Beck and La Peyre: Effects of oyster harvesting activities on Louisiana reef habitat and resident nekton communities 
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6 13 C 
B 
16 
12 ■ 
2 
in 
Lo 8 
-10 -30 
Ik 
o 
o 
-25 -20 
5 13 C 
□ 
□ 
-15 
1 
-10 
Figure § 
Biplot of mean 8 13 C and 8 15 N values of basal food sources and dominant faunal species sampled at 4 sites in coastal 
Louisiana in 2010: (A) Sabine Lake (nonharvested) and Sister Lake (actively harvested) in the summer and (B) northern 
(nonharvested) and southern (actively harvested) Calcasieu Lake in the fall. Error bars are omitted for simplicity; standard 
errors of the mean and sample sizes ( n ) are located in Table 3. Shaded symbols indicate means for harvested sites, and 
open symbols indicate means for nonharvested sites. Symbols for various organisms: large circle=fine particulate organic 
matter, square=marsh plant, x=coarse particulate organic matter, large dash=hooked mussel ( Ischadium recurvum), crossed 
x=eastern oyster ( Crassostrea virginica), diamond=flatback mud crab (Eurypanopeus depressus), short dash=grass shrimp 
( Palaemonetes spp.), triangle=skittlefish ( Gobiesox strumosus ), plus sign=freckled blenny ( Hypsoblennius ionthas), and small 
circle=naked goby (Gobiosoma bosc). 
shell density and vertical relief (Humphries et ah, 
2011b), and reefs with and without the presence of live 
oysters (Tolley and Volety, 2005; Summerhayes et ah, 
2009). Although ecological theory holds that structur- 
ally complex habitats are expected to sustain higher 
densities and more diverse communities than structur- 
ally simple ones, defining structural complexity has 
never been straightforward (Beck, 1998; Bartholomew 
et ah, 2000), and it is not clear whether the harvested 
and nonharvested sites represented different levels of 
complexity or just differences in habitat characteris- 
tics. No consensus exists as to how to define oyster reef 
complexity; in some experiments oyster or shell den- 
sity, vertical relief, or mixtures of unaggregated shells 
(simple) versus clusters (complex) were used, making 
it difficult to determine when complexity had actually 
changed (Grabowski and Powers, 2004; Grabowski et 
al., 2008; Humphries et ah, 2011a). 
The use of similar volumes of reef material in the 
trays may have contributed to the similarity of resi- 
dent communities at our paired sites, but observed dif- 
ferences in the reef matrix may be important in deter- 
mining preferred habitats of resident organisms. The 
use of 5.0 L of local reef substrate (an amount that 
corresponds to 22.7 L/m 2 ) to completely fill each sample 
tray may have resulted in densities of reef material 
that were beyond a threshold at which differences in 
nekton abundances can be noted (e.g., Humphries et 
ah, 2011b). Samples obtained by diving on historic, cre- 
ated, and harvested reefs in the region have provided 
reef material sample volumes up to 11 L/m 2 in the top 
10 cm of substrate (La Peyre et ah, 2014b). The loose 
matrix of substrate material created by dredging and 
filling trays may have resulted in increased small in- 
terstitial spaces and elevated habitat availability. 
Despite this potential criticism, tray substrate differ- 
ences were observed between harvest treatments. The 
similarity of species diversity and community composi- 
tion remains striking and indicates that the sampled 
harvested and nonharvested areas still support similar 
nekton communities, although specific niches for cer- 
tain species were identified by apparent preferences for 
reef subhabitats. The CCA results indicate that the 
bigclaw snapping shrimp ( Alpheus heterochaelis) and 
estuarine mud crab are associated with fragmented 
reef habitats exposed to high levels of chlorophyll-a 
and that the skilletfish and freckled blenny are associ- 
ated with the presence of shell clusters (larger intersti- 
tial spaces) and high densities of live oysters. 
Oysters are known to transfer nutrients from the 
water column to the benthos; however, the observed 
decrease in the number and size of live oysters at 
harvested sites, compared with the number and size 
at nonharvested sites, may have other trophic effects 
beyond a decrease in benthopelagic coupling. Filtration 
rate on a reef is generally held to increase with oys- 
ter biomass (Cloern, 1982; Officer et al., 1982; Dame, 
1996). In our study, mean levels of chlorophyll-a at 
