little lagoon oysters
TRANSCRIPT
Bill Walton
Assistant Professor/Extension Specialist
Auburn University & AL Cooperative Extension
Chris Linder, chrislinder.com
Direct
• Mortality
Smothering, poisoning,
loss of insulation, etc.
• Change in growth rates &
reproductive patterns
• Changes in distribution of
mobile organisms
Indirect
• Physiological changes
Reproductive changes,
changes in growth rates,
change in disease
resistance
• Behavioral changes
• Food web changes
Changes in community
composition (some species
up, some down, etc.)
• Habitat changes
E.g., low oxygen zones
Contaminant
• Type of oil
• Degree of weathering
• Amount of oil
• Duration of oil
• Manner of exposure
• Questions about
dispersant
Organisms
• Life stage
• Reproductive/physiolog
ical state
• Distribution
• Ability to move (or not)
Credit: LaDon Swann
Diagram of fate of oil spilled from Amoco Cadiz in
France in 1979 (Marchand 1979 and Girin 2001)
Different habitats• Shoreline, water column, sea bed, air, upland, etc.
Environmentally sensitive habitats &
organisms• Birds & mammals
• Marshes, mangroves, sea grass beds
• Coral reefs
• Fisheries & aquaculture resources
Sessile (= doesn’t move) adult life stage
Filter and accumulate particles from water
Subject of long-term studies• National Oceanic &
Atmospheric Administration’s (NOAA) Mussel Watch Program
Important keystone species
Subject of important commercial fishery
Number of restoration projects within the state• The Nature Conservancy,
Dauphin Island Sea Lab, University of South Alabama, AL Marine Resources Division, Mobile Bay Oyster Gardening Program, Auburn University Shellfish Lab, etc.
Focus on environmental benefits of oysters• Water clarity, supply of oyster
larvae, habitat creation, shoreline protection, etc.
Oyster reefs in the Gulf of Mexico had recently been classified as in ‘fair condition’, in contrast to most other parts of the world where oyster reef habitat is in severe decline (Beck et al. 2009)
Both public reefs and private leases
Reliance on natural ‘set’
Most harvested oysters
are shucked before
going to market
Large quantities of shell
are produced by
shucking houses
This shell is returned to
the water to sustain reef
habitat both for
conservation and
fisheries
In 2008, the U.S. eastern oyster industry (Crassostreavirginica) produced over 23 million pounds of oysters, valued at almost $82.5 million (NMFS).
By volume, the Gulf of Mexico dominated the harvest, accounting for over 89% of the harvest
By value, however, the Gulf of Mexico obtained only 73% of the total dollar value of the US harvest (NMFS)
Credit: Jim Gossen
Focused on the commodity, shucked product market, the 5-year average value of Gulf of Mexico oysters is $2.88/pound, almost an order of magnitude lower than the 5-year average value of New England oysters (almost entirely aquacultured product intended for the premium, half-shell market) of $24.42/pound (NMFS)
Tremendous variation in
salinity
• Too much freshwater can
be fatal to oysters
• Too much saltwater
favors oyster predators
and diseases
Siltation can smother
oysters
Variations in natural set
Hurricanes
First priority is to protect human heath;
therefore, closures are aggressive and
pro-active• Testing has so far confirmed that the closure
areas have been adequate
Contaminants associated with oil spills are
dangerous
Concerns about use of dispersant• Corexit
Process for re-opening• First, no signs (sheen, smell) of
oil on water
• Second, sensory tests of different species of seafood By species and area
Smelled raw, smelled cooked, tasted cooked
Trained field screeners can detect down to 10 ppm, while trained experts can detect down to 0.5 ppm
• Finally, analytical chemical tests to look for contaminants, including polycyclic aromatic hydrocarbons (PAHs)
Testing is being done for the presence of the components of Corexit
Potential long-term closures
Very possibly re-openings on species by
species basis, possibly varying by region
Long-term monitoring to evaluate risks of
recontamination
Again, this was an immediate effect of the
DHOS
Affected consumption of crawfish, which
are not a marine species and raised well
inshore
Will consumers believe government tests
that indicate that seafood is safe?
Opportunity for the region to embrace a
very high standard of safety and quality?
Natural Resource Damage Assessment• Legal process to determine damages for litigation
across the region
Mussel Watch Program• Historically, two sites in Alabama (Dog River &
Cedar Point Reef)
Large number of natural resource agencies, universities and conservation organizations have begun assessment programs
Mortality• To my knowledge, only
mortalities of adult oysters observed to date have been attributed to freshwater diversions to keep oil away from shore in LA
Changes in growth Reproductive impacts Change in resistance to
disease Reduction in larval
survival/settlement
Hatchery-reared, single oysters are deployed for a 2 month duration.
One cage per site, four 15-oyster replicates in each cage.
Salinity and temperature are collected from deployment sites by way of data-loggers.
Oyster shell metrics, weights and survival are recorded prior to and post deployment.
0 0 0 0 0 0 0 0 0 0 03.33
0 0
53.33
00
10
20
30
40
50
60
OB
PC
WB
LDB
PP
LL
FM
MP
AUSL
AP
HC
BS
SB
CP
DR
GB
Pe
rce
nt
Mo
rta
lity
(%
de
ad
/ 6
0 o
yst
ers
)
Culture Sites
Percent Total Mortality: Fall
8.33
1.67
6.67
3.33
6.67
0 0 0 0 00
1
2
3
4
5
6
7
8
9
SB AP FM PC WB
Pe
rce
nt
Mo
rta
lity
(% d
ea
d/
60
oy
ste
rs)
Culture Sites
Percent Total Site MortalitySummer vs. Fall
Summer
Fall
Preliminary seasonal differences support further multi-season analysis
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Av
era
ge
Gro
wth
(m
m)
Culture Sites
Daily Average Growth: Shell Height, Shell Length and Shell Width
DGRSH
DGRSL
DGRSW
Variations among growth measurements were significantly different between sites
Monitor oyster growth, survival and condition at field sites along AL coast• Possibly expand to FL and MS• Do these vary among sites?
Analyze degree of contamination of tissues• Possibly add sediment and water samples• Do biological responses correlate with contamination?
Conduct this seasonally for at least 3 years to document changes over time• Do these responses change over time?
May also be useful for determining the effects of efforts to prevent contamination
Awaiting research permit