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Intertidal reefs comprised of the eastern oyster (Crassostrea virginica) have long experienced habitat loss, altering habitat patch characteristics of size and distance from edge to interior, potentially influencing spatial dynamics of host-parasite relationships. Using two parasitic relationships, one between eastern oyster host and parasitic oyster pea crab (Zaops ostreum) and the other between a xanthid crab (Eurypanopeus depressus) and a parasitic rhizocephalan barnacle (Loxothylacus panopaei), we examined how host-parasite population characteristics varied on intertidal reefs by season, reef size, and distance from edge to interior. Pea crab prevalence was more related to habitat characteristics rather than host density, as pea crab prevalence was the highest on large reefs and along edges, areas of comparatively lower oyster densities. Reef size did not influence densities of parasitized or non-parasitized xanthid crabs, but densities varied from edge to interior. Non-parasitized xanthids had significantly lower densities along the reef edge compared to more interior reef locations, while parasitized xanthid crabs had no significant edge to interior pattern. Organismal size had a varied relationship based upon habitat characteristics, as pea crab carapace width (CW) varied interactively with season and reef size, whereas CW of parasitized/non-parasitized xanthid crabs varied significantly between edge and interior locations. These results demonstrated that influential habitat characteristics, such as patch size and edge versus interior, are both highly species and host-parasite specific. Therefore, continued habitat alteration and fragmentation of critical marine habitats may further impact spatial dynamics of host-parasite relationships.

The objective of this study was to determine if the placement of dredged material on sediment-starved back barrier marshes in southeastern North Carolina could offset submergence without negatively affecting function. Clean sediment was placed in thickness from 0 to 10 cm on deteriorated and non-deteriorated marsh plots. Original stem densities were greater in non-deteriorated plots (256 stems m-2) compared to deteriorated sites (149 stems m-2). By the second growing season (after sediment additions), stem densities in the deteriorated plots (308 stems m-2) approached levels in the non-deteriorated plots (336 stems m-2). Sediment additions to both non-deteriorated and deteriorated plots resulted in a higher redox potential with plots receiving the most sediment exhibiting the highest Eh values. In deteriorated plots, placement of dredged material had the greatest effect on plant density, but also affected soil oxidation-reduction potential and sediment deposition (or mobility). Following sediment placement, substrate texture and composition incrementally returned to prefill conditions due to a combination of bioturbation and sedimentation. Where infaunal differences occurred, they were generally less abundant in deteriorated plots, but responses to sediment addition were variable. Sediment addition had little effect on the non-deteriorated plots, suggesting that the disposal of certain types of dredged material in marshes may be useful to mitigate the effects of marsh degradation without adversely affecting non-deteriorating marsh.

Researchers have found that human development of floodplains greatly compounds the impacts of hurricanes on water quality and aquatic life.

Habitat heterogeneity is increased in natural systems via habitat loss and fragmentation, which decreases the patch size and alters the amount of edge relative to interior. However, our understanding of how increased habitat heterogeneity influences population dynamics, particularly set within a large scale marine landscape, is relatively incomplete. Eastern oyster Crassostrea virginica populations have drastically declined resulting in fragmentation within and among reefs, thus altering reef size and distances from edge to interior. Over 2 yr (2011 to 2012), we evaluated oyster populations relative to varying distances from the reef edge to interior locations, habitat patch size, and reef type on naturally occurring intertidal fringing and patch reefs in southeastern North Carolina. Additionally, the influences of distance from edge to interior locations and habitat patch size were examined for oyster populations on 3 size classes of created intertidal reefs at 2 locations. The habitat characteristics examined significantly influenced oyster populations, with increased densities towards interior locations on a reef, a trend of overall higher densities on intermediate sized reefs, significantly greater densities on natural patch reefs compared to natural fringing reefs. Density and recruitment patterns suggested differences between edge and interior locations. However, other population characteristics, such as oyster condition and shell height, indicated there may be ecological trade-offs among the habitat characteristics examined. These results suggest intertidal reefs cannot be considered a uniform whole and may have substantially different habitat characteristics, which should be taken into account when further examining habitat fragmentation and restoration success.

In the summer of 1996, southeastern North Carolina, United States, was struck by two hurricanes, with the second (Hurricane Fran) doing considerably more damage than the first (Hurricane Bertha). The Cape Fear watershed, largest in North Carolina, suffered from severe water quality problems for weeks following Fran, including a massive fish kill in the Northeast Cape Fear River. Post-hurricane flooding caused inputs of riparian swamp water to river channels, and sewage treatment plant and pump station power failures caused diversions of millions of liters of raw and partially treated human waste into rivers. Additionally, several swine waste lagoons were breached, overtopped, or inundated, discharging large quantities of concentrated organic waste into the system, particularly into the Northeast Cape Fear River. Dissolved oxygen (DO) decreased to 2 mg/L in the mainstem Cape Fear River, and fell to zero in the Northeast Cape Fear River for >3 wk. Biochemical oxygen demand in the Northeast Cape Fear River was sixfold greater than in the other tributaries, probably as a result of anthropogenically derived inputs. The Cape Fear Estuary also suffered from hypoxia for several weeks. Following Hurricane Fran, ammonium levels in the Northeast Cape Fear River displayed a distinct increase, and total phosphorus reached its highest concentration in 27 yr. The benthic community, which is dominated by opportunistic species typical of oligohaline to mesohaline estuarine areas, showed a mixed response. There was a significant decline in total benthic abundances immediately after Hurricane Fran at an oligohaline station in the Northeast Cape Fear River, with recovery occurring in ∼3 mo. An oligohaline station in the mainstem Cape Fear River, which had relatively rapid DO recovery, did not display significant declines. A mesohaline station 5 km below the confluence of these rivers showed broad and long-lasting benthic declines, but benthic declines were less severe in the lowest reaches of the estuary sampled. The natural hurricane effect of swamp water flooding into river basins led to reduced dissolved oxygen levels and increased light attenuation. However, environmental damage was considerably increased by anthropogenic practices, including the lack of backup generating systems for waste treatment systems and subsequent sewage diversions into rivers, as well as accidents occurring at swine waste lagoons sited on river floodplains.

Invasive species are receiving increased attention both for their direct effects, including competitive displacement and predator-prey interactions, and indirect effects involving ecosystem and habitat alterations. The common reed Phragmites australis is spreading along much of the Atlantic and Gulf coasts of the USA. Its spread is particularly apparent in disturbed oligohaline to mesohaline areas, where it may displace the marsh cordgrass Spartina alterniflora. Because of the different morphologies of these plants, associated sediment effects, and differences in biogeochemical cycling, there is the potential for significant faunal community changes where macrophyte species replacement occurs. We conducted a study in the mesohaline region of Chesapeake Bay to examine differences between benthic communities associated with S. alterniflora and P. australis marshes. Paired P. australis and S. alterniflora marshes were sampled at 4 sites in summer and 2 sites in fall, blocking for tidal height (high marsh versus low marsh) and small-scale topographic features (rivulet and hummock areas in each marsh type). Sediment grain size did not differ between marsh types, and percent organics differed only for P. australis hummock sites compared to other habitat types. Benthic microalgal biomass also did not differ among marsh types. There was only a small effect on faunal abundance patterns, with most species exhibiting slightly higher mean density in Spartina compared to adjacent Phragmites marshes. Much stronger differences in faunal density were observed between hummocks and adjacent rivulets within each marsh type. While macrophyte type had a detectable effect, local microhabitat characteristics had a stronger relation to local faunal abundance patterns. Since such microhabitat characteristics may covary with macrophyte type (although they did not do so in this study). care must be taken in the design and interpretation of comparative marsh studies and more emphasis should be given to including relations of small-scale topographic features with faunal characteristics. In this system and on the scale studied here, macrophyte replacement did not strongly affect the benthic infaunal community.

The presence, abundance, and distribution of organisms within a landscape are highly dependent on the composition, quality, and configuration of habitat patches. Intertidal oyster Crassostrea virginica reefs provide a structured habitat for many organisms; however, declining oyster populations have induced reef fragmentation and loss. Over 2 years (2011–2012), we evaluated naturally occurring fringing and patch intertidal oyster reefs in southeastern North Carolina, USA, to determine how varied reef type, size, and distance from edge to interior influenced the associated benthic macrofauna and mobile nekton. In addition, the effects of size and edge vs. interior were examined on constructed intertidal reefs at 2 different locations. On the natural reefs, species richness of benthic macrofauna and mobile nekton were significantly increased on fringing reefs. Benthic macrofauna richness significantly decreased on large natural reefs, whereas mobile nekton richness significantly increased off of large reefs. Further, associated benthic macrofauna richness significantly decreased along the reef edge, whereas mobile nekton diversity increased along the reef/open bottom interface. Species richness and densities for benthic macrofauna increased with created reef size, while there was greater species richness and diversity and dissimilar communities for mobile nekton along constructed reef edges. Habitat specificity may influence utilization for mobile nekton, as resident organisms with limited vagility had a stronger response to habitat characteristics. Thus, utilization of intertidal oyster reefs can be highly structured by habitat characteristics on many scales, and should be considered when examining species interactions, ecosystem management, and future restoration efforts.

Top-down effects of predators and bottom-up effects related to resource availability can be important in determining community structure and function through both direct and indirect processes. Their relative influence may vary among habitats. We examined the effects of nutrient enhancement and predation in southeastern North Carolina to determine relative effects on benthic macrofaunal communities. Short-term nutrient additions and predator exclusions were conducted in two estuaries to examine main and interactive effects on benthic microalgae and infauna. This experimental approach was complemented by comparisons of microalgal biomass, infaunal abundance and composition, predator abundance and predator exclusion among four estuarine systems that varied in background nutrient levels. In the short-term experiments, nutrient enhancement induced increased microalgal biomass but had limited effects on abundances or sizes of infauna. Predator exclusion increased the density of sedentary and near-surface dwelling fauna, but we did not observe interactions between predation and responses to nutrient additions, as might be predicted from a simple cascade model. General patterns of abundance were explained to a larger extent by interannual and amongestuary patterns. These results indicate a lack of simple trophic cascade responses for this community over a short time scale and little evidence for local interactive effects. The lack of interactive effects may reflect the opportunistic nature of the dominant infaunal species and potentially different time and spatial scales for the effects of predation and resource controls.

Nutrient additions represent an important anthropogenic stress on coastal ecosystems. At moderate levels, increased nutrients may lead to increased primary production and, possibly, to increased biomass of consumers although complex trophic interactions may modify or mask these effects. We examined the influence of nutrient additions and interactive effects of trophic interactions (predation) on benthic infaunal composition and abundances through small-scale field experiments in 2 estuaries that differed in ambient nutrient conditions. A blocked experimental design was used that allowed an assessment of direct nutrient effects in the presence and absence of predation by epibenthic predators as well as an assessment of the independent effects of predation. Benthic microalgal production increased with experimental nutrient additions and was greater when infaunal abundances were lower, but there were no significant interactions between these factors. Increased abundances of one infaunal taxa, Laeonereis culveri, as well as the grazer feeding guild were observed with nutrient additions and a number of taxa exhibited higher abundances with predator exclusion. In contrast to results from freshwater systems there were no significant interactive effects between nutrient additions and predator exclusion as was predicted. The infaunal responses observed here emphasize the importance of both bottom-up (nutrient addition and primary producer driven) and top-down (predation) controls in structuring benthic communities. These processes may work at different spatial and temporal scales, and affect different taxa, making observation of potential interactive effects difficult.

An increase in salt marsh restoration efforts,especially over the last two decades, underscores theneed for effective methods to evaluate long-termsuccess. Most marsh restoration/creation efforts areonly evaluated over the first few years afterestablishment and in many cases only vegetativecharacteristics are examined. This study examinesvegetation as well as dominance and abundance patternsof benthic infauna at three created marsh sites ofvarying ages in Winyah Bay, South Carolina, and acreated marsh site in North Carolina, using data fromearlier studies and from sampling undertaken in 1998. Abundances fluctuated strongly between years, withpatterns of numerical abundance changing betweensites. In contrast, species dominance as measured bypercent occurrence tended to remain constant afterestablishment of a site. The same suite of specieswas dominant at all sites regardless of marsh age oryear of sampling. These results indicate that whilefaunal abundance is an important factor in determiningmarsh function (i.e., are higher trophic levelssupported?), dominance may be as useful in monitoringstability, especially in areas where the faunalassemblage is not closely tied to the vegetativecommunity.[PUBLICATION ABSTRACT]