首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 34 毫秒
1.
This paper documents horizontal and vertical dispersion patterns of a Texas population of the saltmarsh periwinkle, Littoraria irrorata, over a 15-month period. The study was conducted within a tidal marsh on the Anahuac National Wildlife Refuge in Galveston Bay. Two mark-recapture experiments demonstrated that L. irrorata rarely move more than 2 m from their release point over long periods of time and do not home to individual Spartina plants. Adult L. irrorata forage farther away from the base of Spartina stalks at low tide than do juvenile snails. Remaining near the plant base may decrease both temperature and desiccation stress on juveniles. During warm months, L. irrorata climb grass stalks with tidal inundation and forage on the substratum at low tide. Snails are inactive and aggregate in detrital debris at the base of Spartina clumps during the winter. *** DIRECT SUPPORT *** A01BY058 00016  相似文献   

2.
Spartina alterniflora salt marshes along the southeastern United States are some of the most productive and well studied ecosystems in the world. The role of physicochemical forces in regulatingSpartina growth is well understood, while the importance of grazers remains less clear. Recent studies have shown that the abundant marsh periwinkle,Littoraria irrorata, can exert strong control overSpartina through its grazing activities, but relatively little is known about its relative effects in comparison to other marsh plant consumers. To test the relative importance of snail and insect consumers onSpartina biomass, we conducted a 7-mo field experiment testing top-down regulation ofSpartina with all combinations ofL. irrorata (removed, control, c. 215 periwinkles m−2) andSpartina planthopper,Prokelisia marginata (removed, control). Snail removal resulted in a 50% increase inSpartina biomass while removal of planthoppers had no detectable effect. Planthopper density also increased by 50% when snails were excluded. In this South Carolina marsh,L. irrorata exerts a stronger top-down control ofSpartina thanP. marginata. These results indicate trophic cascade regulation ofSpartina salt marsh is more likely to occur through the predator(s)-Littoraria-plant interaction than through the predator(s)-Prokelisia-plant relationship.  相似文献   

3.
Tidal salt marsh is a key defense against, yet is especially vulnerable to, the effects of accelerated sea level rise. To determine whether salt marshes in southern New England will be stable given increasing inundation over the coming decades, we examined current loss patterns, inundation-productivity feedbacks, and sustaining processes. A multi-decadal analysis of salt marsh aerial extent using historic imagery and maps revealed that salt marsh vegetation loss is both widespread and accelerating, with vegetation loss rates over the past four decades summing to 17.3 %. Landward retreat of the marsh edge, widening and headward expansion of tidal channel networks, loss of marsh islands, and the development and enlargement of interior depressions found on the marsh platform contributed to vegetation loss. Inundation due to sea level rise is strongly suggested as a primary driver: vegetation loss rates were significantly negatively correlated with marsh elevation (r 2?=?0.96; p?=?0.0038), with marshes situated below mean high water (MHW) experiencing greater declines than marshes sitting well above MHW. Growth experiments with Spartina alterniflora, the Atlantic salt marsh ecosystem dominant, across a range of elevations and inundation regimes further established that greater inundation decreases belowground biomass production of S. alterniflora and, thus, negatively impacts organic matter accumulation. These results suggest that southern New England salt marshes are already experiencing deterioration and fragmentation in response to sea level rise and may not be stable as tidal flooding increases in the future.  相似文献   

4.
Coastal wetlands, well recognized for their ecosystem services, have faced many threats throughout the USA and elsewhere. While managers require good information on the net impact of these combined stressors on wetlands, little such information exists. We conducted a 4-month mesocosm study to analyze the multiple stressor effects of precipitation changes, sea level rise, and eutrophication on the salt marsh plant Spartina alterniflora. Pots containing plants in an organic soil matrix were positioned in tanks and received Narragansett Bay (RI, USA) water. The study simulated three precipitation levels (ambient daily rain, biweekly storm, and drought), three levels of tidal inundations (high (15 cm below mean high water (MHW)), mean (MHW), and low (15 cm above MHW)), and two nutrient enrichment levels (unenriched and nutrient-enriched bay water). Our results demonstrate that storm and drought stressors led to significantly less above- and belowground biomass than those in ambient rain conditions. Plants that were flooded at high inundation had less belowground biomass, fine roots, and shoots. Nutrients had no detectable effect on aboveground biomass, but the enriched pots had higher stem counts and more fine roots than unenriched pots, in addition to greater CO2 emission rates; however, the unenriched pots had significantly more coarse roots and rhizomes, which help to build peat in organogenic marshes. These results suggest that multiple stressors of altered precipitation, sea level rise, and nutrient enrichment would lead to reduced marsh sustainability.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
Coastal salt marshes represent an important coastal wetland system. In order to protect coastlines from erosion and rapid increase in accumulation rate, Spartina alterniflora (S. alterniflora) was introduced into the Chinese coast. Two study areas (Wanggang and Quanzhou Bay) were selected that represent the plain type and embayment type of the coastal salt marshes. In situ measurements show that the tidal current velocities are stronger on the intertidal mudflat without S. alterniflora than that with S. alterniflora, and the velocity above the canopy surface is larger than that in the salt marsh canopy. The existence of S. alterniflora also influences the velocity structure above the bare flat during ebb tide. With the decrease in current flow velocity when seawater enters into the S. alterniflora marsh, suspended sediments are largely entrapped on the marsh surface, leading to increase in sedimentation rates and change in physical evolution processes of the coastal salt marshes. The highly developed root systemof S. alterniflora induces sediment mixing and exchange between subsurface sediment strata and affects the vertical sediment distribution remarkably. The sedimentation rate of S. alterniflora marsh at the Wanggang area is much higher than the relative sea level rise rate, where rapid progradation of theWanggang saltmarshes that is protecting the coast from sea erosion is observed.  相似文献   

8.
Surface films on marsh creeks form water-air interfaces of high biological activity. The development, movement, deposition, and breakup of the tidal creek surface film in a naturalSpartima alterniflora-dominated salt marsh in Delaware were followed seasonally over tidal cycles. The metabolic activity, i.e., photosynthesis and respiration, of the surface film and underlying water were determined in the field at the time of peak film formation, just prior to high tide, and the particulate material and chlorophylla were quantified over the tidal cycles. The quantities of organic and inorganic components of the particulate material were all significantly higher in the surface film than in the underlying water (on a volume basis). Numbers of algal cells and quantities of chlorophyll were orders of magnitude greater in the surface film than in the water column. Photosynthesis and respiration were significantly higher in the surface film than in the underlying water. The spectrum of fatty acids was more diverse and their total content was significantly greater in the surface film than in the water column, indicating a concentrated food source contributed by the film as well as a biological richness of the film. When water in the creek flooded the marsh plain at high tide, film deposition was greatest on simulated creek bankS. alterniflora stems, compared to stems along rivulets in the marsh and those in the marsh plain. Using surface film dry weight measurements on an areal basis and film velocity in the creek, both measured throughout a tidal cycle during the summer, it was determined that approximately 12 kg (dry weight) of particulate material moved on the creek surface (2 m wide) past a given point on the flood tide, and 14 kg moved in the opposite direction on the ebb tide. The biological and physical data collected in this study illuminate the contribution of the surface film to the biological (food web) and physical (sediment transport and deposition) functions of a salt marsh.  相似文献   

9.
Experimental chambers were used in a Virginia salt marsh to partition the tidal flux of dissolved nutrients occurring at the marsh surface and in the water column. On five dates from June to October 1989, six replicate chambers in the short Spartina alterniflora zone were monitored over complete tidal cycles. When reservoir water, used to simulate tidal flooding in the chambers, was initially low in dissolved nutrients, the marsh surface was a source of both ammonium and phosphate to the water column. Calculations of the physical processes of diffusion and advection could not account for total nutrient release from the marsh surface. We hypothesize the primary source of nutrients was organic matter mineralization in surface sediments, which released nutrients into the flooding water column. Assimilation (uptake) of phosphate measured in water-column incubation experiments was nearly equal to phosphate released from the marsh surface. Surface release of ammonium, however, was somewhat greater than water-column uptake. In this salt marsh, benthic production and release of ammonium and phosphate is comparable in magnitude to pelagic consumption, thereby yielding only a small “net” transfer of these nutrients to the estuary.  相似文献   

10.
Salt marsh systems of the southeastern United States are characterized by extensive stands ofSpartina alterniflora. These marshes may influence the concentrations of material suspended in flooding and receding tidal waters. The ability of aSpartina alterniflora-dominated marsh to influence the concentration of suspended microbial biomass was investigated through the use of a 142-m long flume. The flume extended through stands of tall-, medium-, and short-heightSpartina. Water passing through the tallSpartina lost a considerable portion of microbial biomass. Initial samples from medium-heightSpartina were collected from water that had already passed through the tall grass. These samples contained 20 to 70% less microbial biomass than did water entering the tallSpartina. Calculations of mass transport suggest that the tallSpartina zone of marsh acts as a sink for microbial biomass while the short-heightSpartina tends to export biomass (to the tallSpartina zone). The marsh as a whole acts as a sink for microbial biomass. Transport estimates from 32 individual tide cycles were modeled to obtain an annual estimate of transport. As a consequence of high variability among individual transport estimates, no annual transport estimate could be distingushed from a net-zero transport.  相似文献   

11.
Three coastal salt marshes were surveyed independently by two teams of biologists to determine the upper limit of marsh. Distribution of species and species assemblages were related to surveyed elevations for South Beach marsh, Yaquina River estuary; Drift Creek marsh, Alsea River estuary; and Bandon marsh, Coquille River estuary. A transition zone between marsh and upland was identified by strong dominance ofPotentilla pacifica and the presence ofAchillea millefolium, Angelica lucida, Aster subspicatus, Oenanthe sarmentosa, Trifolium wormskjoldii, andVicia gigantea. Mean elevation of the lower boundary of the transition zone was 1.38 m above National Geodetic Vertical Datum (N.G.V.D.) and the upper boundary of the transition zone was 1.54 m above N. G. V. D. Relation of the upper limit of marsh to tidal datums varied with marsh. Mean elevation of the upper and lower limit of the transition zone was 0.58 m above MHW and 0.36 m above MHW, respectively. The two teams of biologists using the same biological criteria for defining the upper limit of marsh, independently agreed on the elevational position of the upper limit of marsh. Additional research and testing of the definition of the upper limit of marsh is warranted.  相似文献   

12.
Responses ofSpartina alterniflora marsh to combinations of feral horse grazing, clipping, simulated trampling, and a late winter burn were studied on Cumberland Island National Seashore, Georgia. Replicated 200-m2 plots were established and sampled bimonthly from July 1983 to November 1984. Clipping and trampling each reduced peak aboveground biomass by 20% in 1983 and 50% (clipping) and 55% (trampling) in 1984. A March burn reduced peak aboveground biomass by 35% in 1984. Trampling and burning earch reduced net aboveground primary production (NAPP) by 35%, but clipping did not reduce NAPP. Standing stocks of live rhizomes were correlated with aboveground biomass and were reduced with experimental treatments. Abundance of the periwinkle snail (Littorina irrorata) was also reduced. Horse grazing had a substantial impact on standing stocks and NAPP ofSpartina, but grazing was not uniform throughout the marsh. Moderately grazed plots had NAPP reduced by 25% compared to ungrazed plots. Heavily grazed plots had extremely low NAPP, and abovegroundSpartina never exceeded 40 g m?2 dry mass compared to 360 g m?2 within exclosures.  相似文献   

13.
This study provides new insights in the relative role of tidal creeks and the marsh edge in supplying water and sediments to and from tidal marshes for a wide range of tidal inundation cycles with different high water levels and for marsh zones of different developmental stage. Net import or export of water and its constituents (sediments, nutrients, pollutants) to or from tidal marshes has been traditionally estimated based on discharge measurements through a tidal creek. Complementary to this traditional calculation of water and sediment balances based on creek fluxes, we present novel methods to calculate water balances based on digital elevation modeling and sediment balances based on spatial modeling of surface sedimentation measurements. In contrast with spatial interpolation, the presented approach of spatial modeling accounts for the spatial scales at which sedimentation rates vary within tidal marshes. This study shows that for an old, high marsh platform, dissected by a well-developed creek network with adjoining levees and basins, flow paths are different for tidal inundation cycles with different high water levels: during shallow inundation cycles (high water level <0.2 m above the creek banks) almost all water is supplied via the creek system, while during higher inundation cycles (high water level >0.2 m) the percentage of water directly supplied via the marsh edge increases with increasing high water level. This flow pattern is in accordance with the observed decrease in sedimentation rates with increasing distance from creeks and from the marsh edge. On a young, low marsh, characterized by a gently seaward sloping topography, material exchange does not take place predominantly via creeks but the marsh is progressively flooded starting from the marsh edge. As a consequence, the spatial sedimentation pattern is most related to elevation differences and distance from the marsh edge. Our results imply that the traditional measurement of tidal creek fluxes may lead in many cases to incorrect estimations of net sediment or nutrient budgets.  相似文献   

14.
Topsail Sound is a marsh-filled barrier lagoon in southeastern North Carolina. This study quantified changes within a 477-ha tidal marsh located landward of Lea and Coke islands in southern Topsail Sound. Aerial photographs from 1949, 1966, and 1984 were enlarged, and sample areas of salt marsh were digitized and compared. Since 1949, Old Topsail Inlet has migrated southwest 1.2 km. As the inlet migrated, new Spartina alterniflora marsh colonized 33.2 ha of intertidal sand flats within the inlet flood tidal delta, adjacent islands, and primary tidal creeks. Landward of the flood tidal delta, site specific gains and losses of marsh were recorded. It is estimated that since 1949, approximately 34.1 ha of the marsh area occupying the zone landward of the flood tidal delta has drowned. This loss of marsh, combined with the colonization of marsh mentioned above, resulted in a net decrease of 1 ha in the total area of marsh. This study provides evidence that, although lagoonal marshes may be drowning as a result of soil waterlogging, reduced sediment supply, and sea-level rise, potential marsh environments are created by oceanic inputs of sand when inlets migrate.  相似文献   

15.
An analysis of data relatingSpartina alterniflora Loisel. to tidal elevations along the Atlantic and Gulf coasts demonstrated that although this species is primarily confined to the intertidal zone, its elevational limits. of occurrence do not correspond to a consistent elevation relative to a tidal datum in all marsh locations. The variation in the vertical distribution of this species reported among marsh studies was attributed primarily to differences in mean tide range (MTR). A positive correlation between MTR and elevational growth range (r=0.91) demonstrated that theSpartina alterniflora zone expands with increasing tidal amplitude. Differences in MTR among marsh locations accounted for 70 and 68% of the statistical variation in the upper and lower limits, respectively, ofS. alterniflora growth. Among marshes of similar tidal amplitudes, the upper limit of occurrence ofS. alterniflora in northern marshes was significantly lower than that in marshes at lower latitudes. These results, in combination with regional differences in plant species distribution across the upper intertidal zone, suggested that some of the variation in the upper limit was due to latitudinal differences in growth conditions and/or differences in interspecific competition. Local and regional differences in other factors such as salinity, nutrients, or physical disturbance may have also contributed to the variation in the limits of growth relative to a tidal plane within and among marshes.  相似文献   

16.
Flooding of salt marshes controls access to the marsh surface for aquatic organisms and likely regulates the value and use of this habitat for juvenile fishery species. We examined geographic variability in marsh access by measuring tidal flooding characteristics in 15 Spartina alterniflora marshes in the southeastern US between South Texas and lower Chesapeake Bay. Flooding duration and flooding frequency were correlated with the elevation of the marsh edge in relation to mean low water and with the tidal range. Mean annual flooding duration over the years 2006–2008 was highest in Texas (91.5% in Aransas Bay) and North Carolina (89.3% in Pamlico Sound) and lowest in Timbalier Bay, LA (54%) and the lower Carolinas and Georgia (55–57%). We used published data on densities of blue crabs and penaeid shrimps as a measure of habitat selection, and there was a positive relationship between marsh selection and flooding duration.  相似文献   

17.
Most primary production of angiosperms in coastal salt marshes enters the detritivore food web; studies of this link have predominantly focused on one plant species (Spartina alterniflora) and one detritivore species (Littoraria irrorata). In mesocosm experiments, we studied the rates and pattern of decomposition of litter derived from four plant species common in southeastern United States coastal salt marshes and marsh-fringing terrestrial habitats. Crustanceans and gastropods were selected as detritivores feeding on, and affecting degradation of, the litter of two monocotyledons and two dicotyledons. Despite interspecific similarities in consumption, detritivores exhibited species-specific effects on litter chemistry and on the activity of litter-colonizing microbiota. The chemical composition of feces depended upon both the litter type and the detritivores’ species-specific digestive capabilities. Growth rates and survival of detritivores differed among litter species. Different salt marsh detritivores are likely to have different effects on decomposition processes in the salt marsh and cannot be regarded as functionally redundant nor can the litter of different plant species be regard ed as redundant as food for marsh detritivores.  相似文献   

18.
Geomorphology may be an important predictor of vegetation pattern in systems where suceptibility to disturbance is unevenly distributed across the landscape. Salt marsh communities exhibit spatial pattern in vegetation at a variety of spatial scales. In coastal Georgia, the low marsh is a virtual monoculture ofSpartina alterniflora interspersed with patches of species that are more typical of the high marsh. These localized disturbances are most likely created by wrack mats, mats of dead vegetation which can compact and smother underlying vegetation creating bare patches for colonization by high marsh species. We investigated the spatial pattern of disturbed patches along a 2 km section of Dean Creek, a tidal creek at the southwestern end of Sapelo Island, Georgia, U.S. We used a discriminant model to explore the relationship between tidal creek morphology (e.g., the presence of drainage channels and creek bends) and the spatial distribution of disturbed patches. The model predicted vegetation pattern along the creek with relatively high accuracy (>70%). Areas where water movement is slowed or multidirectional (e.g., along creek bends and near drainage channels) were most susceptible to disturbance. Our findings suggest an important functional linkage between geomorphology and vegetation pattern in salt marsh communities.  相似文献   

19.
Salt marsh intertidal creeks are important habitats for dozens of species of nekton, but few studies have attempted to quantify patterns of tidal movement. We used the sweep flume, a new sampling device, to investigate relationships between depth and movements of nekton inside the mouths of intertidal creeks. Sweep flumes located in three creek beds were used to collect nekton at 10 cm increments (10–100 cm of water depth) during flood and ebb tides in the North Inlet, South Carolina, salt marsh. Of the 37 taxa collected, 13 comprised>99.5% of the total catch and were the focus of the analysis. A nonlinear mixed modeling procedure was used to determine, the depth at which each major taxon reached peak abundance during flood tides. With high degrees of spatial and temporal consistency, resident taxa entered early on the rpsing tide and transient taxa entered during mid to late tide. Depths of peak migrations varied among taxa and were consistent between creeks, days (within months), and years. As summer progressed, depths of peak migration increased for young-of-the-yearLeiostomus xanthurus, Lagodon rhomboides, Mugil curema, Eucinostomus argenteus, andLitopenaeus setiferus as their median sizes increased. Within tides, depths of migration increased as a function of size forL. xanthurus andM. curema. Comparisons between flood and ebb tides indicated that most taxa exited the creeks at approximately the same depths at which they entered. Relationships between major taxa pairs suggested that biotic interactions may have contributed to the structure of the migrations observed in this study. Our results are the first to demonstrate quantitatively that the migrations of nektonic taxa into intertidal creeks are structured and related to depth.  相似文献   

20.
Aerial photographs and GIS analysis were used to map the distribution of tidal marsh vegetation along the salinity gradients of the estuaries of the Altamaha and Satilla Rivers in coastal Georgia. Vegetation maps were constructed from 1993 U.S. Geological Survey Digital Orthophoto Quarter Quads, 1∶77,000-scale color infrared photographs taken in 1974 and 1∶24,000-scale black and white photographs taken in 1953, Changes between years were identified using a GIS overlay analysis. Four vegetation classifications were identified and groundtruthed with field surveys: salt marsh (areas containing primarilySpartina alterniflora), brackish marsh (Spartina cynosuroides andS. alterniflora), Juncus (Juncus roemerianus), and fresh marsh (Zizania aquatica, Zizaniopsis miliacae, and others). There was no evidence for an upstream shift in marsh vegetation along the longitudinal axis of either estuary over the time frame of this analysis, which implies there has not been a long-term increase in salinity. Although the inland extent of each marsh zone was further upstream in the Satilla than the Altamaha, they corresponded to similar average high tide salinities in each estuary: areas classified as salt marsh occurred from the mouth up to where average high tide salinity in the water was approximately 15 psu;Juncus ranged from 21 to 1 psu; brackish marsh ranged from 15 to 1 psu; and fresh marsh was upstream of 1 psu. Approximately 63% of the 6,786 ha of tidal marsh vegetation mapped in the Altamaha and 75% of the 10,220 ha mapped in the Satilla remained the same in all 3 yr.Juncus was the dominant classification in the intermediate regions of both estuaries, and shifts between areas classified asJuncus and either brackish or salt marsh constituted the primary vegetation change between 1953 and 1993 (87% of the changes observed in the Altamaha and 95% of those in the Satilla). This analysis suggests that the broad distribution of tidal marsh vegetation along these two estuaries is driven by salinity, but that at the local scale these are dynamic systems with a larger number of factors affecting the frequently changing borders of vegetation patches.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号