Impacts of hypoxia on key Impacts of hypoxia on key benthic infauna and their benthic infauna and their

predators in Chesapeake Bay predators in Chesapeake Bay

Rochelle D. Seitz & W. Chris LongVirginia Institute of Marine Science,

The College of William and Mary

Hypoxia Workshop, March 2007

OutlineOutline

Threats to biodiversityThreats to biodiversity

Overview of hypoxia in Chesapeake BayOverview of hypoxia in Chesapeake Bay

Recent work on hypoxia: prey and predatorsRecent 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 BiodiversityThreats to Biodiversity Overexploitation and HarvestingOverexploitation and Harvesting

• Can contribute to habitat degradationCan contribute to habitat degradation

Introduced SpeciesIntroduced Species

Climate ChangeClimate Change

Habitat Destruction and LossHabitat Destruction and Loss• The single largest threat in terrestrial systemsThe single largest threat in terrestrial systems

Importance of habitat destructionImportance of habitat destruction

……The one process ongoing in the 1980s that will The one process ongoing in the 1980s that will take millions of years to correct is the loss of take millions of years to correct is the loss of genetic and species diversity by the destruction of genetic and species diversity by the destruction of natural habitats… natural habitats… (E.O. Wilson, 1985)(E.O. Wilson, 1985)

……rates of resource collapse increased, and rates of resource collapse increased, and recovery potential, stability, and water quality recovery potential, stability, and water quality decreased exponentially with declining diversity.decreased exponentially with declining diversity.(B. Worm et al., 2006)(B. Worm et al., 2006)

Hypoxia in Chesapeake BayHypoxia in Chesapeake Bay The most well-studied The most well-studied

system in North America system in North America for hypoxiafor hypoxia

Onset of low DO related to Onset of low DO related to European settlement in the European settlement in the 1717thth century century

How are benthic prey and How are benthic prey and predators affected?predators affected?

Human-induced condition (Zimmerman and Canuel 2000)Human-induced condition (Zimmerman and Canuel 2000)

Effects of Hypoxia on BenthosEffects of Hypoxia on Benthos

Mainstem Chesapeake:Mainstem Chesapeake:• Polyhaline mud (13m), not Polyhaline mud (13m), not

exposed to hypoxiaexposed to hypoxia• Hypoxic mud (27m),Hypoxic mud (27m),

oxygen < 2 mg/Loxygen < 2 mg/L

With hypoxia, declines inWith hypoxia, declines in• RichnessRichness• Overall biomassOverall biomass• Biomass of equilibrium (long-Biomass of equilibrium (long-

lived) specieslived) species

Increase in:Increase in:• Opportunist biomassOpportunist biomass

(Modified from Dauer et al. 1992)

Community Measure

mg

AFD

W /0

.02

m2 o

r P

erce

nt

0

20

40

60

80

100

Polyhaline Mud Hypoxic Mud

Study OrganismsStudy Organisms MacomaMacoma balthicabalthica is biomass is biomass

dominant dominant (Baird and Ulanowicz, 1989)(Baird and Ulanowicz, 1989)

Important blue crab prey (~50% Important blue crab prey (~50% of diet) of diet) (Hines et al., 1990)(Hines et al., 1990)

Long lived (~3 yr.) Long lived (~3 yr.)

Can survive for up to 3 weeks in Can survive for up to 3 weeks in hypoxic water hypoxic water (Seitz et al., 2003)(Seitz et al., 2003)

Crabs not present < 3 mg/l DO Crabs not present < 3 mg/l DO (VA trawl survey data)(VA trawl survey data)

Mesocosm Hypoxia ExperimentMesocosm 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 sand15 cm muddy sand 12 12 M. balthicaM. balthica clams transplanted to 0.25 m clams transplanted to 0.25 m22 patch (48/m patch (48/m22)) Two treatments: Normoxia & low DO (< 2 ,mg/l), 3-5 reps of Two treatments: Normoxia & low DO (< 2 ,mg/l), 3-5 reps of

eacheach Predator (intermolt blue crab), acclimated to low DO for 24 Predator (intermolt blue crab), acclimated to low DO for 24

hrs, added and allowed to feed for 2 dayshrs, added and allowed to feed for 2 days

Results: MesocosmResults: Mesocosm Proportional mortality sig. Proportional mortality sig.

higher under normoxia for higher under normoxia for all 3 years (p < 0.01)all 3 years (p < 0.01)

Siphon protrusion Siphon protrusion increased (but no siphon increased (but no siphon nippers)nippers)

Clam burial depth didn’t Clam burial depth didn’t change (in muddy sand)change (in muddy sand)

(Seitz et al. MEPS 2003)

Year

2000 2001

Pro

po

rtio

nal

mo

rtal

ity

(# e

aten

/# t

ran

spla

nte

d)

0.0

0.1

0.2

0.3

0.4

0.5 Low DOHigh DO

1999

Field Hypoxia ExperimentField Hypoxia Experiment Deep areas experience Deep areas experience

hypoxiahypoxia

Caging: clam survival deep Caging: clam survival deep vs. shallow (28 days)vs. shallow (28 days)

Predation higher in deep Predation higher in deep during hypoxiaduring hypoxia

Clams reduced burial Clams reduced burial depth in mud (lab exps)depth in mud (lab exps)

Hypoxia

Before DuringP

red

atio

n r

ate

(day

-1)

0.00

0.01

0.02

0.03Shallow Deep

a

b

a

a

(Long and Seitz, Ecology in review )

Response to hypoxiaResponse to hypoxia

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 benthicBaywide benthic sampling methods sampling methods

Used benthic data from CBP Used benthic data from CBP probability-based samplingprobability-based sampling

9 years (1996-2004), 2500 points9 years (1996-2004), 2500 points

Young Grab: samples 0.044 mYoung Grab: samples 0.044 m22 to 10 cm depth, 0.5 mm meshto 10 cm depth, 0.5 mm mesh

CTD for water-quality CTD for water-quality parametersparameters

Means per meter depthMeans per meter depth

Oxygen, depth, & densityOxygen, depth, & density

Depth (m)

0 10 20 30

Dis

solv

ed O

xyg

en m

g/L

(S

E)

0

1

2

3

4

5

6

7

8P < 0.001R2 = 0.85

Dissolved oxygen (mg/L)

0 2 4 6 8N

um

ber

of

ind

ivid

ual

s/m

2

0

2000

4000

6000

8000

P < 0.001R2 = 79%

ms in prep with Dan Dauer and Roberto Llanso

B-IBI by depthB-IBI by depth Multi-metric indexMulti-metric index DiversityDiversity AbundanceAbundance BiomassBiomass Functional groupsFunctional groups

Sig. linear decline with Sig. linear decline with depth (P < 0.005)depth (P < 0.005)

Increased variance with Increased variance with depth (both low DO & depth (both low DO & normoxic sites)normoxic sites)

2006 worst B-IBI on 2006 worst B-IBI on recordrecord

Depth (m)

0 10 20 30

Ben

thic

In

dex

of

Bio

tic

Inte

gri

ty

0.5

1.0

1.5

2.0

2.5

3.0

3.5

ConclusionsConclusions Mesocosm: Mesocosm: decreaseddecreased blue crab predation during blue crab predation during

hypoxia (consistent with CSM)hypoxia (consistent with CSM) Field experiment: Field experiment: increasedincreased predation during hypoxia predation during hypoxia

(consistent with PSM)(consistent with PSM) Siphon nipping may be important in fieldSiphon 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 Baywide: decreased B-IBI w/ depth, consistent with

hypoxic trends, lowest values in 2006hypoxic trends, lowest values in 2006 Overall trends: no change in fisheries production with Overall trends: no change in fisheries production with

bay-wide increases in hypoxia (Kemp et al. 2005)bay-wide increases in hypoxia (Kemp et al. 2005) Need to better quantify field predation at fine spatial and Need to better quantify field predation at fine spatial and

temporal scales & determine food-web effectstemporal scales & determine food-web effects

SummarySummary

Effects of hypoxia detrimental to Effects of hypoxia detrimental to benthosbenthos

Positive effects of hypoxia on Positive effects of hypoxia on predatorspredators

Habitat degradation leading to loss of Habitat degradation leading to loss of species may affect resilience of the species may affect resilience of the system and must be addressedsystem and must be addressed

Chesapeake

AcknowledgementsAcknowledgements

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)