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.     

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.     

Comparison of fish and macroinvertebrate use of<Emphasis Type="Italic">Typha angustifolia,Phragmites australis</Emphasis>, and treated<Emphasis Type="Italic">Phragmites</Emphasis> marshes along the lower Connecticut River

Since 1965 large areas of lower Connecticut River tidelands have been converted from high diversity brackish meadow andTypha angustifolia marsh to near monocultures ofPhragmites australis. This study addresses the impact ofPhragmites invasion on fish and crustacean use of oligohaline high marsh. During spring tides from early June through early September 2000, fishes and crustaceans leaving flooded marsh along 3 km of the Lieutenant River, a lower Connecticut River tributary, were captured with Breder traps at 90 sites, equally distributed amongPhragmites, Typha, and treated (herbicide and mowing)Phragmites areas. Pit traps, 18 per vegetation type in 2000 and 30 each inPhragmites andTypha in 2001, caught larvae and juveniles at distances of up to 30 m into the marsh interior. There were no significant differences in fish species compositions or abundances among the vegetation types. Size distributions, size specific biomasses, and diets ofFundulus heteroclitus, the numerically dominant fish, were also similar. The shrimpPalaemonetes pugio was more abundant inPhragmites than in other types of vegetation, whereas the fiddler crabUca minax was least numerous inPhragmites. Mean numbers ofF. heteroclitus andP. pugio caught per site event were positively correlated with increasing site hydroperiod. Significantly moreF. heteroclitus were captured along the upper reach of the river where marsh elevations were lower than farther downstream. MoreF. heteroclitus and fewerP. pugio andU. minax were captured during the day than at night. A relatively small number of larval and juvenileFundulus sp. were captured in pit traps, but consistently fewer inPhragmites than inTypha, suggesting thatTypha and brackish meadow marshes may provide better nursery habitat. Vegetation was sampled along a 30 m transect at each trap site in 2000. Plant species diversity was greatest in treatedPhragmites areas and lowest inPhragmites sites.     

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.     

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.     

Valuation of continuous and intermittent<Emphasis Type="Italic">Phragmites</Emphasis> control

Quantifying the relative value ofPhragmites australis andSpartina alterniflora habitat is important to evaluate the benefits and risks of different attempts to addressPhragmites expansion on the U.S. eastern seaboard. Two contrasting approaches commonly used to restore tidal marsh habitats invaded byPhragmites communities involve sprayingPhragmites with herbicide only when its coverage of a particular marsh area is near or close to 100%. Alternatively, after the first application, herbicide is annually applied on any surviving patches ofPhragmites present in a mosaic of other marsh vegetation. A model is introduced to evaluate the relative habitat value of these control regimes, here termed the Intermittent and Continuous. Compared to the Intermittent approach, the area of herbicide application in the Continuous approach is higher in the first 6 yr, but lower the reafter. The cumulative gain in habitat quality after 20 yr in either approach is sensitive to the presumed relative values ofPhragmites versusSpartina habitat, and may even be negative if they are nearly equal. Annual applications of herbicide to patches ofPhragmites appears to generate more habitat value and with less herbicide than occasional applications whenPhragmites cover is at is maximum.     

Ecosystem Engineering Effects of <Emphasis Type="Italic">Aster tripolium</Emphasis> and <Emphasis Type="Italic">Salicornia procumbens</Emphasis> Salt Marsh on Macrofaunal Community Structure

This paper examines how perennial Aster tripolium and annual Salicornia procumbens salt marshes alter the biomass, density, taxon diversity, and community structure of benthic macrofauna, and also examines the role of elevation, sediment grain size, plant cover, and marsh age. Core samples were collected on a fixed grid on an intertidal flat in the Westerschelde estuary (51.4° N, 4.1° E) over 5 years (2004–2008) of salt marsh development. In unvegetated areas, macrobenthic biomass, density, and taxon diversity were highest when elevation was highest, benthic diatoms were most abundant, and sediment median grain size was smallest. In contrast, in salt marsh areas, macrobenthic biomass and taxon diversity increased with median grain size, while the effects of elevation and diatom abundance on macrobenthic biomass, density, and diversity were not significant. In fine sediments, macrofaunal community structure in the salt marsh was particularly affected; common polychaetes such as Nereis diversicolor, Heteromastus filiformis, and Pygospio elegans had low abundance and oligochaetes had high abundance. Marsh age had a negative influence on the density of macrofauna, and A. tripolium stands had lower macrofaunal densities than the younger S. procumbens stands. There were no significant effects of marsh age, plant cover, and vegetation type on macrobenthic biomass, taxon diversity, and community structure. The results highlight that ecosystem engineering effects of salt marsh plants on macrofauna are conditional. Organic enrichment of the sediment and mechanical hindering of macrofaunal activity by plant roots are proposed as plausible mechanisms for the influence of the salt marsh plants on macrofauna.     

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.     

The influence of<Emphasis Type="Italic">Phragmites</Emphasis> (common reed) on the distribution,abundance, and potential prey of a resident marsh fish in the Hackensack Meadowlands,New Jersey

This study investigates the influence ofPhragmites australis (common reed) invasion on the habitat of the resident marsh fish,Fundulus heteroclitus (mummichog) in the Hackensack Meadowlands, New Jersey. These abundant fish play an important role in the transfer of energy from the marsh surface to adjacent subtidal waters and thus estuarine food webs. The objectives of this 2-yr study (1999 and 2000) were to compare the distribution and abundance of the eggs, larvae, juveniles, and adults of mummichog and their invertebrate prey inhabitingSpartina alterniflora-dominated marshes withPhragmites-dominated marshes, and to experimentally investigate the influence of marsh surface microtoprography on larval fish abundance withinPhragmites-dominated marshes. In 2000, we verified that egg deposition does occur inPhragmites-dominated marshes. In both years, the abundance of larvae and small juveniles (4–20 mm TL) inS. alterniflora was significantly greater than inPhragmites-dominated marshes, while larger juveniles and adults (>20 mm TL) were similarly abundant in both habitat types. The overall abundance of larvae and small juveniles was significantly greater in experimentalPhragmites plots in which microtopography was manipulated to resemble that ofSpartina marshes than inPhragmites control plots. Major groups of invertebrate taxa differed between marsh types with potential prey for larval fish being significantly more abundant inS. alterniflora marshes.Phragmites-dominated marshes may not provide the most suitable habitat for the early life-history stages of the mummichog. The low abundance of larvae and small juveniles inPhragmites marshes is likely due to inadequate larval habitat and perhaps decreased prey availability for these early life history stages.     

<Emphasis Type="Italic">Phragmites australis</Emphasis> invasion and expansion in tidal wetlands: Interactions among salinity,sulfide, and hydrology

Through their physiological effects on ion, oxygen, and carbon balance, respectively, salinity, sulfide, and prolonged flooding combine to constrain the invasion and spread ofPhragmites in tidal wetlands. Initial sites of vigorous invasion by seed germination and growth from rhizome fragments appear limited to sections of marsh where salinity is <10‰, sulfide concentrations are less than 0.1 mM, and flooding frequency is less than 10%. In polyhaline tidal wetlands the invasion sites include the upland fringe and some high marsh creek banks. The zones of potential invasion tend to be larger in marshes occupying lower-salinity portions of estuaries and in marshes that have been altered hydrologically. Owing to clonal integration and a positive feedback loop of growth-induced modification of edaphic soil conditions, however, a greater total area of wetland is susceptible toPhragmites expansion away from sites of establishment. Mature clones have been reported growing in different marshes with salinity up to 45‰, sulfide concentration up to 1.75 mM, and flooding frequency up to 100%. ForPhragmites establishment and expansion in tidal marshes, windows of opportunity open with microtopographic enhancement of subsurface drainage patterns, marsh-wide depression of flooding and salinity regimes, and variation in sea level driven by global warming and lunar nodal cycles. To avoidPhragmites monocultures, tidal wetland creation, restoration, and management must be considered within the context of these different scales of plant-environment interaction.     

Reproductive success of wading birds using<Emphasis Type="Italic">Phragmites</Emphasis> marsh and upland nesting habitats

Colonial nesting of long-legged wading birds (Ciconiiformes) in the coastal northeastern U.S. is limited primarily to islands, which provide isolated habitats that are relatively free of ground predators. Estuarine wetlands in this heavily developed region, including foraging wetlands and fringe marshes surrounding nesting islands, are often dominated byPhragmites australis. On Pea Patch Island in Delaware Bay, site of one of the largest and most enduring mixed-species heron colonies on the East Coast, wading birds nest inPhragmites marsh habitat as well as in adjacent upland shrubs and trees. BecausePhragmites is aggressively managed in Delaware Bay, we investigated the relative habitat value of marsh and upland nesting sites for the purpose of developing recommendations for marsh and wildlife management. Utilization of marsh habitat by nesting birds ranged from 27–82% during 1993–1998. Two species (great blue heronArdea herodias and great egretA. alba) never nested inPhragmites, four species (little blue heronEgretta caerulea, snowy egretE. thula, cattle egretBubulcus ibis, and black-crowned night-heronNycticorax nycticorax) nested in approximately equal proportions in both habitats, and one species (glossy ibisPlegadis falcinellus) was largely confined to marsh nesting. Productivity (egg and nestling production) varied between habitats for some species. Cattle egrets produced larger clutches and had higher hatching rates inPhragmites compared to upland habitat. Little blue herons were more successful in the uplands. Managers should retainPhragmites marsh at colony sites, such as Pea Patch Island, where it provides critical habitat for nesting wading birds both as substrate for nesting and buffer habitat to control human disturbance.     

<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.     

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.     

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.     

Discerning vegetation and environmental correlates with subtidal marsh fish assemblage dynamics during<Emphasis Type="Italic">Phragmites</Emphasis> eradication efforts: Interannual trend measures

We examined the 5-yr (1996–2000) response of subtidal marsh creek fishes (2,793 trawls, 47 species, 30,719 fish) to a large marsh restoration project in the upper Delaware Bay, and found that the salinity gradient covaried along with marsh surface vegetation type among two treated and one untreated reference sites, confounding direct comparison of fish utilization. Examination of environmental correlates with monthly yearly trends highlighted differences between potential mechanism driving assemblage dynamics either intrinsic or extrinsic to the marshes. Within-site and among-site differences in fish assemblage, as described by principal components analysis, correlated poorly with marsh vegetation on both seasonal and interannual scales and appeared to driven by larval supply. Assemblage dynamics could be expalined in part by the occurrence of juveniles of transient marine fishes along a salinity gradient (0–15.2%) range in monthly site mean), but were largely determined by fluctuations in the distribution of two transient species: young-of-the-year bay anchovyAnchoa mitchilli and Atlantic croakerMicropogonias undulatus. A minor mode in variance, driven by locally spawned species, was moderately correlated with environmental parameters. Analysis of marshes on an individual basis did not discern additional important gradients. Our findings are in contrast to those in systems dominated by resident species, probably because transient fishes, which often dominante the system, are more plastic to the nature of ecological services or are affected as much by environment outside of the marsh as by that in the marsh.     

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.     

Deterioration of Sediment Quality in Seagrass Meadows (<Emphasis Type="Italic">Posidonia oceanica</Emphasis>) Invaded by Macroalgae (<Emphasis Type="Italic">Caulerpa</Emphasis> sp.)

Species of the macroalgae Caulerpa sp. are increasingly being observed in meadows of the endemic Mediterranean seagrass Posidonia oceanica, and in particular Caulerpa taxifolia, has been considered as an invasive species leading to seagrass decline. Studies have so far failed to reveal the underlying mechanisms of the success of the macroalgae, and here, we examine how biogeochemical changes of the environment associated to indigenous (Caulerpa prolifera) and non-indigenous (Caulerpa racemosa and C. taxifolia) species affect the habitat of P. oceanica. Two of the species (C. prolifera and C. racemosa) affect the sediment biogeochemical conditions by increasing organic matter pools, microbial activity, and sulfide pools of the sediments, and limited effects were found for C. taxifolia. Biomass of the macroalgae contributed to the extent of impacts, and high sulfide invasion into the seagrasses and regression of the meadow were pronounced at the location with the highest Caulerpa biomass. This suggests that Caulerpa invasion contributes to seagrass decline probably because Caulerpa thrives better than the seagrasses in the modified environment.     

Association Between <Emphasis Type="BoldItalic">Fusarium</Emphasis> spp. on <Emphasis Type="BoldItalic">Spartina alterniflora</Emphasis> and Dieback Sites in Connecticut and Massachusetts

Sudden vegetation dieback (SVD) is defined as the loss and lack of recovery of smooth cordgrass (Spartina alterniflora) in salt marshes. A new species of a moderately pathogenic fungus called Fusarium palustre is consistently found in SVD sites, but greenhouse tests revealed that it is not capable of causing mortality of healthy plants. Similarly, root-knot nematodes (Meloidogyne spartinae) are also found in SVD sites, but their incidence in marshes affected by SVD is not known. To understand more about the ecology of F. palustre and M. spartinae, salt marshes along Connecticut’s Long Island Sound and Massachusetts’ Cape Cod that exhibited SVD and those that did not, were visited during the summers of 2007, 2008, and 2009. Belowground and aboveground tissues of smooth cordgrass plants from 18 marshes were removed, washed, and assayed for Fusarium spp. to determine if patterns between the incidence of the different species of Fusarium, their virulence on S. alterniflora, root-knot nematodes (M. spartinae), and the health of the marsh could be revealed. There were significantly more colonies of Fusarium growing from plants in SVD sites (6.1%) than in healthy marshes where no SVD was present (<1.0%). The incidence of Fusarium spp. from plants at the perimeter of the SVD site was not statistically different from asymptomatic plants 10–20 m from the SVD edge. The majority of isolates could be assigned to one of two species, F. palustre or another slightly pathogenic group called Fusarium cf. incarnatum (88% in 2007, 62% in 2008, and 96% in 2009). The ratio of F. palustre to F. cf. incarnatum was 6.7, 2.7, or 2.1 for 2007, 2008, or 2009, respectively. Greenhouse tests on healthy S. alterniflora revealed that isolates of F. palustre were more virulent than F. cf. incarnatum, regardless of whether they were recovered from plants in healthy marshes or in SVD sites. Root-knot nematodes were found sporadically and could not be associated with SVD. Factorial greenhouse experiments did not demonstrate any interaction between F. palustre and M. spartinae providing no experimental evidence that combining Fusarium and root-knot nematodes could cause mortality. The presence of Fusarium on S. alterniflora in healthy marshes also suggests an endophytic relationship that may subsequently function in the breakdown of tissue when plants are compromised.     

Determinants of expansion for<Emphasis Type="Italic">Phragmites australis</Emphasis>, common reed,in natural and impacted coastal marshes

The rapid spread ofPhragmites australis in the coastal marshes of the Northeastern United States has been dramatic and noteworthy in that this native species appears to have gained competitive advantage across a broad range of habitats, from tidal salt marshes to freshwater wetlands. Concomitant with the spread has been a variety of human activities associated with coastal development as well as the displacement of nativeP. australis with aggressive European genotypes. This paper reviews the impacts caused by pure stands ofP. australis on the structure and functions of tidal marshes. To assess the determinants ofP. australis expansion, the physiological tolerance and competitive abilities of this species were examined using a field experiment.P. australis was planted in open tubes paired withSpartina alterniflora, Spartina patens, Juncus gerardii, Lythrum salicaria, andTypha angustifolia in low, medium, and high elevations at mesohaline (14‰), intermediate (18‰), and salt (23‰) marsh locations. Assessment of the physiological tolerance ofP. australis to conditions in tidal brackish and salt marshes indicated this plant is well suited to colonize creek banks as well as upper marsh edges. The competitive ability ofP. australis indicated it was a robust competitor relative to typical salt marsh plants. These results were not surprising since they agreed with field observations by other researchers and fit within current competition models throught to structure plant distribution within tidal marshes. Aspects ofP. australis expansion indicate superior competitive abilities based on attributes that fall outside the typical salt marsh or plant competition models. The alignment of some attributes with human impacts to coastal marshes provides a partial explanation of how this plant competes so well. To curb the spread of this invasive genotype, careful attention needs to be paid to human activities that affect certain marsh functions. Current infestations in tidal marshes should serve as a sentinel to indicate where human actions are likely promoting the invasion (e.g., through hydrologic impacts) and improved management is needed to sustain native plant assemblages (e.g., prohibit filling along margins).     

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.