Impacts of hypoxia on key benthic infauna and their predators in Chesapeake Bay Rochelle D. Seitz & W. Chris Long Virginia Institute of Marine Science, The College of William and Mary Hypoxia Workshop, March 2007

Outline Threats to biodiversity Threats to biodiversity Overview of hypoxia in Chesapeake Bay Overview of hypoxia in Chesapeake Bay Recent work on hypoxia: prey and predators Recent work on hypoxia: prey and predators Part 1: Mesocosm experimentPart 1: Mesocosm experiment Part 2: Field predation experimentPart 2: Field predation experiment Part 3: Benthic long-term trendsPart 3: Benthic long-term trends

Threats to Biodiversity Overexploitation and Harvesting Overexploitation and Harvesting Can contribute to habitat degradationCan contribute to habitat degradation Introduced Species Introduced Species Climate Change Climate Change Habitat Destruction and Loss Habitat Destruction and Loss The single largest threat in terrestrial systemsThe single largest threat in terrestrial systems

Importance of habitat destruction …The one process ongoing in the 1980s that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats… …The one process ongoing in the 1980s that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats… (E.O. Wilson, 1985) …rates of resource collapse increased, and recovery potential, stability, and water quality decreased exponentially with declining diversity. …rates of resource collapse increased, and recovery potential, stability, and water quality decreased exponentially with declining diversity. (B. Worm et al., 2006)

Hypoxia in Chesapeake Bay The most well-studied system in North America for hypoxia The most well-studied system in North America for hypoxia Onset of low DO related to European settlement in the 17 th century Onset of low DO related to European settlement in the 17 th century How are benthic prey and predators affected? How are benthic prey and predators affected? Human-induced condition (Zimmerman and Canuel 2000)

Effects of Hypoxia on Benthos Mainstem Chesapeake: Mainstem Chesapeake: Polyhaline mud (13m), not exposed to hypoxiaPolyhaline mud (13m), not exposed to hypoxia Hypoxic mud (27m),Hypoxic mud (27m), oxygen < 2 mg/L With hypoxia, declines in With hypoxia, declines in RichnessRichness Overall biomassOverall biomass Biomass of equilibrium (long- lived) speciesBiomass of equilibrium (long- lived) species Increase in: Increase in: Opportunist biomassOpportunist biomass (Modified from Dauer et al. 1992)

Study Organisms Macoma balthica is biomass dominant (Baird and Ulanowicz, 1989) Macoma balthica is biomass dominant (Baird and Ulanowicz, 1989) Important blue crab prey (~50% of diet) (Hines et al., 1990) Important blue crab prey (~50% of diet) (Hines et al., 1990) Long lived (~3 yr.) Long lived (~3 yr.) Can survive for up to 3 weeks in hypoxic water (Seitz et al., 2003) Can survive for up to 3 weeks in hypoxic water (Seitz et al., 2003) Crabs not present < 3 mg/l DO (VA trawl survey data) Crabs not present < 3 mg/l DO (VA trawl survey data)

Mesocosm Hypoxia Experiment 12 tanks (1m x 2m x 0.5m; 1200 l) 12 tanks (1m x 2m x 0.5m; 1200 l) 15 cm muddy sand 15 cm muddy sand 12 M. balthica clams transplanted to 0.25 m 2 patch (48/m 2 ) 12 M. balthica clams transplanted to 0.25 m 2 patch (48/m 2 ) Two treatments: Normoxia & low DO (< 2,mg/l), 3-5 reps of each Two treatments: Normoxia & low DO (< 2,mg/l), 3-5 reps of each Predator (intermolt blue crab), acclimated to low DO for 24 hrs, added and allowed to feed for 2 days Predator (intermolt blue crab), acclimated to low DO for 24 hrs, added and allowed to feed for 2 days

Results: Mesocosm Proportional mortality sig. higher under normoxia for all 3 years (p < 0.01) Proportional mortality sig. higher under normoxia for all 3 years (p < 0.01) Siphon protrusion increased (but no siphon nippers) Siphon protrusion increased (but no siphon nippers) Clam burial depth didn’t change (in muddy sand) Clam burial depth didn’t change (in muddy sand) (Seitz et al. MEPS 2003) 1999

Field Hypoxia Experiment Deep areas experience hypoxia Deep areas experience hypoxia Caging: clam survival deep vs. shallow (28 days) Caging: clam survival deep vs. shallow (28 days) Predation higher in deep during hypoxia Predation higher in deep during hypoxia Clams reduced burial depth in mud (lab exps) Clams reduced burial depth in mud (lab exps) (Long and Seitz, Ecology in review )

Response to hypoxia Before hypoxia, predators feed in shallow areas, where prey densities are high. Before hypoxia, predators feed in shallow areas, where prey densities are high During hypoxia, predators move into deep areas to take advantage of stressed prey

Baywide benthic sampling methods Used benthic data from CBP probability-based sampling Used benthic data from CBP probability-based sampling 9 years ( ), 2500 points 9 years ( ), 2500 points Young Grab: samples m 2 to 10 cm depth, 0.5 mm mesh Young Grab: samples m 2 to 10 cm depth, 0.5 mm mesh CTD for water-quality parameters CTD for water-quality parameters Means per meter depth Means per meter depth

Oxygen, depth, & density ms in prep with Dan Dauer and Roberto Llanso

B-IBI by depth  Multi-metric index  Diversity  Abundance  Biomass  Functional groups Sig. linear decline with depth (P < 0.005) Sig. linear decline with depth (P < 0.005) Increased variance with depth (both low DO & normoxic sites) Increased variance with depth (both low DO & normoxic sites) 2006 worst B-IBI on record 2006 worst B-IBI on record

Conclusions Mesocosm: decreased blue crab predation during hypoxia (consistent with CSM) Mesocosm: decreased blue crab predation during hypoxia (consistent with CSM) Field experiment: increased predation during hypoxia (consistent with PSM) Field experiment: increased predation during hypoxia (consistent with PSM) Siphon nipping may be important in field Siphon nipping may be important in field Predation occurs immediately after normoxia returns? Predation occurs immediately after normoxia returns? Predators diving into hypoxia? Predators diving into hypoxia? Baywide: decreased B-IBI w/ depth, consistent with hypoxic trends, lowest values in 2006 Baywide: decreased B-IBI w/ depth, consistent with hypoxic trends, lowest values in 2006 Overall trends: no change in fisheries production with bay-wide increases in hypoxia (Kemp et al. 2005) Overall trends: no change in fisheries production with bay-wide increases in hypoxia (Kemp et al. 2005) Need to better quantify field predation at fine spatial and temporal scales & determine food-web effects Need to better quantify field predation at fine spatial and temporal scales & determine food-web effects

Summary Effects of hypoxia detrimental to benthos Effects of hypoxia detrimental to benthos Positive effects of hypoxia on predators Positive effects of hypoxia on predators Habitat degradation leading to loss of species may affect resilience of the system and must be addressed Habitat degradation leading to loss of species may affect resilience of the system and must be addressed Chesapeake

Acknowledgements Funding by: National Sea Grant, NOAA – Chesapeake Bay Office, VA Commonwealth, EPA, NSF REU program, Chesapeake Bay Program Assistance from: Community Ecology Group & Marine Conservation Biology Group at VIMS, REU students, ODU & Versar (CBP data)