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Bill Walton Assistant Professor/Extension Specialist Auburn University & AL Cooperative Extension Chris Linder, chrislinder.com

Little Lagoon Oysters

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Page 1: Little Lagoon Oysters

Bill Walton

Assistant Professor/Extension Specialist

Auburn University & AL Cooperative Extension

Chris Linder, chrislinder.com

Page 2: Little Lagoon Oysters

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

Page 3: Little Lagoon Oysters

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

Page 4: Little Lagoon Oysters

Diagram of fate of oil spilled from Amoco Cadiz in

France in 1979 (Marchand 1979 and Girin 2001)

Page 5: Little Lagoon Oysters

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

Page 6: Little Lagoon Oysters

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

Page 7: Little Lagoon Oysters
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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.

Page 12: Little Lagoon Oysters

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’

Page 13: Little Lagoon Oysters

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

Page 14: Little Lagoon Oysters

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

Page 15: Little Lagoon Oysters

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)

Page 16: Little Lagoon Oysters

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

Page 17: Little Lagoon Oysters

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

Page 18: Little Lagoon Oysters

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

Page 19: Little Lagoon Oysters

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

Page 20: Little Lagoon Oysters

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?

Page 21: Little Lagoon Oysters

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

Page 22: Little Lagoon Oysters

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

Page 23: Little Lagoon Oysters
Page 24: Little Lagoon Oysters

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.

Page 25: Little Lagoon Oysters

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

Page 26: Little Lagoon Oysters

-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

Page 27: Little Lagoon Oysters

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

Page 28: Little Lagoon Oysters