Impacts of hypoxia on key Impacts of hypoxia on key benthic infauna and their benthic infauna and their predators in Chesapeake predators in Chesapeake Bay Bay Rochelle D. Seitz & W. Chris Long Virginia Institute of Marine Science, The College of William and Mary
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Impacts of hypoxia on key benthic infauna and their predators in Chesapeake Bay
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 Overview of hypoxia in Chesapeake Bay - PowerPoint PPT Presentation
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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-
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
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
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)