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

Hypoxia is common to many systems – –Freshwater & marine – –Especially prevalent in coastal systems 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

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 Hypoxia Research Program

‘50s‘60s‘70s‘80s‘90s Hypoxic (< 2 mg/l) Anoxic (< 0.2 mg/l) Volume x 10 9 m 3 Chesapeake Bay (Hagy 2002) Chesapeake Bay NY PA WV VA DE MD Focus on Chesapeake Bay Explore how hypoxia might be indirectly influencing Chesapeake Bay’s pelagic food web

PiscivorousFish ZooplanktivorousFish Zooplankton Bay anchovy ( Stripedbass Acartia tonsa (copepod)( Chesapeake Bay Pelagic Food Chain 95% of fish biomass (

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

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

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

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

East-west transects sampled while underway , 1997, summer (hypoxic period) Chesapeake Bay Example R/V Cape Henlopen

Dissolved oxygen Dissolved oxygen Zooplankton Zooplankton Temperature Temperature Chlorophyll a Chlorophyll a FishBiomass Chesapeake Bay Field Program

Depth (m) Longitude (degrees) Summer 1996 DO (mg/l) Longitude (degrees) DO (mg/l) Summer 2000 DO (mg/l) Ludsin et al. (in review) Increased Predation Risk Ho 1: Reduce access to bottom during day   predation risk - striped bass are visual predators Longitude (degrees) Fish (dB) Fish (dB) Longitude (degrees) Lat. 1 Day Fish (dB) Depth (m) Lat. 18 Day Longitude (degrees)

Depth (m) Longitude (degrees) Oxygen (mg/l) 0510 Lateral 18 Ludsin et al. (in review) ZP (mg/l) Lateral 20 Ho 2: Hypoxia reduces access to prey  poor growth conditions - zooplankton use hypoxic zone, perhaps as a refuge Hypoxia as a Refuge Longitude (degrees) Depth (m) Summer 2000 Summer 2000

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

Spatially-explicit bioenergetics modeling approach Bay anchovy growth rate potential (GRP) (Brandt et al. 1992) - Expected growth response, given habitat conditions - Good measure of habitat quality Longitude Depth Bottom 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) Habitat Quality Modeling Hypoxia reduces access to prey  poor growth conditions

Fish (dB) < ZP (ml/mm 3 ) 02 4 Oxygen (ml/l) 0510 Temp. (ºC) 1525 GRP (g/g/d) Depth (m) Longitude (degrees) Lateral 18 Lateral 20 Ludsin et al. (in review) Summer 2000 Hypoxia reduces access to zooplankton prey  poor growth Hypoxia reduces access to zooplankton prey  poor growth

Hypoxia can indirectly influence pelagic organisms Conclusions 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

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

Funding Support National Science Foundation NOAA Ecofore Program

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

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