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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 Worlds Surface Freshwater Slide 2 Lake Superior Lake Huron Lake Ontario Lake Erie Lake Michigan 85 m 60 m 150 m 19 m 86 m Mean Depths Slide 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 Slide 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 Slide 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 Slide 6 Dreissenid Mussels The principle cause of changes in native food- web Zebra Quagga Slide 7 QUAGGA MUSSELS AT 110 M PRE DREISSENIDS POST 30mPOST 40m BOTTOM OF LAKE MICHIGAN (east coast) Slide 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 Slide 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 Slide 10 Slide 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 Slide 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% Slide 13 Phytoplankton biomass measured as chlorophyll a Large decrease in spring isothermal period 2007/08 (66%) Slide 14 Phytoplankton Compositional Changes in 2007/08 Spring diatoms decreased significantlyespecially 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 Slide 15 WHY LARGE CHANGES IN 2007/08? Large Populations of Dreissenid mussels became established after 1983/87 and 1995/98 samplings Slide 16 Only time of year Dreissenid filtering is linked to entire water column (monomictic period) WHY BIG CHANGES IN SPRING?? Isothermal mixing.. Slide 17 LESS PHYTOPLANKTON - LARGE INCREASE IN WATER CLARITY In 2010 Secchi disk transparency as high as 32 m off Frankfort Slide 18 Lake Michigan Seasonal Si Utilization (Indicator of Diatom Production) Closed symbols, northern basin Open symbols, southern basin Spring Summer Drawdown EPA_GLNPO data Slide 19 MI/HU Silica Drawdown Becoming like Lake Superior Closed symbols, northern basin Open symbols, southern basin Michigan Superior Huron EPA_GLNPO data Slide 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 Slide 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 Slide 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) Slide 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 Slide 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 Slide 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 Slide 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 Slide 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 Slide 28