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Indirect Effects of Coastal Hypoxia on Planktivore Habitat

This study explores the implications of coastal hypoxia on pelagic food webs and fisheries, focusing on the Chesapeake Bay. It examines the effects of hypoxia on planktivore habitat and its potential impact on the ecosystem.

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Indirect Effects of Coastal Hypoxia on Planktivore Habitat

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  1. Indirect effects of coastal hypoxia on planktivore habitat: implications for pelagic food webs and fisheries Stuart Ludsin, Stephen Brandt & Doran Mason National Oceanic & Atmospheric Administration Great Lakes Environmental Research Laboratory Chris Rae & Hongyan Zhang School of Natural Resources University of Michigan Mike Roman, Bill Boicourt, Dave Kimmel & Krista Hozyash Horn Point Laboratory University of Maryland Xinsheng Zhang National Oceanic & Atmospheric Administration OAA-JHT, Cooperative Oxford Laboratory

  2. Causes of hypoxia are generally understood • Nutrient pollution (cultural eutrophication) • e.g. Gulf of Mexico, Chesapeake Bay • Ecological consequences are less understood • Especially for pelagic organisms General Background • Hypoxia is common to many systems • Freshwater & marine • Especially prevalent in coastal systems

  3. Hypoxia Research Program • Research objectives • Understand hypoxia’s effects on food webs • emphasis on pelagic food webs • Benefit resource management efforts • Should agencies care about hypoxia? • Seek generalities in processes & responses • Comparative systems approach • Chesapeake Bay • Northern Gulf of Mexico • Lake Erie

  4. NY 12 10 8 6 4 2 0 Chesapeake Bay (Hagy 2002) PA Volume x 109 m3 MD WV DE ‘50s ‘60s ‘70s ‘80s ‘90s VA Hypoxic (< 2 mg/l) Anoxic (< 0.2 mg/l) Focus on Chesapeake Bay Explore how hypoxia might be indirectly influencing Chesapeake Bay’s pelagic food web Chesapeake Bay

  5. Chesapeake Bay Pelagic Food Chain Piscivorous Fish Striped bass 95% of fish biomass (www.trophybassonly.com) Bay anchovy (www.njscuba.net) Zooplanktivorous Fish Acartia tonsa (copepod) (www.zp-online.net) Zooplankton

  6. Chesapeake Bay Trends • Bay anchovy  record low levels • Conventional wisdom  striped bass predation to blame Striped bass Poor recruitment Bay anchovy Sources: Bay anchovy: Maryland DNR; striped bass: NMFS

  7. Chesapeake Bay Trends • Is predation only to blame? • - High levels of both predator & prey before 1975 Striped bass Bay anchovy Sources: Bay anchovy: Maryland DNR; Striped bass: NMFS; Oxygen: Hagy et al. (2004)

  8. Chesapeake Bay Hypotheses Hypothesis 1 Reduce access to bottom during day  increase predation risk - striped bass are visual predators Hypoxic Day Warm Striped bass Pycnocline Cool Dark Bay anchovy Day

  9. Chesapeake Bay Hypotheses Hypothesis 2 Ho 2: Hypoxia reduces access to prey  poor growth conditions - zooplankton use hypoxic zone, perhaps as a refuge Hypoxic Day ZP Normoxic Bay anchovy Day

  10. Chesapeake Bay Example • East-west transects sampled while underway • 1996, 1997, 2000 • summer (hypoxic period) www.ocean.udel.edu R/V Cape Henlopen

  11. Chesapeake Bay Field Program • Dissolved oxygen • Zooplankton • Temperature • Chlorophyll a Fish Biomass

  12. 0 0 0 0 10 20 20 20 20 5 40 40 40 40 0 -50 -50 -100 -100 -37 -37 -37 -36.96 -36.96 -36.96 -76.20 -76.20 -76.15 -76.15 Increased Predation Risk Summer 1996 Summer 2000 Ho 1: Reduce access to bottom during day   predation risk - striped bass are visual predators 10 DO (mg/l) DO (mg/l) DO (mg/l) Depth (m) 5 Lat. 1 Day Lat. 18 Day 0 Longitude (degrees) Longitude (degrees) Longitude (degrees) Fish (dB) Fish (dB) Fish (dB) Depth (m) Ludsin et al. (in review) Longitude (degrees) Longitude (degrees)

  13. 0 0 10 10 20 20 30 30 Oxygen (mg/l) 40 40 0 5 10 ZP (mg/l) 4 0 2 -76.48 -76.48 -76.44 -76.44 -76.20 -76.20 -76.15 -76.15 Hypoxia as a Refuge Ho 2: Hypoxia reduces access to prey  poor growth conditions - zooplankton use hypoxic zone, perhaps as a refuge Depth (m) Summer 2000 Lateral 20 Lateral 18 Longitude (degrees) Depth (m) Summer 2000 Longitude (degrees) Ludsin et al. (in review)

  14. Hypoxia as a Refuge Ho 2: Hypoxia reduces access to prey  poor growth conditions - zooplankton use hypoxic zone, perhaps as a refuge Hypoxic cells (< 3 mg/l) Normoxic cells (> 3 mg/l) Ludsin et al. (in review)

  15. Longitude Bottom Depth Habitat Quality Modeling Hypoxia reduces access to prey  poor growth conditions • Bay anchovy growth rate potential (GRP) (Brandt et al. 1992) • - Expected growth response, given habitat conditions • - Good measure of habitat quality • Spatially-explicit bioenergetics modeling approach • Create equal-sized cells • 50 m x 1 m x 1 m • Run bioenergetics model in each cell • - Parameters from Lou and Brandt (1993) Ludsin et al. (in review)

  16. 0 Temp. (ºC) 20 15 25 40 Oxygen (ml/l) 20 0 5 10 40 ZP (ml/mm3) 20 Depth (m) 4 0 2 40 GRP (g/g/d) 20 0.08 0 0.04 40 Fish (dB) 20 -40 <-80 -60 40 -76.20 -76.15 Longitude (degrees) Summer 2000 Lateral 20 Lateral 18 • Hypoxia reduces access to zooplankton prey  poor growth -76.48 -76.44 Ludsin et al. (in review)

  17. Conclusions • Hypoxia can indirectly influence pelagic organisms • Alter distributions & behavior • Diel vertical migration behavior disrupted • Zooplankton using hypoxic zone (perhaps as a refuge) • A likely role in declining bay anchovy recruitment • Hypoxia also may influence top predator dynamics • (Costantini, Ludsin et al. in review) • increased benthos in diets • reduced growth rate • increased disease

  18. Future Research Pending Chesapeake Bay funding • “Comparative Evaluation of Hypoxia’s Effects on the Living Resources of Coastal Ecosystems” • - NOAA-CSCOR Program, 2007-2011 • Test hypotheses, test model predictions • More comprehensive approach • - improved field design (address behavior better) • - diet & growth work • - experimentation • - rigorous modeling (behavioral to ecosystem) • Compare Chesapeake Bay, Gulf of Mexico & Lake Erie

  19. Funding Support National Science Foundation NOAA Ecofore Program

  20. Longitude Bottom Depth Fish Mass Growth Rate (dB/dt) ZP prey Oxygen Temperature Habitat Quality Modeling Bioenergetics Modeling Framework (Kitchell et al. 1977, Hanson et al. 1997) dB/dt = C – (R + E + U) B = bay anchovy biomass C = consumption t = time R = respiration + SDA E = egestion U = excretion

  21. Bay anchovy ZP biomass = 1.75 mg/l Fish mass = 1.75 g Growth rate (g·g·d-1) Oxygen (mg/l) Temperature (˚ C) Habitat Quality Modeling Fish Mass Oxygen Growth Rate (dB/dt) Zooplankton Temperature Positive Negative Ludsin et al. (in review)

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