Oyster Reefs as a Restoration Tool: Do Reef Structure, Physicochemical Conditions, and
Wave Energy Environment Affect Reef Sustainability?
Sandra M. Casas
1
(scasas@lsu.edu) ,
Jerome F. La
1
Peyre ,
Megan La
2
Peyre
1Department
of Veterinary Science, Louisiana State University Agricultural Center, Baton Rouge
2 U.S. Geological Survey, Louisiana Fish and Wildlife Cooperative Research Unit, School of Renewable Natural Resources, LSU AgCenter, Baton Rouge
Results
Oyster spat recruitment
Reefs created by the eastern oyster, C.virginica, provide a variety of
ecological services including habitat creation, water quality maintenance,
and shoreline stabilization. For coastal protection, reefs located near
marshes have been suggested to act as natural breakwaters, absorbing
wave energy and slowing shoreline erosion, and may provide an additional
tool to aid in coastal restoration efforts. However, few data exist to support
decisions related to where reefs may be most sustainable, and ultimately,
where reefs may be successfully used to help with shoreline protection.
40000
Spat number/m2
30000
Objectives
20000
10000
•Spat density in area 7 was significantly greater than in areas 3
and 6 in April, May, September, and October 2009, and in May and
August 2010 (Fig. 4).
3000
•A clear effect of energy site on spat recruitment was not found. In
2000
May 2009 spat density in the low energy sites was higher than in
the medium, while in August 2010 the highest densities occurred in
the medium sites (Fig. 4).
1000
0
April
May
June
July
August
September
April
October
June
May
July
2009
August
September
2010
Figure 4. Monthly mean (±SD) number of spat per m2 on tiles placed at the medium and low wave energy sites in areas 3, 6, and 7
Figure 3. Oyster spat on a tile
Oyster density
12000
Area 7
Area 6
Area 3
2
Oyster density (live + dead oysters/m2)
In February 2009, oyster reefs were created in the northwest (area 3),
northeast (area 6), and south (area 7) of Sister (Caillou) Lake (Figs. 1 & 2).
A medium and low wave energy site was selected in each area. A narrow
reef (25 m long x 0.7 m high x 1.5 m wide) was placed in the low and
medium energy sites, while a wide reef (25 m long x 0.7 m high x 3 m wide)
was only created in the medium energy sites.
2009 two major spawning events occurred in spring and at the end
of the summer, while in 2010 only a moderate spawning event
occurred in summer (Figs. 3 & 4).
4000
This project examined the effects of reef structure (narrow and wide) and
wave energy environment (low and medium) on reef sustainability at three
locations, with locations used as a proxy for environmental conditions.
Materials and Methods
•Spat recruitment was significantly higher in 2009 than in 2010. In
3-Medium
3-Low
6-Medium
6-Low
7-Medium
7-Low
Live oysters-narrow reef-medium wave energy
Dead oysters-narrow reef -medium wave energy
Live oysters-wide reef -medium wave energy
Dead oysters-wide reef-medium wave energy
Live oysters-narrow reef-low wave energy
Dead oysters-narrow reef -low wave energy
9000
6000
3000
0
Jun
Sep
Dec
Mar
Jun
2009
Figure 1. Construction of
reef with oyster shell.
Sep
Jun
Sep
Mar
Dec
Jun
2009
2010
Density (# Live oysters / m )
Introduction
10000
area 3
area 6
area 7
7500
5000
2500
0
Sep
Jun
Sep
2010
Dec
Jun
Mar
Jun
Sep
Dec
Mar
2009
2010
2009
Sep
Jun
Sep
2010
Figure 6. Mean number of live oysters per m2 at narrow reefs in areas
3, 6, and 7.
Figure 5. Mean number of live and dead oysters per m2 in reefs located at the medium and low wave energy sites in areas 3, 6, and 7
Oyster size frequency distribution
25
Oyster spat recruitment: Recruitment was measured from April through
October in 2009 and 2010. Four tiles (31 cm x 31 cm) were placed at every
site and after a month collected and spat number counted.
Oyster density, mortality, and size on the reef: Three quadrat samples (23
cm x 23 cm) were collected from each reef. All spat (< 25 mm), seed (75
mm < X ≥ 25 mm), and market size (≥ 75 mm) live oysters and recently
dead oysters were counted and sized using a caliper. Narrow reefs were
sampled quarterly, and wide reefs were sampled yearly (September 2009,
2010, and 2011).
Environmental variables: Salinity, temperature, dissolved oxygen, turbidity,
total suspended solids, and chlorophyll a were measured monthly.
Statistical analysis: Spat recruitment and the environmental parameters
were analyzed using a three-factor (month, area, and site) analysis of
variance (ANOVA). Oyster density and mortality in the narrow reefs were
analyzed with a three factor (month, area, and site) ANOVA. A three-factor
(sampling time, area, and reef structure) ANOVA was used to compare
oyster density and mortality in the narrow and wide reefs. Pearson
correlation was used to associate oyster and environmental data. Data
were log transformed (oyster density) or arcsine √x transformed (mortality)
when necessary to achieve normality and homogeneity of variance.
Jun
Dec
Mar
Jun
Sep
2010
Sep
2009
Dec
Mar
Jun
Sep
2010
Jun
Sep
Dec
Mar
Jun
2009
LN
-W
M
-N
M
-N
LN
M
LN
-N
M
LN
-N
M
LN
-W
M
-N
M
-N
LN
M
N
L-
-W
M
-N
M
N
L-
-N
M
N
L-
-N
M
N
L-
-N
M
N
L-
-W
M
Jun
M
-N
N
L-
-N
M
N
L-
-W
M
M
-N
N
L-
-N
M
N
L-
-N
M
N
L-
-N
M
N
Sep
2009
Figure 7. Oyster seeds on shells from the reef.
L-
-W
M
-N
M
L-
N
Spat: < 25 mm
Seed: 25-50 mm
Seed: 50-75 mm
Commercial: >75 mm
•Salinity in area 7 (12 ± 5 ppt) was higher than in areas 3 (9 ± 5 ppt) and 6 (9 ± 5 ppt).
•Average concentrations of chlorophyll a in area 3 (17 ± 8 µg/L) tended to be greater
than in 6 (15 ± 8 µg/L) and 7 (15 ± 7 µg/L). Total suspended solids in areas 6 (64 ± 61
mg/L) and 3 (57 ± 50 mg/L) tended to be higher than in 7 (40 ± 32 mg/L), but statistical
differences were not found.
•Spat recruitment was positively correlated with salinity and total suspended solids.
•Oyster mortality was negatively correlated with temperature, salinity, and total
suspended solids.
2000
Area 3
Area 6
1000
Spat
Seed: 25-50 mm
Seed: 50-75 mm
Commercial
0
M-N
M-W
L-N
M-N
M-W
L-N
M-N
M-W
L-N
Sep
September 2010
2010
Figure 8. Frequency of size distribution (%) of the categories spat (<25 mm), seed 25-50 mm, seed 50-75 mm, commercial size (>75 mm) for the oysters at the
medium wave energy site-narrow reef (M-N), medium wave energy site-wide reef (M-W), low wave energy site-narrow reef (L-N) In areas 3,6 and 7.
Environmental parameters
Density (#Live oysters/m2)
50
0
Area 7
3000
75
M
Area 7
Area 7
100
-N
Frequency of size distribution (%)
Area 3
Figure 2. Map showing location of areas 3, 6, and 7 within Sister Lake.
Red arrows point out medium energy sites and yellow arrows mark the
low energy sites. The black arrow in the inset map shows the location of
Sister Lake in Terrebonne Basin in south Louisiana.
Area 6
Area 3
Area 6
Figure 9. Spat (<25 mm), seed: 25-50 mm, seed: 50-75 mm, and
commercial size (>75 mm) density at the medium wave energy sitenarrow reef (M-N), medium wave energy site-wide reef (M-W), low
wave energy site-narrow reef (L-N) in areas 3, 6 and 7.
•Differences in live oyster densities were obtained for the interaction area x month. Density in area 7 was significantly higher than in area 3 and 6 in June
and September 2009 (Fig. 6). Differences in live oyster densities were not found between medium and low energy sites (Fig. 5). Differences in live oyster
densities were not found between narrow and wide reefs (Fig. 5).
•Overall, oysters settled on the reefs suffered elevated mortalities, and area 7 had the greatest mortality (Fig. 5). An effect of energy or reef type on
mortality was not found (Fig. 5).
•Frequency of size distribution differed between locations and sampling times (Fig. 8). After 20 months of their creation, spat constituted 20 to 50% of the
oysters on the reefs while seed constituted 50 to 80% and market size <1% (Fig. 8). In September 2010 (Fig. 9), reefs did not differ in the density of seed and
market size oysters; however, significant differences occurred in the density of spat. Spat density in reefs of area 7 was significantly higher than in areas 3
and 6 (Fig. 9). An effect of the reef type or energy on the spat, seed, or commercial size density was not found (Fig. 9).
Conclusions
Under the conditions tested, wave energy site (medium vs low) and reef type (narrow vs wide) had no detectable effects on oyster density, mortality,
and frequency of size distribution.
 Oyster size distribution and recruitment will continue to be monitored to quantify variation over the years. These data will help define the
parameters that can be used by managers in deciding when and where to use oyster reefs as a tool for shoreline protection.
Acknowledgments
Thanks to Louisiana Department of Wildlife and Fisheries
for funding this project. Mandalay NWR provided lodging
for field work with this project. Shannon Martin, Shea
Miller, Austin Humphries, Ben Eberline, Steve Beck, Anna
Catalanello, Lainey Pitre, Gary Decossas, John Gordon,
and Jessica Furlong helped with field work.