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Marine debris impacts to a tidal fringing-marsh in North Carolina
Marine Pollution Bulletin 62 (2011) 2605–2610
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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Marine debris impacts to a tidal fringing-marsh in North Carolina Amy V. Uhrin ⇑, Jennifer Schellinger 1 National Oceanic and Atmospheric Administration, Center for Coastal Fisheries and Habitat Research, Beaufort, NC 28516, United States
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Keywords: Spartina alterniflora Marine debris Salt marsh Crab pots Vehicle tires North Carolina
We evaluated injuries to Spartina alterniflora by debris items common to North Carolina coastal waters as a function of debris type (wire blue crab pots, vehicle tires, and anthropogenic wood) and deployment duration, and monitored S. alterniflora recovery following debris removal. Injuries sustained by S. alterniflora and subsequent recovery, varied considerably between debris types. Differences were likely due to dissimilarities in the structure and composition of debris. Tires caused an immediate (within 3 weeks) and long-term impact to S. alterniflora; tire footprints remained devoid of vegetation 14 months postremoval. Conversely, crab pot impacts were not as abrupt and recovery was short-term (<10 months). We suggest that removal programs specifically target habitats that are susceptible to negative impacts (e.g., salt marsh) and prone to debris accumulation. Management would benefit from the inclusion of habitat information in removal databases. Published by Elsevier Ltd.
1. Introduction
ine habitats such as seagrass (Uhrin et al., 2005) and hard bottom (Lewis et al., 2009). Although the accumulation of natural tidal wrack and large woody debris has been shown to cause loss of vegetation (Reidenbaugh and Banta, 1980; Bertness and Ellison, 1987; MacLennan, 2005), the degree and duration of anthropogenic debris impacts are not well quantified in salt marsh habitats and could be a source of substantial loss of ecosystem services. Here, we examined the impact of three marine debris types (wire blue crab pots, vehicle tires, and anthropogenic wood) known for their prevalence in or near coastal North Carolina salt marshes as well as their perceived ability to create severe impact footprints following prolonged deployment (i.e., complete devegetation). Anthropogenic woody debris was found to be the dominant debris type (by weight) in local salt marsh debris surveys, typically characterized by sections of dock, duck blinds, pallets, construction debris, and poles from the local pound net fishery (Viehman et al., 2011). These sizable, heavy debris items often have severe impacts associated with them (i.e., complete devegetation; Viehman et al., 2011), similar to natural large woody debris in the Pacific Northwest (MacLennan, 2005). Negative habitat impacts resulting from prolonged deployment of passive fishing gear (e.g., traps and pots) and gear movement have been documented for a number of fisheries worldwide (Caribbean spiny lobster: Sheridan et al., 2003, 2005; Uhrin et al., 2005; Lewis et al., 2009; Caribbean fish species: Quandt, 1999; Appeldoorn et al., 2000; Sheridan et al., 2003, 2005; Norway lobster, brown crab, European lobster, common whelk: Eno et al., 2001; Dungeness crab: June and Antonelis, 2009). Derelict blue crab pots are often found in marsh tidal creeks (Lee, 2009) and occasionally on coastal North Carolina marsh islands (A. Uhrin, pers. obs.). Over 850,000 wire crab pots were reported in use in
Worldwide, salt marshes are among the most ubiquitous coastal wetlands; although plant community composition may differ around the globe, the basic structure and function of salt marshes is similar (Mitsch and Gosselink, 1986). On the east coast of the United States, tidal salt marshes extend southward from Maine to northern Florida. Salt marshes buffer wave energy, stabilize shorelines through sediment accumulation, provide habitat for a number of commercially important fish and shellfish species as well as migratory birds, contribute extensively to coastal primary and secondary production, filter contaminants from both the water column and sediments, and are both sources and sinks of nutrients (Mitsch and Gosselink, 1986; Wiegert and Freeman, 1990). Flooding of marshes at high tide and during storm events allows for the penetration of floating wrack and debris, which subsequently becomes stranded and accumulates in the marsh vegetation during ebb tide (Bertness and Ellison, 1987; Adam, 1990; MacLennan, 2005; Viehman et al., 2011). Stranded debris may shade or crush plants, as well as block access to substrate and influence vegetation zonation by taking up available space (MacLennan, 2005; Hood, 2007). Additionally, debris may be repeatedly dislodged and grounded during tidal cycles. This aperiodic movement of debris across the substrate may serve to increase the area of impact beyond the original debris footprint as has been shown for commercial spiny lobster traps in benthic mar⇑ Corresponding author. Tel.: +1 252 728 8778; fax: +1 252 838 0809. E-mail address: [email protected] (A.V. Uhrin). Present address: Florida State University, Department of Biological Science, Tallahassee, FL 32306, United States. 1
0025-326X/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.marpolbul.2011.10.006
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North Carolina waters in 1998, with an average annual loss rate of 17% (NCDMF, 2004). Given that blue crab pots have a benthic footprint of approximately 0.37 m2, crab pot losses create the potential for nearly 145,000 m2 of impacted habitats annually; however, the proportion of pots impacting salt marshes remains unknown. Vehicle tires often find their way onto salt marshes through a variety of sources. Private waterfront properties and communities sometimes use tires illegally for beach erosion control and shoreline stabilization, frequently in close proximity to fringing wetlands (Subramanian et al., 2008; A. Uhrin, pers. obs). Illegal dumping of tires has increased significantly in North Carolina since 1989, when the Scrap Tire Disposal Act banned the landfill disposal of whole scrap tires (NCDWM, 2000). Dumping activities can negatively impact habitats (EPA, 1998). In addition, approximately 100,000 tires have been removed from North Carolina beaches since 1989, presumably a product of failed artificial tire-reefs established in the mid-1970s and 1980s (AGSMFC, 2004). When tires settle in salt marsh habitats there is the potential for complete devegetation within the tire footprint over time (A. Uhrin, pers. obs.). To our knowledge, there are no studies quantifying the time frame for debris-induced injuries to salt marsh vegetation. This study establishes the time it takes for common types of coastal debris to inflict sustained injury to Spartina alterniflora Loisel (smooth cordgrass) as well as recovery from those injuries. To establish these values, the following null hypotheses were examined: (1) there were no differences in S. alterniflora stem densities and maximum stem heights among controls (no debris) and debris treatments within a given soak time (duration of time spent on the habitat); (2) there were no differences in the response of S. alterniflora to various debris types; and (3) provided that injury was sustained, there were no differences in the recovery trajectories exhibited as a function of debris type. 2. Methods This study was conducted between June 2008 and September 2009 within a tidal fringing-marsh shoreline (34.7204°N, 76.6741°W) located near the National Oceanic and Atmospheric Administration (NOAA) Center for Coastal Fisheries and Habitat Research (CCFHR) in Beaufort, North Carolina (Fig. 1; for a regional
map see Fig. 1 inset B in Viehman et al., 2011). Upper marsh vegetation included Spartina patens, Salicornia virginica, Distichlis spicata, and Juncus roemerianus. The lower marsh was characterized by an approximate 10 m band of S. alterniflora transitioning seaward into a low-sloping mudflat dominated by Crassostrea virginica beds. The impact of standard wire blue crab pots (herein referred to as crab pots; 0.61 0.61 m, 18 gauge plastic coated hex wire, 4.5 kg dry weight) and radial-style, vehicle tires (0.43 m rim diameter, 9.1–10.9 kg dry weight) during the summer growing period were investigated. We also attempted to examine two types of anthropogenic wood: 0.5 0.5 m plywood squares and 0.5 m lengths of 0.05 0.10 m (2’’ 4’’) lumber. Despite securing the wood with hooked rebar (steel reinforcing rod) stakes, both woody debris types were repeatedly dislodged during rising tides following initial deployment and so were permanently removed from their respective plots after 3 weeks post-deployment. No impacts to live stem density or live maximum stem height were apparent during the three-week period and no visible damage to S. alterniflora was observed to have been inflicted by the movement of the woody debris. In June 2008, seven replicates per debris type and an additional seven 0.25 m2 plots free of debris (controls) were randomly distributed along an approximate 75 m linear stretch of the lower marsh. Debris items were secured with rebar stakes flagged with survey tape, including a center stake to be used for monitoring purposes. A single rebar stake flagged with survey tape was installed in the center of the control plots. Plots were monitored weekly for impacts. At each monitoring event, debris items were carefully removed from their respective plots and the area within the footprint of the debris was evaluated by centering a 0.25 m2 PVC quadrat over the debris footprint (Fig. 2) and counting the number of live and dead S. alterniflora stems occurring within the quadrat. In addition, the height of the five tallest live stems (if any) was measured to the nearest 0.5 cm. Because tire footprints extended beyond a single, centered quadrat, at each monitoring event, two quadrats were haphazardly placed and sampled on either side of, centered to, and abutting the central rebar stake (Fig. 2). Measurements from these two quadrats were then averaged. Upon observation of a sustained (three consecutive monitoring events), statistically significant decline in live stem density and live maximum stem height, debris items were removed (Week 9 for vehicle tires and Week 13 for crab pots) and plots continued to be monitored for natural recovery using the methods described above. Plots were not monitored during the seasonal winter dieback (November 13, 2008 through April 3, 2009), except once in February 2009 to check experimental progress.
2.1. Data analysis
Fig. 1. Tidal fringing-marsh used in the current study, located near the National Oceanic and Atmospheric Administration (NOAA) Center for Coastal Fisheries and Habitat Research (CCFHR) in Beaufort, North Carolina. For a regional map, see Fig. 1 (inset B) in Viehman et al. (2011).
Comparisons of live stem density (scaled to 1 m2 values) and maximum live stem height were made between control and debris plots. Normality was tested using the Shapiro–Wilk test (Shapiro and Wilk, 1965). Bartlett’s test (Snedecor and Cochran, 1989) and the F-max test (Hartley, 1950) were used to test for homogeneity of variances. Transformations were unable to correct for assumption violations; therefore, non-parametric Wilcoxon–Mann– Whitney tests (two-sided; Wilcoxon, 1945; Mann and Whitney, 1947) were used for both variables. Preliminary Wilcoxon– Mann–Whitney tests (two-sided) were utilized to determine initiation of impacts (first time period with significant differences). All statistical analyses were performed using SAS Version 9.1.3 (PROC NPAR1WAY; SAS, 2002).
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Fig. 2. Typical placement of the sampling quadrats for crab pot (top) and vehicle tire plots (bottom). The stabilizing rebar stakes in the top photo were located at opposing pot corners. The rebar stake located in the center of the tire was removed for the photo; however, pink flagging tape denotes its location. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3. Results Ambient live stem densities and maximum live stem heights for S. alterniflora (i.e., control plot averages) were within ranges reported for comparable natural salt marsh habitat in the region with similar patterns of seasonality (Hettler, 1989; Currin et al., 2008). We observed that crab pots and vehicle tires resting on top of S. alterniflora for extended periods caused stems to become broken or abraded. In the tire footprints, stems were also crushed into the underlying sediments, likely suffocating the plants and leading to eventual senescence of above-ground biomass and complete loss of vegetation. After 8 weeks of crab pot deployment (June 11 to August 6, 2008), an initial significant decline in maximum live stem height was observed for S. alterniflora versus control plots (30%; p = 0.0297; Fig. 3). A significant decline in S. alterniflora live stem density (56.4%; p = 0.0152; Fig. 3) was not observed until Week 11 post-deployment (August 27, 2008); live stem densities remained significantly depressed through Weeks 12 and 13 (p = 0.0033 and 0.0106; Fig. 3). Following their initial decline at Week 8, maximum live stem heights remained significantly depressed during each monitoring event through Week 13 (p = 0.0021; Fig. 3). At Week 13 (September 10, 2008), all crab pots
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Fig. 3. Live stem density (# live stems/m2; top) and maximum stem height (cm; bottom) as a function of debris deployment time (means; error bars = SEs; N = 7).
were removed, and their respective plots were then monitored for recovery beginning the following week. At the time of crab pot removal, maximum live stem height and live stem density had declined by 57.3% and 67.4% respectively, relative to the control plots (Fig. 3). Following crab pot removal, maximum live stem heights had recovered to control values at Week 22 post-removal (February 12, 2009; p = 0.1747; Fig. 4), with both plot types exhibiting a seasonal decline. Following the winter die-back, maximum live stem heights for both crab pot and control plots continually increased through the spring and summer of 2009. No significant differences were observed for the remainder of the study (up to Week 52; September 4, 2009; Fig. 4) with the exception of Week 33 when crab pot plots exhibited a short-lived decline (April 23, 2009; p = 0.0298; Fig. 4). Conversely, live stem densities remained depressed until Week 42 post-removal (June 25, 2009), at which point live stem densities were not significantly different from controls (p = 0.0960; Fig. 4), a trend that continued throughout the remainder of the study. After only 3 weeks of tire deployment (June 11 to July 2, 2008), S. alterniflora exhibited a significant decline in live stem density compared to control values (53.8% loss; p = 0.0021; Fig. 3). This decline was sustained through Week 9 (August 13, 2008; 60.5% loss; p = 0.0072; Fig. 3) when in fact all marsh grass located within the direct footprint of the tires had been completely killed. Despite 100% loss in the tire footprints, live grass which had escaped direct
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Fig. 4. Live stem density (# live stems/m2; top) and maximum stem height (cm; bottom) following removal of wire crab pots (means; error bars = SEs; N = 7). The data gap from November 13, 2008 through April 3, 2009 indicates the winter marsh die-off during which time the plots were not continuously monitored.
impact from the tires, remained present within the centers of tires (Fig. 2). The nature of our sampling design included measurements from these plants and masked the true effect of complete loss of vegetation from within tire footprints (i.e., where live stem density was zero and therefore maximum live stem height was zero), thereby constraining our ability to accurately assess tire impacts. At Week 9, maximum live stem heights remained not significantly different from control plots (p = 0.2502; Fig. 3). Given 100% mortality in the tire footprints and the uncertainty that the live center plants would exhibit stem height differences before the natural seasonal decline, the tires were removed at Week 9 and the plots were monitored for recovery beginning the following week (Fig. 5). Following tire removal, live stem densities within the tire footprint showed no signs of recovery throughout the remainder of the study (up to Week 56; September 4, 2009; Fig. 5); despite the continued presence of S. alterniflora within the centers of tires, the footprints remained devoid of vegetation. Although live stem densities of plants from within the tire centers were not significantly different than control plots at Weeks 49 and 53 post-removal (July 16 and August 14, 2009; p = 0.4428 and 0.1585, respectively; Fig. 5), this recovery was short-lived as significant declines were found during subsequent monitoring events through the end of the study (Week 56; p = 0.0389). An immediate significant decline in maximum live stem height occurred the first week following tire removal (August 20, 2008; p = 0.0106; Fig. 5) and maximum live
Fig. 5. Live stem density (# live stems/m2; top) and maximum stem height (cm; bottom) following removal of rubber vehicle tires (means; error bars = SEs; N = 7). The data gap from November 13, 2008 through April 3, 2009 indicates the winter marsh die-off during which time the plots were not continuously monitored.
stem heights continued to decline leading into the winter die-off (through February 12, 2009; p = 0.0409; Fig. 5). As the spring monitoring progressed, live stem heights oscillated between values similar to controls and values significantly less than controls, but appeared to stabilize by Week 45 post-removal (June 19, 2009; p = 0.6093; Fig. 5). Maximum live stem heights remained similar to controls through the remainder of the study period with each plot exhibiting continually increasing live stem heights through Week 56.
4. Discussion This study demonstrates the potential for marine debris, specifically wire blue crab pots and especially vehicle tires, to negatively impact S. alterniflora in coastal North Carolina. Our observations show that crab pots and vehicle tires resting on top of marsh grass for extended periods cause stems and blades to become broken or abraded, which may disrupt normal function. Stems and blades are also crushed into the underlying sediments, likely suffocating the plants and leading to eventual senescence of above-ground biomass. Because salt marsh grasses buffer wave energy, stabilize sediments, prevent erosion, and recycle nutrients, impacts from debris leading to plant loss or changes in plant density may reduce these functions on a local scale (Mitsch and Gosselink, 1986; Möller and Spencer, 2002; Widdows et al., 2008). Salt marsh grasses also serve
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as habitat, refuge, and food for a number of ecologically and commercially important species (see reviews by Craig and Crowder, 2000 and Levin and Talley, 2000). Changes in vegetation resulting from debris impacts may influence faunal abundance and distribution, resource availability, and food web linkages (Pennings et al., 1998; Levin and Talley, 2000; Parker et al., 2008). Injuries sustained by S. alterniflora and the subsequent recovery thereof varied considerably between the two debris types. Vehicle tires, the heavier of the debris, were observed to crush plants into the sediment, leading to breakage, suffocation (presumed), and eventual death and senescence of all plants within the direct tire footprint by Week 9. Conversely, the comparatively lightweight, open structure of crab pots reduced the level of physical compression of stems. Initially, vertical stem growth may have been inhibited by the hex wire of the bottom of the crab pot (i.e., stems would have to fit through an individual hexagon) with the ability to rebound following pot removal. The hex wire sides of crab pots also permit light penetration, which may have delayed impact responses due to the ability of the plants to continue to photosynthesize compared to complete blockage of incident radiation within tire footprints. The lack of plant recovery from within tire footprints by the end of the study period indicates an immediate and long-term (>1 year) impact to S. alterniflora. Factors not investigated here which may contribute to impacts include belowground damage to rhizomes/roots, disruption of clonal integration, and toxicity to plants resulting from tire leachates. Progress has been made to reduce unwanted tire debris. As of 2009, nearly 9 million tires have been cleared from illegal dump sites in North Carolina (NCDENR, 2010). While removal programs in North Carolina have consistently reduced the amount of tire debris in the environment, we suggest that these programs specifically target habitats that are susceptible to negative impacts (e.g., salt marsh) and prone to tire accumulation. Management could also be enhanced by the inclusion of habitat information in association with debris abundance data in removal databases which would serve to direct future conservation efforts towards especially vulnerable habitats. For example, although North Carolina Big Sweep provides cleanup data by county, miles of shoreline cleared, and debris type, no habitat information is appended (OC, 2010). On a number of occasions during initial site reconnaissance and as part of salt marsh debris surveys conducted by Viehman et al. (2011), we observed derelict crab pots to be completely overgrown with S. alterniflora, to a point where the pot was unidentifiable and had been visually and physically incorporated into the marsh landscape (A. Uhrin, pers. obs.). These pots were so bound by vegetation that attempts at extraction often resulted in damage to the plants, including uprooting (A. Uhrin, pers. obs.). These crab pot ‘‘hummocks’’ appear to add structure to the marsh landscape which may provide habitat for some fauna. However, if the overgrown pots are situated at the edge of a marsh and subject to erosion from waves and currents, plants may be more readily dislodged due to their being entwined with the pot structure. We theorize that plants associated with these overgrown pots may also be more susceptible to uprooting during high wind events such as tropical storms and hurricanes, however, those dynamics were not examined here. Although S. alterniflora was negatively impacted by crab pots as a function of deployment duration, the effects were short-term (<10 months). Given the ability of S. alterniflora to recover from crab pot impacts, the potential incorporation of pots into the overall marsh landscape, the reduced numbers of pots observed to be stranded in the marsh interior (versus tidal creeks adjacent to marshes; Lee, 2009), and the potential for crab pot ‘‘hummocks’’ to enhance habitat structure, we conclude that derelict crab pots do not pose an immediate, direct threat to S. alterniflora in this
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region. We suspect that removal efforts would be better served by focusing on derelict pots that remain submerged and continue to fish, with resulting high blue crab and bycatch mortality rates (Guillory et al., 2001; NCDMF, 2004; Poon, 2005; Havens et al., 2008). In 2004, in recognition of bycatch impacts stemming from prolonged deployment of submerged gear, the North Carolina Division of Marine Fisheries shortened the crab pot attendance period from 7 to 5 days and extended the pot cleanup period by 9 days (NCDMF, 2004). In addition to bycatch issues, submerged derelict crab pots may impact benthic habitats including locally prominent seagrass beds composed of Zostera marina (eelgrass). Although individual crab pots have a relatively small benthic footprint (0.37 m2), the large numbers of pots that are lost annually may result in cumulative effects to submerged aquatic vegetation (Stephan et al., 2000), and movement of derelict pots during storm events may create paths of seagrass damage or completely denuded patches as has been shown for spiny lobster traps in south Florida (Uhrin et al., 2005). Tidal currents are known to create scour areas that are devoid of vegetation around derelict wire Dungeness crab pots found in Puget Sound eelgrass beds, and obvious pot footprints with little or no eelgrass present have been observed following pot removal (June and Antonelis, 2009). Conversely, wire blue crab pots experimentally-deployed on unvegetated substrate serve as immediate habitat for fouling organisms with subsequent usage of the encrusted pots by motile species (Havens et al., 2008; Manley et al., 2009). Although the encrusted pots continue to trap organisms, Havens et al. (2008) suggest eventual pot degradation (>1 year) such that confinement potential ceases and the pots serve entirely as habitat (Havens et al., 2008). Due to local substrate limitations, a number of states in the southeastern United States are examining the efficacy of using derelict crab pots as a foundation substrate in oyster restoration (Brumbaugh et al., 2009; Manley et al., 2009; Kreutzer, 2010; Joel Fodrie, pers. com.). Anthropogenic woody debris was found to be the dominant debris type (by weight) in local salt marsh debris surveys, typically characterized by sections of dock, duck blinds, pallets, construction debris, and poles from the local pound net fishery (Viehman et al., 2011). These sizable, heavy debris items often have severe impacts associated with them (i.e., complete devegetation; Viehman et al., 2011) similar to natural, large woody debris in salt marshes of the Pacific Northwest (MacLennan, 2005). Repeated dislodgement of the lumber pieces used in the current study prevented a thorough evaluation of this debris type, and suggest that perhaps any impacts associated with small woody debris would result from debris movement as opposed to debris stranding. The disturbance and recovery dynamics of impacts from large, anthropogenic, woody debris warrant further examination in this region.
Acknowledgments This study was funded by the NOAA Marine Debris Program as well as additional direct support from the NOAA National Centers for Coastal Ocean Science. We remember D. Ahrenholz and appreciate his generous donation of the crab pots used in this study. We thank the North Carolina Division of Marine Fisheries for providing the vehicle tires. We acknowledge the efforts of V. McDonough, J. Vander Pluym, S. Viehman, and P. Whitfield on proposal submissions. This work would not have been possible without additional field, technical, and administrative support from C. Currin, G. Fisher, L. Goshe, B. Harrison, M. LaCroix, S. Leahy, D. Meyer, K. Rudd, K. Strauss, C. Taylor, B. Tiedeman, J. Vander Pluym, S. Viehman, and P. Whitfield. We would like to thank P. Delano, M. Fonseca, D. Johnson, P. Marraro, J. Vander Pluym, S. Viehman, P. Whitfield, and the anonymous journal reviewers for critiquing the manuscript.
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Mann, H.B., Whitney, D.R., 1947. On a test of whether one of two random variables is stochastically larger than the other. Annals of Mathematical Statistics 18, 50– 60. Mitsch, W.J., Gosselink, J.G., 1986. Wetlands. Van Nostrand Reinhold Inc., New York, p. 539. Möller, I., Spencer, T., 2002. Wave dissipation over macro-tidal saltmarshes: effects of marsh edge typology and vegetation change. Journal of Coastal Research SI 36, 506–521. NCDENR (North Carolina Department of Environment and Natural Resources), 2010. North Carolina solid waste management annual report: FY 2008–2009. North Carolina Department of Environment and Natural Resources, Raleigh, North Carolina. Available at: (accessed 3.10.11). NCDMF (North Carolina Division of Marine Fisheries), 2004. North Carolina fishery management plan: blue crab. North Carolina Department of Environment and Natural Resources, Division of Marine Fisheries, Morehead City, North Carolina. Available at: (accessed 3.10.11). NCDWM (North Carolina Division of Waste Management). 2000. Scrap tire management special report. North Carolina Department of Environment and Natural Resources, Division of Waste Management, Raleigh, North Carolina. Available at: (accessed 3.10.10). OC (Ocean Conservancy), 2010. International Coastal Cleanup 2010 report: trash travels. Ocean Conservancy, Washington DC. Available at: (accessed 3.10.11). Parker, J.D., Montoya, J.P., Hay, M.E., 2008. A specialist detritivore links Spartina alterniflora to salt marsh food webs. Marine Ecology Progress Series 364, 87–95. Pennings, S.C., Carefoot, T.H., Siska, E.L., Chase, M.E., Page, T.A., 1998. Feeding preference of a generalist salt-marsh crab: relative importance of multiple plant traits. Ecology 79, 1968–1979. Poon, A.M., 2005. Haunted waters: an estimate of ghost fishing of crabs and lobsters by traps. M.S. Thesis, The University of British Columbia, Vancouver, British Columbia, Canada, p. 135. Quandt, A., 1999. Assessment of fish trap damage on coral reefs around St. Thomas, USVI. University of the Virgin Islands, St. Thomas, USVI, unpublished report, p. 11. Reidenbaugh, T.G., Banta, W.C., 1980. Origin and effects of Spartina wrack in a Virginia salt marsh. Gulf Research Reports 6 (4), 393–401. SAS Institute Inc., 2002. SAS 9.1.3 software package. SAS Institute, Cary, North Carolina. Shapiro, S.S., Wilk, M.B., 1965. An analysis of variance test for normality (complete samples). Biometrika 52 (3–4), 591–611. Sheridan, P., Hill, R., Matthews, G., Appeldoorn, R., 2003. The effects of trap fishing in coralline habitats: What do we know? How do we learn more? Proceedings of the Gulf and Caribbean Fisheries Institute 54, 1–12. Sheridan, P., Hill, R., Matthews, G., Appeldoorn, R., Kojis, B., Matthews, T., 2005. Does trap fishing impact coral reef ecosystems? An update. Proceedings of the Gulf and Caribbean Fisheries Institute 56, 511–519. Snedecor, G.W., Cochran, W.G., 1989. Statistical Methods, eighth ed. Iowa State University Press, Ames, Iowa, p. 593. Stephan, C.D., Peuser, R.I., Fonseca, M.S., 2000. Evaluating fishing gear impacts to submerged aquatic vegetation and determining mitigation strategies. Atlantic States Marine Fisheries Commission, ASMFC Habitat Management Series Number 5. Atlantic States Marine Fisheries Commission, Washington, D.C., p. 38. Available at: (accessed 3.10.10). Uhrin, A.V., Fonseca, M.S., DiDomenico, G.P., 2005. Effect of Caribbean spiny lobster traps on seagrass beds of the Florida Keys National Marine Sanctuary: damage assessment and evaluation of recovery. American Fisheries Society Symposium 41, 579–588. Viehman, S., Vander Pluym, J., Schellinger, J., 2011. Characterization of marine debris in North Carolina salt marshes. Marine Pollution Bulletin 62, 2771–2779. Widdows, J., Pope, N.D., Brinsley, M.D., 2008. Effect of Spartina anglica stems on near-bed hydrodynamics, sediment erodability and morphological changes on an intertidal mudflat. Marine Ecology Progress Series 362, 45–57. Wiegert, R.G., Freeman, B.J., 1990. Tidal salt marshes of the southeast Atlantic coast: a community profile. US Fish and Wildlife Service Biological Report 85(7.29). US Department of Interior, Fish and Wildlife Service, Washington, D.C., p. 70. Available at: (accessed 3.10.11). Wilcoxon, F., 1945. Individual comparisons by ranking methods. Biometrics Bulletin 1, 80–83.
Contents lists available at SciVerse ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Marine debris impacts to a tidal fringing-marsh in North Carolina Amy V. Uhrin ⇑, Jennifer Schellinger 1 National Oceanic and Atmospheric Administration, Center for Coastal Fisheries and Habitat Research, Beaufort, NC 28516, United States
a r t i c l e
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a b s t r a c t
Keywords: Spartina alterniflora Marine debris Salt marsh Crab pots Vehicle tires North Carolina
We evaluated injuries to Spartina alterniflora by debris items common to North Carolina coastal waters as a function of debris type (wire blue crab pots, vehicle tires, and anthropogenic wood) and deployment duration, and monitored S. alterniflora recovery following debris removal. Injuries sustained by S. alterniflora and subsequent recovery, varied considerably between debris types. Differences were likely due to dissimilarities in the structure and composition of debris. Tires caused an immediate (within 3 weeks) and long-term impact to S. alterniflora; tire footprints remained devoid of vegetation 14 months postremoval. Conversely, crab pot impacts were not as abrupt and recovery was short-term (<10 months). We suggest that removal programs specifically target habitats that are susceptible to negative impacts (e.g., salt marsh) and prone to debris accumulation. Management would benefit from the inclusion of habitat information in removal databases. Published by Elsevier Ltd.
1. Introduction
ine habitats such as seagrass (Uhrin et al., 2005) and hard bottom (Lewis et al., 2009). Although the accumulation of natural tidal wrack and large woody debris has been shown to cause loss of vegetation (Reidenbaugh and Banta, 1980; Bertness and Ellison, 1987; MacLennan, 2005), the degree and duration of anthropogenic debris impacts are not well quantified in salt marsh habitats and could be a source of substantial loss of ecosystem services. Here, we examined the impact of three marine debris types (wire blue crab pots, vehicle tires, and anthropogenic wood) known for their prevalence in or near coastal North Carolina salt marshes as well as their perceived ability to create severe impact footprints following prolonged deployment (i.e., complete devegetation). Anthropogenic woody debris was found to be the dominant debris type (by weight) in local salt marsh debris surveys, typically characterized by sections of dock, duck blinds, pallets, construction debris, and poles from the local pound net fishery (Viehman et al., 2011). These sizable, heavy debris items often have severe impacts associated with them (i.e., complete devegetation; Viehman et al., 2011), similar to natural large woody debris in the Pacific Northwest (MacLennan, 2005). Negative habitat impacts resulting from prolonged deployment of passive fishing gear (e.g., traps and pots) and gear movement have been documented for a number of fisheries worldwide (Caribbean spiny lobster: Sheridan et al., 2003, 2005; Uhrin et al., 2005; Lewis et al., 2009; Caribbean fish species: Quandt, 1999; Appeldoorn et al., 2000; Sheridan et al., 2003, 2005; Norway lobster, brown crab, European lobster, common whelk: Eno et al., 2001; Dungeness crab: June and Antonelis, 2009). Derelict blue crab pots are often found in marsh tidal creeks (Lee, 2009) and occasionally on coastal North Carolina marsh islands (A. Uhrin, pers. obs.). Over 850,000 wire crab pots were reported in use in
Worldwide, salt marshes are among the most ubiquitous coastal wetlands; although plant community composition may differ around the globe, the basic structure and function of salt marshes is similar (Mitsch and Gosselink, 1986). On the east coast of the United States, tidal salt marshes extend southward from Maine to northern Florida. Salt marshes buffer wave energy, stabilize shorelines through sediment accumulation, provide habitat for a number of commercially important fish and shellfish species as well as migratory birds, contribute extensively to coastal primary and secondary production, filter contaminants from both the water column and sediments, and are both sources and sinks of nutrients (Mitsch and Gosselink, 1986; Wiegert and Freeman, 1990). Flooding of marshes at high tide and during storm events allows for the penetration of floating wrack and debris, which subsequently becomes stranded and accumulates in the marsh vegetation during ebb tide (Bertness and Ellison, 1987; Adam, 1990; MacLennan, 2005; Viehman et al., 2011). Stranded debris may shade or crush plants, as well as block access to substrate and influence vegetation zonation by taking up available space (MacLennan, 2005; Hood, 2007). Additionally, debris may be repeatedly dislodged and grounded during tidal cycles. This aperiodic movement of debris across the substrate may serve to increase the area of impact beyond the original debris footprint as has been shown for commercial spiny lobster traps in benthic mar⇑ Corresponding author. Tel.: +1 252 728 8778; fax: +1 252 838 0809. E-mail address: [email protected] (A.V. Uhrin). Present address: Florida State University, Department of Biological Science, Tallahassee, FL 32306, United States. 1
0025-326X/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.marpolbul.2011.10.006
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North Carolina waters in 1998, with an average annual loss rate of 17% (NCDMF, 2004). Given that blue crab pots have a benthic footprint of approximately 0.37 m2, crab pot losses create the potential for nearly 145,000 m2 of impacted habitats annually; however, the proportion of pots impacting salt marshes remains unknown. Vehicle tires often find their way onto salt marshes through a variety of sources. Private waterfront properties and communities sometimes use tires illegally for beach erosion control and shoreline stabilization, frequently in close proximity to fringing wetlands (Subramanian et al., 2008; A. Uhrin, pers. obs). Illegal dumping of tires has increased significantly in North Carolina since 1989, when the Scrap Tire Disposal Act banned the landfill disposal of whole scrap tires (NCDWM, 2000). Dumping activities can negatively impact habitats (EPA, 1998). In addition, approximately 100,000 tires have been removed from North Carolina beaches since 1989, presumably a product of failed artificial tire-reefs established in the mid-1970s and 1980s (AGSMFC, 2004). When tires settle in salt marsh habitats there is the potential for complete devegetation within the tire footprint over time (A. Uhrin, pers. obs.). To our knowledge, there are no studies quantifying the time frame for debris-induced injuries to salt marsh vegetation. This study establishes the time it takes for common types of coastal debris to inflict sustained injury to Spartina alterniflora Loisel (smooth cordgrass) as well as recovery from those injuries. To establish these values, the following null hypotheses were examined: (1) there were no differences in S. alterniflora stem densities and maximum stem heights among controls (no debris) and debris treatments within a given soak time (duration of time spent on the habitat); (2) there were no differences in the response of S. alterniflora to various debris types; and (3) provided that injury was sustained, there were no differences in the recovery trajectories exhibited as a function of debris type. 2. Methods This study was conducted between June 2008 and September 2009 within a tidal fringing-marsh shoreline (34.7204°N, 76.6741°W) located near the National Oceanic and Atmospheric Administration (NOAA) Center for Coastal Fisheries and Habitat Research (CCFHR) in Beaufort, North Carolina (Fig. 1; for a regional
map see Fig. 1 inset B in Viehman et al., 2011). Upper marsh vegetation included Spartina patens, Salicornia virginica, Distichlis spicata, and Juncus roemerianus. The lower marsh was characterized by an approximate 10 m band of S. alterniflora transitioning seaward into a low-sloping mudflat dominated by Crassostrea virginica beds. The impact of standard wire blue crab pots (herein referred to as crab pots; 0.61 0.61 m, 18 gauge plastic coated hex wire, 4.5 kg dry weight) and radial-style, vehicle tires (0.43 m rim diameter, 9.1–10.9 kg dry weight) during the summer growing period were investigated. We also attempted to examine two types of anthropogenic wood: 0.5 0.5 m plywood squares and 0.5 m lengths of 0.05 0.10 m (2’’ 4’’) lumber. Despite securing the wood with hooked rebar (steel reinforcing rod) stakes, both woody debris types were repeatedly dislodged during rising tides following initial deployment and so were permanently removed from their respective plots after 3 weeks post-deployment. No impacts to live stem density or live maximum stem height were apparent during the three-week period and no visible damage to S. alterniflora was observed to have been inflicted by the movement of the woody debris. In June 2008, seven replicates per debris type and an additional seven 0.25 m2 plots free of debris (controls) were randomly distributed along an approximate 75 m linear stretch of the lower marsh. Debris items were secured with rebar stakes flagged with survey tape, including a center stake to be used for monitoring purposes. A single rebar stake flagged with survey tape was installed in the center of the control plots. Plots were monitored weekly for impacts. At each monitoring event, debris items were carefully removed from their respective plots and the area within the footprint of the debris was evaluated by centering a 0.25 m2 PVC quadrat over the debris footprint (Fig. 2) and counting the number of live and dead S. alterniflora stems occurring within the quadrat. In addition, the height of the five tallest live stems (if any) was measured to the nearest 0.5 cm. Because tire footprints extended beyond a single, centered quadrat, at each monitoring event, two quadrats were haphazardly placed and sampled on either side of, centered to, and abutting the central rebar stake (Fig. 2). Measurements from these two quadrats were then averaged. Upon observation of a sustained (three consecutive monitoring events), statistically significant decline in live stem density and live maximum stem height, debris items were removed (Week 9 for vehicle tires and Week 13 for crab pots) and plots continued to be monitored for natural recovery using the methods described above. Plots were not monitored during the seasonal winter dieback (November 13, 2008 through April 3, 2009), except once in February 2009 to check experimental progress.
2.1. Data analysis
Fig. 1. Tidal fringing-marsh used in the current study, located near the National Oceanic and Atmospheric Administration (NOAA) Center for Coastal Fisheries and Habitat Research (CCFHR) in Beaufort, North Carolina. For a regional map, see Fig. 1 (inset B) in Viehman et al. (2011).
Comparisons of live stem density (scaled to 1 m2 values) and maximum live stem height were made between control and debris plots. Normality was tested using the Shapiro–Wilk test (Shapiro and Wilk, 1965). Bartlett’s test (Snedecor and Cochran, 1989) and the F-max test (Hartley, 1950) were used to test for homogeneity of variances. Transformations were unable to correct for assumption violations; therefore, non-parametric Wilcoxon–Mann– Whitney tests (two-sided; Wilcoxon, 1945; Mann and Whitney, 1947) were used for both variables. Preliminary Wilcoxon– Mann–Whitney tests (two-sided) were utilized to determine initiation of impacts (first time period with significant differences). All statistical analyses were performed using SAS Version 9.1.3 (PROC NPAR1WAY; SAS, 2002).
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Fig. 2. Typical placement of the sampling quadrats for crab pot (top) and vehicle tire plots (bottom). The stabilizing rebar stakes in the top photo were located at opposing pot corners. The rebar stake located in the center of the tire was removed for the photo; however, pink flagging tape denotes its location. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3. Results Ambient live stem densities and maximum live stem heights for S. alterniflora (i.e., control plot averages) were within ranges reported for comparable natural salt marsh habitat in the region with similar patterns of seasonality (Hettler, 1989; Currin et al., 2008). We observed that crab pots and vehicle tires resting on top of S. alterniflora for extended periods caused stems to become broken or abraded. In the tire footprints, stems were also crushed into the underlying sediments, likely suffocating the plants and leading to eventual senescence of above-ground biomass and complete loss of vegetation. After 8 weeks of crab pot deployment (June 11 to August 6, 2008), an initial significant decline in maximum live stem height was observed for S. alterniflora versus control plots (30%; p = 0.0297; Fig. 3). A significant decline in S. alterniflora live stem density (56.4%; p = 0.0152; Fig. 3) was not observed until Week 11 post-deployment (August 27, 2008); live stem densities remained significantly depressed through Weeks 12 and 13 (p = 0.0033 and 0.0106; Fig. 3). Following their initial decline at Week 8, maximum live stem heights remained significantly depressed during each monitoring event through Week 13 (p = 0.0021; Fig. 3). At Week 13 (September 10, 2008), all crab pots
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Fig. 3. Live stem density (# live stems/m2; top) and maximum stem height (cm; bottom) as a function of debris deployment time (means; error bars = SEs; N = 7).
were removed, and their respective plots were then monitored for recovery beginning the following week. At the time of crab pot removal, maximum live stem height and live stem density had declined by 57.3% and 67.4% respectively, relative to the control plots (Fig. 3). Following crab pot removal, maximum live stem heights had recovered to control values at Week 22 post-removal (February 12, 2009; p = 0.1747; Fig. 4), with both plot types exhibiting a seasonal decline. Following the winter die-back, maximum live stem heights for both crab pot and control plots continually increased through the spring and summer of 2009. No significant differences were observed for the remainder of the study (up to Week 52; September 4, 2009; Fig. 4) with the exception of Week 33 when crab pot plots exhibited a short-lived decline (April 23, 2009; p = 0.0298; Fig. 4). Conversely, live stem densities remained depressed until Week 42 post-removal (June 25, 2009), at which point live stem densities were not significantly different from controls (p = 0.0960; Fig. 4), a trend that continued throughout the remainder of the study. After only 3 weeks of tire deployment (June 11 to July 2, 2008), S. alterniflora exhibited a significant decline in live stem density compared to control values (53.8% loss; p = 0.0021; Fig. 3). This decline was sustained through Week 9 (August 13, 2008; 60.5% loss; p = 0.0072; Fig. 3) when in fact all marsh grass located within the direct footprint of the tires had been completely killed. Despite 100% loss in the tire footprints, live grass which had escaped direct
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Fig. 4. Live stem density (# live stems/m2; top) and maximum stem height (cm; bottom) following removal of wire crab pots (means; error bars = SEs; N = 7). The data gap from November 13, 2008 through April 3, 2009 indicates the winter marsh die-off during which time the plots were not continuously monitored.
impact from the tires, remained present within the centers of tires (Fig. 2). The nature of our sampling design included measurements from these plants and masked the true effect of complete loss of vegetation from within tire footprints (i.e., where live stem density was zero and therefore maximum live stem height was zero), thereby constraining our ability to accurately assess tire impacts. At Week 9, maximum live stem heights remained not significantly different from control plots (p = 0.2502; Fig. 3). Given 100% mortality in the tire footprints and the uncertainty that the live center plants would exhibit stem height differences before the natural seasonal decline, the tires were removed at Week 9 and the plots were monitored for recovery beginning the following week (Fig. 5). Following tire removal, live stem densities within the tire footprint showed no signs of recovery throughout the remainder of the study (up to Week 56; September 4, 2009; Fig. 5); despite the continued presence of S. alterniflora within the centers of tires, the footprints remained devoid of vegetation. Although live stem densities of plants from within the tire centers were not significantly different than control plots at Weeks 49 and 53 post-removal (July 16 and August 14, 2009; p = 0.4428 and 0.1585, respectively; Fig. 5), this recovery was short-lived as significant declines were found during subsequent monitoring events through the end of the study (Week 56; p = 0.0389). An immediate significant decline in maximum live stem height occurred the first week following tire removal (August 20, 2008; p = 0.0106; Fig. 5) and maximum live
Fig. 5. Live stem density (# live stems/m2; top) and maximum stem height (cm; bottom) following removal of rubber vehicle tires (means; error bars = SEs; N = 7). The data gap from November 13, 2008 through April 3, 2009 indicates the winter marsh die-off during which time the plots were not continuously monitored.
stem heights continued to decline leading into the winter die-off (through February 12, 2009; p = 0.0409; Fig. 5). As the spring monitoring progressed, live stem heights oscillated between values similar to controls and values significantly less than controls, but appeared to stabilize by Week 45 post-removal (June 19, 2009; p = 0.6093; Fig. 5). Maximum live stem heights remained similar to controls through the remainder of the study period with each plot exhibiting continually increasing live stem heights through Week 56.
4. Discussion This study demonstrates the potential for marine debris, specifically wire blue crab pots and especially vehicle tires, to negatively impact S. alterniflora in coastal North Carolina. Our observations show that crab pots and vehicle tires resting on top of marsh grass for extended periods cause stems and blades to become broken or abraded, which may disrupt normal function. Stems and blades are also crushed into the underlying sediments, likely suffocating the plants and leading to eventual senescence of above-ground biomass. Because salt marsh grasses buffer wave energy, stabilize sediments, prevent erosion, and recycle nutrients, impacts from debris leading to plant loss or changes in plant density may reduce these functions on a local scale (Mitsch and Gosselink, 1986; Möller and Spencer, 2002; Widdows et al., 2008). Salt marsh grasses also serve
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as habitat, refuge, and food for a number of ecologically and commercially important species (see reviews by Craig and Crowder, 2000 and Levin and Talley, 2000). Changes in vegetation resulting from debris impacts may influence faunal abundance and distribution, resource availability, and food web linkages (Pennings et al., 1998; Levin and Talley, 2000; Parker et al., 2008). Injuries sustained by S. alterniflora and the subsequent recovery thereof varied considerably between the two debris types. Vehicle tires, the heavier of the debris, were observed to crush plants into the sediment, leading to breakage, suffocation (presumed), and eventual death and senescence of all plants within the direct tire footprint by Week 9. Conversely, the comparatively lightweight, open structure of crab pots reduced the level of physical compression of stems. Initially, vertical stem growth may have been inhibited by the hex wire of the bottom of the crab pot (i.e., stems would have to fit through an individual hexagon) with the ability to rebound following pot removal. The hex wire sides of crab pots also permit light penetration, which may have delayed impact responses due to the ability of the plants to continue to photosynthesize compared to complete blockage of incident radiation within tire footprints. The lack of plant recovery from within tire footprints by the end of the study period indicates an immediate and long-term (>1 year) impact to S. alterniflora. Factors not investigated here which may contribute to impacts include belowground damage to rhizomes/roots, disruption of clonal integration, and toxicity to plants resulting from tire leachates. Progress has been made to reduce unwanted tire debris. As of 2009, nearly 9 million tires have been cleared from illegal dump sites in North Carolina (NCDENR, 2010). While removal programs in North Carolina have consistently reduced the amount of tire debris in the environment, we suggest that these programs specifically target habitats that are susceptible to negative impacts (e.g., salt marsh) and prone to tire accumulation. Management could also be enhanced by the inclusion of habitat information in association with debris abundance data in removal databases which would serve to direct future conservation efforts towards especially vulnerable habitats. For example, although North Carolina Big Sweep provides cleanup data by county, miles of shoreline cleared, and debris type, no habitat information is appended (OC, 2010). On a number of occasions during initial site reconnaissance and as part of salt marsh debris surveys conducted by Viehman et al. (2011), we observed derelict crab pots to be completely overgrown with S. alterniflora, to a point where the pot was unidentifiable and had been visually and physically incorporated into the marsh landscape (A. Uhrin, pers. obs.). These pots were so bound by vegetation that attempts at extraction often resulted in damage to the plants, including uprooting (A. Uhrin, pers. obs.). These crab pot ‘‘hummocks’’ appear to add structure to the marsh landscape which may provide habitat for some fauna. However, if the overgrown pots are situated at the edge of a marsh and subject to erosion from waves and currents, plants may be more readily dislodged due to their being entwined with the pot structure. We theorize that plants associated with these overgrown pots may also be more susceptible to uprooting during high wind events such as tropical storms and hurricanes, however, those dynamics were not examined here. Although S. alterniflora was negatively impacted by crab pots as a function of deployment duration, the effects were short-term (<10 months). Given the ability of S. alterniflora to recover from crab pot impacts, the potential incorporation of pots into the overall marsh landscape, the reduced numbers of pots observed to be stranded in the marsh interior (versus tidal creeks adjacent to marshes; Lee, 2009), and the potential for crab pot ‘‘hummocks’’ to enhance habitat structure, we conclude that derelict crab pots do not pose an immediate, direct threat to S. alterniflora in this
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region. We suspect that removal efforts would be better served by focusing on derelict pots that remain submerged and continue to fish, with resulting high blue crab and bycatch mortality rates (Guillory et al., 2001; NCDMF, 2004; Poon, 2005; Havens et al., 2008). In 2004, in recognition of bycatch impacts stemming from prolonged deployment of submerged gear, the North Carolina Division of Marine Fisheries shortened the crab pot attendance period from 7 to 5 days and extended the pot cleanup period by 9 days (NCDMF, 2004). In addition to bycatch issues, submerged derelict crab pots may impact benthic habitats including locally prominent seagrass beds composed of Zostera marina (eelgrass). Although individual crab pots have a relatively small benthic footprint (0.37 m2), the large numbers of pots that are lost annually may result in cumulative effects to submerged aquatic vegetation (Stephan et al., 2000), and movement of derelict pots during storm events may create paths of seagrass damage or completely denuded patches as has been shown for spiny lobster traps in south Florida (Uhrin et al., 2005). Tidal currents are known to create scour areas that are devoid of vegetation around derelict wire Dungeness crab pots found in Puget Sound eelgrass beds, and obvious pot footprints with little or no eelgrass present have been observed following pot removal (June and Antonelis, 2009). Conversely, wire blue crab pots experimentally-deployed on unvegetated substrate serve as immediate habitat for fouling organisms with subsequent usage of the encrusted pots by motile species (Havens et al., 2008; Manley et al., 2009). Although the encrusted pots continue to trap organisms, Havens et al. (2008) suggest eventual pot degradation (>1 year) such that confinement potential ceases and the pots serve entirely as habitat (Havens et al., 2008). Due to local substrate limitations, a number of states in the southeastern United States are examining the efficacy of using derelict crab pots as a foundation substrate in oyster restoration (Brumbaugh et al., 2009; Manley et al., 2009; Kreutzer, 2010; Joel Fodrie, pers. com.). Anthropogenic woody debris was found to be the dominant debris type (by weight) in local salt marsh debris surveys, typically characterized by sections of dock, duck blinds, pallets, construction debris, and poles from the local pound net fishery (Viehman et al., 2011). These sizable, heavy debris items often have severe impacts associated with them (i.e., complete devegetation; Viehman et al., 2011) similar to natural, large woody debris in salt marshes of the Pacific Northwest (MacLennan, 2005). Repeated dislodgement of the lumber pieces used in the current study prevented a thorough evaluation of this debris type, and suggest that perhaps any impacts associated with small woody debris would result from debris movement as opposed to debris stranding. The disturbance and recovery dynamics of impacts from large, anthropogenic, woody debris warrant further examination in this region.
Acknowledgments This study was funded by the NOAA Marine Debris Program as well as additional direct support from the NOAA National Centers for Coastal Ocean Science. We remember D. Ahrenholz and appreciate his generous donation of the crab pots used in this study. We thank the North Carolina Division of Marine Fisheries for providing the vehicle tires. We acknowledge the efforts of V. McDonough, J. Vander Pluym, S. Viehman, and P. Whitfield on proposal submissions. This work would not have been possible without additional field, technical, and administrative support from C. Currin, G. Fisher, L. Goshe, B. Harrison, M. LaCroix, S. Leahy, D. Meyer, K. Rudd, K. Strauss, C. Taylor, B. Tiedeman, J. Vander Pluym, S. Viehman, and P. Whitfield. We would like to thank P. Delano, M. Fonseca, D. Johnson, P. Marraro, J. Vander Pluym, S. Viehman, P. Whitfield, and the anonymous journal reviewers for critiquing the manuscript.
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