327 
NOAA 
National Marine 
Fisheries Service 
Fishery Bulletin 
.%• established 1881 
Spencer F. Baird 
First U S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Effects of oyster harvest activities on Louisiana 
reef habitat and resident nekton communities 
1 School of Renewable Natural Resources 
Louisiana State University Agricultural Center 
124 Renewable Natural Resources Bldg. 
Baton Rouge, Louisiana 70803 
2 U.S. Geological Survey 
Louisiana Cooperative Fish and Wildlife Research Unit 
School of Renewable Natural Resources 
Louisiana State University Agricultural Center 
124C Renewable Natural Resources Bldg. 
Baton Rouge, Louisiana 70803 
Abstract— Oysters are often cited as 
“ecosystem engineers” because they 
modify their environment. Coastal 
Louisiana contains extensive oyster 
reef areas that have been harvested 
for decades, and whether differences 
in habitat functions exist between 
those areas and nonharvested reefs 
is unclear. We compared reef physi- 
cal structure and resident commu- 
nity metrics between these 2 sub- 
tidal reef types. Harvested reefs 
were more fragmented and had low- 
er densities of live eastern oysters 
( Crassostrea virginica) and hooked 
mussels (Ischadium recurvum) than 
the nonharvested reefs. Stable iso- 
tope values ( 13 C and 15 N) of domi- 
nant nekton species and basal food 
sources were used to compare food 
web characteristics. Nonpelagic 
source contributions and trophic 
positions of dominant species were 
slightly elevated at harvested sites. 
Oyster harvesting appeared to have 
decreased the number of large oys- 
ters and to have increased the per- 
centage of reefs that were nonliving 
by decreasing water column filtra- 
tion and benthopelagic coupling. The 
differences in reef matrix composi- 
tion, however, had little effect on 
resident nekton communities. Un- 
derstanding the thresholds of reef 
habitat areas, the oyster density or 
oyster size distribution below which 
ecosystem services may be compro- 
mised, remains key to sustainable 
management. 
Manuscript submitted 9 January 2014. 
Manuscript accepted 21 May 2015. 
Fish. Bull. 113:327-340 (2015) 
Online publication date: 9 June 2015. 
doi: 10.7755/FB.113.3.8 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Steve Beck 1 
Megan K. La Peyre (contact autSior ) 1 - 2 
Email address for contact author: mlapey@lsu.edu 
Ecologists have long recognized the 
importance of “ecosystem engineers” 
in organizing and maintaining eco- 
systems through their modification 
of the availability of resources in 
the environment (Jones et ah, 1994, 
1997). Oysters are commonly ac- 
knowledged as ecosystem engineers 
of shallow-water estuaries. Oysters 
modify the local environment by pro- 
viding refuge and foraging habitat 
(Peterson et ah, 2003; Coen et ah, 
2007), by altering local hydrodynam- 
ic processes (Lenihan, 1999), and by 
affecting local water quality (Newell 
et ah, 2005; Piehler and Smyth, 2011; 
zu Ermgassen et ah, 2013). Glob- 
ally, more than 85% of oyster reefs 
have been identified as functionally 
extinct; disease, poor water quality, 
and destruction of the physical habi- 
tat have been identified as the major 
proximate causes (Beck et ah, 2011). 
More specifically, the loss of vertical 
relief and complexity of oyster reefs, 
largely a result of commercial har- 
vesting, is often cited as the primary 
factor that drives reef decline (Roths- 
child et ah, 1994; Kirby, 2004). 
Changes in the physical structure 
of reefs through natural processes, 
such as storm events or human ac- 
tivities associated with harvest, may 
affect the habitat value of reefs by 
altering refuge availability and reef 
community structure (Breitburg, 
1999; Soniat et ah, 2004; Humphries 
et ah, 2011a). Alteration of the physi- 
cal structure of reefs directly affects 
nekton populations by changing the 
availability of potential habitat, and 
several studies have highlighted the 
cascading effects of altered reef prop- 
erties on trophic dynamics within an 
oyster reef community (Lenihan et ah, 
2001; Grabowski and Powers, 2004; 
Grabowski et ah, 2008). Other stud- 
ies have highlighted the impacts of re- 
duced biomass of oysters, or other fil- 
ter feeding organisms, on ambient wa- 
ter quality (Cloern, 1982; Fulford et 
ah, 2007; zu Ermgassen et ah, 2013). 
More than 40% of the commer- 
cial production of the eastern oyster 
(Crassostrea virginica ) in the conti- 
nental United States occurs in coast- 
al Louisiana estuaries (LDWF 1 ), and 
oysters are the dominant reef-form- 
1 LDWF (Louisiana Department of Wildl- 
life and Fisheries). 2012. Oyster stock 
assessment report of the public oyster 
areas in Louisiana: seed grounds and 
seed reservations. Oyster Data Rep. 
Ser. 18, 88 p. [Available from Louisiana 
Dep. Wildl. Fish., RO. Box 98000, Baton 
Rouge, LA 70898.] 
