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1.
This study investigates the influence of Phragmites 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 inhabiting Spartina alterniflora-dominated marshes with Phragmites-dominated marshes, and to experimentally investigate the influence of marsh surface microtoprography on larval fish abundance
within Phragmites-dominated marshes. In 2000, we verified that egg deposition does occur in Phragmites-dominated marshes. In both years, the abundance of larvae and small juveniles (4–20 mm TL) in S. alterniflora was significantly greater than in Phragmites-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 experimental Phragmites plots in which microtopography was manipulated to resemble that of Spartina marshes than in Phragmites control plots. Major groups of invertebrate taxa differed between marsh types with potential prey for larval fish being significantly
more abundant in S. 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 in Phragmites marshes is likely due to inadequate larval habitat and perhaps decreased prey availability for these early life history stages. 相似文献
2.
Phragmites expansion rates (linear at 1–3% yr −1) and impacts of this expansion on high marsh macroinvertebrates, aboveground production, and litter decomposition from Phragmites and other marsh graminoids were studied along a polyhaline to oligohaline gradient. These parameters, and fish use of creeks and high marsh, were also studied in Phragmites control sites (herbicide, mowing, and combined herbicide/mow treatments). Phragmites clones established without obvious site preferences on oligohaline marshes, expanding radially. At higher salinities, Phragmites preferentially colonized creekbank levees and disturbed upland borders, then expanded into the central marsh. Hydroperiods, but not salinities or water table, distinguished Phragmites-dominated transects. Pooled samples of Phragmites leaves, stems, and flowers decompose more slowly than other marsh angiosperms; Phragmites leaves alone decompose as or more rapidly than those of cattail. Aboveground Phragmites production was 1,300 to 2,400 g m −2 (about 23% of this as leaves), versus 600–800 g m −2 for polyhaline to mesohaline meadow and 1,300 g m −2 for oligohaline cattail-sedge marsh. Macroinvertebrates appear largely unaffected by Phragmites expansion or control efforts; distribution and densities are unrelated to elevation or hydroperiod, but densities are positively related to litter cover. Dominant fish captured leaving flooded marsh were Fundulus heteroclitus and Anguilla rostrata; both preyed heavily on marsh macroinvertebrates. A. rostrata and Morone americana tended to be more common in Phragmites, but otherwise there were no major differences in use patterns between Phragmites and brackish meadow vegetation. SAV and macroalgal cover were markedly lower within a Phragmites-dominated creek versus one with Spartina-dominated banks. The same fish species assemblage was trapped in both plus a third within the herbicide/mow treatment. Fish biomass was greatest from the Spartina creek and lowest from the Phragmites creek, reflecting abundances of F. heteroclitus. Mowing depressed Phragmites aboveground production and increased stem density, but was ineffective for control. Phragmites, Spartina patens, and Juncus gerardii frequencies after herbicide-only treatment were 0.53-0.21; total live cover was <8% with a heavy litter and dense standing dead stems. After two growing seasons Agrostis stolonifera/S. patens/J. gerardii brackish meadow characterized most of the herbicide/mow treatment area; Phragmites frequency here was 0.53, contributing 3% cover. Both values more than doubled after four years; a single treatment is ineffective for long-term Phragmites control. 相似文献
3.
The invasion of Spartina 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 veersus Spartina 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 in Spartina and in broken stems of Phragmites 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 on Phragmites-dominated (mean CUPE=0.02, n=7 ind) marsh surface relative to Spartina (mean CPUE=2.31). These findings, and similar results for fish abundance in 1997 and 1998, indicate that the Spartima marsh surface is likely essential fish habitat for this species because it provides habitat for larvae and small juveniles, while Phragmites does not. The Phragmites invasion in brackish marshes may be having deleterious effects on fish populations and possibly on predators that prey upon F. heteroclitus, and as a result, marsh secondary production. 相似文献
4.
Modification of brackish marshes by nonindigenous Phragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes, Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect
of the Phragmites invasion on resident marsh surface fishes by examining the population response of Fundulus heteroclitus (mummichog, 5–48 mm TL) and F. luciae (spotfin killifish, 5–41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New
Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort of F. heteroclitus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites.
A similar pattern was documented for F. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and
late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we
collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as the Phragmites invasion progresses, there is a decline in habitat function for larval and juvenile F. heteroclitus and an increased risk of extirpation of F. luciae from brackish marshes along the east coast of the U.S. 相似文献
5.
In recent decades, marshes naturally dominated by Spartina spp. have been replaced by Phragmites 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, especially Fundulus spp. These potential changes in marsh habitat and function have resulted in numerous attempts to remove Phragmites and restore Spartina spp. To evaluate the response of marsh surface fishes to Phragmites treatment, we examined fish use in the brackish water reaches of Alloway Creek in the Delaware Bay estuary. Reference Phragmites habitats were compared with reference Spartina alterniflora-dominated habitats and sites treated (1996–1998) to remove Phragmites 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) and Spartina (CPUE=0.81) sites with significantly lower values at Phragmites (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 and Spartina habitats. These observations suggest that the restored marsh is providing habitat (water-filled depressions on the marsh surface) for young-of-the-year Fundulus spp. These marshes are responding favorably to the restoration based on the much greater abundance of fish in restored versus Phragmites habitats and the overall similarity between restored and Spartina habitats. 相似文献
6.
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 by Phragmites 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 in Phragmites marsh habitat as well as in adjacent upland shrubs and trees. Because Phragmites 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 heron Ardea herodias and great egret A. alba) never nested in Phragmites, four species (little blue heron Egretta caerulea, snowy egret E. thula, cattle egret Bubulcus ibis, and black-crowned night-heron Nycticorax nycticorax) nested in approximately equal proportions in both habitats, and one species (glossy ibis Plegadis 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 in Phragmites compared to upland habitat. Little blue herons were more successful in the uplands. Managers should retain Phragmites 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. 相似文献
7.
Since 1965 large areas of lower Connecticut River tidelands have been converted from high diversity brackish meadow and Typha angustifolia marsh to near monocultures of Phragmites australis. This study addresses the impact of Phragmites 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 among Phragmites, Typha, and treated (herbicide and mowing) Phragmites areas. Pit traps, 18 per vegetation type in 2000 and 30 each in Phragmites and Typha 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 of Fundulus heteroclitus, the numerically dominant fish, were also similar. The shrimp Palaemonetes pugio was more abundant in Phragmites than in other types of vegetation, whereas the fiddler crab Uca minax was least numerous in Phragmites. Mean numbers of F. heteroclitus and P. pugio caught per site event were positively correlated with increasing site hydroperiod. Significantly more F. heteroclitus were captured along the upper reach of the river where marsh elevations were lower than farther downstream. More F. heteroclitus and fewer P. pugio and U. minax were captured during the day than at night. A relatively small number of larval and juvenile Fundulus sp. were captured in pit traps, but consistently fewer in Phragmites than in Typha, suggesting that Typha 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 treated Phragmites areas and lowest in Phragmites sites. 相似文献
8.
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 of Phragmites 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 to Phragmites 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 by Spartina) 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 in Spartina (natural and treated sites) and Phragmites 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
in Spartina, suggesting differences in the marsh surfaces used as feeding habitats with Spartina 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. 相似文献
9.
The tidally inundated marsh surface is an importnat site for energy exchanges for many resident and transient species. In
many areas along the East Coast of the U.S. the dominant vegetation, Spartina alterniflora, has been replaced by the common reed ( Phragmites australis). This shift has caused concern about the impact of Phragmites on marsh fauna but research in this area has been limited. During 1997 and 1998, we examined the effect of Phragmites on fish and decapod crustacean use of the marsh surface in the brackish water reaches of the Mullica River, in southern New
Jersey, U.S. Fish and decapod crustaceans were sampled with an array of shallow pit traps (rectangular glass dishes, 27.5×17.5×3.7
cm) and with flumes (1.3 m wide×10 m long of 3.2-mm mesh). Fish (2–60 mm TL) dominated pit trap collections with Fundulus heteroclitus and Fundulus luciae significantly more abundant at Spartina sites. Fundulus heteroclitus was also the dominant fish (15–275 mm TL) collected in flumes but collections with this gear, including a number of species
not collected in pit traps, showed no distinct preferences for different marsh vegetation types. Decapod crustaceans (1–48
mm CW) collected in pit traps were generally less abundant than fishes with Callinectes sapidus and Palaemonetes spp. most abundant in Spartina, while Rhithropanopeus harrisii was most abundant in Phragmites. The same decapod crustacean species (2–186 mm CW) dominanted the flume collections and, similar to the pattern of fish collected
by the flumes, there were no distinct habitat preferences for different marsh vegetation types. As a result of these observations,
with different sampling techniques, it appears there is an overall negative effect of Phragmites on larval and small juvenile fish but less or no effect on larger fish and decapods crustaceans. 相似文献
10.
The invasion of Phragmites australis into tidal marshes formerly dominated by Spartina alterniflora has resulted in considerable interest in the consequences of this invasion for the ecological functions of marsh habitat. We examined the provision of trophic support for a resident marsh fish, Fundulus heteroclitus, in marshes dominated by P. australis, by S. alterniflora, and in restored marshes, using multiple stable isotope analysis. We first evaluated our ability to distinguish among potential primary producers using the multiple stable isotope approach. Within a tidal creek system we found significant marsh and elevation effects on microalgal isotope values, and sufficient variability and overlap in primary producer isotope values to create some difficulty in identifying unique end members. The food webs supporting F. heteroclitus production were examined using dual isotope plots. At both sites, the δ 13C values of F. heteroclitus were clustered over values for benthic microalgae (BMI) and approximately midway between δ 13C values of Spartina and Phragmites. Based on comparisons of fish and primary producer δ 13C, δ 15N, and δ 34S values, and consideration of F. heteroclitus feeding habits, we conclude that BMI were a significant component of the food web supporting F. heteroclitus in these brackish marshes, especially recently-hatched fish occupying pools on the marsh surface. A 2‰ difference in δ 13C between Fundulus occupying nearly adjacent Spartina and Phragmites marshes may be indicative of relatively less reliance on BMI and greater reliance on Phragmites production in Phragmites-dominated marshes, a conclusion consistent with the reduced BMI biomass found in Phragmites marshes. The mean δ 13C value of F. heteroclitus from restored marshes was intermediate between values of fish from naturally occurring Spartina marshes and areas invaded by Phragmites. We also examined the isotopic evidence for ontogenetic changes in the trophic position of larval and juvenile F. heteroclitus. We found significant positive relationships between F. heteroclitus δ 15N values and total length, reflective of an increase in trophic position as fish grow. F. heteroclitus δ 15N values indicate that these fish are feeding approximately two trophic levels above primary producers. 相似文献
11.
Phragmites australis (common reed) has been increasing in brackish tidal wetlands of the eastern United States coast over the last century. Whereas several researchers have documented changes in community structure, this research explores the effects of Phragmites expansion on aboveground biomass and soil properties. We used historical aerial photography and a global positioning system (GPS) to identify and age Phragmites patches within a high marsh dominated by shortgrasses ( Spartina patens and Distichlis spicata). Plots along transects were established within the vegetation types to represent a gradient of species dominance and a variety of ages of the Phragmites plots. In comparison to neighboring shortgrass communities, Phragmites communities were found to have nearly 10 times the live aboveground biomass. They also had lower soil salinity at the surface, a lower water level, less pronounced microtopographic relief, and higher redox potentials. These soil factors were correlated with the age and biomass of Phragmites communities, were increasingly different with increasing Phragmites dominance along the transects, and were increasingly altered by the ages of Phragmites communities until the factors stabilized in plots of 8 yr to 15 yr of age. We propose that Phragmites expansion plays an important role in altering these soil properties and suggest a variety of mechanisms to explain these alterations. 相似文献
12.
We assess the probability and importance of different spatial distributions of Phragmites australis (Trin Ex Steud) within brackish tidal marshes of the mid-Atlantic United States coast. The comparative impact of Phragmites expansion on the larger coupled marsh-estuary system may partially be a function of the landscape area dominated by Phragmites, the landscape position occupied by Phragmites, the landscape pattern created by Phragmites expansions, and the resulting impact on tidal drainage networks. We find evidence that Phragmites establishment can occur at many landscape positions, and that Phragmites spread within a marsh can occur via colonization (new patches), linear clonal growth (along a preferred axis), or circular clonal growth (non-directional, random spread). Early intervals of Phragmites spread were dominated by colonization for all sites except for Piermont Marsh (which appeared to be dominated by linear clonal growth) and Lang Tract (which appeared to be dominated by circular clonal growth). Although 46–100% of new patches of Phragmites occurred within 5 m of drainages, at only one site (Piermont Marsh, New York) did Phragmites populations remain concentrated along creek banks. Except for Iona Island, New York, which appears to be in an early stage of Phragmites invasion, patch dynamics at all sites showed an increase followed by a decrease in patch number, as independent patches became established, expanded, and coalesced. We also found some evidence for a loss of first order streams at later stages of Phragmites invasions in several sites (Hog Island, Lang Tract, Silver Run). 相似文献
13.
Negative connotations of invasive plants worldwide have implicated them as the bearers of unfavorable ecosystem change. We
contrasted 5-yr-old and 20-yr-old Phragmites populations with pre-invasion areas occupied by Typha spp. and Panicum virgatum in an oligohaline tidal marsh of Chesapeake Bay. Peak live biomass was 3 times greater, while standing dead and litter was
twice as great in the 20-yr-old Phragmites. It is this abundance of concentrated litter on the marsh surface of mature Phragmites populations that we implicate as encouraging the trapping of organic and mineral matter. The rate of vertical accretion in
20-yr-old Phragmites populations is 3–4 mm yr −1 above the adjacent populations. By integrating the constant initial concentration and constant rate of supply models on individual 210Pb cores, we estimate that Phragmites populations require a minimum of 7-yr post-colonization to enhance rates of accretion in this system. In ligh of the considerable
loss of marsh habitat from relative sea-level rise, this finding contests the view that invasion creates strictly undesirable
change at the ecosystem level. 相似文献
14.
Through their physiological effects on ion, oxygen, and carbon balance, respectively, salinity, sulfide, and prolonged flooding
combine to constrain the invasion and spread of Phragmites 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 to Phragmites 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%. For Phragmites 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 avoid Phragmites monocultures, tidal wetland creation, restoration, and management must be considered within the context of these different
scales of plant-environment interaction. 相似文献
15.
The extensive spread of Phragmites 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 in Phragmites marshes. Microbial populations associated with invasive Phragmites 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 with Phragmites and Spartina 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. 相似文献
16.
For a common, widespread, and familiar plant, Phragmites australis engenders an enormous level of scientific controversy and emotional conflict. In parts of the world, Phragmites is an important component of healthy ecosystems and an integral (if now minor) contributor to human economies. In other places
it is an invading, unfriendly, and ugly weed. To some scientists and environmentalists, Phragmites is an indicator of and key factor in landscape degradation and habitat deterioration. To others, it is a valiant remnant
of nature, providing a relatively rich ecology where there might otherwise be only barren and eroding ground. Our review of
the literature leads us to conclude that Phragmites is simply a biological entity. It is not inherently good or bad, since its evolution, biology, and ecology do not give it
a value. The controversy over Phragmites, its role in the ecosystem, and the need for and intensity of management efforts are all artifacts of human perspectives.
Effective, consistent management decisions (for either control or enhancement of Phragmites) can only be made on the basis of site-specific scientific findings, a consideration of technologies with their needed level-of-effort,
and explicit exposition of the human values driving the management options. We present a simple decision model to illustrate
the interaction of these management components for Phragmites in the environment. 相似文献
17.
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-CO 2. 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% 14CO 2 ± 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. 相似文献
18.
The invasion and expansion of the introduced haplotype of Phragmites australis across North America is of growing concern. Previous studies in the Chesapeake Bay region found that Phragmites was more abundant, had higher foliar nitrogen, and produced more viable seeds in brackish wetland subestuaries with more
anthropogenic development of the watershed. Here, we focus on a different scale and address issues related to the invasion
of Phragmites within a single subestuary, the Rhode River. We evaluated patterns in seed viability, foliar nutrient concentrations, patch
size, and genetic variation in ten Phragmites patches in wetlands that occur in the side of the subestuary that is surrounded by forest and 10 patches in wetlands that
are in the side of the subestuary that has extensive anthropogenic development. Seed viability varied from 0–60% among the
20 patches but did not differ significantly between patches on the developed vs. forested sides of the Rhode River. Foliar
nutrients also did not differ between patches on the two sides of the Rhode River. Seed viability, however, was negatively
related to foliar nutrients. Most Phragmites patches consisted of >1 genotype. Larger patches had multiple genotypes, and patches with more genotypes produced more viable
seeds. Our study indicates that the Rhode River subestuary behaves as one system with no differences in the measured Phragmites variables between the forested vs. developed sides of the watershed. Our findings also suggest a cyclical process by which
Phragmites can spread: larger patches contain more genetic diversity, which increases the chances for cross-fertilization. The subsequent
increased production of viable seeds can increase local levels of genetic diversity, which can further facilitate the spread
of Phragmites by seed. 相似文献
19.
Sediment microphytobenthos, such as diatoms and photosynthetic bacteria, are functionally important components of food webs
and are key mediators of nutrient dynamics in marine wetlands. The medium to long-term recovery of benthic microproducers
in restored habitats designed to improve degraded coastal wetland sites is largely unknown. Using taxon-specific photopigments,
we describe the composition of microphytobenthic communities in a large restoration site in southern California and differences
in the temporal recovery of biomass (chlorophyll a), composition, and taxonomic diversity between vegetated Spartina foliosa salt marsh and unvegetated mudflat. Visually distinct, spatially discreet, microphytobenthic patches appeared after no more
than 7 mo within the restoration site and were distinguished by significant differences in biomass, taxonomic diversity, and
the relative abundance of cyanobacteria versus diatoms. Sediment chlorophyll a concentrations within the restored site were similar to concentrations in nearby natural habitat 0.2–2.2 yr following marsh
creation, suggesting rapid colonization by microproducers. Restored Spartina marsh very rapidly (between 0.2 and 1.2 yr) acquired microphytobenthic communities of similar composition and diversity to
those in natural Spartina habitat, but restored mudflats took at least 1.6 to 2.2 yr to resemble natural mudflats. These results suggest relatively
rapid recovery of microphytobenthic communities at the level of major taxonomic groups. Sediment features, such as pore water
salinity and Spartina density, explained little variation in microphytobenthic taxonomic composition. The data imply that provision of structural
heterogeneity in wetland construction (such as pools and vascular plants) might speed development of microproducer communities,
but no direct seeding of sediment microfloras may be necessary. 相似文献
20.
We examined fish assemblages in tidal salt marsh creeks in Delaware Bay in order to evaluate their response to treatment forPhragmites removal following initial treatment in 1996. In Alloway Crrek, a tributary to Delaware Bay, reference creeks draining marsh of untreatedPhragmites or naturally occurringSpartina were compared with creeks in marshes treated forPhragmites removal. These reference and treated creeks occur in close proximity and share many characteristics including salinity, temperature, dissolved oxygen, and turbidity, although creeks inPhragmites sites differed slightly in bathymetry. We analyzed a time series of otter trawl collections (22 monthly sample periods from 1999 to 2001) for differences in juvenile fish assemblage among creeks with different vegetation history. Periodically, young-of-the-year (YOY) and age 1+ white perch (Morone americana), YOY spot (Leiostomus xanthurus), YOY Atlantic menhaden (Brevoortia tyrannus), and other species were relatively more abundant atPhragmites sites, but other dominant species were preiodically abundant at all sites. Among-treatment differences based on principal response curves analysis accounted for about 19% of the total species variation, but differences varied widely among sample periods and there is little or no indication of a trend over the 3-yr period. Larger collections were often associated with subtidal structure, which was more common atPhragmites sites and potentially represents a sampling artifact. Assemblages of creeks with differing vegetation history differ weakly but recognizably, suggesting slow or little response to treatment, at least based on otter trawl collections in subtidal marsh creeks. 相似文献
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