A comparison of sediment microbial communities associated with<Emphasis Type="Italic">Phragmites australis</Emphasis> and<Emphasis Type="Italic">Spartina alterniflora</Emphasis> in two brackish wetlands of New Jersey

The extensive spread ofPhragmites australis throughout brackish marshes on the East Coast of the United States is a major factor governing management and restoration decisions because it is assumed that biogeochemical functions are altered by the invasion. Microbial activity is important in providing wetland biogeochemical functions such as carbon and nitrogen cycling, but there is little known about sediment microbial communities inPhragmites marshes. Microbial populations associated with invasivePhragmites vegetation and with native salt marsh cordgrass,Spartina alterniflora, may differ in the relative abundance of microbial taxa (community structure) and in the ability of this biota to decompose organic substrates (community biogeochemical function). This study compares sediment microbial communities associated withPhragmites andSpartina vegetation in an undisturbed brackish marsh near Tuckerton, New Jersey (MUL), and in a brackish marsh in the anthropogenically affected Hackensack meadowlands (SMC). We use phospholipid fatty acid (PLFA) analysis and enzymataic activity to profile sediment microbial communities associated with both plants in each site. Sediment analyses include bulk density, total organic matter, and root biomass. PLFA profiles indicate that the microbial communities differ between sites with the undisturbed site exhibiting greater fatty acid richness (62 PLFA recovered from MUL versus 38 from SMC). Activity of the 5 enzymes analyzed (β-glucosidase, acid phosphatase, chitobiase, and 2 oxidases) was higher in the undisturbed site. Differences between vegetation species as measured by Principal Components Analysis were significantly greater at the undisturbed MUL site than at SMC, and patterns of enzyme activity and PLFAs did not correspond to patterns of root biomass. We suggest that in natural wetland sediments, macrophyte rhizosphere effects influence the community composition of sediment microbial populations. Physical and chemical site disturbances may impose limits on these rhizosphere effects, decreasing sediment microbial diversity and potentially, microbial biogeochemical functions.     

The Intertidal Burrowing Crab <Emphasis Type="Italic">Neohelice</Emphasis> (=<Emphasis Type="Italic">Chasmagnathus</Emphasis>) <Emphasis Type="Italic">granulata</Emphasis> Positively Affects Foraging of Rodents in South Western Atlantic Salt Marshes

The role of positive and indirect interactions is often crucial in communities with intense abiotic stress such as salt marshes. The burrowing crab, Neohelice (=Chasmagnathus) granulata, is the dominant benthic macroinvertebrate of southwest Atlantic marshes (southern Brazil to Northern Argentinean Patagonia), having strong direct and indirect effects on marsh soil and, in consequence, on marsh vegetation and primary consumers. In this work, we investigate if this crab indirectly modifies habitat use by the granivorous rodents, Akodon azarae and Oligoryzomys flavescens, by increasing nutrient availability and thus enhancing seed production by the marsh plant Spartina densiflora. The study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°32′ S). Rodent frequencies in S. densiflora were positively correlated with crab densities throughout the low and middle marsh. Additionally, the highest quality of S. densiflora and inflorescence density was recorded at the highest crab densities. Experimental manipulation of crab densities shows that N. granulata indirectly enhances the performance of S. densiflora (e.g., decreased fiber content and C/N ratios) and increases density of seeds. Moreover, N. granulata also facilitates S. densiflora seed availability to rodents by concentrating them in sediment mound at their burrows entrances. Experimental rodent exclusions showed that rodent species used S. densiflora seeds, a variable positively related to crab burrow density. Thus, our results show that N. granulata drives the granivorous rodent distribution and the intensity of seeds–rodent interaction trough facilitative and indirect interactions in marsh community.     

Gulf Ribbed Mussels (<Emphasis Type="Italic">Geukensia granosissima</Emphasis>) Increase Methane Emissions from a Coastal <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Marsh

Understanding methane emissions from natural sources is becoming increasingly important with future climactic uncertainty. Wetlands are the single largest natural source of methane; however, little attention has been given to how biota and interactions between aboveground and belowground communities may affect methane emission rates in these systems. To investigate the effects of vegetative disturbance and belowground biogeochemical alterations induced by biota on methane emissions in situ, we manipulated densities of Littoraria irrorata (marsh periwinkle snails) and Geukensia granosissima (gulf ribbed mussels) inside fenced enclosures within a Spartina alterniflora salt marsh and measured methane emissions and sediment extracellular enzyme activity (phosphatase, β-glucosidase, cellobiohydrolase, N-acetyl-β-D-glucosaminidase, peroxidase, and phenol oxidase) over the course of a year. Changes in snail density did not have an effect on methane emission; however, increased densities of ribbed mussels significantly increased the emission of methane. Sediment extracellular enzyme activities for phosphatase, cellobiohydrolase, N-acetyl-β-D-glucosaminidase, and phenol oxidase were correlated to methane emission, and none of the enzymes assayed were affected by the snail and mussel density treatments. While methane emissions from salt marsh ecosystems are lower than those from freshwater systems, the high degree of variability in emission rates and the potential for interactions with naturally occurring biota that increase emissions warrant further investigations into salt marsh methane dynamics.     

<Emphasis Type="Italic">Spartina alterniflora</Emphasis> Biomass Allocation and Temperature: Implications for Salt Marsh Persistence with Sea-Level Rise

To predict the impacts of climate change, a better understanding is needed of the foundation species that build and maintain biogenic ecosystems. Spartina alterniflora Loisel (smooth cordgrass) is the dominant salt marsh-building plant along the US Atlantic coast. It maintains salt marsh elevation relative to sea level by the accumulation of aboveground biomass, which promotes sediment deposition and belowground biomass, which accretes as peat. Peat accumulation is particularly important in elevation maintenance at high latitudes where sediment supply tends to be limited. Latitudinal variation in S. alterniflora growth was quantified in eight salt marshes from Massachusetts to South Carolina. The hypothesis that allocation to aboveground and belowground biomass is phenotypically plastic was tested with transplant experiments among a subset of salt marshes along this gradient. Reciprocal transplants revealed that northern S. alterniflora decreased allocation to belowground biomass when grown in the south. Some northern plants also died when moved south, suggesting that northern S. alterniflora may be stressed by future warming. Southern plants that were moved north showed phenotypic plasticity in biomass allocation, but no mortality. Belowground biomass also decomposed more quickly in southern marshes. Our results suggest that warming will lead northern S. alterniflora to decrease belowground allocation and that belowground biomass will decompose more quickly, thus decreasing peat accumulation. Gradual temperature increases may allow for adaptation and acclimation, but our results suggest that warming will lower the ability of salt marshes to withstand sea-level rise.     

<Emphasis Type="Italic">Deepwater Horizon</Emphasis> Oil Spill Impacts on Salt Marsh Fiddler Crabs (<Emphasis Type="Italic">Uca</Emphasis> spp.)

The Deepwater Horizon oil spill was the largest marine oil spill in US waters to date and one of the largest worldwide. Impacts of this spill on salt marsh vegetation have been well documented, although impacts on marsh macroinvertebrates have received less attention. To examine impacts of the oil spill on an important marsh invertebrate and ecosystem engineer, we conducted a meta-analysis on fiddler crabs (Uca spp.) using published sources and newly available Natural Resources Damage Assessment (NRDA) and Gulf of Mexico Research Initiative (GoMRI) data. Fiddler crabs influence marsh ecosystem structure and function through their burrowing and feeding activities and are key prey for a number of marsh and estuarine predators. We tested the hypothesis that the spill affected fiddler crab burrow density (crab abundance), burrow diameter (crab size), and crab species composition. Averaged across multiple studies, sites, and years, our synthesis revealed a negative effect of oiling on all three metrics. Burrow densities were reduced by 39 % in oiled sites, with impacts and incomplete recovery observed over 2010–2014. Burrow diameters were reduced from 2010 to 2011, but appeared to have recovered by 2012. Fiddler crab species composition was altered through at least 2013 and only returned to reference conditions where marsh vegetation recovered, via restoration planting in one case. Given the spatial and temporal extent of data analyzed, this synthesis provides compelling evidence that the Deepwater Horizon spill suppressed populations of fiddler crabs in oiled marshes, likely affecting other ecosystem attributes, including marsh productivity, marsh soil characteristics, and associated predators.     

Utilization of <Emphasis Type="Italic">Spartina</Emphasis>- and <Emphasis Type="Italic">Phragmites</Emphasis>-Derived Dissolved Organic Matter by Bacteria and Ribbed Mussels (<Emphasis Type="Italic">Geukensia demissa</Emphasis>) from Delaware Bay Salt Marshes

Phragmites australis has been invading Spartina-alterniflora-dominated salt marshes throughout the mid-Atlantic. Although, Phragmites has high rates of primary production, it is not known whether this species supports lower trophic levels of a marsh food web in the same manner as Spartina. Using several related photochemical and biological assays, we compared patterns of organic matter flow of plant primary production through a key salt marsh metazoan, the ribbed mussel (Geukensia demissa), using a bacterial intermediate. Dissolved organic matter (DOM) was derived from plants collected from a Delaware Bay salt marsh and grown in the laboratory with ¹⁴C-CO₂. Bacterial utilization of plant-derived DOM measured as carbon mineralization revealed that both species provided bioavailable DOM to native salt marsh bacteria. Total carbon mineralization after 19 days was higher for Spartina treatments (36% ¹⁴CO₂ ± 3 SE) compared with Phragmites treatments (29% ±2 SE; Wilcoxon–Kruskal–Wallis rank sums test, P < 0.01). Pre-exposing DOM to natural sunlight only enhanced or decreased bioavailability of the DOM to the bacterioplankton during initial measurements (e.g., 7 days or less) but these differences were not significant over the course of the incubations. Mixtures of ¹⁴C-labeled bacterioplankton (and possibly organic flocs) from ¹⁴C-DOM treatments were cleared by G. demissa at similar rates between Spartina and Phragmites treatments. Moreover, ¹⁴C assimilation efficiencies for material ingested by mussels were high for both plant sources ranging from 74% to 90% and not significantly different between plant sources. Sunlight exposure did not affect the nutritional value of the bacterioplankton DOM assemblage for mussels. There are many possible trophic and habitat differences between Spartina- and Phragmites-dominated marshes that could affect G. demissa but the fate of vascular plant dissolved organic carbon in the DOM to bacterioplankton to mussel trophic pathway appears comparable between these marsh types.     

Links Between Bottom-Water Anoxia,the Polychaete <Emphasis Type="Italic">Nereis diversicolor</Emphasis>, and the Growth of Green-Algal Mats

Sediment–water incubations were used to study effects of episodic anoxia on filamentous Ulva sp. Treatments included undisturbed sediment with (AnoxSed) and without (NatSed) exposure to 5 days of anoxia, and cores with only the top 0.5 cm of sediment (SurfSed; no macrofauna, restricted pore-water nutrient pool). All three treatments contained Ulva propagules. An Ulva mat developed in the SurfSed, and after the anoxic period in the AnoxSed cores. No growth was observed in the NatSed treatment. In the AnoxSed, Ulva was progressively removed upon reoxygenation through grazing by Nereis. The results suggest that episodic anoxia stimulates the growth of macroalgal mats not only by increasing the availability of nutrients from the sediment, but also by reducing macrofaunal grazing pressure. Infauna (grazing and bioturbation), benthic microalgae (nutrient competition and retention), and pore-water nutrients appear key components in a biogeochemical network with complex feedbacks controlling the growth of green-algal mats in shallow-water systems.     

Growth and production of the mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>) in a restored salt marsh

The mummichog,Fundulus heteroclitus, is one of the most important macrofaunal components of salt marsh surfaces and an important link to subtidal areas of the adjacent estuary along the east coast of the U.S. We estimated growth, population size, and production of the mummichog in a restored marsh in order to improve our understanding of the role of this resident fish and to evaluate the success of the restoration. The restored marsh, covering 234 ha, was a former salt hay farm located in the mesohaline portion of Delaware Bay that was restored to tidal influence in August 1996. We separated the mummichog population into two components based on life history stage and summer habitat use patterns. One component, consisting of adults and large young-of-the-year (YOY), exhibited tidal movements to and from the marsh surface and the subtidal creeks. These were examined with an intensive mark and recapture program using coded wire tags. Another component, consisting of small YOY, remained on the marsh surface throughout the tidal cycle. Throw traps were used to sample these small YOY. The mean annual population density of adults and large YOY for the entire marsh was approximately 1.2 fish m⁻² and mean monthly density peaked at 2.9 fish m⁻². The mean annual density of small YOY on the marsh surface was 15.1 fish m⁻² and mean monthly density peaked at 41.4 fish m⁻². Size and season influenced the growth rate of individual fish and instantaneous growth rates ranged from 0.03 to 2.26 mo⁻¹. Total annual mummichog production was estimated to be 8.37 g dw m⁻² yr⁻¹, with adults and large YOY contributing 28.4% (2.38 g dw m⁻² yr⁻¹) and small YOY on the marsh surface contributing 71.6% (5.99 g dw m⁻² yr⁻¹). The seasonal use and population densities were comparable to previous studies in natural marshes while growth and production of mummichog in this restored marsh appeared to be higher. Coupled with the results of other studies on the feeding, movement, and habitat use of this species in this restored marsh, the species has responded well to the restoration.     

Tidal hydrology and habitat utilization by resident nekton in<Emphasis Type="Italic">Pragmites</Emphasis> and Non-<Emphasis Type="Italic">Phragmites</Emphasis> Marshes

We compared nekton densities over a range of measured flooding conditions and locations withinPhragmites australis andSpartina alterniflora (salt marsh cordgrass) at the Charles Wheeler Salt Marsh, located on the lower Housatonic River estuary in southwestern Connecticut. Nekton were sampled on nine spring high tide events from May to October 2000 using bottomless lift nets positioned between 0–5 and 10–20 m from the creek edge. Flooding depth, duration, and frequency were measured from each vegetation type during each sampling month. Benthic macroinvertebrate density was also measured within each vegetation type in May, July, and September. Frequency of flooding was 52% lower and flooding depth and duration were also significantly reduced inP. australis relative toS. alterniflora. A total of 4,197 individuals representing 7 species, mostlyPalaemonetes pugio (dagger-blade grass shrimp) andFundulus heteroclitus (common mummichog), were captured.P. pugio densities were significantly greater inS. alterniflora as were benthic macroinvertebrate density and taxa richness during May, but not during June or October. Total fish density was not significantly different betweenP. australis andS. alterniflora and was independent of location on the marsh. Significantly more juvenileF. heteroclitus were collected withinS. alterniflora relative toP. australis in June and July, suggesting that recruitment of this species may be lower inP. australis habitat. Fish density generally did not vary predictably across the range of flooding depth and duration; there was a positive relationship between flooding depth and fish density inS. alterniflora. The measured reduction in flooding frequency (52%) withinP. australis at the Housatonic site would result in an average total monthly fish use, expressed as density, of 447 ind m⁻² forP. australis and 947 ind m⁻² forS. alterniflora. WhenP. australis expansion results in reduction of flooding frequency and duration, nekton community composition can change, access to the marsh surface is reduced twofold, and nursery habitat function may be impaired.     

Mechanisms of marsh habitat alteration due to<Emphasis Type="Italic">Phragmites</Emphasis>: Response of young-of-the-year mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>) to treatment for<Emphasis Type="Italic">Phragmites</Emphasis> removal

In recent decades, marshes naturally dominated bySpartina spp. have been replaced byPhragmites australis throughout the northeastern United States. We suggest that early in this invasion there was little effect on the fish fauna. As the invasion proceeds, the marsh surface habitat became more altered (i.e., elevated, flattened, reduced water-filled depressions, and reduced standing water), which resulted in a reduction of feeding, reproduction, and nursery function for fishes, especiallyFundulus spp. These potential changes in marsh habitat and function have resulted in numerous attempts to removePhragmites and restoreSpartina spp. To evaluate the response of marsh surface fishes toPhragmites treatment, we examined fish use in the brackish water reaches of Alloway Creek in the Delaware Bay estuary. ReferencePhragmites habitats were compared with referenceSpartina alterniflora-dominated habitats and sites treated (1996–1998) to removePhragmites to restore former vegetation (i.e., restored, now comprised of 100%Spartina). Fish were sampled with an array (n=9 at each site) of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7 cm). Small individuals (mean=17.5, 5–45 mm TL) dominated all pit trap collections. Fish abundance was highest at the restored (catch per unit effort [CPUE]=2.16) andSpartina (CPUE=0.81) sites with significantly lower values atPhragmites (CPUE=0.05) habitats. Samples were dominated by young-of-the-year mummichog,Fundulus heteroclitus (98% of total fish, n=631). The only other fish species collected was spotfin killifish,Fundulus luciae (2% of total catch, n=14), which was only present in restored andSpartina habitats. These observations suggest that the restored marsh is providing habitat (water-filled depressions on the marsh surface) for young-of-the-yearFundulus spp. These marshes are responding favorably to the restoration based on the much greater abundance of fish in restored versusPhragmites habitats and the overall similarity between restored andSpartina habitats.     

Connectivity Among Salt Marsh Subhabitats: Residency and Movements of the Mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>)

We examined connectivity among marsh subhabitats to determine the structural limits and important components of a polyhaline salt marsh by studying the patterns of abundance, residency, and movement of a numerically and ecologically dominant nektonic fish (mummichog, Fundulus heteroclitus). We captured, tagged (n = 14,040 individuals, 30–110 mm), and recaptured from Feb 2001 to Jul 2002, although most recaptures (75–95% by tagging location) occurred within 150 days. Seasonal residency and movements were common among most subhabitats based on catch per unit effort and recapture per unit effort. Thus, these (marsh pools, intertidal and subtidal creeks, and marsh surface) should be considered natural subhabitats within New England type salt marshes. Further, all these subhabitat types should be included in studies of salt marsh nekton and marsh restoration and creation activities.     

Comparison of Nekton Use for Cordgrass <Emphasis Type="Italic">Spartina alterniflora</Emphasis> and Bulrush <Emphasis Type="Italic">Scirpus mariqueter</Emphasis> Marshes in the Yangtze River Estuary,China

To test whether invasive Spartina alterniflora marshes were functionally equivalent to native Scirpus mariqueter marshes, the present study used bottomless lift nets (20 m²) during 12 high-tide events from August to October 2008 to compare nekton densities and biomass between the two marsh types in the Dongtan wetland. A total of eight species of fish, two species of shrimp, and three species of crab were collected. So-iny mullet Chelon haematocheilus, keeled mullet Liza carinata, Asian freshwater goby Acanthogobius ommaturus, and ridge-tail prawn Exopalaemon carinicauda dominated samples from the two marsh types and accounted for over 90% of the total catch. There were significantly greater densities and biomass (p < 0.05) of total nekton (all species combined) and two mullets (C. haematocheilus and L. carinata) in S. alterniflora marshes than in S. mariqueter marshes in August 2008, while no significant differences (p > 0.05) between the two marsh types were observed for densities and biomass of any species or total nekton in September and October 2008. Non-metric multidimensional scaling ordination did not show clear separation of samples between the two marsh types (r = 0.071, p = 0.159). Furthermore, there were no habitat-specific differences (p > 0.05) in the size distributions of the three numerically dominant species (C. haematocheilus, L. carinata, and A. ommaturus). We concluded that S. alterniflora marshes were utilized by nekton in a fashion similar to their utilization of native S. mariqueter marshes under similar physical conditions.     

Predation by the black-clawed mud crab,<Emphasis Type="Italic">Panopeus herbstii</Emphasis>, in Mid-Atlantic salt marshes: Further evidence for top-down control of marsh grass production

Although top-down control of plant growth has been shown in a variety of marine systems, it is widely thought to be unimportant in salt marshes. Recent caging experiments in Virginia and Georgia have challenged this notion and shown that the dominant marsh grazer (the periwinkle,Littoraria irrorata) not only suppresses plant growth, but can denude marsh substrate at high densities. In these same marshes, our field observations suggest that the black-clawed mud crab,Panopeus herbstii, is an abundant and potentially important top-down determinant of periwinkle density. No studies have quantitatively examinedPanopeus distribution or trophic interactions in marsh systems, and its potential impacts on community structure remained unexplored. We investigated distribution and feeding habits ofPanopeus in eight salt marshes along the Mid-Atlantic seashore (Delaware-North Carolina). We found that mud crabs were abundant in tall (4–82 ind m^?2), intermediate (0–15 ind m^?2), and short-form (0–5 ind m^?2)Spartina alterniflora zones in all marshes and that crab densities were negatively correlated with tidal height and positively correlated with bivalve density. Excavation of crab lairs r?utinely produced shells of plant-grazing snails (up to 36 lair^?1) and bivalves. Lab experiments confirmed that mud crabs readily consume these abundant marsh molluscs. To experimentally examine potential community effects of observed predation patterns, we manipulated crab and periwinkle densities in a 1-mo field experiment. Results showed thatPanopeus can suppress gastropod abundance and that predation rates increase with increasing snail density. In turn, crab suppression of snail density reduces grazing intensity on salt marsh cordgrass, suggesting presence of a trophic cascade. These results indicate that this previously under-appreciated consumer is an important and indirect determinant of community structure and contribute to a growing body of evidence challenging the long-standing notion that consumers play a minor role in regulating marsh plant growth.     

Blue crab,<Emphasis Type="Italic">Callinectes sapidus</Emphasis>, response to the invasive common reed,<Emphasis Type="Italic">Phragmites australis</Emphasis>: Abundance,size, sex ratio,and molting frequency

Much effort has been directed recently at restoring marshes, by the removal of the invasive common reed,Phragmites australis, yet it is not clear how fish and invertebrates have responded either to the invasion ofPhragmites or to marsh restoration. The blue crab,Callinectes sapidus, uses marsh habitats during much of its benthic life. We investigated the response of blue crabs toPhragmites invasion and restoration efforts by comparing crab abundance (catch per unit effort), mean size and size frequency distribution, sex ratio, and molting of crabs in three physically similar areas differing in marsh vegetation;Spartina-dominated,Phragmites-dominated, and a treated area (Phragmites removed and now dominated bySpartina) in one marsh in the upper portion of Delaware Bay. Field sampling occurred monthly (April to November) from 1999 to 2001 using replicate daytime otter trawls in large marsh creeks. Crabs were categorized by carapace width into recruits (<30 mm), juveniles (30–115 mm), and adults (>115 mm). Juveniles dominated the system, representing 69.4% of all crabs. Similar monthly increases in mean size and molting patterns during the growing season (May–August) occurred inSpartina (natural and treated sites) andPhragmites sites suggesting that, subtidal habitats, used for molting, in these areas do not differ. More juveniles in the feeding molt stage (i.e., intermolt) than in other molt stages and more recruits predominantly in the feeding molt stage than adults were inSpartina, suggesting differences in the marsh surfaces used as feeding habitats withSpartina being preferred. Sex ratios of each life history stage were skewed towards males, but this was related to the low salinity of Alloway Creek, rather than marsh surface vegetation. Our results suggest that marsh surface vegetation influences the way blue crabs use marsh surface habitats, thus restoration efforts focusing on changing vegetation type may have a positive influence on blue crabs.     

Habitat use and movement of the mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>) in a restored salt marsh

The mummichog,Fundulus heteroclitus, is one of the most abundant macrofaunal components of salt marsh ecosystems along the east coast of the United States. During April–November 1998, we determined the habitat use and movement patterns of young-of-the-year (YOY) and adult mummichogs in a restored marsh, formerly a salt hay farm, and an adjacent creek in order to expand our understanding of the ecology of the species and evaluate the success of the restoration. Four major fish habitat types (large first-order natural creek, second-order created creek, linear drainage ditch, and marsh surface) were identified within the study site. Patterns of relative abundance and mark and recapture using coded wire tags were used to determine the habitat use, tidal movements, home range, and site fidelity of the species within these habitat types. A total of 14,784 fish, ranging from 20–100 mm SL, were captured with wire mesh traps and tagged, and 1,521 (10.3%) fish were recaptured. A variety of gears were used to attempt to recapture fish across all habitat types, including wire mesh traps, push nets, and otter trawls. Based on abundance and recaptures of tagged fish, the YOY and adults primarily used the shallow subtidal and intertidal areas of the created creek, the intertidal drainage ditches, and the marsh surface of the restored marsh but not the larger, first-order natural creek. At low tide, large numbers were found in the subtidal areas of the created creek; these then moved onto the marsh surface on the flooding tide. Elevation, and thus hydroperiod, appeared to influence the microscale use of the marsh surface. We estimated the home range of adults and large YOY (20–100 mm SL) to be 15 ha at high tide, which was much larger than previously quantified. There was strong site fidelity to the created creek at low tide. The habitat use and movement patterns of the mummichog appeared similar to that reported for natural marshes. Coupled with the results of other studies on the feeding, growth, and production of this species in this restoreh, the species appeared to have responded well to the restoration.     

Post-settlement alteration of spatial patterns of soft shell clam (<Emphasis Type="Italic">Mya arenaria</Emphasis>) recruits

To examine the roles of settlement and early post-settlement processes in patterns of recruitment of the soft shell clamMya arenaria, abundance of juvenileMya at three intertidal sites in Barnstable Harbor, Massachusetts, was monitored over two settlement seasons. Two peaks of settlement occurred in 1998 (July and September) and one peak was recorded in June 1999, indicating that a late season settlement event is not a consistent feature at this site. Abundance of recent settlers (i.e., early recruits, < 1 week past settlement) varied significantly among the tidal flats (sites) that were separated by hundreds of meters to kilometers, but not among plots meters apart. Differences in abundance of settlers likely resulted in these differences in early-recruit abundance among sites. Settlement was greatest at the site with the greatest variability in flow speed. Sites also differed to some extent in their sediment characteristics and macrofaunal assemblages, which may influence larval substrate choice. Between-site differences in abundance ofMya decreased after settlement. The rate of decline of abundance varied among cohorts and sites. Comparison of abundance of recent settlers (up to 145,000 m⁻²) to that of juveniles > 3-mm shell length at the end of the settlement season (up to 60 m⁻²) indicated large losses of individuals during the early post-settlement period. This study demonstrates that spatial patterns inMya abundance can change substantially during the early post-settlement period, and that high mortality rates can result in cohorts contributing little to the population size even when rates of settlement are high.     

Determination of Trophic Transfer at a Created Intertidal Oyster (<Emphasis Type="Italic">Crassostrea ariakensis</Emphasis>) Reef in the Yangtze River Estuary Using Stable Isotope Analyses

Oysters can create reefs that provide habitat for associated species resulting in elevated resident abundances, lower mortality rates, and increased growth and survivorship compared to other estuarine habitats. However, there is a need to quantify trophic relationships and transfer at created oyster reefs to provide a better understanding of their potential in creating suitable nekton habitat. Stable isotope analyses (δ¹³C and δ¹⁵N) were conducted to examine the organic matter sources and potential energy flow pathways at a created intertidal oyster (Crassostrea ariakensis; hereinafter, oyster) reef and adjacent salt marsh in the Yangtze River estuary, China. The δ¹³C values of most reef-associated species (22 of 37) were intermediate between those of suspended particle organic matter (POM) and benthic microalgae (BMI), indicating that both POM and BMI are the major organic matter sources at the created oyster reef. The sessile and motile macrofauna colonizing the reef make up the main prey of transient nekton (e.g., spotted sea bass, Asian paddle crab, and green mud crab), thus suggesting that the associated community was most important in supporting higher trophic levels as opposed to the direct dietary subsidy of oysters. The created oyster reef consistently supported higher trophic levels than the adjacent salt marsh habitat due to the dominance of secondary consumers. These results indicate that through the provision of habitat for associated species, created oyster reefs provide suitable habitat and support a higher average trophic level than adjacent salt marsh in the Yangtze River estuary.     

Impact of common reed,<Emphasis Type="Italic">Phragmites australis</Emphasis>, on essential fish habitat: Influence on reproduction,embryological development,and larval abundance of mummichog (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>)

The invasion ofSpartina marshes by the common reed,Phragmites australis, along the east coast of the United States over the last several decades has been well documented, although we know little about the impact of this invasion on the fish fauna and the few published papers seem contradictory. During 1999–2000 (May–September) we evaluated the fish response to vegetation type (Phragmites australis veersusSpartina alterniflora) by monitoring several aspects of fish early life history (egg deposition, embryonic development, hatching success, and larval and juvenile abundance) in low salinity marshes in the Mullica River in southern New Jersey. The dominant fish species using the marsh surface,Fundulus heteroclitus (93% of total catch, n=996 individuals), reproduced in both vegetation types with eggs deposited in leaf axils near the base of the plant inSpartina and in broken stems ofPhragmites during both years. These eggs also undergo successful embryonic development to hatching in both vegetation types. Larval and juvenile (5–75 mm total length, but 95% < 34 mm TL) abundance of this species is much reduced onPhragmites-dominated (mean CUPE=0.02, n=7 ind) marsh surface relative toSpartina (mean CPUE=2.31). These findings, and similar results for fish abundance in 1997 and 1998, indicate that theSpartima marsh surface is likely essential fish habitat for this species because it provides habitat for larvae and small juveniles, whilePhragmites does not. ThePhragmites invasion in brackish marshes may be having deleterious effects on fish populations and possibly on predators that prey uponF. heteroclitus, and as a result, marsh secondary production.     

Influence of Organic Enrichment and <Emphasis Type="Italic">Spisula subtruncata</Emphasis> (da Costa, 1778) on Oxygen and Nutrient Fluxes in Fine Sand Sediments

The role of labile organic material and macrofaunal activity in benthic respiration and nutrient regeneration have been tested in sublittoral fine sand sediments from the Gulf of Valencia (northwestern Mediterranean Sea). Three experimental setups were made using benthic chambers. One experiment was performed in-situ through the annual cycle in a well-sorted fine sand community. The remaining experiments were carried out with mesocosms under laboratory conditions: one with different concentrations of organic enrichment (mussel meat and concentrated diatoms culture), and the other adding two different densities of the endofaunal bivalve Spisula subtruncata. Biochemical variables in surface sediment and changes in oxygen consumption and nutrient fluxes throughout incubation period were studied in each experiment. In the in situ incubations, dissolved oxygen (DO) fluxes showed a strong correlation with sedimentary biopolymeric fraction of organic carbon. Organic enrichment in the laboratory experiments was responsible for increased benthic respiration. However, sediment response (expressed as DO uptake and dissolved inorganic nitrogen—DIN—release) between oligotrophic and eutrophic conditions was more intense than between eutrophic and hypertrophic conditions. S. subtruncata abundances close to 400 and 850 ind m^?2 also intensified benthic metabolism. DO uptake and DIN production in mesocosms with added fauna were between 60 and 75 % and 65–100 % higher than in the control treatment respectively. The results of these three experiments suggest that the macrobenthic community may increase the benthic respiration by roughly a factor of two in these bottoms, where S. subtruncata is one of the dominant species. Both organic enrichment and macrobenthic community in general, and S. subtruncata in particular, did not seem to have a relevant role in P and Si cycles in these sediments.     

Effects of an Omnivorous Katydid,Salinity, and Nutrients on a Planthopper-<Emphasis Type="Italic">Spartina</Emphasis> Food Web

Top–down and bottom–up effects interact to structure communities, especially in salt marshes, which contain strong gradients in bottom–up drivers such as salinity and nutrients. How omnivorous consumers respond to variation in prey availability and plant quality is poorly understood. We used a mesocosm experiment to examine how salinity, nutrients, an omnivore (the katydid Orchelimum fidicinium) and an herbivore (the planthopper Prokelisia spp.) interacted to structure a simplified salt marsh food web based on the marsh grass Spartina alterniflora. Bottom–up effects were strong, with both salinity and nutrients decreasing leaf C/N and increasing Prokelisia abundance. Top–down effects on plants were also strong, with both the herbivore and the omnivore affecting S. alterniflora traits and growth, especially when nutrients or salt were added. In contrast, top–down control by Orchelimum of Prokelisia was independent of bottom–up conditions. Orchelimum grew best on a diet containing both Spartina and Prokelisia, and in contrast to a sympatric omnivorous crab, did not shift to an animal-based diet when prey were present, suggesting that it is constrained to consume a mixed diet. These results suggest that the trophic effects of omnivores depend on omnivore behavior, dietary constraints, and ability to suppress lower trophic levels, and that omnivorous katydids may play a previously unrecognized role in salt marsh food webs.