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Habitat use of intertidal eastern oyster (crassostrea virginica) reefs by Nekton in South Carolina estuaries.

Abstract The majority of recent studies investigating the habitat value of intertidal oyster reefs have compared the nektonic assemblages on natural oyster reefs, salt marshes, mud bottom, and subtidal oyster shell habitats using methods that involve some degree of habitat disturbance. The current study used a novel, non-destructive sampling approach involving the deployment of a drop net around study plots to compare the nektonic assemblages associated with intertidal oyster reefs (natural and enhanced) with those of neighboring soft sediment habitats at 3 sites in South Carolina. At each site, the nektonic organisms collected on a reef plot were compared with those collected on an adjacent control plot lacking a structurally complex habitat. Nekton abundance was significantly higher on the reef plot compared with the control plot at all 3 sites. Nekton abundance also varied among seasons, with the greatest numbers occurring during summer compared with spring and fall. Notably, grass shrimp (Palaemonetes spp.) were especially dominant on reef plots. A total of 60 taxa were identified, 57 of which were identified to species level. Reef plots exhibited significantly greater taxon richness than control plots. The number of taxa present also accumulated over time at a higher rate on the reef plots than on the control plots at 2 of the 3 sites. Among the 60 taxa collected, 36 were found on both the reef and control plots, whereas 14 taxa were unique to the reef plots. For data pooled across all sites and seasons, 33 taxa were more numerous on reef plots than control plots, 3 taxa occurred in equal numbers, and 24 taxa were more numerous on control plots. For taxa collected on more than 1 occasion, paired t-tests performed with Bonferroni-adjusted significance thresholds revealed that Alpheus heterochaelis and Palaernonetes spp. were significantly more abundant on the reef plots than on the control plots, whereas unadjusted analyses revealed the same pattern for Gobiosoma bosc, Menidia menidia, and Fundulus heteroclitus. In contrast, no taxa were significantly more abundant on the control plots at either significance threshold. Although nekton abundance was generally higher on the reef plots, measures of diversity were significantly higher on the control plots, regardless of season, site, or date. Greater abundance of a limited number of species on the reef plots accounted for lower evenness and therefore lower diversity measures for this treatment. Overall, community structure was driven more by site than by treatment, whereas the seasonal occurrences of certain species on the reef plots highlighted the importance of oyster reefs as essential fish habitat for the critical life stages of finfish species with complex life histories.

KEY WORDS: Crassostrea virginica, eastern oyster, oyster reefs, nekton, habitat utilization, ecologic services, habitat restoration

INTRODUCTION

The concept of ecosystem engineers was defined by Jones et al. (1994) as "organisms that directly or indirectly modulate the availability of resources (other than themselves) to other species by causing physical state changes in biotic or abiotic materials (p. 374)." Oysters are considered ecosystem engineers because of the variety of ecosystem services that they provide (e.g., Grabowski & Peterson 2003, ASMFC 2007). These services include the stabilization of sediment and shorelines (Dame & Patten 1981, Hadley et al. 2010) and the enhancement of water filtration (Newell 1988), benthic-pelagic coupling, and water quality (Dame & Libes 1993, Dame et al. 2001). Oyster reefs also provide feeding and refuge habitats for other organisms (e.g., Gutierrez et al. 2003), attracting diverse assemblages of other invertebrates and fishes (e.g., Bahr & Lanier 1981, Newell 1988, Coen et al. 1999a, Mann & Harding 1998, Breitburg 1999, Tolley & Volety 2005). Numerous species prey directly on oysters, including xanthid crabs, such as the stone crab Menippe mercenaria, and the Atlantic mud crab Panopeus herbstii (Tolley & Volety 2005). In turn, several finfishes, including the naked goby Gobiosoma bosc and the striped blenny Chasmodes bosquianus, are known to feed on these xanthid crabs, generating trophic complexity and the potential for the formation of trophic cascades (Grabowski 2004). Mann and Harding (1998) investigated the trophic interactions among oysters, fishes, and benthic predators on restored oyster reefs and showed that small and intermediate-size fishes, such as gobies (e.g., seaboard goby Gobiosoma ginsburgi and Gobiosoma bosc) and blennies (e.g., feather blenny Hypsoblennius hentz and C. bosquianus), were abundant in Chesapeake Bay oyster reef-dominated ecosystems. The presence of these species on reef structures is thought to attract larger pelagic predatory species, such as striped bass Morone saxatilis, bluefish Pomatomus saltatrix, weakfish Cynoscion regalis, southern flounder Paralichthys lethostigma, sheepshead Archosargus probatocephalus, and spotted seatrout Cynoscion nebulosus. Other benthic predators, such as the Atlantic blue crab Callinectes sapidus, have also been shown to be associated strongly with Crassostrea virginica reefs (Mann & Harding 1998). In general, it appears that the diverse range of organisms associated with oyster reefs creates complex food webs that sustain higher trophic levels than surrounding sediment or marsh habitats (Wrast 2008, Quan et al. 2012).

Several studies have shown that the 3-dimensional structure of oyster reefs attracts greater numbers of resident and transient nektonic species than sand- or mud-bottom habitats (Posey et al. 1999, Harding & Mann 2001, Lenihan et al. 2001, Plunket & La Peyre 2005, Coen et al. 2007). Breitburg (1999) defined 3 groups of nekton associated with subtidal C. virginica reefs in the Chesapeake Bay: (1) reef residents, whose primary habitat is the reef; (2) faeultative residents generally associated with structured habitats; and (3) transient species, which forage on or near the reef but are wide ranging. Furthermore, a number of oyster reef resident fishes, including G. bosc, C. bosquianus, H. hentz, freckled blenny Hypsoblennius ionthas, skilletfish Gobiesox strumosus, oyster toadfish Opsanus tau, and gulf toadfish Opsanus beta, have been shown to be dependent on oysters for reproduction, depositing their eggs on or inside oyster shells (Breitburg 1999, Coen et al. 1999b).

Despite their clear ecologic importance, populations of C. virginica have declined along much of the mid-Atlantic coast of the United States during the past century as a result of a combination of overharvesting (Gross & Smyth 1946), habitat degradation (Rothschild et al. 1994), reduced water quality (Seliger et al. 1985), disease (Ford & Tripp 1996, Lenihan et al. 1999), the interactions among these factors (Lenihan & Peterson 1998), and ecosystem shifts (Rothschild et al. 1994, Luckenbach et al. 1999, Dame et al. 2002). Indeed, Newell (1988) estimated that oysters in the Chesapeake Bay had been reduced to 1% of their historic biomass. Furthermore, the global extent of oyster reefs is estimated to have been reduced to approximately 15% of its 18th-century level (see the recent review by Beck et al. (2009)).

Due to the widespread depletion of oysters, and the recognition of their ecological and economic importance, habitat restoration and enhancements projects have been widely practiced for many years. Until the late 1990s, however, these projects were focused primarily on the fishery enhancement of C. virginica stocks, although a few also included measurements of water quality to assess changes caused by oyster filtration activities (see review by MacKenzie 1963, Coen & Luckenbach 2000, Peterson et al. 2003). Since that time, C. virginica restoration efforts have begun to focus increasingly on restoring ecosystem services, including the provision of habitat for other macrofauna (e.g., Coen et al. 1999b, Coen et al. 2007, Geraldi et al. 2009, Hadley et al. 2010). Although data exist on the broad diversity of fauna associated with natural oyster reefs, the majority of studies investigating oyster reef nekton community composition have focused on natural, subtidal oyster reefs. By comparison, relatively little is known about these communities on restored or enhanced oyster reefs, or in areas where oysters occur intertidally (Tolley & Volety 2005).

This study focused on natural and enhanced oyster reef habitats in the coastal waters of South Carolina, where more than 95% of C. virginica oyster reefs occur in the intertidal zone (e.g., Bahr & Lanier 1981, Burrell 1986). Since oyster depletion in South Carolina has been much less extensive than in many other areas, such as the Chesapeake Bay, natural populations of C. virginica produce very high levels of natural oyster recruitment (>4,000 oysters/[m.sup.2], South Carolina Department of Natural Resources (SCDNR), unpubl, data). Consequently, the provision of suitable substrate has proved to be a successful strategy for oyster reef restoration and enhancement efforts, many of which have used alternative materials as a result of the cost and limited availability of natural oyster shell (see Brumbaugh and Coen (2009) for review). The primary aim of this study was to compare nekton community composition on both natural and enhanced intertidal oyster reefs in South Carolina. Specifically, we compared the nektonic organisms collected on a reef plot with those collected on an adjacent control plot (i.e., bare sand or mud substrate without oyster reef habitat) at three sites. In addition, we examined temporal changes in nekton community composition by sampling on multiple occasions throughout the year, including spring, summer, and fall.

MATERIALS AND METHODS

Study Sites

Three independent stretches of shoreline along the South Carolina coastline that were similar in surrounding soft sediment habitat and that included either an enhanced intertidal oyster reef (2 sites) or a natural intertidal oyster reef (1 site) were chosen as study sites (Fig. 1). For the purposes of this study, an enhanced oyster reef is defined as solid suitable substrate established for the purpose of creating an oyster reef in an area where there is no evidence that a natural oyster reef existed previously. The tidal range at each site was between 1.5 m and 2.0 m. Each site contained an intertidal oyster reef plot with a lower edge that extended to at least the mean low water mark and that was situated along a stretch of at least 80 m of otherwise uninterrupted shoreline comprising intertidal soft sediment habitat. At each site, the reef plot was paired with a control plot containing no structurally complex benthic habitat (i.e., just bare sand or mud). Each control plot was located approximately 30 m from its paired reef plot at the same tidal elevation and on an equivalent surface sediment type.

The most northerly site comprised a 1-y-old enhanced oyster reef plot that was located along the Atlantic Intraeoastal Waterway (ICW, Fig. 1; 33.079520[degrees] N, 79.445368[degrees] W) on Jeremy Island in McClellanville, SC. The enhanced reef was built using 8 arrays of concrete oyster "castles" (Allied Concrete Company) constructed intertidally in a linear configuration at the mean low water mark in July 2009 as part of a collaborative project between the South Carolina Chapter of The Nature Conservancy and the SCDNR. Each oyster castle array comprised 13 interlocking concrete blocks (castles) arranged in a pyramid with 8 castles on the base layer (in a 3 x 3 arrangement with no center block to increase interstitial space), 4 castles in the middle layer that locked the base layer castles in place, and a single castle on the top that locked the middle castles in place. Each of the castles was 30.5 x 30.5 x 20.3 cm, such that each array was approximately 1 x 1 m wide at the base and 0.5 m high at the center. Arrays were placed 1.8 m apart and constituted a total reef footprint of 8 [m.sup.2]. Between the deployment of the oyster castles and the initiation of sampling, oysters recruited to this substrate at high densities, thereby presenting complex biogenie reef habitat for utilization by nektonic organisms. The ICW site had a sandy substrate and was located near a maritime forest with sparse amounts of cordgrass Spartina alterniflora nearby. The second site comprised a 7-y-old enhanced oyster reef located at Fort Johnson in the Charleston Harbor (FJ, Fig. 1; 32.751199[degrees] N, 79.901606[degrees] W). The settlement substrate for the oyster reef at this site was deployed in 2003 by SCDNR's South Carolina Oyster Restoration and Enhancement (SCORE) Program and constituted nylon bags (23 L) filled with recycled oyster shell (12-20 kg). This enhanced reef measured 23 x 4 m (92 [m.sup.2]) and was built on sandy bottom with a S. alterniflora salt marsh located directly inshore of the uppermost part of the reef. The third site comprised a more than 5-y-old natural oyster reef in First Sister Creek, near the Folly River, SC (FR, Fig. 1; 32.899719[degrees]N, 79.935581[degrees]W), with the upper reef margin situated in close proximity (2-3 m) to a dense S. alterniflora salt marsh habitat. The age of this reef was determined through multidecadal aerial surveys performed by the SCDNR (unpubl. data). At both the Fort Johnson and First Sister Creek sites, the reef plots constituted oyster reefs with high percentage cover (>90%) of live oysters within the reef footprints.

Drop Net Sampling Method

The drop net sampling method developed for this study was a reversed modification of the approach described by Wenner et al. (1996). This method involved suspending a bundled net near the top of 3-m-tall poles positioned around the perimeter of each sampling plot. Nets were positioned around 2 rectangular sampling plots (i.e., reef and control plots), each measuring 24 x 5 m (120 [m.sup.2]). Each drop net was 2.5 m in height and 60 m in length, and consisted of a 6.35-mm (0.25-inch) delta mesh seine net. The net was suspended around the perimeter of each plot using stainless steel brackets attached to 3-m aluminum poles (10 per plot) that held the top of the net above the water at high tide and 2 m above the sediment, allowing organisms to enter and exit the study plots during the incoming tide. At high tide, trigger lines equipped with cotter pins that held the net within the brackets were used to release the weighted bottom of the net, allowing it to drop to the sediment and completely encircle the nektonic organisms within each plot. After deploying the pair of nets at a site, the bottom of each net was secured in place using metal stakes to prevent the net from lifting off the sediment surface as a result of the action of currents, wind, and waves. More details of the specifications of this sampling method can be found in Joyce (2011).

Data Collection

Nekton samples were acquired on dates when a spring high tide occurred between 7 AM and 12 noon. This ensured that sites would be completely exposed during low tide, maximizing the ability to collect all the nektonic organisms as the tide receded. These tides also allowed daylight sampling, which made it easier to find and collect all captured nekton, and standardized sampling time, which is known to affect intertidal nekton composition (e.g., Gibson et al. 1998).

A total of 30 sampling dates (10 per site) occurred between March 30, 2010, and December 21, 2010. The interval between sampling dates at each site ranged from 15-45 days, depending on tide and weather conditions, although the majority of samples (>70%) had intervals of 27-33 days (i.e., approximately 1 sample/mo). Sampling dates were categorized as spring (March to May), summer (June to September) or fall (October to December), based on periods of rising, stable, or decreasing water temperatures, respectively (Fig. 2A). At each site, there were 3 sampling dates in spring, 4 in summer, and 3 in fall.

Salinity (measured in practical salinity units), surface seawater temperature (measured in degrees Celsius), and dissolved oxygen (measured in milligrams per liter) were measured at high tide using a hand-held meter (model no. 85; YSI, Inc., Yellow Springs, Ohio). When the tide had receded to a water depth of 0.3-0.6 m within each plot, dip netting for nektonic organisms began. All nekton collected were placed in buckets (~20 L) of ambient seawater and aerated. Each plot was dip netted continuously until either no more organisms were captured or the water had subsided completely from the plot and the area could be checked thoroughly for nektonic organisms using visual surveillance and manual collection. For each sampling event, equivalent effort was directed toward sampling the reef plot and the control plot. The first few individuals of each new species encountered throughout the study were euthanized using dissolved C[O.sub.2] (Burns & McMahan 1995) and stored in 10% seawater-buffered formalin to serve as voucher specimens as part of the College of Charleston's Grice Marine Laboratory Fish and Invertebrate Collection. All organisms were identified to the lowest taxonomic level possible. Most organisms were identified and measured in the field so that live specimens could be returned to the water immediately adjacent to the sample plots. All species netted directly from the water column were included in our analyses, including some considered traditionally as benthic (e.g., bigclaw snapping shrimp Alpheus heterochaelis).

Statistical Methods

Seawater Physical Data

Two-way ANOVAs were used to test whether physical conditions (temperature, salinity, and dissolved oxygen) differed among sites and seasons. Site and season, and the interaction between them, were entered as fixed factors.

Analysis of Nekton Abundance, Richness, and Diversity Indices

Our primary objective was to explore the effects of treatment (reef vs. control) and season on nekton abundance, taxon richness, and nekton diversity. Data for nekton abundance were transformed ([log.sub.10][x + 1]) to meet normality assumptions. Nekton diversity was estimated using the Shannon index (H') and the reciprocal of the Simpson index (D) using the equations provided in Krebs (1999). Nekton abundance, taxon richness, and taxon diversity were each analyzed using mixed-model ANOVAs that incorporated site (ICW, FJ, FR) as a blocked random factor, treatment (control, reef) and season (spring, summer, fall) as fixed factors, and sampling date (nested within season) as a random factor. The interaction between season and treatment was also tested, but interactions involving random factors were not (Zar 1998). Variations around means are reported as [+ or -] 1 standard error.

Treatment Effects for Individual Taxa

For each taxon collected on more than 1 occasion, a 2-tailed paired t-test was used to test whether its abundance differed significantly between the reef plots and the control plots. Data were pooled from all sampling events and paired by site and date (i.e., adjacent reef and control plots sampled on the same day). Pairs of zero-catch data were excluded from the analyses. A Bonferroni-corrected significance threshold of 0.05/n was applied to control for multiple tests, where n is the number of taxa tested.

Community Structure

Nektonic faunal assemblages were compared among sites and between treatments using cluster analysis (Community Analysis Program IV; Pisces Conservation Ltd., UK) of abundance and composition data. Cluster analysis allowed similar groups of taxa (based on abundance) to be identified using average distances in a Bray-Curtis dissimilarity matrix (Field et al. 1982). Data were transformed ([log.sub.e][x + 1]) to reduce scalar differences in abundance values.

RESULTS

Seawater Physical Data

Mean surface seawater temperature across all sites was 21.1 [degrees]C (range, 16.5-25.6[degrees]C), 29.6[degrees]C (range, 27.7-31.9[degrees]C), and 15.8[degrees]C (range, 7.4-21.9[degrees]C) during spring, summer, and fall, respectively. Temperature varied significantly with season (P < 0.001, [F.sub.2,20] = 29.8) but not site (Fig. 2A). Mean salinity across all sites was 27.4 (range, 20.2-33.1), 31.8 (range, 27.0-35.4), and 30.4 (range, 25.1-34.5) during spring, summer, and fall, respectively. Salinity varied significantly both among seasons (P = 0.006, [F.sub.2,20] = 6.6) and among sites (P < 0.001, [F.sub.2,20] = 12.9); however, the interaction between these factors was not significant. FR was generally the most saline site, and FJ was the least saline site. Both FJ and ICW experienced lower salinities (20.2-22.0) in early spring before switching to more stable, higher salinity regimes thereafter (Fig. 2B). Mean dissolved oxygen across all sites was 5.6 mg/L (range 4.3-6.5 mg/L), 4.6 mg/L (range, 3.8-5.4 mg/L), and 6.1 mg/L (range, 5.3-8.0 rag/L) during spring, summer, and fall, respectively. Dissolved oxygen varied significantly among seasons (P < 0.001, [F.sub.2,18] = 11.5), with lower values in the summer attributable to higher water temperatures. There was no significant difference in dissolved oxygen levels among sites, and no significant interaction between site and season (Fig. 2C).

Nekton Abundance

A total of 12,161 nektonic organisms were collected, including 5,004 from FR, 4,326 from FJ, and 2,831 from ICW. Total abundance by season (across all sites) was 2,274 during spring, 8,475 during summer, and 1,412 during fall. By treatment, total abundance was 10,291 across all reef plots compared with 1,870 across all control plots (Table 1). Reef plots supported a significantly greater abundance of nekton than control plots (P < 0.001, [F.sub.1,45] = 48.5), with overall mean catches per sample of 343.0 [+ or -] 67.3 organisms and 62.3 [+ or -] 11.8 organisms, respectively. Nekton abundance also varied among seasons (P = 0.010, [F.sub.2,45] = 9.6), with the greatest numbers occurring during the summer (Table 2, Fig. 3A).

It was notable that grass shrimp (Palaemonetes spp.) were especially dominant on reef plots (mean, 90.3% of nekton abundance per reef plot compared with 54.0% on control plots). A second analysis was therefore run with Palaemonetes spp. data removed to test whether this taxon alone was responsible for the higher nekton abundance on reef plots. The mean adjusted nekton abundance (i.e., with Palaemonetes spp. data excluded) per sample across all reef plots and all control plots was 64.2 [+ or -] 12.0 organisms and 40.3 [+ or -] 9.2 organisms, respectively, with the reef values being significantly greater (P = 0.004). Adjusted nekton abundance did not vary significantly among seasons, despite varying among dates within season (P < 0.001, [F.sub.7,45] = 4.5) (Table 2, Fig. 3B).

Taxon Richness

A total of 60 taxa were identified, of which 57 were identified to the species level. Those not identified to species were Palaemonetes spp. (n = 9,026), Blenniidae sp. (n = 1), and mantis shrimp Squilla sp. (n = 3). Although fin ray counts were not used to determine species in all Menidia specimens collected, all were assumed to be the Atlantic silverside Menidia menidia rather than the inland silverside Menidia beryllina, given that all voucher specimens were confirmed as M. menidia, and that M. menidia typically inhabit higher salinity waters, such as those sampled here (Fay et al. 1983). Twenty-nine taxa were collected in spring, 48 in summer, and 40 in fall (Table 3). A total of 50 taxa were found on reef plots compared with 46 on control plots. FR yielded a total of 42 taxa, compared with 36 from FJ and 37 from ICW. The mean richness per sample was 9.1 [+ or -] 0.8 for all reef plots and 7.2 [+ or -] 0.9 for all control plots, with reef plots having a significantly greater taxon richness (P = 0.029, [F.sub.1,45] = 5.1; Table 2, Fig. 3C). There were no significant effects of season, season x treatment, or site on taxon richness, although taxon richness did vary significantly among dates within season (P = 0.00l, [F.sub.7,45] = 4.5). The number of taxa present accumulated with the number of sampling events at a higher rate on reef plots compared with control plots at both FJ and FR (Fig. 4A, B), but not at ICW (Fig. 4C).

Diversity Indices

Simpson's index (D) could not be calculated for 3 samples because of insufficient catches (i.e., data excluded were 2 fall dates from the FJ control plot and 1 fall date from the FR control plot when [less than or equal to] 1 taxon was encountered). Diversity indices ranged from 1.07-8.45 for the Simpson index (D) and 0.00-2.24 for the Shannon index (H'). Across all reef and all control plots, mean D per sample was 1.72 [+ or -] 0.12 and 3.51 [+ or -] 0.39, respectively, whereas mean H' was 0.77 [+ or -] 0.07 and 1.14 [+ or -] 0.12, respectively. Both indices were significantly lower on the reef plots (H': P = 0.018, F1,45 = 6.0; D: P < 0.001, [F.sub.1,42] = 18.3), regardless of season, site, or date (Table 2, Fig. 3D, E).

Treatment Effects for Individual Taxa

Of the 60 taxa collected, 36 were found on both reef plots and control plots. Fourteen taxa were unique to the reef plots, whereas 10 taxa were unique to the control plots (Table 1). For data pooled across all sites and seasons, 33 taxa were found to be more numerous on reef plots than control plots, 3 taxa occurred in equal numbers, and 24 taxa were more numerous on control plots than reef plots (Fig. 5). Forty-four taxa were collected on more than 1 occasion, allowing paired t-tests comparing reef plot abundance and control plot abundance to be performed. The bigclaw snapping shrimp A. heterochaelis and Palaemonetes spp. were significantly more abundant on the reef plots at the Bonferroni-adjusted significance threshold, [alpha] of 0.05/44 = 0.001 (P < 0.001 for both taxa; [t.sub.6] = 7.0, [t.sub.29] = 4.1, respectively; Fig. 5). The naked goby G. bosc (P = 0.004, [t.sub.11] = 3.6), mummichog Fundulus heteroclitus (P = 0.008, [t.sub.18] = 3.0), and M. menidia (P = 0.039, [t.sub.18] = 2.2) were also all more abundant on the reef plots at the unadjusted significance threshold ([alpha] = 0.05, Fig. 5). No taxa were significantly more abundant on the control plots for these analyses.

Community Structure

The cluster analysis of overall community structure for data pooled across seasons (Fig. 6A) revealed that plots grouped more closely by site than by treatment. The relative influence of site and treatment on the patterns of plot groupings, however, varied with season. For the spring data alone, groupings were governed primarily by treatment (Fig. 6B), whereas for the summer data alone, groupings were governed primarily by site (Fig. 6C). ICW was less similar to the other 2 sites in summer, mainly because of the lack of transient marine and estuarine species such as C. regalis, southern kingfish Menticirrhus americanus, summer flounder Paralichthys dentatus, P. lethostigma, hogchoker Trinectes maculatus, Spanish mackerel Scomberomorus maculatus, and A. probatocephalus. During the fall, cluster groupings were influenced primarily by site, with FR and ICW grouping together (Fig. 6D). The FJ control plot, however, was a notable outlier during the fall as a result of the extremely low catches of nekton at this site (i.e., only 4 organisms collected), whereas the greater nekton abundance and diversity at the FJ reef plot resulted in it grouping together with FR and ICW (Fig. 6D).

DISCUSSION

This study demonstrates that nekton abundance and community composition are clearly affected by the presence of intertidal oyster reefs. Nekton abundance was significantly greater on the reef plot than on its paired control plot at each of the 3 sites investigated. For data pooled across all sites and seasons, 33 taxa were found to be more numerous on reef plots than control plots. Furthermore, for the 44 taxa collected on more than 1 occasion, 2 taxa (A. heterochaelis and Palaemonetes spp.) to 5 taxa (previous taxa plus G. bosc, M. menidia, and F. heteroclitus) were significantly more abundant on the reef plot than the control plot, whereas no taxa were significantly more abundant on the control plot. The rates at which new species were encountered in our collections over time (i.e., the steepness of the curves shown in Fig. 4) were generally greatest during the summer, followed by the spring. Conversely, relatively few new species were encountered during the fall. This seasonal pattern is likely to be a result of the shoreward and northerly movement of species that spend the winter either offshore or at more southerly latitudes. New species were encountered at higher rates on the reef plots than on the control plots at both FJ and FR, but not at ICW (Fig. 4), possibly because the reef at ICW was established more recently and had a smaller footprint than at the other sites. Future monitoring on the reef plot at the ICW site may help to differentiate the driving mechanisms there.

Although taxon richness was significantly greater on the reef plots than on the control plots, both species diversity indices were greater for the control plots, regardless of site, date, or season. This may be a result of the incorporation of species evenness when calculating diversity using Shannon (H') and Simpson (D) diversity indices, which calculate species heterogeneity. Specifically, Palaemonetes spp., M. menidia, and Anehoa mitchilli were all collected in much higher relative abundance than other species in the reef plots compared with the control plots, which would generate comparatively lower species diversity indices, despite the fact that taxon richness was higher in the reef plots. A possible explanation for why some species were collected in much greater abundance than others may be a result of their social behavior. Taxa such as Palaemonetes spp., M. menidia, and A. mitchilli tend to form large, dense aggregations, whereas many other species such as inshore lizardfish Synodus foetens, pinfish Lagodon rhomboides, and red drum Sciaenops ocellatus tend to be either solitary or found in smaller groups.

In the current study, the greatest abundance of nektonic organisms was collected at the natural reef (FR), with intermediate abundance collected at the older, enhanced reef (F J) and the lowest overall abundance collected at the most recently established enhanced reef (ICW). This trend is intuitive if, as the created reef ages, it increases in structural complexity, attracts more organisms, and begins functioning more similarly to a natural reef (as supported by Fager (1971), Hueckel and Buckley (1987), Van Dolah et al. (1988), Jensen et al. (1994), Relini et al. (1994), and Thanner et al. (2006)). In addition to differences in reef age, the spatial extent of the reef footprint within the sampling plot varied among sites, and this may have affected nekton abundance, particularly for taxa that are known to be associated closely with oyster reefs. Differentiating the effects of reef age, substrate, salinity, and the distribution of surrounding habitats would require sampling a greater number of sites, for which the newly developed method described here would be well suited. Although expanding the number of sites investigated was beyond the scope of the current study, such efforts offer productive opportunities for future research.

When comparing the nekton communities among sites using cluster analysis, the ICW reef tended to be more closely related to the FR reef than to the FJ reef, although there were seasonal differences. Although site was a more important factor driving cluster formation in summer and fall, treatment had a greater influence in the spring, although the ICW control site still grouped together with the other reef sites before the control sites from FR and FJ. This may be explained, in part, by salinity, which has been shown to be an important factor in determining oyster reef community composition (e.g., Tolley et al. 2006), and tended to be lowest at F J, except during the spring. It is possible that salinity had a greater effect on species composition than on taxon richness. Some of the species driving the cluster separation of FJ were those that use more brackish habitats during juvenile and subadult life stages--namely, A. probatocephalus (Jennings 1985), Atlantic menhaden Brevoortia tyrannus (Rogers & Van Den Avyle 1983), C. nebulosus (Johnson & Seaman 1986), striped killifish Fundulus majalis (Abraham 1985), M. americanus, Atlantic croaker Micropogonias undulatus (Lassuy 1983), P. dentatus (Gilbert 1986), P. lethostigma (Gilbert 1986), black drum Pogonias cromis (Sutter et al. 1986), S. ocellatus (Reagan 1985), and T. maculatus (Dovel et al. 1969). The greater similarity of species community composition between ICW and FR compared with FJ for the combined data set demonstrates that site (primarily salinity) had a stronger influence on overall nekton species community composition than treatment in our study.

The patterns of associations of species communities with particular sites and treatments grouping together was maintained during the summer, but changed during the spring and fall. Because spring and fall are the 2 major migration periods for many species that move in and out of estuaries in the southeastern United States, the migration patterns of certain species (e.g., A. mitchilli, pigfish Orthopristis chrysoptera, gray snapper Lutjanus griseus, and spot Leiostornus xanthurus) may have affected the community structure during these seasons. An additional factor in the species community composition in the spring could also be the enhanced recruitment of juvenile and larval fish to the reef plots based on the protection and food resources afforded by reef habitat. Elevated abundance on the reef plots support the dogma that oyster reefs are an important habitat for these species and indicate that the increased habitat complexity that reefs offer has a greater effect on community structure than site during certain seasons. Based on our analyses, the species most likely driving these associations include G. bosc, A. heteroehaelis, M. menidia, Palaemonetes spp., and F. heteroclitus. These species were found more commonly on the reef plot than on the control plot at both ICW and FR, which would explain why the nektonic communities in the reef plot at these 2 sites were associated more closely during the spring than at other times of the year.

The collection and relative abundance of several species (e.g., A. mitchilli, O. chrysoptera, L. griseus, and L. xanthurus) at certain times of year in this study appear to support the seasonal migration patterns described by Adams (1976). Bay anchovies A. mitchilli were collected year-round in the current study, and since they are migratory, schooling fish, there were major fluctuations in their abundance among individual sampling events and between treatments. According to the system proposed by Breitburg (1999), A. mitchilli is a transient species (see Introduction for definitions), and despite being highly mobile, it was collected in greater abundance on the reef plots than on the control plots. Since A. mitchilli, along with other transient species (e.g., the broad-striped anchovy Anchoa hepsetus, and M. menidia), is planktivorous, it may be attracted to the increased zooplankton densities associated with oyster reefs (Harding 2001). Although only a few individuals of O. chrysoptera were collected in the current study, this species was collected in August, which is consistent with the data reported by Adams (1976).

The collection method presented here allowed plots to be sampled repeatedly over a relatively short timeframe without significant disturbance to the habitat plots under investigation. This allowed nekton to be compared among sites, between treatments, and over time. Previous attempts to document the nektonic communities in restored or enhanced intertidal oyster reef habitats have typically used methods that are destructive (e.g., trawling), intensive in terms of personnel (e.g., lift nets), or can only sample a small area (e.g., habitat trays). Such methods also tend to capture mostly smaller, relatively sedentary organisms, rather than the larger, more motile nektonic organisms (e.g., anchovies, silversides, mullets (Lehnert & Allen 2002)). Furthermore, our drop net method requires relatively few people, samples a relatively large area (i.e., 120-[m.sup.2] study plots), and can be applied to both intertidal oyster reef and soft bottom habitats to evaluate nektonic communities quantitatively in terms of both their abundance and diversity. Although our sampling method involved some degree of habitat disturbance (e.g., temporary installation of net poles), no permanent damage to the study plots, particularly the reefs themselves, occurred. The degree of habitat disturbance associated with our method was less than that of Wenner et al. (1996), which involved considerable sediment disturbance by digging ditches around the study plots on each sampling occasion. Wenner et al. (1996) reported greater abundance of small species (e.g., Palaemonetes spp., white shrimp Litopenaeus setiferus, A. mitehilli) than our study, which we attribute to their use of a smaller mesh size (i.e., 3.20 mm compared with our 6.35-mm mesh). Our sampling method enclosed a large area relative to other sampling techniques, such as habitat traps or quadrats, and also captured a wide size range of nekton, from Palaemonetes spp. (<10 mm) to bonnethead shark Sphyrna tiburo (>1,000 mm). Surprisingly, however, only young-of-the-year S. ocellatus and C. nebulosus were collected, despite the known association of older individuals of these species with oyster reef habitat (see, for example, Bortone (2003) and Arnott et al. (2010), respectively).

The results from this study provide important findings on intertidal oyster reef ecologic services, specifically in the context of habitat provision for nektonic species. Additional issues that arose during the study for future consideration, however, include investigating the effects of the proximity and density of adjacent S. alterniflora habitat, water quality parameters, and substrate type on nekton abundance and diversity. These effects could be tested readily using the established sampling method described here through further sampling over additional years and with the inclusion of more field sites. The findings in this study support the importance of intertidal oyster reefs as critical habitat for nektonic organisms, and validate that the addition of suitable structures in intertidal estuaries along the South Carolina coast, by initiating the development of oyster reefs, increases nekton abundance and species richness within that area. Although the creation of habitat increases nekton abundance and species richness in a short timeframe (within 1 y of creation), it may take several years for that habitat to support nekton abundance and species compositions that are similar to natural oyster reefs. Conversely, when creating an enhanced oyster reef by adding substrate to a mud- or sand-bottom habitat, it is important to consider that certain species rely on these soft sediment natural habitats for a portion of their life cycle. Adding substrate to naturally occurring soft sediment habitats could cause reductions in these types of habitat, resulting in localized harm to species that are adapted to use them. Therefore, it is important to ensure that a balanced mosaic of habitat types is maintained within our coastal marine and estuarine environments.

ACKNOWLEDGMENTS

We thank the Southeast Area Monitoring and Assessment Program (SEAMAP) of the National Marine Fisheries Service (NMFS), The Nature Conservancy's Global Marine Team, and the NOAA Restoration Center's Community-Based Restoration Matching Grants Program for funding this study. The College of Charleston Grice Marine Laboratory's Fish and Invertebrate Collection staff assisted in the identification and accession of voucher specimens. Numerous people helped with field collections, including Amanda Fornal, Benjamin Stone, Michelle Willis, Patrick Biondo, Mark Stratton, Michelle Pate, William Sautter, Alex Woods, Peter Lempesis, Rebecca Cope, David Murray, Bryan Danson, Elise Clopton, Daniel Hawkins, Steven Long, Jared Hulteen, Sean Garrett, and Jennifer Scales. This publication represents SCDNR Marine Resources Research Institute contribution no. 699.

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PETER R. KINGSLEY-SMITH, (1) * RYAN E. JOYCE, (2) STEPHEN A. ARNOTT, (1) WILLIAM A. ROUMILLAT, (1) CHRISTOPHER J. MCDONOUGH (1) AND MARCEL J. M. REICHERT (1)

(1) Marine Resources Research Institute, South Carolina Department of Natural Resources, 217 Fort Johnson Road, Charleston, SC 29422-2559; (2) Grice Marine Laboratory, College of Charleston, 205 Fort Johnson Road, Charleston, SC 29412

* Corresponding author. E-mail: kingsleysmithp@dnr.sc.gov

DOI: 10.2983/035.031.0413

TABLE 1.
Abundance of nektonic organisms collected in drop net samples between
March 30, 2010, and December 21, 2010, fisted by site and treatment.

                                                   Fort Johnson

Family           Species            Common Name    Cntrl  Reef

Alpheidae        Alpheus            Bigclaw         --       --
                   heterochaelis *    snapping
                                      shrimp
Palaemonidae     Palaemonetes spp.  Grass shrimp   344    2,561
Penaeidae        Farfantepenaeus    Brown shrimp    41       55
                   aztecus
                 Litopenaeus        White shrimp   170       14
                   setiferus
Portunidae       Callinectes        Atlantic blue   60       98
                   sapidus            crab
                 Callinectes        Lesser blue      7        7
                   similis            crab
Squillidae       Squilla sp.        Mantis shrimp   --       --
Atherinidae      Menidia menidia    Atlantic        13      116
                                      silverside
Batrachoididae   Opsanus tau *      Oyster          --       --
                                      toadfish
Belonidae        Strongylura        Atlantic        --       --
                   marina *           needlefish
Blenniidae       Unknown *          Unknown         --       --
                 Hypsoblennius      Feather          1       --
                   hentz              blenny
Paralichthyidae  Citharichthys      Bay whiff       --       --
                   spilopterus
                   ([dagger])
                 Etropus crossotus  Fringed         --       --
                                      flounder
                 Paralichthys       Summer           3        1
                   dentatus           flounder
                 Paralichthys       Southern         1       11
                   lethostigma        flounder
Carangidae       Chloroscomhrus     Atlantic         7       26
                   chrysurus          bumper
                 Selene vomer       Lookdown        --       --
                   ([dagger])
                 Trachinotus        Permit          --       --
                   falcatus
Clupeidae        Brevoortia         Atlantic        --        1
                   tyrannus *         menhaden
                 Opisthonema        Atlantic         1       --
                   oglinum            threadfin
                                      herring
Cynoglossidae    Symphurus          Blackcheek      19        1
                   plagiusa           tonguefish
Cyprinodontidae  Cyprinodon         Sheepshead      --        3
                   variegatus         minnow
                   variegatus
                 Fundulus           Mummichog        1       69
                   heteroclitus
                 Fundulus majalis   Striped          5       59
                                      killifish
Diodontidae      Chilomycterus      Striped         --        3
                   schoepfi           burrfish
Engraulidae      Anchoa hepsetus    Striped          1        7
                                      anchovy
                 Anchoa mitchilli   Bay anchovy     79      389
Gerreidae        Diapterus          Irish pompano   --       --
                   auratus *
                 Eucinostomus       Silver jenny    --       --
                   gula ([dagger])
Gobiidae         Ctenogobius        Darter goby     --       --
                   boleosoma
                   ([dagger])
                 Gobiosoma bosc     Naked goby      --        2
                 Microgobius        Green goby      --       --
                   thalassinus
                   ([dagger])
Haemulidae       Orthopristis       Pigfish         --       --
                   chrysoptera *
Lutjanidae       Lutjanus griseus   Gray snapper    --       --
Monocanthidae    Stephanolepis      Planehead       --       --
                   hispidus           filefish
Mugilidae        Mugil cephalus *   Striped         --       37
                                      mullet
                 Mugil curema       White mullet     1       11
Poeciliidae      Poecilia           Sailfin molly   --       --
                   latipinna
Pomacentridae    Abudefduf          Sergeant        --       --
                   saxatilis *        major
Sciaenidae       Bairdiella         Silver perch     4    3
                   chrysoura
                 Cynoscion          Spotted          2    2
                   nebulosos          seatrout
                 Cynoscion          Weakfish         1       --
                   regalis
                 Larimus            Banded drum     --       --
                   fasciatus *
                 Leiostomus         Spot             2       15
                   xanthurus
                 Menticirrhus       Southern        34        2
                   americanos         kingfish
                 Micropogonias      Atlantic         1       --
                   undulatus          croaker
                   ([dagger])
                 Sciaenops          Red drum        --        3
                   ocellatus *
Scombridae       Scomberomorus      Spanish          3       --
                   maculatus          mackerel
                   ([dagger])
Soleidae         Trinectes          Hogchoker        1       --
                   maculatus
                   ([dagger])
Sparidae         Archosargus        Sheepshead      --       18
                   probatoce-
                   phalus *
                 Lagodon            Pinfish         --        1
                   rhomboides
Sphyraenidae     Sphyraena          Guachanche      --       --
                   guachancho         barracuda
                   ([dagger])
Syngnathidae     Syngnathuse        Chain           --       --
                   louisiana          pipefish
Synodontidae     Synodus foetens    Inshore         --       --
                                      lizardfish
Triglidae        Prionotus          Bighead sea     --       --
                   tribulus           robin
Dasyatidae       Dasyatis sabina    Atlantic        --       --
                   ([dagger])         stingray
Gymnuridae       Gymnura micrura *  Smooth          --        2
                                      butterfly
                                      ray
Sphyrnidae       Sphyrna tiburo *   Bonnethead      --       --
                                      shark
Loliginidae      Lolliguncula       Atlantic         2        3
                   brevis             brief
                                      squid

                                    TOTAL          804    3,522

                                                   Folly River

Family           Species            Common Name    Cntrl          Reef

Alpheidae        Alpheus            Bigclaw         --                5
                   heterochaelis *    snapping
                                      shrimp
Palaemonidae     Palaemonetes spp.  Grass shrimp    71            3,867
Penaeidae        Farfantepenaeus    Brown shrimp    11               13
                   aztecus
                 Litopenaeus        White shrimp    41               29
                   setiferus
Portunidae       Callinectes        Atlantic blue   21               16
                   sapidus            crab
                 Callinectes        Lesser blue     15                2
                   similis            crab
Squillidae       Squilla sp.        Mantis shrimp    1                2
Atherinidae      Menidia menidia    Atlantic        30               51
                                      silverside
Batrachoididae   Opsanus tau *      Oyster          --                4
                                      toadfish
Belonidae        Strongylura        Atlantic        --                2
                   marina *           needlefish
Blenniidae       Unknown *          Unknown         --                l
                 Hypsoblennius      Feather         --                1
                   hentz              blenny
Paralichthyidae  Citharichthys      Bay whiff        5               --
                   spilopterus
                   ([dagger])
                 Etropus crossotus  Fringed          7               --
                                      flounder
                 Paralichthys       Summer          --               --
                   dentatus           flounder
                 Paralichthys       Southern        --               --
                   lethostigma        flounder
Carangidae       Chloroscomhrus     Atlantic         2               --
                   chrysurus          bumper
                 Selene vomer       Lookdown         1               --
                   ([dagger])
                 Trachinotus        Permit          --                1
                   falcatus
Clupeidae        Brevoortia         Atlantic        --               --
                   tyrannus *         menhaden
                 Opisthonema        Atlantic        --               23
                   oglinum            threadfin
                                      herring
Cynoglossidae    Symphurus          Blackcheek       6               --
                   plagiusa           tonguefish
Cyprinodontidae  Cyprinodon         Sheepshead      --               --
                   variegatus         minnow
                   variegatus
                 Fundulus           Mummichog        2               47
                   heteroclitus
                 Fundulus majalis   Striped         --               --
                                      killifish
Diodontidae      Chilomycterus      Striped         --                2
                   schoepfi           burrfish
Engraulidae      Anchoa hepsetus    Striped         17               10
                                      anchovy
                 Anchoa mitchilli   Bay anchovy    240              371
Gerreidae        Diapterus          Irish pompano  --                --
                   auratus *
                 Eucinostomus       Silver jenny     4               --
                   gula ([dagger])
Gobiidae         Ctenogobius        Darter goby      2               --
                   boleosoma
                   ([dagger])
                 Gobiosoma bosc     Naked goby       2                6
                 Microgobius        Green goby       1               --
                   thalassinus
                   ([dagger])
Haemulidae       Orthopristis       Pigfish         --                1
                   chrysoptera *
Lutjanidae       Lutjanus griseus   Gray snapper    --                1
Monocanthidae    Stephanolepis      Planehead        1                1
                   hispidus           filefish
Mugilidae        Mugil cephalus *   Striped         --                1
                                      mullet
                 Mugil curema       White mullet    --                1
Poeciliidae      Poecilia           Sailfin molly   --               --
                   latipinna
Pomacentridae    Abudefduf          Sergeant        --               --
                   saxatilis *        major
Sciaenidae       Bairdiella         Silver perch    --                1
                   chrysoura
                 Cynoscion          Spotted         --               --
                   nebulosos          seatrout
                 Cynoscion          Weakfish        --                1
                   regalis
                 Larimus            Banded drum     --               --
                   fasciatus *
                 Leiostomus         Spot             2               --
                   xanthurus
                 Menticirrhus       Southern        --               --
                   americanos         kingfish
                 Micropogonias      Atlantic        --               --
                   undulatus          croaker
                   ([dagger])
                 Sciaenops          Red drum        --               --
                   ocellatus *
Scombridae       Scomberomorus      Spanish         --               --
                   maculatus          mackerel
                   ([dagger])
Soleidae         Trinectes          Hogchoker       --               --
                   maculatus
                   ([dagger])
Sparidae         Archosargus        Sheepshead      --               --
                   probatoce-
                   phalus *
                 Lagodon            Pinfish        ([dagger]) --      2
                   rhomboides
Sphyraenidae     Sphyraena          Guachanche      --               --
                   guachancho         barracuda
                   ([dagger])
Syngnathidae     Syngnathuse        Chain            7                3
                   louisiana          pipefish
Synodontidae     Synodus foetens    Inshore         --                1
                                      lizardfish
Triglidae        Prionotus          Bighead sea      1              --
                   tribulus           robin
Dasyatidae       Dasyatis sabina    Atlantic         2              --
                   ([dagger])         stingray
Gymnuridae       Gymnura micrura *  Smooth          --              --
                                      butterfly
                                      ray
Sphyrnidae       Sphyrna tiburo *   Bonnethead      --                1
                                      shark
Loliginidae      Lolliguncula       Atlantic        17               28
                   brevis             brief
                                      squid

                                    TOTAL          509            4,495

                                                       ICW

Family           Species            Common Name    Cntrl  Reef   Total

Alpheidae        Alpheus            Bigclaw         --        4       9
                   heterochaelis *    snapping
                                      shrimp
Palaemonidae     Palaemonetes spp.  Grass shrimp   247    1,936   9,026
Penaeidae        Farfantepenaeus    Brown shrimp    34       68     222
                   aztecus
                 Litopenaeus        White shrimp     7        3     264
                   setiferus
Portunidae       Callinectes        Atlantic blue   27       57     279
                   sapidus            crab
                 Callinectes        Lesser blue     52      101     184
                   similis            crab
Squillidae       Squilla sp.        Mantis shrimp   --       --       3
Atherinidae      Menidia menidia    Atlantic         4        3     217
                                      silverside
Batrachoididae   Opsanus tau *      Oyster          --       --       4
                                      toadfish
Belonidae        Strongylura        Atlantic        --       --       4
                   marina *           needlefish
Blenniidae       Unknown *          Unknown         --       --       1
                 Hypsoblennius      Feather         --       --       2
                   hentz              blenny
Paralichthyidae  Citharichthys      Bay whiff       --       --       5
                   spilopterus
                   ([dagger])
                 Etropus crossotus  Fringed          7        6      20
                                      flounder
                 Paralichthys       Summer           1        1       6
                   dentatus           flounder
                 Paralichthys       Southern        --       --      12
                   lethostigma        flounder
Carangidae       Chloroscomhrus     Atlantic        --       --      35
                   chrysurus          bumper
                 Selene vomer       Lookdown         2       --       3
                   ([dagger])
                 Trachinotus        Permit           3       --       4
                   falcatus
Clupeidae        Brevoortia         Atlantic        --       --       1
                   tyrannus *         menhaden
                 Opisthonema        Atlantic        --       --      24
                   oglinum            threadfin
                                      herring
Cynoglossidae    Symphurus          Blackcheek       9       20      55
                   plagiusa           tonguefish
Cyprinodontidae  Cyprinodon         Sheepshead       1       --       4
                   variegatus         minnow
                   variegatus
                 Fundulus           Mummichog        5       18     142
                   heteroclitus
                 Fundulus majalis   Striped          3        5      72
                                      killifish
Diodontidae      Chilomycterus      Striped         11        2      18
                   schoepfi           burrfish
Engraulidae      Anchoa hepsetus    Striped          1        1      37
                                      anchovy
                 Anchoa mitchilli   Bay anchovy     32        6   1,117
Gerreidae        Diapterus          Irish pompano   --        1       1
                   auratus *
                 Eucinostomus       Silver jenny     1       --       5
                   gula ([dagger])
Gobiidae         Ctenogobius        Darter goby     --       --       2
                   boleosoma
                   ([dagger])
                 Gobiosoma bosc     Naked goby      --       14      24
                 Microgobius        Green goby      --       --       1
                   thalassinus
                   ([dagger])
Haemulidae       Orthopristis       Pigfish         --       --       1
                   chrysoptera *
Lutjanidae       Lutjanus griseus   Gray snapper     3        3       7
Monocanthidae    Stephanolepis      Planehead       24        3      29
                   hispidus           filefish
Mugilidae        Mugil cephalus *   Striped         --        1      39
                                      mullet
                 Mugil curema       White mullet     2       --      15
Poeciliidae      Poecilia           Sailfin molly    3        1       4
                   latipinna
Pomacentridae    Abudefduf          Sergeant        --        1       1
                   saxatilis *        major
Sciaenidae       Bairdiella         Silver perch     2       --      10
                   chrysoura
                 Cynoscion          Spotted          1        3       8
                   nebulosos          seatrout
                 Cynoscion          Weakfish        --       --       2
                   regalis
                 Larimus            Banded drum     --        1       1
                   fasciatus *
                 Leiostomus         Spot             1        2      22
                   xanthurus
                 Menticirrhus       Southern        --       --      36
                   americanos         kingfish
                 Micropogonias      Atlantic        --       --       1
                   undulatus          croaker
                   ([dagger])
                 Sciaenops          Red drum        --       --       3
                   ocellatus *
Scombridae       Scomberomorus      Spanish         --       --       3
                   maculatus          mackerel
                   ([dagger])
Soleidae         Trinectes          Hogchoker       --       --       1
                   maculatus
                   ([dagger])
Sparidae         Archosargus        Sheepshead      --       --      18
                   probatoce-
                   phalus *
                 Lagodon            Pinfish          1        1       5
                   rhomboides
Sphyraenidae     Sphyraena          Guachanche       2       --       2
                   guachancho         barracuda
                   ([dagger])
Syngnathidae     Syngnathuse        Chain            6       --      16
                   louisiana          pipefish
Synodontidae     Synodus foetens    Inshore          2        1       4
                                      lizardfish
Triglidae        Prionotus          Bighead sea     18        4      23
                   tribulus           robin
Dasyatidae       Dasyatis sabina    Atlantic        --       --       2
                   ([dagger])         stingray
Gymnuridae       Gymnura micrura *  Smooth          --       --       2
                                      butterfly
                                      ray
Sphyrnidae       Sphyrna tiburo *   Bonnethead      --       --       1
                                      shark
Loliginidae      Lolliguncula       Atlantic        45        7     102
                   brevis             brief
                                      squid

                                    TOTAL          557    2,274  12,161

* Species unique to reef plots.

([dagger]) Species unique to control plots.

Cntrl, control; ICW, Atlantic Intracoastal Waterway.

TABLE 2.
P values from mixed-model ANOVAs testing the effects of
site, season, date (nested within season), and treatment on total
nekton abundance, adjusted total nekton abundance (Palaemonetes
spp. data removed), taxon richness, and diversity
indices (Shannon H' and Simpson D).

                                                Adjusted
Factor                      Abundance           Abundance   Richness

Site                 0.509                      0.193       0.451
Season               0.010 ([double dagger])#   0.174       0.098
Date (Season)        0.093                      0.001#      0.001#
Treatment            0.001 *#                   0.004 *#    0.029 *#
Season x treatment   0.903                      0.536       0.912

Factor                      H'                   D

Site                 0.569               0.529
Season               0.846               0.522
Date (Season)        0.052               0.498
Treatment            0.018 ([dagger])#   0.001 ([dagger])#
Season x treatment   0.149               0.401

* Greater on reef plots.

([dagger]) Greater on control plots.

([double dagger]) Greater in summer.

P-values shown in bold indicate significant effects of factors on
nekton parameters (i.e., <0.05).

Note: P-values significant effects of factors on nekton parameters
(i.e., <0.05) are indicated with #.

TABLE 3.
Total nekton abundance listed by species and month in order of
earliest to latest encounter date.

                                      Spring

Species                     Mar   Apr    May     Jun

Anchoa mitchilli               1    35     126       5
Bairdiella chrysoura           1   --      --        1
Cyprinodon variegatus          1
  variegatus
Poecilia latipinna             1
Callinectes sapidus            2    10      36      29
Fundulus heteroclitus          3    35       9      15
Palaemonetes spp.             14   463   1,297   1,109
Strongylura marina                   1       1
Paralichthys dentatus                1               1
Opsanustau                           1
Archosargus                          1
  probatocephalus
Paralichthys lethostigma             2       7
Fundulus majalis                     3               4
Alpheus heterochaelis                3
Gobiosoma base                       7               3
Leiostomus xanthurus                13       7
Menidia menidia                     17      88      17
Anchoa hepsetus                              1       1
Callinectes similis                          1       2
Stephanolepis hispidus                       1
Gymnura micrura                              1
Citharichthys spilopterus                    1
Brevoortia tyrannus                          1
Micropogonias undulatus                      1
Syngnathus louisianae                        2       3
Lagodon rhomboides                           2
Lolliguncula brevis                          5       1
Mugil cephalus                              35
Farfantepenaeus aztecus                     37      13
Chilomycterus schoepfi                               1
Mugil curema                                         1
Sphyrna tiburo                                       1
Synodus foetens                                      2
Etropus crossotus                                    6
Cynoscion nebulosus
Selene vomer
Prionotus tribulus
Blenniidae sp.
Squilla sp.
Hypsoblennius hentz
Menticirrhus americanus
Symphurus plagiusa
Litopenaeus setiferus
Dasyatis sabina
Orthopristis chrysoptera
Trinectes maculates
Cynoscion regalis
Chloroscombrus
  chrysours
Sciaenops ocellatus
Scomberomorus
  maculates
Trachinotusfalcatus
Lutjanus griseus
Opisthonema oglinum
Abudefduf saxatilis
Larimus fasciatus
Microgobius thalassinus
Ctenogobius boleosoma
Sphyraena guachancho
Eucinostomus gula
Diapterus auratus

                                    Summer

Species                      Jul     Aug     Sept

Anchoa mitchilli                43     308     319
Bairdiella chrysoura             5       3     --
Cyprinodon variegatus            1       2
  variegatus
Poecilia latipinna
Callinectes sapidus             79      43      38
Fundulus heteroclitus           46       9      19
Palaemonetes spp.            2,284   1,340   1,735
Strongylura marina               2
Paralichthys dentatus            2       1
Opsanustau                               2
Archosargus                              2
  probatocephalus
Paralichthys lethostigma                 3
Fundulus majalis                37      14
Alpheus heterochaelis                    1       3
Gobiosoma base                   3       2       7
Leiostomus xanthurus             1
Menidia menidia                 16       5      41
Anchoa hepsetus                 26       5       3
Callinectes similis             27       4      95
Stephanolepis hispidus           1               8
Gymnura micrura                                  1
Citharichthys spilopterus
Brevoortia tyrannus
Micropogonias undulatus
Syngnathus louisianae            3       1       2
Lagodon rhomboides               2
Lolliguncula brevis             27       8      37
Mugil cephalus
Farfantepenaeus aztecus         43      15      88
Chilomycterus schoepfi           3       2       7
Mugil curema                     4       8
Sphyrna tiburo
Synodus foetens                  2
Etropus crossotus                4               6
Cynoscion nebulosus              1       3       4
Selene vomer                     1               2
Prionotus tribulus               1               6
Blenniidae sp.                   1
Squilla sp.                      2       1
Hypsoblennius hentz              2
Menticirrhus americanus          7      27       2
Symphurus plagiusa              38               3
Litopenaeus setiferus           76     150      12
Dasyatis sabina                          1       1
Orthopristis chrysoptera                 1
Trinectes maculates                      1
Cynoscion regalis                        2
Chloroscombrus                          26       9
  chrysours
Sciaenops ocellatus                              1
Scomberomorus                                    1
  maculates
Trachinotusfalcatus                              2
Lutjanus griseus                                 5
Opisthonema oglinum                             23
Abudefduf saxatilis
Larimus fasciatus
Microgobius thalassinus
Ctenogobius boleosoma
Sphyraena guachancho
Eucinostomus gula
Diapterus auratus

                                  Fall

Species                     Oct   Nov   Dec

Anchoa mitchilli              84   196   --
Bairdiella chrysoura         --    --
Cyprinodon variegatus
  variegatus
Poecilia latipinna
Callinectes sapidus           25    10     7
Fundulus heteroclitus          2     3     1
Palaemonetes spp.            374   226   184
Strongylura marina
Paralichthys dentatus          1
Opsanustau                           1
Archosargus                         14     1
  probatocephalus
Paralichthys lethostigma
Fundulus majalis               5           9
Alpheus heterochaelis          1           1
Gobiosoma base                 1           1
Leiostomus xanthurus                 1
Menidia menidia               14    17     2
Anchoa hepsetus                1
Callinectes similis           44    10     1
Stephanolepis hispidus        13     6
Gymnura micrura
Citharichthys spilopterus      4
Brevoortia tyrannus
Micropogonias undulatus
Syngnathus louisianae          4     1
Lagodon rhomboides             1
Lolliguncula brevis           11    13
Mugil cephalus                       1     3
Farfantepenaeus aztecus       12    14
Chilomycterus schoepfi         5
Mugil curema                   1           1
Sphyrna tiburo
Synodus foetens
Etropus crossotus              4
Cynoscion nebulosus
Selene vomer
Prionotus tribulus            14     2
Blenniidae sp.
Squilla sp.
Hypsoblennius hentz
Menticirrhus americanus
Symphurus plagiusa            13     1
Litopenaeus setiferus         22     4
Dasyatis sabina
Orthopristis chrysoptera
Trinectes maculates
Cynoscion regalis
Chloroscombrus
  chrysours
Sciaenops ocellatus            2
Scomberomorus                  2
  maculates
Trachinotusfalcatus            2
Lutjanus griseus               2
Opisthonema oglinum            1
Abudefduf saxatilis            1
Larimus fasciatus              1
Microgobius thalassinus        1
Ctenogobius boleosoma          2
Sphyraena guachancho           2
Eucinostomus gula              4           1
Diapterus auratus                          1
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Article Details
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Author:Kingsley-Smith, Peter R.; Joyce, Ryan E.; Arnott, Stephen A.; Roumillat, William A.; McDonough, Chri
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:1USA
Date:Dec 1, 2012
Words:10669
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