Effects of shoreline reef creation on edge erosion, marsh resilience and nekton

assemblages in south Louisiana

Megan La Peyre U.S. Geological Survey, Louisiana Fish and Wildlife Cooperative Research Unit

School of Renewable Natural ResourcesLouisiana State University Agricultural Center

Baton Rouge, LA

Austin HumphriesSchool of Renewable Natural Resources

Louisiana State University Agricultural CenterBaton Rouge, LA

Photo by Tyrone Turner – National Geographic

Wetland loss

64 – 91 km2 y-1

25% of nation’s total fishery production in lower 48

Louisiana’s 2007 Master Plan:1) hydrologic restoration2) shore protection

> 500 projects

Shore ProtectionTires, Wooden Structures, Christmas trees, ConcreteLimestone rock

- costly ($1 million / mile)- heavy (sink)- imported from out-of-state

Oyster reefs - native - sustainable - potential added ecosystem benefits

research objectives:examine effects of created reef size, shoreline orientation, and location on:

1. shoreline erosion2. nekton (fish and decapod crustaceans) use3. reef sustainability/oyster populations (Casas poster)

West

South

North

Sister Lake

Gulf of Mexico

“low” energy shorelines“medium” energy shorelines

reef establishment: march 2009

Cost: < $300,000/linear mile“narrow” = 25 m x 1 m x 1 m“wide” = 25 m x 2 m x 1 m

Measured quarterly:• Shoreline position• Soil characteristics• Vegetation• Nekton use

approach

0%

20%

40%

60%

80%

100%

north west south

% s

peci

es c

ompo

sitio

n S. americanus

J. roemerianus

S. patens

S. alterniflora

D. spicata

B. maritimus

Similar production at all sites: 805.9 ± 74.0 g m-2

marsh vegetation community

5

15

25

35

southnorth west

% s

oil o

rgan

ic m

atte

r A

B B

Universal soil loss equation: increase OM 1-3%, reduces erosion 20-33%

marsh soil properties

0

0.2

0.4

0.6

Medium Low

Shor

elin

e re

trea

t (cm

d-1)

Narrow ReefWide ReefReference

AB

A

AB

BB

Energy Environment

shoreline change

**site interaction

0

0.2

0.4

0.6

0.8

Medium Energy

North West South

Narrow Reef

Wide Reef

Reference

Shor

elin

e re

trea

t (cm

d-1)

Gulf of Mexico

April 2009-August 2010

shoreline effects

- sites experienced extremely high erosion (1-3 m/18 mo)

- at low energy sites reefs failed to reduce retreat

- at medium energy sites, site-specific effects

Restoration implications:1) Need to understand local site environment, such as

currents, morphology, bathymetry2) Understand local weather patterns and in particular,

dominant storm passages

TraysSeine

shoreline

reef

Gillnetsampling nekton

Quarterly: March, June, August, December 2009, 2010

0

50

100

150

200

250

1

3

4

5

fall winter

CPU

E

Water quality: only difference between sites in salinity

Season

WestNorthSouth

transient species

Gulf of Mexico

Spring Summer Fall Winter

8.6 ± 0.59.2 ± 0.4

12.4 ± 0.5

Resident abundance

0

20

40

60

80

100

CPU

E

June Aug Dec March

ReefMud

2009 2010

0 1 2 3 40

20

40

60

80

100

CPU

E (#

indi

vidu

als/

tray

)

Tray shell volume (L)

Adj r2 = 0.22

Does shell quantity impact resident abundance?

HighLow

Four treatments

Mud bottomCage structureCage plus low volumeCage plus high shell volume

abundance

diversity

0

5

10

15

20

25

30

Mud Cage Low High

0

0.5

1

1.5

2

2.5

3

Mud Cage Low High

Shan

non

dive

rsity

(H’)

Mea

n ab

unda

nce

(# o

f ind

²)ˉ

aa

a

b

b

b

b b

Freq

uenc

y of

siz

e di

strib

utio

n (%

)

0

25

50

75

100

M-NM-W

L-N

September 2010

Spat: < 25 mm Seed: 25-50 mm Seed: 50-75 mm Commercial: >75 mm

West North South

Oys

ter d

ensi

ty (m

2 )

0

3000

6000

deadlive

West North South

M-NM-W

L-N M-NM-W

L-NM-NM-W

L-NM-NM-W

L-N M-NM-W

L-N

M-N = medium energy, narrow reefM-W = medium energy, wide reefL-N = low energy, narrow reef

June 2010

POSTER: Casas et al.

nekton support - transient abundance not affected by reef presence

- possible redundancy of marsh edge habitat- residents more abundant and diverse at reef sites- presence of structure per se most important factor

determining assemblages

Restoration implications: 1) How do spatial location and adjacent habitats affect

added value of reefs to transients2) Does added structure impact resident communities?

3) How might resident species, oyster population structure affect nekton communities?

What factors influence the value of restored fringing reefs for resident or transient nekton?

1) characteristics of structure 2) functional response of nekton

What are the key parameters to consider to identify the most viable shorelines for shore protection ?

1) local site conditions: energy, currents, morphology2) oyster population response

Vermilion Bay

Grand Isle, Breton Sound, Biloxi Marsh

Experimental lab and field studies:- Location effects (shoreline, nekton, oyster populations)- Base material, size, design- Link oyster physiology, oyster population structure with nekton

use- Foraging success with different structure

Sister Lake

FundingLouisiana Department of Wildlife and Fisheries

AcknowledgmentsLA DWF – Heather Finley, Patrick Banks, Steve Hein, Willie Cheramie LSU – Shea Miller, Shannon Martin, Steve Beck, Ben Eberline, Anna Catalanello, John Gordon, Gary Decossas, Lainey Pitre, Matt Kimball Community - Wilson Voisin, Stephen Champagne, Antill Pipeline Construction Co.

CollaboratorsJerome La Peyre, Louisiana State University AgCenterSandra Casas-Liste, Louisiana State University AgCenter