Effects of saltmarsh invasion by Spartina alterniflora on arthropod community structure and diets

Invasive plants strongly affect physical and biotic environments of native ecosystems. Insects and other arthropods as one of the major components of many ecosystems are very sensitive to subtle changes in abiotic and biotic environments. We examined the effects of exotic Spartina alterniflora invasion on community structure and diets of arthropods in a saltmarsh previously dominated by native Phragmites australis in Yangtze River estuary through net sweeping and plant harvesting methods and stable isotope analysis. Our results showed that diversity indices were not significantly different between exotic and native plant communities, but the total abundance of insects estimated through plant harvesting method was found to be lower in Spartina monoculture than that in Phragmites monoculture. Community structure of insects in Spartina monoculture was dissimilar to that in Phragmites monoculture and Phragmites–Spartina mixture. Moreover, stable carbon isotope patterns of arthropods were significantly different between Phragmites and Spartina monocultures. Although some native arthropods (perhaps generalists) shifted their diets, many native taxa did prefer Phragmites to Spartina even in Spartina monoculture. Spartina invasions resulted in reduced abundances of some arthropds, and increased dominance of others feeding preferably on Spartina. This study provides evidence that invasive plants can change the community structure and diets of native arthropods, which will eventually alter the arthropod food web, and affect the integrity and functioning of native ecosystems within a nature reserve that has been set aside for conserving the native biodiversity and maintaining the ecosystem integrity. In this sense, Spartina invasions in the Yangtze River estuary need to be managed appropriately.     

Relationships between vegetation zonation and environmental factors in newly formed tidal marshes of the Yangtze River estuary

The Yangtze River delta is characterized by rapidly accreting sediments that form tidal flats that are quickly colonized by emergent vegetation including Scirpus mariqueter and the invasive species Spartina alterniflora. We measured soil surface elevation, water table depth, soil salinity, water content and compaction in the tidal flat, the Scirpus and Spartina zones and their borders to identify relationships between environmental factors and colonization by Scirpus and Spartina. With increasing elevation from tidal flat to Spartina, inundation frequency and duration, moisture and depth to water table decreased whereas soil salinity, temperature and compaction increased. High soil moisture and groundwater and low salinity were the characteristics of the tidal flat and its border with Scirpus. The Spartina zone and its border with Scirpus were characterized by greater salinity and elevation relative to the other zones. Our findings suggest that soil salinity controls patterns of plant zonation in the newly formed tidal salt marshes whereas elevation is of secondary importance. Our results suggest that patterns of vegetation zonation in tidal marshes of the Yangtze River delta are controlled by environmental factors, especially (low) salinity that favors colonization by Scirpus in the lower elevations of the marsh.     

Exotic Spartina alterniflora provides compatible habitats for native estuarine crab Sesarma dehaani in the Yangtze River estuary

Although the impact of plant invasions on benthic communities, especially burrowing crabs, has received increasing attention, the results from past studies are mixed. The exotic plant Spartina alterniflora has become the most abundant species in the salt marshes of the Yangtze River estuary since it was first found just over a decade ago, but its effects on crabs in the salt marshes is largely unknown. To examine whether the invasions of this exotic plant affected native crabs, we compared the biomass and abundance of the dominant burrowing crab Sesarma dehaani in an exotic Spartina marsh, native Phragmites australis marsh and mudflats of the Yangtze River estuary, China. To explain the differences of S. dehaani populations between different habitats, feeding preference of S. dehaani for Spartina and Phragmites was investigated. Results showed crab abundance and biomass in the Spartina marsh were significantly greater than those in the Phragmites marsh and mudflats. Soil water content and plant community characteristics in the Spartina marsh also significantly differed in the Phragmites marsh and mudflats. Moreover, the feeding preference experiment showed that crabs consumed Spartina more than twice as much as Phragmites. In summary, this study showed that Spartina provided compatible habitats for native crab S. dehaani through offering suitable food source and moderate environmental conditions.     

Determinants of seed bank dynamics of two dominant helophytes in a tidal salt marsh

We investigated dynamics and spatial distribution of Scirpus mariqueter and Spartina alterniflora seed banks at Chongming Dongtan in the Yangtze River estuary, China. Five sites along an elevational gradient were chosen, one in each of the main zones (mudflat, Scirpus monoculture, Scirpus–Spartina mixture, Spartina monoculture and Spartina–Phragmites mixture). Three surveys were performed just after seed rain, before germination and after germination, respectively. During the period of November 2005 to May 2006, soil seed density of Scirpus mariqueter declined by 36%, and that of Spartina alterniflora by 58%. The spatial distributions of their seed banks were also different. Soil seed density of Scirpus mariqueter was not determined directly by seed production, but positively correlated with total aboveground biomass of the whole plant community. On the contrary, soil seed density of Spartina alterniflora just after seed rain (November) was significantly correlated with seed production, but had a poor relationship with the community's aboveground biomass. Our results indicated that other factors such as tidal movement might have had great influence on dispersal of Scirpus mariqueter, which would also affect its population dynamics. The understanding of this process can help us improve the conservation and restoration efforts.     

Invasion of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> Enhanced Ecosystem Carbon and Nitrogen Stocks in the Yangtze Estuary,China

Whether plant invasion increases ecosystem carbon (C) stocks is controversial largely due to the lack of knowledge about differences in ecophysiological properties between invasive and native species. We conducted a field experiment in which we measured ecophysiological properties to explore the response of the ecosystem C stocks to the invasion of Spartina alterniflora (Spartina) in wetlands dominated by native Scirpus mariqueter (Scirpus) and Phragmites australis (Phragmites) in the Yangtze Estuary, China. We measured growing season length, leaf area index (LAI), net photosynthetic rate (Pn), root biomass, net primary production (NPP), litter quality and litter decomposition, plant and soil C and nitrogen (N) stocks in ecosystems dominated by the three species. Our results showed that Spartina had a longer growing season, higher LAI, higher Pn, and greater root biomass than Scirpus and Phragmites. Net primary production (NPP) was 2.16 kg C m⁻² y⁻¹ in Spartina ecosystems, which was, on average, 1.44 and 0.47 kg C m⁻² y⁻¹ greater than that in Scirpus and Phragmites ecosystems, respectively. The litter decomposition rate, particularly the belowground decomposition rate, was lower for Spartina than Scirpus and Phragmites due to the lower litter quality of Spartina. The ecosystem C stock (20.94 kg m⁻²) for Spartina was greater than that for Scirpus (17.07 kg m⁻²), Phragmites (19.51 kg m⁻²) and the mudflats (15.12 kg m⁻²). Additionally, Spartina ecosystems had a significantly greater N stock (698.8 g m⁻²) than Scirpus (597.1 g m⁻²), Phragmites ecosystems (578.2 g m⁻²) and the mudflats (375.1 g m⁻²). Our results suggest that Spartina invasion altered ecophysiological processes, resulted in changes in NPP and litter decomposition, and ultimately led to enhanced ecosystem C and N stocks in the invaded ecosystems in comparison to the ecosystems with native species.     

Influence of submergence on growth of seedlings of Scirpus lacustris and Phragmites australis

• 1 Seeds of Scirpus lacustris and Phragmites australis were germinated in early June, and twenty-four seedlings of each species were subsequently exposed to submerged conditions (eight seedlings at each of the water depths 0.2, 0.4 and 0.8m), in outdoor 500–1 tanks in southern Sweden. Weight and shoot length of the plants were measured in September.
• 2 The Phragmites seedlings did not show any significant growth when submerged. The Scirpus seedlings, however, developed submerged leaves and exhibited considerable submerged growth. One Scirpus plant, in shallow water (0.2m), had developed an aerial shoot by September. Shoot length of the remaining (submerged) Scirpus plants was positively related to plant weight within water depth treatments, and was higher, in relation to plant weight, in deeper water. Mean weight in September of the submerged Scirpus plants decreased with increased water depth.
• 3 In south Swedish lakes with a lowered water table, Scirpus often occupies large areas on the lakeward side of the reed belt, which is generally dominated by Phragmites. The differences between the two species, in performance of submerged seedlings, suggest that this zonation may be created through successful submerged seedling establishment of Scirpus on the lakeward side of Phragmites.

     

Litter pool sizes,decomposition, and nitrogen dynamics in <Emphasis Type="Italic">Spartina alterniflora</Emphasis>-invaded and native coastal marshlands of the Yangtze Estuary

Past studies have focused primarily on the effects of invasive plants on litter decomposition at soil surfaces. In natural ecosystems, however, considerable amounts of litter may be at aerial and belowground positions. This study was designed to examine the effects of Spartina alterniflora invasion on the pool sizes and decomposition of aerial, surficial, and belowground litter in coastal marshlands, the Yangtze Estuary, which were originally occupied by two native species, Scirpus mariqueter and Phragmites australis. We collected aerial and surficial litter of the three species once a month and belowground litter once every 2 months. We used the litterbag method to quantify litter decomposition at the aerial, surficial and belowground positions for the three species. Yearly averaged litter mass in the Spartina stands was 1.99 kg m⁻²; this was 250 and 22.8% higher than that in the Scirpus (0.57 kg m⁻²) and Phragmites (1.62 kg m⁻²) stands, respectively. The litter in the Spartina stands was primarily distributed in the air (45%) and belowground (48%), while Scirpus and Phragmites litter was mainly allocated to belowground positions (85 and 59%, respectively). The averaged decomposition rates of aerial, surficial, and belowground litter were 0.82, 1.83, and 1.27 year⁻¹ for Spartina, respectively; these were 52, 62 and 69% of those for Scirpus litter at corresponding positions and 158, 144 and 78% of those for Phragmites litter, respectively. The differences in decomposition rates between Spartina and the two native species were largely due to differences in litter quality among the three species, particularly for the belowground litter. The absolute amount of nitrogen increased during the decomposition of Spartina stem, sheath and root litter, while the amount of nitrogen in Scirpus and Phragmites litter declined during decomposition for all tissue types. Our results suggest that Spartina invasion altered the carbon and nitrogen cycling in the coastal marshlands of China.     

Effects of exotic <Emphasis Type="Italic">Spartina alterniflora</Emphasis> on the habitat patch associations of breeding saltmarsh birds at Chongming Dongtan in the Yangtze River estuary,China

Smooth cordgrass (Spartina alterniflora) is one of the most invasive exotic plants of saltmarshes worldwide. To understand the effects of smooth cordgrass invasion on the habitat use and selection by breeding saltmarsh birds, we compared species number and abundance of breeding birds in native reed (Phragmites australis) and smooth cordgrass-invaded habitats (reed-cordgrass mixed habitats and cordgrass monocultures) at Chongming Dongtan in the Yangtze River estuary, China. We further examined the similarity of bird communities in different habitats and habitat selection by dominant bird species. For saltmarsh generalists, species number and abundance did not differ among the habitats. For saltmarsh specialists, species number and abundance did not differ in reed monocultures and reed-cordgrass mixed habitats but were significantly lower in cordgrass monocultures than in reed monocultures and reed-cordgrass mixed habitats. ANOSIM indicated that the difference in bird communities was larger between cordgrass monocultures and the habitats with reed than between the habitats with reed. The saltmarsh specialists preferred reed monocultures, while saltmarsh generalists avoided reed monocultures. Most species indicated no selection (neither preferred nor avoided) on reed-cordgrass mixed habitats, and no species preferred the cordgrass monocultures. The use of cordgrass monocultures by the common saltmarsh birds was negatively related to their body size. This study suggests that the spread of exotic smooth cordgrass has greatly affected the species composition and structure of local bird communities and has been especially disadvantageous to the saltmarsh specialists.     

崇明东滩盐沼植被扩散格局及其形成机制

长江河口盐沼植被的形成和演化是生物与其生长环境相互作用的结果。以崇明东滩盐沼植被典型扩散前沿为研究对象,2011至2012年期间调查了盐沼植被扩散前沿实生苗扩散、定居以及形成的扩散格局,同时测定了盐沼植被扩散前沿的潮滩冲淤动态和水文动力条件。研究结果表明,崇明东滩盐沼植被在扩散前沿形成了互花米草-光滩(Spartina alterniflora-Mudflat,SM)和互花米草-海三棱藨草-光滩(Spartina alterniflora-Scirpus mariqueter-Mudflat,SSM)两种典型的扩散格局。冲淤动态和水文动力条件是影响盐沼植被扩散格局的重要因子,尤其是在4—6月盐沼植物实生苗传播和定居的关键阶段。在此基础上,分析了东滩盐沼植被扩散前沿的生物-物理相互作用以及盐沼植被扩散格局的形成机制。研究结果不仅有助于理解长江河口地区盐沼植被扩散的生物物理过程,并对全球气候变化和海平面上升条件下滨海生态系统动态预测与湿地保护与管理具有重要的意义。     

Distribution of saltmarsh plant communities associated with environmental factors along a latitudinal gradient on the south‐west Atlantic coast

Aim To produce an inventory of south‐west Atlantic saltmarshes (from latitude 31°48′ S to 43°20′ S) using remotely sensed images and field sampling; to quantify their total area; to describe the biogeographical variation of the main habitats characterized by dominant vascular plants, in relation to major environmental factors; to test the hypothesis of predominance of the reversal pattern in plant distribution (sedges and grasses dominate the lower, regularly inundated zones, while the upper zones are occupied by more halophytic species) previously described; and to compare these south‐west Atlantic saltmarshes with others world‐wide. Location South‐western Atlantic saltmarshes Methods Field samples of dominant emergent plant species positioned by the global positioning system (GPS) were obtained from most coastal saltmarshes (14) between southern Brazil and northern Patagonia, Argentina. Landsat satellite images were obtained and coastal saltmarsh habitats were quantified by supervised classification, utilizing points gathered in the field. Results Three main plant species dominated the low and middle intertidal saltmarsh, Spartina alterniflora Loesel., Spartina densiflora Brong. and Sarcocornia perennis (P. Mill.) A.J. Scott. The total area of the studied coastal saltmarshes was 2133 km², comprising 380 km² of Sp. alterniflora marsh, 366 km² of Sp. densiflora marsh, 746 km² of Sar. perennis marsh and 641 km² of brackish marsh (dominated by Juncus acutus L., Juncus kraussii Hochst., Scirpus maritimus L., Scirpus americanus Pers. and Phragmites australis (Cav.) Trin.). Cluster analysis showed three habitat types: saltmarshes dominated by (1) Sp. densiflora and brackish species,(2) Sp. alterniflora and Sar. perennis and (3) Sp.densiflora only. The analysis of abiotic variables showed significant differences between groups of habitats and coordinated gradients of the abiotic variables. The south‐west Atlantic coast showed decreasing mean annual rainfall (1200 to 196 mm) and increasing mean tidal amplitude (< 0.5 to > 2.5 m) from latitude 31° to 43°. Main conclusions South‐west Atlantic saltmarshes are globally important by virtue of their total extent. Remote sensing showed that the reversal pattern in plant distribution is not widespread. Indeed, south‐west Atlantic saltmarshes are better characterized by the presence of the halophytic genera Spartina and Sarcocornia. Our results support the interpretation that south‐west Atlantic saltmarshes constitute a class of temperate type (sensu Adam, 1990 ) with transitional characteristics between Australasian–South African saltmarshes and west Atlantic saltmarshes.     

Effects of salt marsh invasion by Spartina alterniflora on sulfate-reducing bacteria in the Yangtze River estuary,China

To investigate how plant invasion affects sulfate-reducing bacteria (SRB) responsible for sulfate reduction, we conducted a comparative study of diversity and composition of SRB in rhizosphere soils of invasive exotic species (Spartina alterniflora) and two native species (Phragmites australis and Scirpus mariqueter) on Jiuduansha Island located in the Yangtze River estuary, China. Throughout the growing season, profiles of DGGE fingerprints of SRB had distinct variations in relation to phenological stages of these three plant species. The higher richness and abundance of SRB in the rhizospheres of native plants mainly occurred when the plants were in vegetative growth and reproductive stages. However, the higher richness and abundance of SRB also occurred in the late growing season (senescent stage) of S. alterniflora rhizosphere, during which Desulfobulbus, Desulfuromonas, Desulfovibrio, and Firmicutes were dominant. Our results adding to our previous studies suggested that abundant SRB in late stage might have close relationships with decomposition of soil organic matters produced by S. alterniflora.     

Bioturbation of Burrowing Crabs Promotes Sediment Turnover and Carbon and Nitrogen Movements in an Estuarine Salt Marsh

Ecological functions of bioturbation in ecosystems have received increasing attention over the recent decades, and crab burrowing has been considered as one of the major bioturbations affecting the physical and chemical processes in salt marshes. This study assessed the integrated effects of crab excavating and burrow mimic trapping on sediment turnover and vertical C and N distributions in a Chinese salt marsh in the Yangtze River estuary. Crab burrowing increased soil water content and the turnover of carbon and nitrogen and decreased bulk soil density. Vertical movement of materials, nutrient cycling and reuse driven by crab burrowing might be obstructed by vegetation (Phragmites australis and Spartina alterniflora communities). The amount of soil excavated by crab burrowing was higher than that deposited into burrow mimics. In Phragmites marshes, Spartina marshes and unvegetated mudflats, net transport of soil to the marsh surface was 171.73, 109.54, and 374.95 g m⁻² d⁻¹, respectively; and the corresponding estimated soil turnover time was 2.89, 4.07 and 1.83 years, respectively. Crab burrowing in salt marshes can mix surface and deeper soil over a period of years, accelerating litter decomposition and promoting the efficient reuse of nutrients by plants. Therefore, bioturbation affects soil physical processes and functioning of ecosystems, and needs to be addressed in ecosystem management.     

Impact of hydrodynamic changes on the zonation of helophytes

Water movement has a strong impact on the development and persistence of helophyte stands along large water bodies. The decline ofScirpus andPhragmites stands in the Rhine-Meuse estuary (The Netherlands), due to changed hydrodynamic conditions (reduced tidal action, increased shoreline erosion), illustrates the effects of large-scale hydrological regulation. Hydrodynamic factors partly explain the distribution and composition of helophyte vegetation bordering the open water. A vertical zonation emerges during the stages of dispersal, germination, seedling establishment and adult growth of the plants. Differences between species may result in the occupation of different water-depth zones. Additionally, gradients of wave exposure result in a horizontal zonation along water bodies. Restrictions to helophyte development due to the hydrological regime and wave attack should be taken into account in wetland restoration studies. Water-level management, instead of a strict control of water levels, should be one of the key elements of water management in the future.     

The Effect of Zostera noltii, Spartina maritima and Scirpus maritimus on Sediment Pore-water Profiles in a Temperate Intertidal Estuary

The objective of the present work was to study the effect of plants common in temperate latitudes (Zostera noltii, Spartina maritima and Scirpus maritimus) on sediment nutrient profiles, and to compare it to sand- and mud-flats without vegetation. The study focused on the organic matter contents, the concentration of dissolved inorganic nutrients (PO₄–P, NH₃–N, NO₃–N), an on the estimation of the total amount of these nutrients during day and night conditions and their potential net-fluxes. It was also hypothesised that in an estuarine system, different plants may have specific effects, and consequently different contributions to the system nutrient dynamics as a whole. Sediment profiles of loss on ignition (LOI) showed an increase of the organic matter contents from sand-flat, to Zostera, Spartina, mud-flat and Scirpus. Statistically, there were significant differences between sediment profiles of phosphate, ammonia and nitrate (Mann-Whitney test, p<0.05), during day and night periods. These results suggest that there is an intense mobility of nutrients in the sediment, showing a day-night variation of nutrient concentrations in the pore-water. In the plants’ rhizosphere, the day-night variation of nutrients seemed dependent on plant biomass and penetration of the roots. Additionally, coupling between plant and sediment seems to be a species-specific process. In spring, Scirpus salt marsh reaches the maximum density and biomass, and despite the higher organic matter contents in the plant covered sediment, Scirpus acts as a sink of nutrients. In contrast, the top 10 cm of the sediment in the Spartina salt marsh and in the Zostera beds may contribute to the efflux of nutrients during the night period, especially phosphate.     

潮间带盐沼植物种子及实生苗漂浮起动临界剪切应力研究

盐沼是分布在海陆过渡区域,以大型草本植物为优势种的潮间带生态系统。在潮间带生态系统中,盐沼植物的种子和实生苗在潮流作用下的漂浮起动是盐沼植物自然扩散的重要前提,决定了盐沼植物能否实现有效扩散和长距离传播。然而,目前缺乏有关盐沼植物繁殖体在复杂潮滩环境下漂浮起动扩散过程的定量研究。以长江口典型盐沼先锋物种海三棱藨草(Scirpus mariqueter)为研究对象,应用U-GEMS微观侵蚀系统,测定了在不同沉积物底质条件下,海三棱藨草种子及不同萌发阶段实生苗漂浮起动时的临界剪切应力,定量分析不同萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的影响。研究结果表明：(1)不同种子萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的临界剪切应力均有极显著影响(P<0.01);(2)随着萌发阶段的进展,海三棱藨草实生苗漂浮起动所需的临界剪切应力逐渐减小,因而随潮流漂浮起动进而扩散的机会也相应增大;(3)相比于淤泥质潮滩底质,海三棱藨草种子和实生苗在粉砂质潮滩更易于漂浮起动。研究结果丰富了盐沼植物在潮间带自然扩散过程和机理的研究,也为今后长江口及其他区域开展高效、低成本、以种子为修复...     

Behavioral Responses and Interactions of Estuarine Animals With an Invasive Marsh Plant: A Laboratory Analysis

Invasion by Phragmites australis into tidal marshes previously dominated by Spartina alterniflora is viewed as a serious environmental threat along the Atlantic coast of the US, but little is known about the relative habitat value of the two plants for most estuarine species. This study was designed to investigate behavioral responses, in the laboratory, of three species to the two plants. Fiddler crabs, Uca pugnax, grass shrimp, Palaemonetes pugio, and larval mummichogs (killifish), Fundulus heteroclitus were introduced into aquaria with a bare area, an area with dead Phragmites stems, and an area with dead Spartina stems. All species distributed themselves equally between the Spartina and the Phragmites. The behavior of larval mummichogs in the tanks with predators was observed. In the presence and absence of stems, they utilized the surface of the water as a refuge, as well as the stems, when present. This behavior was equally as effective as being among the stems in promoting larval survival. In microcosms with blocks of marsh with living plants, fiddler crabs and grass shrimp again did not show a preference for either species of plant, while juvenile and adult mummichogs were not consistent. Small fish chose Spartina when in the small microcosm and had no preference in the large one. Large fish chose Spartina in the small microcosm and Phragmites in the large one. Predation by adult mummichogs on grass shrimp was comparable in Spartina and Phragmites microcosms, and predation on tethered shrimp was equivalent in adjacent Spartina and Phragmites marshes in the field.     

The extended phenology of <Emphasis Type="Italic">Spartina</Emphasis> invasion alters a native herbivorous insect’s abundance and diet in a Chinese salt marsh

Plant invasions can alter the trophic interactions of invaded ecosystems because of phenological differences between native and invasive plants that may affect the population dynamics and diets of indigenous arthropod herbivores. This issue, however, has seldom been studied. We here report on how abundance and diet of a local tussock moth (Laelia coenosa) are affected by the invasive plant Spartina alterniflora in a Chinese salt marsh previously dominated by the moth’s native host plant, Phragmites australis. We monitored the population dynamics of L. coenosa from four types of hosts: (1) Phragmites in its monoculture, (2) Spartina in its monoculture, and either (3) Phragmites, or (4) Spartina in Phragmites–Spartina mixtures. Additionally, we tested the diet of L. coenosa from the mixtures with isotope analysis. We found that the larval densities of L. coenosa were similar on Spartina and Phragmites in their respective monocultures and mixtures in summer but were greater on Spartina than on Phragmites in autumn. Stable isotope analysis showed that Spartina was a food resource for L. coenosa. The change in the insect’s population dynamics associated with Spartina invasion might be caused by phenological differences between Spartina and Phragmites in that Spartina has a longer growing season than Phragmites. Our study indicates that the extended phenology of Spartina invasion has altered the abundance and diet of the indigenous herbivorous insect (L. coenosa) previously feeding on native Phragmites. We predict such alternation may increase the consuming pressure to native plants via apparent competition, and thereby may facilitate the further invasion of the exotic plants in the salt marsh.     

Restoration of Arthropod Assemblages in a Spartina Salt Marsh following Removal of the Invasive Plant Phragmites australis

Invasive plants are one of the most serious threats to native species assemblages and have been responsible for the degradation of natural habitats worldwide. As a result, removal of invasive species and reestablishment of natural vegetation have been attempted in order to restore biodiversity and ecosystem function. This study examined how native arthropod assemblages, an abundant and functionally important group of organisms in many ecosystems, are affected by the incursion of the invasive wetland plant Phragmites australis and if the restoration of the native vegetation in brackish Spartina alterniflora marshes results in the reestablishment of the arthropod community. The invasion of Phragmites into a coastal Spartina marsh in southern New Jersey seriously altered arthropod assemblages and trophic structure by changing the abundance of trophic groups (detritivores, herbivores, carnivores) and their taxonomic composition. Herbivore assemblages shifted from the dominance of external free‐living specialists (e.g., planthoppers) in Spartina to concealed feeders in Phragmites (stem‐feeding cecidomyiids). Moreover, free‐living arthropods in Phragmites became dominated by detritivores such as Collembola and chironomids. The dominant marsh spiders, web‐building linyphiids, were significantly reduced in Phragmites habitats, likely caused by differences in the physical environment of the invaded habitats (e.g., lower stem densities). Thus, trophic structure of arthropod assemblages in Phragmites, as seen in the large shifts in feeding guilds, was significantly different from that in Spartina. Removal of Phragmites with the herbicide glyphosate resulted in the rapid return of Spartina (≤5 yrs). Moreover, return of the dominant vegetation was accompanied by the recovery of most original habitat characteristics (e.g., live and dead plant biomass, water flow rate). The arthropod assemblage associated with Spartina also quickly returned to its preinvasion state and was not distinguishable from that in uninvaded Spartina reference sites. This study provides evidence that the reestablishment of native vegetation in areas previously altered by an invasive plant can result in the rapid recovery of the native arthropod assemblage associated with the restored habitat.     

Mosquito distribution in a saltmarsh: determinants of eggs in a variable environment

Two saltmarsh mosquitoes dominate the transmission of Ross River virus (RRV, Togoviridae: Alphavirus), one of Australia's most prominent mosquito‐borne diseases. Ecologically, saltmarshes vary in their structure, including habitat types, hydrological regimes, and diversity of aquatic fauna, all of which drive mosquito oviposition behavior. Understanding the distribution of vector mosquitoes within saltmarshes can inform early warning systems, surveillance, and management of vector populations. The aim of this study was to identify the distribution of Ae. camptorhynchus, a known vector for RRV, across a saltmarsh and investigate the influence that other invertebrate assemblage might have on Ae. camptorhynchus egg dispersal. We demonstrate that vegetation is a strong indicator for Ae. camptorhynchus egg distribution, and this was not correlated with elevation or other invertebrates located at this saltmarsh. Also, habitats within this marsh are less frequently inundated, resulting in dryer conditions. We conclude that this information can be applied in vector surveillance and monitoring of temperate saltmarsh environments and also provides a baseline for future investigations into understanding mosquito vector habitat requirements.     

Spread of Exotic Cordgrasses and Hybrids (Spartina sp.) in the Tidal Marshes of San Francisco Bay, California, USA

Four species of exotic cordgrass (Spartina sp.) occur in the San Francisco estuary in addition to the California native Spartina foliosa. Our goal was to map the location and extent of all non-native Spartina in the estuary. Hybrids of S. alterniflora and S. foliosa are by far the most numerous exotic and are spreading rapidly. Radiating from sites of deliberate introduction, S. alterniflora and hybrids now cover ca. 190 ha, mainly in the South and Central Bay. Estimates of rate of aerial increase range from a constant value to an accelerating rate of increase. This could be due to the proliferation of hybrid clones capable of rapid expansion and having superior seed set and siring abilities. The total coverage of 195 ha by hybrids and other exotic cordgrass species is slightly less than 1% of the Bay's tidal mudflats and marshes. Spartina anglica has not spread beyond its original 1970s introduction site. Spartina densiflora has spread to cover over 5 ha at 3 sites in the Central Bay. Spartina patens has expanded from 2 plants in 1970 to 42 plants at one site in Suisun Bay. Spartina seed floats on the tide, giving it the potential to export this invasion throughout the San Francisco estuary, and to estuaries outside of the Golden Gate. We found isolated plants of S. alterniflora and S. densiflora in outer coast estuaries north of the Bay suggesting the likelihood for the San Francisco Bay populations to found others on the Pacific coast.