1. Influence of hypoxia on the distribution, behavior, and foraging of zooplankton and planktivorous fish in central Lake Erie: Field observations & future directions Hank Vanderploeg, GLERL Stuart Ludsin, GLERL Steve Pothoven, GLERL Tomas Höök, CILER Univ. of Michigan James Roberts, Univ. of Michigan Steve Ruberg, GLERL Joann Cavaletto, GLERL James Liebig, GLERL Gregory Lang, GLERL Stephen Brandt, GLERL

2. Hypoxia is an old problem in freshwater—Results for Cyclops bicuspidatus (Einsle 1965) This species is very tolerant of low oxygen (~ 0.1mg/L)

3. 1. Hypoxia will disrupt vertical migration behavior –Reduce time spent on bottom 2. Hypoxia will influence horizontal movement –Fish will move into oxygenated, shallow nearshore zones 3. Hypoxia will reduce availability of prey, both ZP & benthic macroinvertebrate prey –ZP use hypoxia as a refuge from predation –Hypoxia reduces benthic prey abundance 4. Fish consumption & condition will decline Original Lake Erie Fish-Centric Hypotheses

4. Playing chess with death—a zooplankton-centric view Scene from Bergman’s “The Seventh Seal”

5. Death normally comes in two forms: predation and starvation Zooplankton vertical migration is strategy to minimize overlap with visually preying invertebrate and vertebrate (fish) predators— conspicuous or unprotected (spineless) zooplankton move to lower light levels Move into upper favorable (temperature and food) areas at night. Predator abundance is assessed by kairomones. When many predators, the zooplankter (prey) must play chess to avoid overlap.

6. The Great Lakes have both visual invertebrate & and vertebrate predators—Lake Michigan example

7. Playing chess with death—the piscine players Scene from Bergman’s “The Seventh Seal”

8. USGS-NAS Emerald shiner: Epilimnetic planktivore Rainbow Smelt: Planktivore-benthivore Dominant planktivores of Lake Erie and their Vanderploeg & Scavia (1979) selectivity coefficients (W´) pre-hypoxia Prey size

9. Hypoxia, another form of death, alters the game—some hypotheses: Differential tolerance of zooplankton to hypoxia allows some species to enter the hypoxic zone to escape predators—the refuge Others will be forced out and trapped in lighted areas above—the hypoxia-light trap.

10. Dissolved Oxygen (mg/l) September Diel Station B August Lake Erie Some results before and after major hypoxia will give us some insights

11. General Methods—What we did

12. Trawling (fish species & samples for diet & ration work) Zooplankton net and pump sampling (zooplankton) Ponar sampling (benthic macroinvertebrates) Zooplankton Temperature Dissolved oxygen Light levels Chlorophyll a Fish Biomass Introduction to Study Systems & General Methods

13. Lake Erie Field Program (IFYLE 2005) Diel (24-hr) Transect (day-night) Source: Don Coles EPA-GLNPO R/V Lake Guardian (180’) NOAA-GLERL R/V Laurentian (80’) Transect B Diel Station B

15. Dissolved Oxygen (mg/l) Transect B Ho 2: Hypoxia will alter horizontal distribution of abundance –Fish will move into oxygenated, shallow nearshore zones September August October Lake Erie

16. Latitude (degrees) Depth (m) Day Night Temp (º C) DO (mg/l) Fish (dB) (August – Pre-Hypoxia) Ho 2: Hypoxia will alter horizontal distribution of abundance Lake Erie Ludsin, Vanderploeg & Ruberg, unpub

17. Latitude (degrees) Depth (m) Temp (º C) DO (mg/l) Fish (dB) (September – Peak Hypoxia) Ho 2: Hypoxia will alter horizontal distribution of abundance DayNight Lake Erie Ludsin, Vanderploeg & Ruberg, unpub

18. Latitude (degrees) Depth (m) Temp (º C) DO (mg/l) Fish (dB) (October – Post Hypoxia) Ho 2: Hypoxia will alter horizontal distribution of abundance Day Night –Reject: Fish move into oxygenated waters, but offshore Lake Erie Ludsin, Vanderploeg & Ruberg, unpub

19. Playing chess with death—Insights from pre-hypoxia (control) & hypoxia distributions and prey selection Scene from Bergman’s “The Seventh Seal”

30. USGS-NAS Emerald shiner: Epilimnetic planktivore Rainbow Smelt: Planktivore-benthivore Selectivity coefficient of Vanderploeg & Scavia (W´) for Emerald shiner and Rainbow Smelt in August 2005 Prey size

31. USGS-NAS Emerald shiner: Epilimnetic planktivore Rainbow smelt: Planktivore-benthivore Prey size Selectivity coefficient of Vanderploeg & Scavia (W´) for emerald shiner and rainbow smelt in September 2005

32. What’s going on down there? Present status: Heavy emphasis in IFYLE Hypoxia study on upper food web (fish and location of fish food) We do know, however: Mesozooplankton and microzooplankton distribution relative to hypoxia response is species specific Microzooplankton grazing dominates during the summer Bacteria-based food web becomes important in hypoxic zone

33. What’s going on down there? For the development of a conceptual framework we’d like to know: What is the minimum oxygen concentration a zooplankter (species by species) is willing to enter yet survive under various predation risk scenarios? How does feeding and behavior vary with oxygen concentration? What is the joint distribution of meso-and microzooplankton around hypoxic zones How is production and predation risk affected?

34. We know something about Daphnia foraging in hypoxic areas but nothing for copepods, the dominants in the Great Lakes, or for visual invertebrate predators From Heisey & Porter (1977)

35. Some possible lab approaches to define spatial rules of food web assembly (“indirect effects”) Observe location of position of zooplankton in laboratory water columns with gradients of light, temperature, kairomones of potential predators & oxygen Directly observe behavior and foraging in hypoxic water columns. Observe effect of hypoxia on visual predation (both invertebrate & vertebrate)—have predators watch TV

36. Inside the lab

37. Outside the lab: keeping the predator in focus