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 Resources
Louisiana State University Agricultural Center
Baton Rouge, LA
Austin Humphries
School of Renewable Natural Resources
Louisiana State University Agricultural Center
Baton Rouge, LA
Wetland loss
64 – 91 km2 y-1
25% of nation’s total
fishery production
in lower 48
Photo by Tyrone Turner – National Geographic
> 500 projects
Louisiana’s 2007 Master Plan:
1) hydrologic restoration
2) shore protection
Shore Protection
Tires, Wooden Structures,
Christmas trees, Concrete
Limestone 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 erosion
2. nekton (fish and decapod crustaceans) use
3. reef sustainability/oyster populations (Casas poster)
North
West
Sister Lake
South
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
approach
Measured quarterly:
• Shoreline position
• Soil characteristics
• Vegetation
• Nekton use
% species composition
marsh vegetation community
100%
S. americanus
80%
J. roemerianus
S. patens
60%
S. alterniflora
D. spicata
40%
B. maritimus
20%
0%
north
west
south
Similar production at all sites: 805.9 ± 74.0 g m-2
marsh soil properties
% soil organic matter
35
A
25
15
B
B
north
west
5
south
Universal soil loss equation: increase OM 1-3%, reduces erosion 20-33%
shoreline change
Narrow Reef
A
Shoreline retreat (cm d-1)
0.6
**site interaction
Wide Reef
Reference
AB
AB
0.4
B
B
0.2
0
Medium
Energy Environment
Low
Shoreline retreat (cm d-1)
0.8
April 2009-August 2010
Narrow Reef
Wide Reef
Reference
0.6
0.4
0.2
0
North
West
South
Medium Energy
Gulf of Mexico
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, bathymetry
2) Understand local weather patterns and in particular,
dominant storm passages
Gillnet
sampling nekton
Seine
shoreline
reef
Quarterly: March, June, August, December 2009, 2010
Trays
CPUE
250
West
200
North
transient
species
South
150
100
50
0
Spring
Summer
Fall
Winter
9.2 ± 0.4
5
8.6 ± 0.5
4
3Water
quality: only
difference between
1sites in salinity
12.4 ± 0.5
fall
Season
winter
Gulf of Mexico
Reef
Mud
120
CPUE
100
Resident abundance
80
60
40
20
0
June
Aug
2009
Dec
March
2010
Does shell quantity impact resident abundance?
100
Adj r2 = 0.22
CPUE
(# individuals/tray)
80
60
40
20
0
0
1
2
Tray shell volume (L)
3
4
Low
High
Four treatments
Mud bottom
Cage structure
Cage plus low volume
Cage plus high shell volume
Mean abundance (# of indˉ²)
b
30
b
25
20
abundance
15
10
a
a
5
0
Mud
Cage
Low
High
Shannon diversity (H’)
3
b
2.5
b
2
1.5
b
a
diversity
1
0.5
0
Mud
Cage
Low
High
nekton support
- transient abundance
not affected
by reef presence
Restoration
implications:
- possible redundancy of marsh edge habitat
1) How do spatial location and adjacent habitats affect
- residents more abundant and diverse at reef sites
addedper
value
of reefs
to factor
transients
- presence of structure
se most
important
determining assemblages
2) Does added structure impact resident communities?
3) How might resident species, oyster population structure
affect nekton communities?
dead
live
Oyster density (m2)
6000
M-N = medium energy, narrow reef
M-W = medium energy, wide reef
L-N = low energy, narrow reef
June 2010
3000
0
West
POSTER: Casas et al.
North
South
Frequency of size distribution (%)
100
September 2010
75
50
Spat: < 25 mm
Seed: 25-50 mm
Seed: 50-75 mm
Commercial: >75 mm
25
0
West
North
South
What are the key parameters to consider to identify the most
viable shorelines for shore protection ?
1) local site conditions: energy, currents, morphology
2) oyster population response
What factors influence the value of restored fringing reefs for
resident or transient nekton?
1) characteristics of structure
2) functional response of nekton
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
Vermilion Bay
Grand Isle, Breton Sound, Biloxi Marsh
Sister Lake
Funding
Louisiana Department of Wildlife and Fisheries
Collaborators
Jerome La Peyre, Louisiana State University AgCenter
Sandra Casas-Liste, Louisiana State University AgCenter
Acknowledgments
LA 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.