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1.
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
2.
The distribution and salinity preference of immature bull sharks ( Carcharhinus leucas) were examined based on the results of longline surveys in three adjacent estuarine habitats in southwest Florida: the Caloosahatchee
River, San Carlos Bay, and Pine Island Sound. Mean sizes were significantly different between each of these areas indicating
the occurrence of size-based habitat partitioning. Neonate and young-of-the-year animals occurred in the Caloosahatchee River
and juveniles older than 1 year occurred in the adjacent embayments. Habitat partitioning may reduce intraspecific predation
risk and increase survival of young animals. Classification tree analysis showed that both temperature and salinity were important
factors in determining the occurrence and catch per unit effort (CPUE) of immature C. leucas. The CPUE of <1 year old C. leucas was highest at temperatures over 29°C and in areas with salinities between 7‰ and 17.5‰ Although they are able to osmoregulate
in salinities from fresh to fully marine, young C. leucas may have a salinity preference. Reasons for this preference are unknown, but need to be further investigated. 相似文献
3.
Delaware Bay is one of the largest estuaries on the U.S. eastern seaboard and is flanked by some of the most extensive salt marshes found in the northeastern U.S. While physicochemical and biotic gradients are known to occur along the long axis of the bay, no studies to date have investigated how the fish assemblage found in salt marsh creeks vary along this axis. The marshes of the lower portion of the bay, with higher salinity, are dominated by Spartina spp., while the marshes of the upper portion, with lower salinity, are currently composed primarily of common reed, Phragmites australis, S. alterniflora, or combinations of both. Extensive daytime sampling (n=815 tows) during May–November 1996 was conducted with otter trawls (4.9 m, 6 mm mesh) in six intertidal and subtidal marsh creek systems (upper and lower portions of each creek) where creek channel depths ranged from 1.4–2.8 m at high tide. The fish taxa of the marsh creeks was composed of 40 species that were dominated by demersal and pelagic forms including sciaenids (5 species), percichthyids (2), and clupeids (7), many of which are transients that spawn outside the bay but the early life history stages are abundant within the bay. The most abundant species were Morone americana (24.3% of the total catch), Cynoscion regalis (15.4%), Micropogonias undulatus (15.3%), Anchoa mitchilli (12.0%), and Trinectes maculatus (10.8%). Non-metric Multi-Dimensional Scaling ordination of catch per unit effort (CPUE) data indicated two fish assemblages that were largely independent of the two major vegetation types, but generally corresponded with spatial variation in salinity. This relationship was more complex because some of the species for which we could discriminate different age classes by size had different patterns of distribution along the salinity gradient. 相似文献
4.
The first advisory to limit consumption of Florida Bay fish due to mercury was issued in 1995. Studies done by others in the
late 1990s found elevated water column concentrations of both total Hg (THg) and methylmercury (MeHg) in creeks discharging
from the Everglades, which had its own recognized mercury problem. To investigate the significance of allochthonous MeHg discharging
from the upstream freshwater Everglades, we collected surface water and sediment along two transects from 2000 to 2002. Concentrations
of THg and MeHg, ranging from 0.36 ng THg/L to 5.98 ng THg/L and from <0.02 ng MeHg/L to 1.79 ng MeHg/L, were elevated in
the mangrove transition zone when compared both to upstream canals and the open waters of Florida Bay. Sediment concentrations
ranged from 5.8 ng THg/g to 145.6 ng THg/g and from 0.05 ng MeHg/g to 5.4 ng MeHg/g, with MeHg as a percentage of THg occasionally
elevated in the open bay. Methylation assays indicated that sediments from Florida Bay have the potential to methylate Hg.
Assessment of mass loading suggests that canals delivering stormwater from the northern Everglades are not as large a source
as direct atmospheric deposition and in situ methylation, especially within the mangrove transition zone. 相似文献
5.
Increases in relative sea level are fragmenting the emergent vegetation of Louisiana’s coastal marshes. Nekton abundance is
likely impacted by salinity and whether emergent vegetation is replaced by submerged aquatic vegetation (SAV) or open water.
To assess these effects, we sampled nekton densities along a salinity gradient (categorized as freshwater, intermediate, and
brackish marsh) in fragmented and non-fragmented areas. Total nekton density increased strongly with SAV in brackish marsh
but only weakly in freshwater marsh ( F
2,238 = 10.03, p < 0.0001). Freshwater and intermediate marshes had higher nekton densities when fragmented than when non-fragmented; this
relationship was reversed in brackish marsh ( F
2,238 = 8.89, p = 0.0002). Fragmentation, SAV, and salinity interacted to affect the densities of Gambusia affinis, Poecilia latipinna, Cyprinodon variegates, and Lucania parva. Our results suggest that the presence of both emergent vegetation and SAV was necessary for maintaining high nekton densities,
with this combination being especially important in brackish marshes. 相似文献
6.
Biomass, net primary productivity (NPP), foliar elemental content, and demography of Thalassia testudinum were monitored in populations from five sites across Florida Bay beginning in January 2001. Sites were selected to take advantage
of the spatial variability in phosphorus (P) availability and salinity climates across the bay. Aboveground biomass and NPP
of T. testudinum were determined five to six times annually. Short-shoot demography, belowground biomass, and belowground NPP were assessed
from a single destructive harvest at each site and short-shoot cohorts were estimated from leaf scar counts multiplied by
site-specific leaf production rates. Biomass, relative growth rate (RGR), and overall NPP were positively correlated with
P availability. Additionally, a positive correlation between P availability and the ratio of photosynthetic to non-photosynthetic
biomass suggests that T. testudinum increases allocation to aboveground biomass as P availability increases. Population turnover increased with P availability,
evident in positive correlations of recruitment and mortality rates with P availability. Departures from seasonally modeled
estimates of RGR were found to be influenced by salinity, which depressed RGR when below 20 psu or above 40 psu. Freshwater
management in the headwaters of Florida Bay will alter salinity and nutrient climates. It is becoming clear that such changes
will affect T. testudinum, with likely feedbacks on ecosystem structure, function, and habitat quality. 相似文献
7.
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
8.
This study examined the effects of watershed development on macrobenthic communities in tidal creeks of Charleston Harbor, South Carolina, U.S. Two types of creeks were evaluated: upland creeks which drained watersheds consisting of at least 15% terrestrial land cover, and salt marsh creeks which drained no upland habitat (i.e., only intertidal habitat). Samples of macrobenthic organisms were taken along the longitudinal axis of twenty-three primary (first order) tidal creeks. Water and sediment quality data were also collected including measurements of dissolved oxygen, salinity, temperature, sediment characteristics, and toxic chemicals in the creek sediments. Hypoxic conditions occurred more than 15% of the time in both reference and developed creeks and were a natural attribute of these systems. The most severe and frequent hypoxia occurred in impacted salt marsh creeks. Salinity fluctuations were the greatest in developed upland creeks and salinity range was identified as a potentially reliable indicator of the degree to which watershed development has altered hydrodynamic processes. The creeks draining urban and industrial watersheds were degraded environments characterized by watersheds with high (>50%) levels of impervious surface, broad fluctuations in salinity, severe hypoxia, and potentially toxic levels of chemicals in the sediment. These creeks had low macrobenthic diversity and abundance and were numerically dominated by the oligochaete Monopylephorus rubroniveus in mud sediments, and the polychaete Laeoreis culveri in sand sediments. Suburban watersheds had 15–35% impervious surface and creeks draining them were exposed to frequent hypoxia and broad salinity fluctuations. The levels of chemical contaminants in sediments of suburban and impacted salt marsh creeks were generally not different from the levels in reference creeks. Macrobenthic diversity and abundance were higher for suburban and impacted salt marsh creeks than for urban and industrial creeks. However, suburban and salt marsh impacted creeks were numerically dominated by a few pollution indicative species including the oligochaetes M. rubroniveus and Tubificoides brownae and the polychaete L. culveri. These creeks appear to be exhibiting early signs of degradation (e.g., a simplified food web). Two promising community-level macrobenthic metrics for assessing environmental quality were identified: the proportional abundance of pollution indicative taxa, and the proportional abundance of pollution sensitive taxa. These indicators were significantly (p<0.05) correlated with the salinity range, the level of chemical contaminants in sediments, and amount of impervious surface in the watershed. 相似文献
9.
0-group sea bass, Dicentrarchus labrax, colonize intertidal marsh creeks of Mont Saint Michel Bay, France, on spring tides (e.g., 43% of the tides) during flood
and return to coastal waters during ebb. Most arrived with empty stomachs (33%), and feed actively during their short stay
in the creeks (from 1 to 2 h) where they consumed on average a minimum of 8% of their body weight. During flood tide, diet
was dominated by mysids, Neomysis integer, which feed on marsh detritus. During ebb, when young sea bass left tidal marsh creeks, the majority had full stomachs (more
than 98%) and diet was dominated by the most abundant marsh (including vegetated tidal flats and associated marsh creeks)
resident amphipod, Orchestia gammarellus. Temporal and tidal effects on diet composition were shown to be insignificant. Foraging in vegetated flats occurs very rarely
since they are only flooded by about 5% of the tides. It was shown that primary and secondary production of intertidal salt
marshes play a fundamental role in the feeding of 0-group sea bass. This suggests that the well known nursery function of
estuarine systems, which is usually restricted to subtidal and intertidal flats, ought to be extended to the supratidal, vegetated
marshes and mainly to intertidal marsh creeks. 相似文献
10.
To assess the potential for habitat isolation effects on estuarine nekton, we used two species with different dispersal abilities
and life history strategies, mummichog ( Fundulus heteroclitus) and pinfish ( Lagodon rhomboides) to examine: (1) distribution trends among estuarine shallow-water flat and various intertidal salt marsh habitats and (2)
the influence of salt marsh habitat size and isolation. Collections were conducted using baited minnow traps set within nonisolated
interior marshes (interior), nonisolated fringing marshes (nonisolated), isolated island marshes (isolated), and shallow-water
flat habitats (flat) that were adjacent to isolated and nonisolated marshes. Size range of individuals collected included
juvenile and adult F. heteroclitus (20–82-mm standard length) and L. rhomboides (22–151-mm standard length). During high tide, F. heteroclitus exclusively used marsh habitats, particularly high marsh, whereas L. rhomboides used marshes and flats. F. heteroclitus abundance followed an interior > nonisolated > isolated pattern. L. rhomboides abundance patterns were less consistent but followed a nonisolated > isolated > interior pattern. A size-dependent water
depth relationship was observed for both species and suggests size class partitioning of marsh and flat habitats during high
tide. Minimum water depth (~31 cm) restricted L. rhomboides populations in marshes, while maximum water depth (~69 cm) restricted F. heteroclitus population use of marshes and movement between marsh habitats. Disparities in F. heteroclitus young of year contribution between isolated compared to nonisolated and interior marsh types suggests isolated marshes acted
as population sinks and were dependent on adult emigrants. Resident and transient salt marsh nekton species utilize estuarine
habitats in different ways and these fundamental differences can translate into how estuarine landscape might affect nekton. 相似文献
11.
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
12.
We examined the distribution of nekton across the marsh landscape using a 1-m 2 drop sampler to compare nekton densities across three different salinity zones (intermediate, brackish, saline), three pond
sizes (diameter <40 m = small, ∼250–300 m = medium, >750 m = large), and two habitat types (pond, adjacent marsh) in the Barataria
Bay Estuary, Louisiana. Nekton assemblages of ponds and the adjacent marsh appeared to be structured by the responses of individual
species to the estuarine salinity gradient at the landscape scale and to pond habitat attributes locally. Our results indicate
that ponds in the brackish and saline zones are more important nursery areas for most fishery species than ponds in the intermediate
zone. Medium and large ponds supported higher densities of most species than small ponds. Most species of nekton were associated
with vegetation structure, and individuals of these species were either concentrated among plant stems at the marsh edge or
within submerged aquatic vegetation in ponds. 相似文献
13.
The mummichog, Fundulus heteroclitus, is one of the most important macrofaunal components of salt marsh surfaces and an important link to subtidal areas of the
adjacent estuary along the east coast of the U.S. We estimated growth, population size, and production of the mummichog in
a restored marsh in order to improve our understanding of the role of this resident fish and to evaluate the success of the
restoration. The restored marsh, covering 234 ha, was a former salt hay farm located in the mesohaline portion of Delaware
Bay that was restored to tidal influence in August 1996. We separated the mummichog population into two components based on
life history stage and summer habitat use patterns. One component, consisting of adults and large young-of-the-year (YOY),
exhibited tidal movements to and from the marsh surface and the subtidal creeks. These were examined with an intensive mark
and recapture program using coded wire tags. Another component, consisting of small YOY, remained on the marsh surface throughout
the tidal cycle. Throw traps were used to sample these small YOY. The mean annual population density of adults and large YOY
for the entire marsh was approximately 1.2 fish m −2 and mean monthly density peaked at 2.9 fish m −2. The mean annual density of small YOY on the marsh surface was 15.1 fish m −2 and mean monthly density peaked at 41.4 fish m −2. Size and season influenced the growth rate of individual fish and instantaneous growth rates ranged from 0.03 to 2.26 mo −1. Total annual mummichog production was estimated to be 8.37 g dw m −2 yr −1, with adults and large YOY contributing 28.4% (2.38 g dw m −2 yr −1) and small YOY on the marsh surface contributing 71.6% (5.99 g dw m −2 yr −1). The seasonal use and population densities were comparable to previous studies in natural marshes while growth and production
of mummichog in this restored marsh appeared to be higher. Coupled with the results of other studies on the feeding, movement,
and habitat use of this species in this restored marsh, the species has responded well to the restoration. 相似文献
14.
The stable isotope signatures of marine transient and resident nekton were used to investigate trophic linkages between primary
producers, marsh macrophytes, phytoplankton, benthic microalgae, and consumers within the Delaware Bay. A whole estuary approach
was used to compare the flux of nutrients from primary producers to juvenile weakfish ( Cynoscion regalis), bay anchovy ( Anchoa mitchilli), and white perch ( Morone americana) in open waters of the lower and upper Bay and adjacent salt marshes dominated by either Spartina alterniflora or Phragmites australis. Our results suggest that trophic linkages vary significantly along the salinity gradient, reflecting the transition from Spartina to Phragmites-dominated marshes, and secondarily, in a marsh to open water (offshore) direction at a given salinity. Superimposed on this
pattern was a gradient in the proximate use of organic matter that depended on life history traits of each species ranging
from pelagic to benthic in the order bay anchovy > weakfish > white perch. 相似文献
15.
In a continuing effort to monitor the fish response to marsh restoration (resumed tidal flow, creation of creeks), we compared
qualitative and quantitative data on species richness, abundance, assemblage structure and growth between pre-restoration
and post-restoration conditions at two former salt hay farms relative to a reference marsh in the mesohaline portion of Delaware
Bay. The most extensive comparison, during April–November 1998, sampled fish populations in large marsh creeks with otter
trawls and in small marsh creeks with weirs. Species richness and abundance increased dramatically after restoration. Subsequent
comparisons indicated that fish size, assemblage structure, and growth of one of the dominant species, Micropogonias undulatus, was similar between reference and restored marshes 1 and 2 yr post-restoration. Total fish abundance and abundance of the
dominant species was greater, often by an order of magnitude, in one of the older restored sites (2 yr post-restoration),
while the other restored site (1 yr post-restoration) had values similar to the reference marsh. The success of the restoration
at the time of this study suggests that return of the tidal flow and increased marsh area and edge in intertidal and subtidal
creeks relative to the former salt hay farms contributed to the quick response of resident and transient young-of-the-year
fishes. 相似文献
16.
We examined connectivity among marsh subhabitats to determine the structural limits and important components of a polyhaline
salt marsh by studying the patterns of abundance, residency, and movement of a numerically and ecologically dominant nektonic
fish (mummichog, Fundulus heteroclitus). We captured, tagged ( n = 14,040 individuals, 30–110 mm), and recaptured from Feb 2001 to Jul 2002, although most recaptures (75–95% by tagging location)
occurred within 150 days. Seasonal residency and movements were common among most subhabitats based on catch per unit effort
and recapture per unit effort. Thus, these (marsh pools, intertidal and subtidal creeks, and marsh surface) should be considered
natural subhabitats within New England type salt marshes. Further, all these subhabitat types should be included in studies
of salt marsh nekton and marsh restoration and creation activities. 相似文献
17.
Effective sampling of marsh nekton is difficult due to the organisms’ use of the marsh-edge and/or marsh surface during high tide. Quantitative sampling approaches currently used are expensive, require permanent structures, and can require a considerable number of personnel for implementation. Our purpose was to assess the use of Breder traps (T) as a sampling method capable of documenting relative abundance of nekton. We sampled marsh habitats (within 1 m of marsh grass) in five bayous using seines at high (HS) and low (LS) tide and compared them with rank abundance and similarity data. Seining (n=3/tidal stage) was conducted adjacent to each set of traps (n=4) which were retrieved at low tide. Four transient (Engraulidae, 34.7%; Penaeidae, 12.4%; Portunidae, 6.8%; and Sciaenidae, 1.2%) and four resident families (Palaemonidae, 28.1% Fundulidae, 9.2%; Atherinidae, 3.2%; and Gobiidae, 1.1%) met our requirements (≥1% of all nekton captured) for analysis and accounted for 96.6% of the total nekton captured. High seine and LS collections were most similar (Jaccard's index, 0.58), followed by T and LS (0.46) and HS and T (0.37). Transient families were captured in greatest numbers and higher rank with seines (LS>HS>T) while two resident families (Palaemonidae and Fundulidae) dominated T collections (T>LS>HS). Our data suggests that Breder traps adequately sample resident nekton which use the marsh surface and should be considered in future studies which require only CPUE estimates of abundance. 相似文献
18.
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
19.
Anammox bacteria are widespread in the marine environment, but studies of anammox in marshes and other wetlands are still
scarce. In this study, the role of anammox in nitrogen removal from marsh sediments was surveyed in four vegetation types
characteristic of New England marshes and in unvegetated tidal creeks. The sites spanned a salinity gradient from 0 to 20 psu.
The impact of nitrogen loading on the role of anammox in marsh sediments was studied in a marsh fertilization experiment and
in marshes with high nitrogen loading entering through ground water. In all locations, nitrogen removal through anammox was
low compared to denitrification, with anammox accounting for less than 3% of the total N 2 production. The highest relative importance of anammox was found in the sediments of freshwater-dominated marshes, where
anammox approached 3%, whereas anammox was of lesser importance in saline marsh sediments. Increased nitrogen loading, in
the form of nitrate from natural or artificial sources, did not impact the relative importance of anammox, which remained
low in all the nitrogen enriched locations (<1%). 相似文献
20.
We examined the contrasting, effects of floods and droughts produced by large changes in local climatology on vegetation patterns
in Nueces marsh, a semi-arid subtropical salt marsh in south Texas from 1995 to 2005. Climate variations during the study
included an initial 4-yr period of moderate conditions, followed by a 2-yr interval of drought, and a recent 4-yr wet period
that included large-scale floods. Variation in freshwater inflow, rainfall, and potential evapotranspiration were used in
conjunction with field measurements of salinity, inorganic nitrogen, and vegetation structure collected at sites located at
varying distances from Nueces Bay. Tidal creek salinities varied with Nueces Bay salinity, with strength of effect inversely
related to distance from the bay. Mean (±standard deviation) pore water salinities ranged from 59±54‰ at two high, marsh stations
farthest from the bay (10.1 km distant) to 30±21‰ in soil at a low marsh site closest to the bay (0.5 km distant). Mean pore
water ammonium was also higher at stations most distant from the bay; nitrate + nitrite did not exhibit a high marsh to low
marsh gradient. Nueces Bay salinity decreased substantially when the 10-d cumulative mean daily Nueces River flows exceeded
10 m 3 s −1. During periods of low and moderate flood frequency (flows mostly below 10 m 3 s −1), vegetation assemblages were dominated by stress-tolerant clonal plants. A catastrophic flood, which immersed vegetation
for several weeks between July and September 2002, resulted in extensive plant mortality, but within months, unvegetated areas
were rapidly colonized by the obligate annual Salicornia bigelovii. With the end of major flooding by late 2004, plant community structure began a return to pre-drought assemblages at high
and middle marsh stations by summer 2005. At the low marsh station, new conditions favored clonal dominants ( Spartina alterniflora and Borrichia frutescens), with the latter replacing Salicornia virginica as the dominant species. Our results support the theory that the importance of competition and abiotic stress in determining
community composition are inversely related. 相似文献
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