Post-mortem ecosystem engineering by oysters creates habitat for a rare marsh plant

Oysters are ecosystem engineers in marine ecosystems, but the functions of oyster shell deposits in intertidal salt marshes are not well understood. The annual plant Suaeda linearis is associated with oyster shell deposits in Georgia salt marshes. We hypothesized that oyster shell deposits promoted the distribution of Suaeda linearis by engineering soil conditions unfavorable to dominant salt marsh plants of the region (the shrub Borrichia frutescens, the rush Juncus roemerianus, and the grass Spartina alterniflora). We tested this hypothesis using common garden pot experiments and field transplant experiments. Suaeda linearis thrived in Borrichia frutescens stands in the absence of neighbors, but was suppressed by Borrichia frutescens in the with-neighbor treatment, suggesting that Suaeda linearis was excluded from Borrichia frutescens stands by interspecific competition. Suaeda linearis plants all died in Juncus roemerianus and Spartina alterniflora stands, regardless of neighbor treatments, indicating that Suaeda linearis is excluded from these habitats by physical stress (likely water-logging). In contrast, Borrichia frutescens, Juncus roemerianus, and Spartina alterniflora all performed poorly in Suaeda linearis stands regardless of neighbor treatments, probably due to physical stresses such as low soil water content and low organic matter content. Thus, oyster shell deposits play an important ecosystem engineering role in influencing salt marsh plant communities by providing a unique niche for Suaeda linearis, which otherwise would be rare or absent in salt marshes in the southeastern US. Since the success of Suaeda linearis is linked to the success of oysters, efforts to protect and restore oyster reefs may also benefit salt marsh plant communities.     

Contemporary distributions of saltmarsh diatoms in the Seymour–Belize Inlet Complex, British Columbia, Canada: Implications for studies of sea-level change

Surface diatom samples were collected from two saltmarshes in the Seymour–Belize Inlet Complex on the mainland coast of British Columbia to examine the controls on diatom distribution and provide training sets for regional studies of sea-level change. Cluster analysis and detrended correspondence analysis (DCA) were used to examine diatom distributions within and between the two marshes whilst canonical correspondence analysis (CCA) and partial canonical correspondence analysis (pCCA) were used to analyse species–environment relationships. The diatom assemblages were shown to be quite different between the two marshes, Waump and Wawwat'l. Q-mode cluster analysis separated the diatom assemblages from Waump into three zones corresponding to recognized vegetation zones; diatom zone C corresponds to the high marsh and is dominated by Pinnularia obscura, Caloneis bacillum and Diploneis ovalis, zone B spans the high- and mid marsh and is characterised by Fragilaria exigua, Nitzchia palea and D. ovalis, whilst zone A from the low marsh/tidal flat includes high frequencies of Diploneis smithii, Ctenophora pulchella and F. exigua. Three different diatom zones were recognised at Wawwat'l; two upper zones, E and F, corresponding to the mid-marsh which are dominated by mixed abundances of N. palea and Fragilaria construens var. venter, Navicula peregrina and Navicula clementis and zone D from the low marsh/tidal flat with increased frequencies of F. exigua and Achnanthes delicatula. At Waump, the major controls on diatom distribution were found to be elevation and to a lesser extent pH, whilst at Wawwat'l, the primary controls were grain size/organic content, conductivity and elevation. The results confirm that saltmarsh diatoms may have potential for future sea-level studies in this region. However, caution must be exercised as the significant difference in the diatom assemblages between the two marshes suggests that the diatoms are responding to a number of environmental variables on a local scale. Some of this variation may reflect highly seasonal changes in sedimentation and salinity resulting from the proximity of the marshes to adjacent streams which are subject to spring freshet. Local differences in elevation between the collected samples may also account for some of the assemblage variability. The results emphasize the great diversity and high sensitivity of intertidal diatom species to environmental controls.     

Experimental warming causes rapid loss of plant diversity in New England salt marshes

Anthropogenic climate change is predicted to cause widespread biodiversity loss due to shifts in species' distributions, but these predictions rarely incorporate ecological associations such as zonation. Here, we predict the decline of a diverse assemblage of mid-latitude salt marsh plants, based on an ecosystem warming experiment. In New England salt marshes, a guild of halophytic forbs occupies stressful, waterlogged pannes. At three sites, experimental warming of < 4 °C led to diversity declines in pannes and rapid takeover by a competitive dominant, Spartina patens . In Rhode Island, near their southern range limit, pannes were more sensitive to warming than farther north, and panne area also declined in control plots over the three-season experiment. These results suggest that warming will rapidly reduce plant diversity in New England salt marshes by eliminating a high diversity zone. Biodiversity in zoned ecosystems may be more affected by climate-driven shifts in zonation than by individual species' distribution shifts.     

Distribution of modern salt-marsh foraminifera in the Albemarle–Pamlico estuarine system of North Carolina, USA: Implications for sea-level research

We described the distributions of foraminifera from ten physiographically distinct salt marshes in the Albemarle–Pamlico estuarine system, North Carolina using 193 surface samples. We defined elevation-dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis. Additionally, seven principal biozones of salt-marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier-island inlets. High salinity sites along the southern Outer Banks are associated with sub-tidal calcareous assemblages, low marshes dominated by Miliammina fusca and high marsh environments defined by Haplophragmoides wilberti, Trochammina inflata and Arenoparrella mexicana. In contrast, lower salinity marshes have Ammobaculites spp. in sub-tidal settings, Miliammina fusca-dominated low marshes and high marsh settings characterized by Jadammina macrescens. Spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity, suggests that datasets of modern salt-marsh foraminifera from multiple environments would be appropriate for reconstructing Holocene relative sea level in North Carolina.     

High site fidelity and low site connectivity in temperate salt marsh fish populations: a stable isotope approach

Adult and juvenile fish utilise salt marshes for food and shelter at high tide, moving into adjacent sublittoral regions during low tide. Understanding whether there are high levels of site fidelity for different species of coastal fish has important implications for habitat conservation and the design of marine protected areas. We hypothesised that common salt marsh fish species would demonstrate a high site fidelity, resulting in minimal inter-marsh connectivity. Carbon (¹³C) and nitrogen (¹⁵N) stable isotope ratios of larvae and juveniles of five common salt marsh fish (Atherina presbyter, Chelon labrosus, Clupea harengus, Dicentrarchus labrax, Pomatoschistus microps), seven types of primary producer and seven secondary consumer food sources were sampled in five salt marshes within two estuary complexes along the coast of south-east England. Significant differences in ¹³C and ¹⁵N signatures between salt marshes indicated distinct sub-populations utilising the area of estuary around each salt marsh, and limited connectivity, even within the same estuary complex. ¹⁵N ratios were responsible for the majority of inter-marsh differences for each species and showed similar site-specific patterns in ratios in primary producers, secondary consumers and fish. Fish diets (derived from isotope mixing models) varied between species but were mostly consistent between marsh sites, indicating that dietary shifts were not the source of variability of the inter-marsh isotopic signatures within species. These results demonstrate that for some common coastal fish species, high levels of site fidelity result in individual salt marshes operating as discrete habitats for fish assemblages.     

Nitrogen addition does not reduce belowground competition in a salt marsh clonal plant community in Mississippi (USA)

Previous studies have suggested that belowground competition for nutrients influences plant zonation in salt marshes. In this study, I tested the hypothesis that competition for nitrogen structured a clonal plant community in a nitrogen-limited salt marsh in coastal Mississippi, USA. In contrast to most previous field studies that have investigated mechanisms of competition, I examined clonal growth responses of established genets of a nitrogen-demanding low-intertidal species (Spartina alterniflora) to nitrogen addition and the removal of a nitrogen-conserving high-intertidal species (Juncus roemerianus). Nitrogen addition stimulated clonal invasion of the Juncus zone by Spartina but did not reduce the significant competitive effects of Juncus on Spartina. Simulated Juncus shade did not reduce invasion of the Juncus zone by Spartina, indicating that belowground competition reduced clonal invasion. In the last year of the study, the border shifted unexpectedly towards the Spartina zone, resulting in competitive displacement of Spartina by Juncus. Nitrogen addition did not prevent or slow this displacement, further contradicting the nitrogen competition hypothesis. Although growth rates were much more strongly limited by nitrogen in Spartina than in Juncus, nitrogen addition did not cause the displacement of Juncus by Spartina after three growing seasons. I conclude that zonation of Spartina and Juncus is maintained by preemption of space and greater tolerance of low nitrogen supplies by Juncus in the high marsh. These results contrast sharply with findings of reduced belowground competition with nutrient addition in previous studies and highlight the important role of nutrient-mediated competition for space between clonal plants.     

Variation in nutrient availability and plant species diversity across forb and graminoid zones of a Northern New England high salt marsh

Plant zonation patterns across New England salt marshes have been investigated for years, but how nutrient availability differs between zones has received little attention. We investigated how N availability, P availability, and plant N status varied across Juncus gerardii, Spartina patens, and mixed forb zones of a Northern New England high salt marsh. We also investigated relationships between several edaphic factors and community production and diversity across the high marsh. P availability, soil salinity, and soil moisture were higher in the mixed forb zone than in the two graminoid zones. NH⁺ ₄-N availability was highest in the J. gerardii zone, but NO^– ₃-N availability and mid season net N mineralization rates did not vary among zones. Plant tissue N concentrations were highest in the mixed forb zone and lowest in the S. patens zone, reflecting plant physiologies more so than soil N availability. Community production was highest in the J. gerardii zone and was positively correlated with N availability and negatively correlated with soil moisture. Plant species diversity was highest in the mixed forb zone and was positively correlated with P availability and soil salinity. Thus, nutrient availability, plant N status, and plant species diversity varied across zones of this high marsh. Further investigation is needed to ascertain if soil nutrient availability influences or is a result of the production and diversity differences that exist between vegetation zones of New England high salt marshes.     

长江河口潮间带盐沼植被分布区及邻近光滩鱼类组成特征

研究鱼类群落在不同生境中的差异或者变化,是评价与预测生境丧失、环境退化等对湿地生物多样性与生态系统功能影响的重要基础。2006年4—11月,在长江河口崇明东滩盐沼植被分布区(简称草滩)和邻近的光滩区域分别设置采样站位,每月大潮期采用定制插网对鱼类群落进行了取样调查。分析研究了长江河口潮间带盐沼植被分布区和邻近光滩区域的鱼类组成及其月际变化,并对影响鱼类分布的主要因子进行了探讨。调查期间共采集鱼类标本1638尾,分属9目14科22种;其中,淡水鱼类2种,定居性河口鱼类12种,海洋鱼类5种,洄游鱼类3种。植被分布区和光滩区域鱼类组成及优势种特征存在明显差异。调查期间,植被分布区记录鱼类13种,主要优势种为斑尾刺虾虎鱼(Acanthogobius ommaturus)、鲻(Mugil cephalus)和棱鮻(Liza carinatus)(IRI>20),其他种类基本不具有优势度特征(IRI<0.05);光滩区域记录鱼类20种,主要优势种鲻(IRI>20),其他包括斑尾刺虾虎鱼、狼牙鳗虾虎鱼(Taenioides rubicundus)、棱鮻和棘头梅童鱼(Collichthys lucidus)也具有一定的优势特征(20>IRI>10);两个区域共有种为11种,部分种类只出现在光滩或植被分布区,但主要优势种均为定居性河口鱼类。与世界其他河口盐沼湿地鱼类研究结果不同的是,光滩区域记录的鱼类物种数、个体数、生物量和整体物种多样性水平均高于植被分布区;光滩和植被分布区鱼类相应的量比关系存在明显的月际变化,但两种生境鱼类组成间的关联性和差异性均不显著。通过比较两种生境共有的优势种体长发现,长江河口盐沼植被分布区鱼类优势种的平均体长大于光滩区域,而且植被分布区部分优势种体长的上、下限范围也大于光滩区域。长江河口盐沼植被分布区,除了育幼场外,还是许多鱼类成鱼的重要栖息地。影响河口潮间带盐沼湿地鱼类组成与分布的主要因素包括鱼类自身的生物学与生活史特征、饵料生物的组成与分布、植被出现与表形特征等生物因素和水温、盐度、淡水径流、潮汐特性等非生物因素,其对长江河口潮间带盐沼湿地中鱼类群落的组成与分布的综合作用机理有待进一步研究。     

Gross nitrous oxide production drives net nitrous oxide fluxes across a salt marsh landscape

Sea level rise will change inundation regimes in salt marshes, altering redox dynamics that control nitrification – a potential source of the potent greenhouse gas, nitrous oxide (N₂O) – and denitrification, a major nitrogen (N) loss pathway in coastal ecosystems and both a source and sink of N₂O. Measurements of net N₂O fluxes alone yield little insight into the different effects of redox conditions on N₂O production and consumption. We used in situ measurements of gross N₂O fluxes across a salt marsh elevation gradient to determine how soil N₂O emissions in coastal ecosystems may respond to future sea level rise. Soil redox declined as marsh elevation decreased, with lower soil nitrate and higher ferrous iron in the low marsh compared to the mid and high marshes (P < 0.001 for both). In addition, soil oxygen concentrations were lower in the low and mid‐marshes relative to the high marsh (P < 0.001). Net N₂O fluxes differed significantly among marsh zones (P = 0.009), averaging 9.8 ± 5.4 μg N m^?2 h^?1, ?2.2 ± 0.9 μg N m^?2 h^?1, and 0.67 ± 0.57 μg N m^?2 h^?1 in the low, mid, and high marshes, respectively. Both net N₂O release and uptake were observed in the low and high marshes, but the mid‐marsh was consistently a net N₂O sink. Gross N₂O production was highest in the low marsh and lowest in the mid‐marsh (P = 0.02), whereas gross N₂O consumption did not differ among marsh zones. Thus, variability in gross N₂O production rates drove the differences in net N₂O flux among marsh zones. Our results suggest that future studies should focus on elucidating controls on the processes producing, rather than consuming, N₂O in salt marshes to improve our predictions of changes in net N₂O fluxes caused by future sea level rise.     

Temporal and spatial variation of arbuscular mycorrhizas in salt marsh plants of the Tagus estuary (Portugal)

The factors which may influence temporal and spatial variation in plant arbuscular mycorrhizal (AM) colonization and propagule occurrence were evaluated in a Portuguese salt marsh poor in plant diversity. Two distinct sites were studied: a more-flooded (low marsh) and a less-flooded zone (high marsh). AM root colonization, AM fungal spore number and inoculum potential, soil edaphic parameters and tidal flooding time periods were analysed. Levels of AM colonization were considerable in Aster tripolium and Inula crithmoides but very low in Puccinellia maritima and non-existent in Spartina maritima, Halimione portulacoides, Arthrocnemum fruticosum and Arthrocnemum perenne. Fungal diversity was very low, with Glomus geosporum dominant at both marsh zones. Colonization showed no spatial variation within marsh zones but temporal variation was observed in the high marsh, dependent on plant phenological phases. In the low marsh, no significantly seasonal variation was observed. Apparently, plant phenological events were diluted by stressful conditions (e.g. flooding, salinity). Spore density was significantly different between marsh zones and showed temporal variation in both zones. This study showed that distribution of mycorrhizas in salt marsh is more dependent on host plant species than on environmental stresses.     

植被类型对盐沼湿地空气生境节肢动物功能群的影响

2007年4-11月,在长江口崇明东滩盐沼湿地的芦苇带、海三棱藨草带和互花米草带设置固定样地,每月小潮期对空气生境的节肢动物进行了扫网取样调查。在此基础上,分析研究了盐沼湿地空气生境节肢动物功能群特征以及植被类型的影响,特别是对互花米草的生态效应进行了进一步讨论。调查期间共获得节肢动物标本3778头,分属2纲11目37科49种。根据不同种类的营养特征将其划分为植食性、捕食寄生性和腐食性三大功能群。其中,植食性功能群的种类、数量最为丰富,涉及1纲6目19科25种,物种数占总数的51.0%,个体数占总数的86.2%;捕食寄生性功能群次之,涉及2纲7目15科21种,物种数占总数的42.9%,个体数占总数的7.8%;腐食性功能群种类、数量最少,涉及1纲1目3科3种,物种数占总数的6.1%,个体数占总数的6.0%。不同植被带捕食寄生性功能群与植食性功能群均具有一定的"天敌跟随"特征,但主要表现在物种数上,而在个体数上的对应关系并不明显。不同植被带功能群的组成、多样性及月际变化特征存在一定差异,但是植被类型对功能群的影响并不显著。与已有研究结果不同,研究中外来种互花米草对空气生境的节肢动物并未表现出显著的负面影响,相应节肢动物功能群的物种数、个体数、多样性、月际变化等特征与其他植被带并没有显著差异。就植食性功能群而言,尽管互花米草带植食性功能群的个体数明显低于其它植被带,但是物种数并没有减少,相应的作用机理还有待进一步研究。     

The Contribution of Mangrove Expansion to Salt Marsh Loss on the Texas Gulf Coast

Landscape-level shifts in plant species distribution and abundance can fundamentally change the ecology of an ecosystem. Such shifts are occurring within mangrove-marsh ecotones, where over the last few decades, relatively mild winters have led to mangrove expansion into areas previously occupied by salt marsh plants. On the Texas (USA) coast of the western Gulf of Mexico, most cases of mangrove expansion have been documented within specific bays or watersheds. Based on this body of relatively small-scale work and broader global patterns of mangrove expansion, we hypothesized that there has been a recent regional-level displacement of salt marshes by mangroves. We classified Landsat-5 Thematic Mapper images using artificial neural networks to quantify black mangrove (Avicennia germinans) expansion and salt marsh (Spartina alterniflora and other grass and forb species) loss over 20 years across the entire Texas coast. Between 1990 and 2010, mangrove area grew by 16.1 km², a 74% increase. Concurrently, salt marsh area decreased by 77.8 km², a 24% net loss. Only 6% of that loss was attributable to mangrove expansion; most salt marsh was lost due to conversion to tidal flats or water, likely a result of relative sea level rise. Our research confirmed that mangroves are expanding and, in some instances, displacing salt marshes at certain locations. However, this shift is not widespread when analyzed at a larger, regional level. Rather, local, relative sea level rise was indirectly implicated as another important driver causing regional-level salt marsh loss. Climate change is expected to accelerate both sea level rise and mangrove expansion; these mechanisms are likely to interact synergistically and contribute to salt marsh loss.     

Notes On The Occurrence Of Clathrus Cancellatus,Tournf., In Argyllshire

Background: Estuaries are characterised by salinity gradients and regular flooding events. These environmental factors form stress gradients, along which species composition changes.

Aims: Analyse and compare patterns of plant species diversity along the estuarine salinity and flooding gradients of the Elbe and Connecticut Rivers.

Methods: Vegetation was sampled at three elevations (low, mid, high) in five sites of each marsh type (fresh, brackish, salt) in both estuaries. Patterns of species density (SD) and evenness (E) along the gradients were analysed and compared between the two estuaries with three-factor ANOVAs.

Results: The regional species pool was 33% higher for the Connecticut than for the Elbe. SD of fresh marshes (19 ± 2.2) was more than twice in the Connecticut than in the Elbe. We found an overall increase in SD from low to high elevation and from salt to freshwater marshes in both estuaries. However, SD and E were strongly depressed at intermediate elevations in the Elbe fresh and brackish marshes.

Conclusions: Although diversity patterns in the two estuaries show overall similarities, patterns of SD and E differ, when particular elevational zones and marsh types are compared. We hypothesise this to be due to evolutionary and historical influences on the regional species pools, shaping the impact of local biotic and abiotic processes.     

Plathelminth abundance in North Sea salt marshes: environmental instability causes high diversity

Although supralittoral salt marshes are habitats of high environmental instability, the meiofauna is rich in species and abundance is high. The community structure of free-living Plathelminthes (Turbellaria) in these salt marshes is described. On an average, 104 individuals are found below an area of 10 cm². The average species density in ungrazed salt marshes is 11.3 below 10 cm² and 45.2 below 100 cm², indicating strong small-scale heterogenity. The faunal similarity between sediment and the corresponding above-ground vegetation is higher than between adjacent sample sites. Species prefer distinct ranges of salinity. In the lower part of the supralittoral salt marshes, the annual fluctuations of salinity are strongest and highly unpredictable. This region is richest in plathelminth species and abundance; diversity is highest, and the faunal composition of parallel samples is quite similar. In the upper part of the supralittoral salt marshes, the annual variability of salinity is lower, plathelminths are poor in species diversity and abundance. Parallel samples often have no species in common. Thus, those salt marsh regions with the most unstable environment are inhabited by the most diverse species assemblage. Compared to other littoral zones of the North Sea, however, plathelminth diversity in salt marshes is low. The observed plathelminth diversity pattern can apparently be explained by the dynamic equilibrium model (Huston, 1979).     

Ecological processes shaping Central Patagonian salt marsh landscapes

Plant zonation is one of the most conspicuous ecological features of salt marshes worldwide. In this work we used a combination of field transplant and greenhouse experiments to evaluate the importance of interspecific interactions and physical stress in the determination of the major plant zonation patterns in Central Patagonian salt marshes. There, Spartina alterniflora dominates the low marsh, and Sarcocornia perennis the high marsh. We addressed two questions: (i) What prevents Spartina alterniflora from colonizing the Sarcocornia perennis‐dominated high marsh zone? and (ii) What prevents Sarcocornia perennis from colonizing the Spartina alterniflora‐dominated low marsh zone? Our experimental transplants combined with neighbour exclusion treatments showed that the presence of Sarcocornia perennis negatively affects Spartina alterniflora, preventing it from surviving and/or spreading. Complementary field transplant and greenhouse experiments showed that Sarcocornia perennis did not survive the frequent tidal submersion by approximately 1.5 m of turbid seawater in the Spartina alterniflora zone, but its survival was independent of the presence of Spartina neighbours, and of the strong soil anoxia as well. Our results suggest that Spartina alterniflora is excluded by Sarcocornia perennis towards the low marsh, where frequent and prolonged submersion limit the survival of the latter. We provide and discuss key baseline information to facilitate the future design of ecophysiological experiments designed to accurately identify the exact mechanisms acting in every situation.     

Role of biotic interactions and physical factors in determining the distribution of marsh species along an estuarine salinity gradient

Understanding the mechanisms that shape plant distribution patterns is a major goal in ecology. We investigated the role of biotic interactions (competition and facilitation) and abiotic factors in creating horizontal plant zonation along salinity gradients in the Elbe estuary. We conducted reciprocal transplant experiments with four dominant species from salt and tidal freshwater marshes at two tidal elevations. Ten individuals of each species were transplanted as sods to the opposing marsh type and within their native marsh (two sites each). Transplants were placed at the centre of 9‐m² plots along a line parallel to the river bank. In order to disentangle abiotic and biotic influences, we set up plots with and without neighbouring vegetation, resulting in five replicates per site. Freshwater species (Bolboschoenus maritimus and Phragmites australis) transplanted to salt marshes performed poorly regardless of whether neighbouring vegetation was present or not, although 50–70% of the transplants did survive. Growth of Phragmites transplants was impaired also by competition in freshwater marshes. Salt marsh species (Spartina anglica and Puccinellia maritima) had extremely low biomass when transplanted to freshwater marshes and 80–100% died in the presence of neighbours. Without neighbours, biomass of salt marsh species in freshwater marshes was similar to or higher than that in salt marshes. Our results indicate that salt marsh species are precluded from freshwater marshes by competition, whereas freshwater species are excluded from salt marshes by physical stress. Thus, our study provides the first experimental evidence from a European estuary for the general theory that species boundaries along environmental gradients are determined by physical factors towards the harsh end and by competitive ability towards the benign end of the gradient. We generally found no significant impact of competition in salt marshes, indicating a shift in the importance of competition along the estuarine gradient.     

The roles of elevation and salinity as primary controls on living foraminiferal distributions: Cowpen Marsh, Tees Estuary, UK

Benthic foraminiferal assemblages in subrecent deposits are commonly used to reconstruct past sea level. Interpretations are generally made by comparison with either modern dead or total (live plus dead) assemblages. In both cases there will have been post-mortem changes that have differentially affected preservation. It is therefore important to establish the primary ecological controls by analysis of the living assemblages. We have determined the spatial and temporal variability of intertidal benthic foraminifera in the surface (0–1 cm) sediments from a time series survey of 31 sampling stations at Cowpen Marsh, for a period of 12 months. We counted 112,067 live foraminifera assigned to 28 species. The fauna was dominated by two agglutinated species (Jadammina macrescens and Trochammina inflata) on the high and middle marshes, and three calcareous species (Elphidium williamsoni, Haynesina germanica and Quinqueloculina spp.) on the low marsh and tidal flat.The standing crop of the whole intertidal zone, including the high, middle, low marsh and tidal flat habitats, and the individual species varied both temporally and spatially. The standing crop of the intertidal zone as a whole was greatest in the summer months and showed a positive correlation with elevation. The standing crops of the high and middle marshes showed similar temporal variation with peaks in summer and autumn and a trough in winter. The low marsh showed numerous peaks and troughs of standing crop during the year, whereas the tidal flat showed a single peak in summer. The standing crops of Jadammina macrescens and Trochammina inflata on the high and middle marshes peaked from April to May and August to October with troughs in winter. These agglutinated species showed a strong correlation with elevation. Haynesina germanica peaked in May to August and November to January on the low marsh, whereas on the tidal flat there was a single peak in July. The standing crops of E. williamsoni on the low marsh and tidal flat were relatively high in June and May, and July, respectively. Quinqueloculina spp. peaked in May to July on the low marsh and July on the tidal flat. The species was also found in the middle marsh from July to May and high marsh from September to November. Haynesina germanica showed a strong negative correlation with elevation, whereas the other two dominant calcareous species demonstrated weak negative correlations with both elevation and salinity.Reconstructing former sea level depends primarily on the recognition of high and middle marsh assemblages and in this study these are shown to be strongly controlled by elevation rather than salinity. Caution may be needed in interpreting low marsh and tidal flat data as salinity plays a more important role here.     

Palynomorph distribution in a mangrove ecosystem along environmental and salinity gradient: a tool for palaeoecological reconstruction

Pollen assemblages closely reflect the local vegetation that characterizes the salinity status, providing useful analogs for paleoecologxical reconstruction in regional deposits. Palynological evidences of surface sediments from the Coringa mangrove wetland were correlated with the physicochemical and sediment salinity records to observe the relationship between them. The statistical analysis of the data obtained here revealed a marked horizontal salinity gradient from north to south.. In this study, ordination (detrended correspondence analysis) of palynomorph groups has identified a salinity gradient of 1.1 to 3.0 PSU from the north to the south in the wetland. High palynomorph deposition and lower salinity are observed along channel margins due to the mixing of estuarine water during the rainy season. The mudflats along the transects show a lower diversity of plants in the pollen record and high total dissolved solids (TDS) than commonly found in the coastal wetlands. The presence of scrubby halophytic vegetation in the upper saltmarsh and oligohaline-freshwater vegetation in the low tidal saline marshes is a zonation pattern related to the localized influence of freshwater conditions. Palynomarine Index (PMI) reveals the highest freshwater/tidal inundation along Ramannapalem due to the presence of numerous riverine channels while the remaining part of the wetland has restricted tidal inundation leading to the conversion of mangrove forests to salt pans and paddy fields. Thus, the health and productivity of the mangrove ecosystem are also governed by hydrodynamics, catchment land use, water discharge in the channels, and tidal flushing.

     

Does National Wetland Inventory class consistently identify vegetation and edaphic differences in Oregon tidal wetlands?

Accurately mapping, modeling, and managing the diversity of wetlands present in estuaries often relies on habitat classification systems that consistently identify differences in biotic structure or other ecosystem characteristics between classes. We used field data from four Oregon estuaries to test for differences in vegetation structure and edaphic characteristics among three tidal emergent marsh classes derived from National Wetlands Inventory (NWI) data: low estuarine marsh, high estuarine marsh, and tidal palustrine marsh. Independently of NWI class, we also evaluated the number and types of plant assemblages present and how edaphic variables, non-native plant cover, and plant species richness varied among them. Pore water salinity varied most strongly across marsh classes, with sediment carbon and nitrogen content, grain size and marsh surface elevation showing smaller differences. Cover of common vascular plant species differed between marsh classes and overall vegetation composition was somewhat distinct among marsh types. High estuarine marsh had the largest species pools. However, plot-level plant diversity was similar among marsh classes. Non-native species cover was highest in tidal palustrine and high estuarine marshes. The marshes in the study contained a large number of plant assemblages with most occurring across more than one marsh class. The more common assemblages occurred along a continuum of tidal elevation, soil salinity, and edaphic characteristics, with varying plant richness and non-native cover. Our data suggest that NWI classes are useful for differentiating several general features of Oregon tidal marsh structure, but that more detailed information on plant assemblages found within those wetland classes would allow more precise characterization of additional wetland features such as edaphic conditions and plant diversity.     

The macrobenthos in Spartina alterniflora salt marshes of the Wanggang tidal-flat,Jiangsu coast,China

On the Jiangsu coast, eastern China, Spartina alterniflora, which was introduced artificially into the region, is becoming a dominant plant species in the inter-tidal salt marshes. In order to evaluate the environmental and ecological impact of the colonization of S. alterniflora, we carried out investigations into the benthic macrofauna of the Spartina marshes of the Wanggang area, central Jiangsu coast, in 2006 and 2007. Based on analysis of the data sets obtained, 12 species of macrobenthos have been identified for the Wanggang salt marsh, including S. alterniflora, Cerithidea cingulata, Littorna scabra, Bithynia fuchsiana, Macrophthalmus japonicus, Uca arcuata, Nereis sp., Boleophthalmus petinirostris, Cyclina sinensis, Bullacta exarata, Angustassiminea castanea and Glaucomya chinensis. The results indicate that some of the native species have adapted to the new ecological environment associated with the cordgrass S. alterniflora. The biomass of macrobenthos varies significantly over different parts of the salt marsh. Further, there is a seasonal change in bio-density, with the density in summer (July and August) > autumn (November) > early summer (May). At the landward edge and over the central part of the S. alterniflora marsh, the bio-diversity is higher than the other areas of the marsh.