Mid-Continent Ecology Division Jack Kelly Peder Yurista. University of WI - Superior

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1 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 27

2 Contributors Great Lakes National Program Office David Rockwell Mid-Continent Ecology Division Jack Kelly Peder Yurista University of WI - Superior Mary Balcer Kurt Schmude Travis Mangan Steve Hagedorn Heidi Schaeffer Heidi Saillard

3 Fisheries Management Goal Maintain Balance Between Density of Predators and Prey

4 Components of Food Web Physical Features Temperature Light Predators Salmonids Phytoplankton Crustacean Zooplankton Cladocerans Copepods Planktivorous Forage Fish Nutrients Phosphorus Benthos Diporeia

5 Limiting Factors in Lake Superior Cold Water temperatures

6 Spring Water Temperatures Temperature (C) Superior

7 Spring Water Temperatures Temperature (C) Superior Michigan Huron

8 Summer Water Temperatures 25 Temperature (C) Superior Offshore Nearshore

9 Summer Water Temperatures 25 Temperature (C) Superior Huron Michigan

10 Limiting Factors in Lake Superior Cold water temperatures Low Levels of Nutrients

11 Effects on Food Web Physical Features Temperature Light Predators Salmonids Phytoplankton Crustacean Zooplankton Cladocerans Copepods Planktivorous Forage Fish Nutrients Phosphorus Benthos Diporeia

12 Effects on Food Web Physical Features Temperature Light Predators Salmonids Phytoplankton Crustacean Zooplankton Cladocerans Copepods Planktivorous Forage Fish Nutrients Phosphorus Benthos Diporeia

13 Spring Phosphorus Levels 7 6 Total P (ug P/L) Superior

14 Spring Phosphorus Levels 7 6 Total P(ug/L) Superior Huron Michigan

15 Limiting Factors Cold Water temperatures Low Levels of Nutrients Lead to lower primary productivity

16 Spring Chlorophyll Chlrophyll a (ug/l) Huron Superior Michigan

17 Lake Superior Chlorophyll 2 Chlorophyll (ug/l) summer spring

18 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

19 Relative abundance (%) Total phosphorus concentration (µg/l) Euan Reavie

20 Spring Phytoplankton Biomass from Community Integrated Samples 8, 7, 6, Biomass (ug/m3) 5, 4, 3, 2, 1, Superior Centric Diatoms Pennate Diatoms Chlorophytes Chrysophytes Cryptophytes Cyanophytes Dinoflagellates Others

21 Spring Phytoplankton Biomass 25, Total Biomass (ug/m3) 2, 15, 1, 5, Superior Michigan Huron

22 35, Summer Phytoplankton Biomass from Community Integrated Samples 3, Biomass (ug/m3) 25, 2, 15, 1, 5, Superior Centric Diatoms Pennate Diatoms Chlorophytes Chrysophytes Cryptophytes Cyanophytes Dinoflagellates Others

23 Zooplankton community Depends on phytoplankton abundance and species composition Certain types of zooplankton are important food for fish

24 Relative size of common zooplankton Cladocerans Cyclopoid Copepods Calanoid Copepods

25 Relative size of common zooplankton Cladocerans Cyclopoid Copepods Diporeia Calanoid Copepods

26 Mysis Opossum shrimp GLERL photo gallery

27 Community Composition Spring Zooplankton Density 1,4 1,2 1, Density (#/m 3 ) Daphnia Bosminids Other Cladocerans Immature Cyclopoids Adult Cyclopoids Immature Calanoids Adult Calanoids

28 Density (#/m3) 8, 7, 6, 5, 4, 3, 2, 1, Spring Zooplankton Density SUPERIOR MICHIGAN HURON

29 Lake Superior - Spring Length (mm) Adult Calanoids Imm Calanoids Adult Cyclopoids Imm Cyclopoids Biomass (ug/m 3 )

30 Summer Zooplankton Density Density (#/m 3 ) 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, Adult Calanoids Imm Calanoids Adult Cyclopoids Imm Cyclopoids Other Cladocerans Bosminids Daphnia

31 Summer Zooplankton Density 25, Density (#/m3) 2, 15, 1, 5, Superior Michigan Huron

32 Lake Superior - Summer Biomass (ug/m 3 ) Adult Calanoids Imm Calanoids Adult Cyclopoids Imm Cyclopoids Other Cladocerans Bosminids Daphnia Length (mm)

33 Lake Superior - Summer Biomass (ug/m 3 ) Adult Calanoids Imm Calanoids Adult Cyclopoids Imm Cyclopoids Other Cladocerans Bosminids Daphnia Length (mm)

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35 Nearshore Zooplankton Summer 25 3, 25, Ad Calanoids imm cal ad Cyc imm cyc 2, 15, bytho other cla daphnia 1, bosminid 5, SN95 SN127 SN143 SN13 SN7 SN147 SN159 SN35 SN19 SN99 SN29 SN19 SN12 SN135 SN13 SN145 SN81 SN11 SN33 SN129 SN17 SN97 Density (#/m3)

36 Threats to Lower Food Web Introduction of non-native native species Competitors Predators

37 Invertebrate Predators Bythotrephes and Cercopagis Invertebrate predators would select smaller or slower prey - cladocerans

38 Changes in Food Web Physical Features Temperature Light Predators Salmonids Phytoplankton Crustacean Zooplankton Cladocerans Copepods Bythotrephes Cercopagis Forage Fish Coregonids Nutrients Phosphorus Benthos Diporeia

39 Dreissenid mussels Zebra and quagga mussels Filter algae and small zooplankton Change flow of nutrients to offshore regions of lakes

40 Changes in Food Web Physical Features Temperature Light Predators Salmonids Phytoplankton Crustacean Zooplankton Cladocerans Copepods Forage Fish Coregonids Nutrients Phosphorus Benthos Diporeia Dreissenid mussels

41 Diporeia Abundance Density (#/m2) Lake Superior Diporeia - Moderate depths

42 Diporeia Abundance Lake Superior Diporeia Density at Deep Stations # m Year

43 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

44 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 Near-shore zooplankton populations are more variable in density and composition

45 Summary Offshore Diporeia density is low Abundance is greater at moderate depths These regions can serve as nursery areas for fish

46 Summary Low abundance of non-native 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