338 
Fishery Bulletin 113(3) 
harvested sites consistently were double the levels at 
nonharvested sites. The reduced number of large oys- 
ters and mussels combined with a probable reduction 
in overall numbers of other sessile filter-feeding organ- 
isms at harvested reefs may contribute to decreased 
filtration capacity (Dame et al., 1989; Cressman et al., 
2003). 
Resident communities at both types of oyster reefs 
appear to depend primarily on pelagic basal food sourc- 
es (i.e., FPOM). The increase in the fractions of detrital 
source (i.e., marsh plant), combined with elevated chlo- 
rophyll-a levels, indicates a reduction in benthopelagic 
coupling services at harvested reefs. Benthic microal- 
gae could also contribute to the food webs of oyster reef 
communities; however, in San Antonio Bay, Texas (also 
a shallow, turbid estuary), the microphytobenthos con- 
tributed less than 2% of the primary production found 
in the water column (MacIntyre and Cullen, 1996). 
Benthic macroalgae, seagrass epiphytes, and upstream 
terrestrial plant matter can also contribute to the bas- 
al food source (Abeels et al., 2012), but these sources 
were not observed within the studied reef areas. 
Trophic position of resident organisms on harvested 
oyster reefs was slightly elevated in comparison with 
nonharvested reefs, but trophic order was maintained. 
Although deriving a TEF specific to these systems may 
result in different estimates of trophic positions, the 
trends observed would not change. Differences in tro- 
phic position of resident species have also been found 
between reefs and mud-bottom sites (Quan et al., 2012) 
and between reefs that were experiencing different riv- 
erine exposures (Abeels et al., 2012). 
In these instances, trophic shifts may be attributed to 
increased infaunal diversity associated with combined 
mud and shell substrate or to increased phytoplankton 
abundance from riverine inputs. For example, there is 
evidence that a lower abundance of filter feeders may 
result in increased zooplankton abundance (Lonsdale 
et al., 2009) and potentially in a more diverse plank- 
tonic community. Elevated chlorophyll-a levels indicate 
increased phytoplankton abundance at harvested sites. 
Increased planktonic diversity or higher densities of 
top planktonic predators (ctenophores) could explain 
the increase in the trophic position of CPOM at har- 
vested reefs. For the remainder of species, the mainte- 
nance of the trophic order for the 2 reef types and the 
lack of consistent difference in convex hull areas is an 
indication that the differences in the reef matrix be- 
tween the harvested and nonharvested sites that were 
documented in this study did not result in significant 
changes in feeding behaviors, but the observed shifts 
in trophic positions and CCA results indicate that reef 
alteration may have affected the planktonic and infau- 
nal forage base. 
Changes in populations of oysters and in the bio- 
genic reefs that these ecosystem engineers create are 
predicted to have effects on surrounding community 
structure and ecosystem processes. The results of 
this study indicate that, on the public oyster grounds 
in Louisiana, effects of harvesting are subtle for reef 
types in close proximity (northern and southern Cal- 
casieu Lake) and for those across larger areas (Sabine 
and Sister lakes). Oyster harvesting practices that al- 
ter the reef matrix yet preserve live oysters and reef 
substrate may still provide important habitat for the 
resident nekton community. What has yet to be exam- 
ined is whether there is a threshold of reef habitat 
area, oyster density, or oyster size distribution below 
which ecosystem services will be severely compromised. 
Acknowledgments 
Funding for this project was provided by the Louisiana 
Department of Wildlife and Fisheries through support 
to the Louisiana Cooperative Fish and Wildlife Unit 
of the U.S. Geological Survey. We thank P. Banks, B. 
Fry, J. Fleeger, M. Kaller, S. Miller, B. Eberline, J. Fur- 
long, C. Hodnett, C. Duplechain, L. Broussard, G. De- 
cossas, A. Catalanello, M. Fries, W. Sheftall, C. Brown, 
A. DaSilva, D. Klimesh, H. Beck, and S. Piazza for field 
and laboratory support. We thank Aswani Volety for 
comments on an early draft of this manuscript. This 
manuscript was also significantly improved by exten- 
sive reviewer comments. This study was performed un- 
der the auspices of Louisiana State University IACUC 
protocols 08-005 and 11-006. 
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