Eastern oyster population ecology and landscape characteristics in Ninigret Pond,

Rhode Island

Brown, D., DeAngelis, B., Stills, B.

The Nature Conservancy (1)

NOA Restoration Center (2)

University of Rhode Island (3)

Project Background

• Global loss in oyster reef habitat and ecological services

• E-NGO, academic, state-federal agency interest in oyster habitat and population enhancement, with complimentary yet conflicting goals, e.g.:– Fisheries enhancement

– Water quality improvement

– Shoreline improvement and resiliency

• Local, state, and regional goals cannot be determined or evaluated without population and ecological baselines

Rhode Island Objectives• Establish restoration baselines and identify needs

• Characterize natural and restored beds

• Identify environmental and biological constraints

General Approach• Standardized assessment and mapping of natural oyster beds

• Population inventory and habitat characterization

• Oyster settlement collection and body condition index

• Larval presence and density

Case Site – Ninigret (Charlestown Pond)

• Largest coastal lagoon

– Pond area: 7.38 km-2

– Watershed area: 6,000 acres

– Mean depth: 1.31 m

– Tidal fluctuations: 7-16 cm (Bothroyd et al., 1985)

• Historical collapse of oyster reefs (Lee, 1980; Simpson, 1977)

– Permanent breach way increased sedimentation, increased salinity

• Rise in oyster aquaculture (3.8 acres under cultivation, 2011)

• Wild stock estimated at 24,200 (Ganz et al., 1984)

Oysterscape

Rock reef, mudRip-rap

Rock reef, sand

Sand-cobble, shoal

Sand bar reef

Rip-rap

Sand-cobble, shoal

Sand bar reef

Rip-rap

Sand-cobble, shoal

Populations delineated by d-GPS. Outer bounds are smoothed by 0.1-m and represent areas with oyster densities greater than 5 m-2

Substrate Preferences

A. Sand-cobble aggregate

B. Sand-shell aggregate

C. Rip-rap revetment

Sand-

shell

Sand-c

obbl

e

Roc

k

Rip-r

ap

160

140

120

100

80

60

40

20

0

San

d-sh

ell

San

d-co

bble

Roc

k

Rip-r

ap

Live (m)

Substrate

Dead (m)

A, B

A

C A

B

A

GLM: F = 5.1, p = 0.034GLM: F= 9.2, p = 0.001

D. Rock

Substrate Preferences

A. Sand-cobble aggregate

B. Sand-shell aggregate

C. Rip-rap revetment D. Rock

140

120

100

80

60

40

20

0

16

12

8

4

0

140

120

100

80

60

40

200

16

12

8

4

0

Cobble

SH (mm)

Fre

qu

en

cy

Rip-rap

Rock Shell

Greater occurrence of adults, decreased harvesting pressure

Substrate Characteristics

A. Sand-cobble aggregate

B. Sand-shell aggregate

C. Rip-rap revetment D. Rock

40

30

20

10

0

SSNEFNFCSSNEFNFC

60

45

30

15

0

LocationSSNEFNFCSSNEFNFC

40

30

20

10

0

Course (%) Sand (%)

Fines (%)

Sand

Shell

Habitat

1-5 mm, * 106-710 µm, *

≤ 106 µm Difference between sand-silt and sand-shell composition (F = 7.8, p <0.05), but no difference between locations (F = 3.17, p > 0.05)

Substrate Characteristics

A. Sand-cobble aggregate

B. Sand-shell aggregate

C. Rip-rap revetment

Location SSNEFNFCSSNEFNFC

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

To

tal

Org

an

ic C

arb

on

, L

OI

(%) Sand

Shell

Habitat

Location F = 32.8, p = 0.01

GLM: Habitat F = 23.6, p =0.04

D. Rock

SSNEFNFC

120

90

60

30

0

SSNEFNFC

Live (m)

Location

Dead (m)

FC

FN

NE

SS

Location

140120100806040200

20

10

0

140120100806040200

20

10

0

Fort Neck

SH (mm)

Fre

qu

en

cy

Foster Cove

Ninigret East

Population Demographics

Greater occurrence of adults, Closed Shellfish Management Area

Wild Oyster Population in Open Shellfish

Management Area (Ninigret Pond, 2011)

Wild Oyster Population in Closed Shellfish

Management Area (Ninigret Pond, 2011)

• Fishing pressure? Disease?

• What is the variation in female

fecundity on effective population size?

Larval and Spat Recruitment

Month

Sept

embe

r

Augu

stJu

lyJu

neMay

Sept

embe

r

Augu

stJu

lyJu

neMay

Sept

embe

r

Augu

stJu

lyJu

neMay

Sept

embe

r

Augu

stJu

lyJu

neMay

Sept

embe

r

Augu

stJu

lyJu

neMay

14

12

10

8

6

4

2

0

Sp

at

(m2

)

FC

FN

GP

NE

SS

LocationWhen does recruitment occur?

Peaks in June, and September

Month

Sept

embe

r

Augu

stJu

lyJu

ne

Sept

embe

r

Augu

stJu

lyJu

ne

Sept

embe

r

Augu

stJu

lyJu

ne

Sept

embe

r

Augu

stJu

lyJu

ne

Sept

embe

r

Augu

stJu

lyJu

ne

Sept

embe

r

Augu

stJu

lyJu

ne

90

80

70

60

50

40

30

20

10

0

Mean

Larv

al D

en

sit

y (

± 1

SE

) / L

Farms

FC

FN

GP

NE

SS

Location

Oyster spat, 16 day

August, AvgWS 4.25

m/s

May, AvgWS 4.91m/s June, AvgWS 4.49 m/s July, AvgWS 4.28 m/s

September, AvgWS 4.27 m/s

Wind driven dispersion

Environmental Constraints

35

30

25

20

15

May

Septem

ber

August

JulyJu

ne

May

25.0

22.5

20.0

17.5

15.0

Month2M

ay

Septem

ber

August

July

June

May

6.0

4.5

3.0

1.5

0.0

10

8

6

4

Salinity (%) Temp (°C)

Chl a (µg/l) DO (mg/l)

FC

FN

GP

NE

SS

Location

Spawning events

Higher settlement at lower salinities

120100806040200

35

30

25

20

15

10

5

Mean Adult Oyster m-2

Me

an

Oyste

r La

rva

e L Farms

FC

FN

GP

NE

SS

Location

Predicted relationship

Biomass DW g/m-2 Area (m-2) Total DW (lbs)

Foster Cove 656 1496 2157

Fort Neck 536 1087 1281

Spawner Sanctuary 519 66 75

Ninigret East 711 982 1535

Total Wild 2422 3631 5047

Aquaculture 1000 15378 33788

Adult/Recruit Relationships

• Oyster larvae is a function of the number of adult broodstock, water retention (hydrology), and substrate quality

• Oyster larvae was present in both Aquaculture and Grassy Point sites which neighbor oyster aquaculture leases and don’t have natural beds

• It appears aquacultured oysters may be a source for wild oyster stocks

• Evaluate larval contribution from

oyster aquaculture to wild stock

• Develop multi-reef framework

• Evaluate population connectivity

and resiliency

Current and Future Goals

• Settlement occurred above sediments,

areas with lower salinity and water

residency times

• Test vertical height, and substrate

type (rugosity)

• Reef Design

• 2/3 surf clam, 1/3 oyster shell

• Veneer – bagged oyster shell

• Base – loose surf clam shell

Evaluate Reef Design

Experimental reefs mimicking natural reef design

through shape, and vertical relief or height.

60 cm bed height

Questions and Thank you!If interested in volunteering for the 2013 reef construction

please let us know!E: dsbrown@tnc.org

P: 860-271-3535

This work is partially funded by:

• USDA NRCS Conservation Technical Assistance

• TNC-NOAA Community Restoration Program

• RI CRMC Habitat Trust Fund