepods Cladocerans Daphnia Phytoplankton 0.001- 0.1 mm (floating algae) Diatoms

24. Wet Weight Biomass in Lake Michigan (g m -2 ) 423 g is shell 1) No nutritional value to fish 2) Energetic cost for fish to handle and pass 3) Energetic cost for mussel to produce The Problem With Shells: Bottom Line: Mussels are an energy sink Benthic food-web shift

25. 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

26. 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

27. Management in Post-Dreissenid Period 1.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 3. Collapse and impairment of key commercial and recreational fisheries ? NEW SPATIAL AND TEMPORAL MANAGEMENT GOALS