Beck and La Peyre: Effects of oyster harvesting activities on Louisiana reef habitat and resident nekton communities 
335 
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Figure 4 
Canonical correspondence biplot relating species abundances with hab- 
itat variables at actively harvested and nonharvested oyster reefs of 
coastal Louisiana during 2010. The horizontal axis accounts for 58.3% 
of variation (eigenvalue: 0.11), and the vertical axis accounts for 27.7% 
of variation (eigenvalue: 0.05). Species abbreviations: Asp=bigclaw 
snapping shrimp (Alpheus heterochaelis ), Ed=flatback mud crab ( Eu - 
rypanopeus depressus, Gb=naked goby ( Gobiosoma bosc), Gs =skil- 
letfish ( Gobiesox strumosus ), Hi=freckled blenny ( Hypsoblennius 
lonthas ), Ps=oystershell mud crab ( Panopeus Si?npsoni), Pspp=grass 
shrimp ( Palaemonetes spp.), Rh= estuarine mud crab (Rhithropanopeus 
harrisii). 
For the fall sampling, pelagic source 
contributions were also found to contrib- 
ute more to the resident community food 
web than the nonpelagic sources at both 
harvested and nonharvested sites. Pelag- 
ic source contributions were elevated at 
the harvested site for all organisms ex- 
cept skil letfish. The trophic positions of 
all organisms were elevated at the har- 
vested site, except that of eastern oysters. 
Discussion 
Oyster reef structure, as defined by the 
extent of solid reef, number and size of 
live oysters, number of mussels, and in- 
terstitial space, can be substantially al- 
tered by oyster harvesting activities in 
coastal Louisiana. Such changes in reef 
structure did not translate into signifi- 
cant differences in the resident nekton 
community. Although harvested reefs 
were more fragmented and sometimes 
had fewer living oysters and mussels 
than nonharvested reefs, habitat use 
and food resources associated with the 
2 types of reefs were similar. These re- 
sults indicate that, although oyster har- 
vest can change the composition of the 
reef matrix and alter habitat complexity, 
as long as adequate structural material 
is maintained, a reef provides suitable 
habitat for resident communities of small 
organisms. 
Most models of reef degradation from 
harvest indicate that a loss of vertical re- 
lief and complexity lead toward increased 
stress on an oyster population and loss 
of oyster reef function (Rothschild et al., 
1994; Lenihan and Peterson, 1998; Leni- 
han, 1999); however, we dealt with subtidal reefs with 
limited vertical relief. Vertical relief of all reefs in our 
study ranged from 10 to 20 cm, and reefs were located 
in depths of 1.2-2. 9 m. Whether nonharvested reefs 
lacked relief because of degradation from historic ac- 
tivities or as a result of environmental constraints is 
unknown because of a lack of data from the early part 
of the 20 th century. 
In contrast with a lack of difference in vertical relief, 
harvested and nonharvested reefs differed substantial- 
ly in the composition of reef matrix. As expected, more 
large live oysters, as well as less reef fragmentation 
and loose shells, were found at nonharvested sites than 
at the harvested reef areas. The lack of larger oysters 
at harvested reefs, a direct consequence of harvest ac- 
tivities, has been documented previously (Lenihan and 
Micheli, 2000; Lenihan and Peterson, 2004). The in- 
crease in fragmentation and loose shells at harvested 
sites may be due to physical damage from a dredge or 
due to the frequent placement of shells as cultch by the 
Louisiana Department of Wildlife and Fisheries within 
the harvested sites (LDWF 2 ). The combined effects of 
more loose shells, fewer shell clusters, and solid reef 
area may make the harvested reefs more susceptible 
to complete reef loss with overharvesting and with the 
scattering and sedimentation that occurs during storm 
events. However, as noted previously, flat reefs without 
small-scale changes in vertical relief are typical of this 
region. Many of these reefs have existed and been har- 
vested since record keeping began around 1900. 
Despite these differences in the oyster reef matrix, 
there were no consistent differences between treat- 
ments in the overall abundance or diversity of reef- 
associated nekton communities during fall and summer 
sampling. This lack of difference in nekton density at 
reefs with different physical and biological character- 
istics is similar to that found with other studies of ar- 
tificial reefs of varying heights (Lenihan et al., 2001), 
