328 
Fishery Bulletin 113(3) 
ing organism within these estuaries. Harvest activi- 
ties occur across large areas of oyster reefs (LDWF 1 ), 
but the effects of harvest and management on resident 
nekton communities, reef structure, and trophic inter- 
actions have yet to be quantified. Reefs in this region 
are characterized as largely subtidal, located in a mic- 
rotidal, well-mixed environment, and have limited ver- 
tical relief (<50 cm). Therefore, the effects of harvesting 
on reefs in Louisiana may not be evident in large-scale 
changes in vertical relief but may be observed more in 
oyster density and size and in alteration of the reef 
matrix; oyster density and size, and alteration of the 
reef matrix may in turn affect refuge value and filtra- 
tion capacity of an oyster reef (e.g., Summerhayes et 
al., 2009; La Peyre et ah, 2014a). 
We compared reef physical structure and resident 
community metrics on commercially harvested and 
nonharvested oyster reefs in coastal Louisiana. We 
quantified and characterized the abundance and com- 
position of the resident nekton community at these 
oyster reefs. These data were examined to determine 
whether any differences in resident nekton community 
structure could be attributed to changes in reef char- 
acteristics. Lastly, using stable isotope analyses, we ex- 
amined whether differences in reef characteristics were 
associated with differences in food web dynamics, such 
as the contributions of basal food sources, trophic level, 
and niche breadth of abundant resident organisms. 
Materials and methods 
Study area 
This study was conducted on subtidal reefs located in 
estuarine shallow-water areas of coastal Louisiana. The 
coastal bays and estuaries in Louisiana are microtidal 
(tidal range: <1 m), and most water depths were within 
a range of 1-4 m. Oyster reefs are located in mid-sa- 
linity (salinity range=5-25) areas within the extensive 
salt and brackish marsh regions of the Louisiana coast 
and tend to cover large, heterogeneous areas. The reefs 
are often extensive and unmapped, and, therefore, they 
are difficult to delineate. We selected paired harvested 
and nonharvested sites, all located within similar sa- 
linity zones and on public oyster seed grounds that are 
managed by the Louisiana Department of Wildlife and 
Fisheries (LDWF 2 , 2010; Fig. 1). For this study, harvest 
activities included removal of oysters for harvesting, as 
well as management activities, such as deposition of 
cultch (i.e., shell and limestone) to provide recruitment 
substrate. Nonharvested reefs were areas where it has 
been illegal to harvest oysters for several decades. 
Two sites, Sabine Lake and northern Calcasieu 
Lake, have been closed to harvesting activities for more 
2 LDWF (Louisiana Dep.Wildl. Fish.). 2010. Oyster stock 
assessment report of the public oyster areas in Louisiana: 
seed grounds and seed reservations. Oyster Data Rep. Ser. 
16, 92 p. [Available at website.] 
than 50 years, and they are the only substantial non- 
harvested subtidal oyster reefs in the state. There is no 
evidence that cultch deposition has occurred at these 
sites in the last 50 years. The sites were initially closed 
for health concerns that no longer persist, and over the 
last 5 years, there has been enormous pressure to open 
these areas to harvest. The remaining 2 areas, south- 
ern Calcasieu Lake and Sister Lake, are actively har- 
vested with dredges. The most recent cultch deposition 
in these areas occurred on southern Calcasieu Lake in 
2009 (0.06 km 2 of no. 57 limestone), and on Sister Lake 
in 2009 (0.63 km 2 of no. 57 limestone). 
Sites were paired on the basis of ecological similar- 
ity and not proximity. The sites of northern and south- 
ern Calcasieu Lake were sampled as 1 pair; these 2 
sites are located within the same waterbody and ex- 
perience similar salinity regimes (long-term mean sa- 
linity: 13.9-16.1) and storm events. Sabine Lake and 
Sister Lake were paired because of similarities in sa- 
linity regimes (long-term mean salinity: 11.9-15.1) and 
water depths, and both sites are considered interior, 
large, shallow waterbodies. Although these 2 sites were 
farther apart from one another geographically than the 
other paired sites, the assumption was made that if 
harvest causes significant effects on the habitat, dif- 
ferences that result from harvest activities would be 
greater than differences associated with actual coastal 
location. 
Data collection 
Field data Reefs were located within each site with 
side-scan sonar data (ENCOS 3 ) for Sabine, Southern 
Calcasieu, and Sister lake sites and with GPS coordi- 
nates from a planting of oyster shell cultch in 1969 
for northern Calcasieu Lake. At each of the 4 sites, 3 
sample stations, measuring 10 mxlO m, were estab- 
lished on reef habitat located more than 100 m from 
the marsh edge and in the centers of reef areas to re- 
move confounding effects of adjacent habitats and reef 
edge (Fig. 2; Acosta and Robertson, 2002; Grabowski 
et ah, 2005). At each sample station, reef structure, 
water quality, and resident nekton communities were 
sampled according to protocols listed below. All sample 
stations in Sabine Lake and Sister Lake were sampled 
twice during summer (July-August) 2010, and all sam- 
ple stations in northern and southern sites in Lake 
Calcasieu were sampled twice during fall (September- 
October) 2010. 
For each summer sampling event, 3 replicate sam- 
ples per station were taken (with trays, which are de- 
scribed in the next section); because of high tray loss 
in the summer, 4 replicate samples were taken per 
sample station for each fall sampling event to increase 
3 ENCOS. 2008. Water bottom assessment of selected por- 
tions of public oyster seed grounds within Cameron Parish, 
Louisiana: Calcasieu and Sabine Lakes, 391 p. Prepared for 
the Louisiana Dep. Wildl. Fish. [Available from Louisiana 
Dep. Wildl. Fish., P.O. Box 98000, Baton Rouge, LA 70898.] 
