Determinants of expansion for<Emphasis Type="Italic">Phragmites australis</Emphasis>, common reed,in natural and impacted coastal marshes

The rapid spread ofPhragmites australis in the coastal marshes of the Northeastern United States has been dramatic and noteworthy in that this native species appears to have gained competitive advantage across a broad range of habitats, from tidal salt marshes to freshwater wetlands. Concomitant with the spread has been a variety of human activities associated with coastal development as well as the displacement of nativeP. australis with aggressive European genotypes. This paper reviews the impacts caused by pure stands ofP. australis on the structure and functions of tidal marshes. To assess the determinants ofP. australis expansion, the physiological tolerance and competitive abilities of this species were examined using a field experiment.P. australis was planted in open tubes paired withSpartina alterniflora, Spartina patens, Juncus gerardii, Lythrum salicaria, andTypha angustifolia in low, medium, and high elevations at mesohaline (14‰), intermediate (18‰), and salt (23‰) marsh locations. Assessment of the physiological tolerance ofP. australis to conditions in tidal brackish and salt marshes indicated this plant is well suited to colonize creek banks as well as upper marsh edges. The competitive ability ofP. australis indicated it was a robust competitor relative to typical salt marsh plants. These results were not surprising since they agreed with field observations by other researchers and fit within current competition models throught to structure plant distribution within tidal marshes. Aspects ofP. australis expansion indicate superior competitive abilities based on attributes that fall outside the typical salt marsh or plant competition models. The alignment of some attributes with human impacts to coastal marshes provides a partial explanation of how this plant competes so well. To curb the spread of this invasive genotype, careful attention needs to be paid to human activities that affect certain marsh functions. Current infestations in tidal marshes should serve as a sentinel to indicate where human actions are likely promoting the invasion (e.g., through hydrologic impacts) and improved management is needed to sustain native plant assemblages (e.g., prohibit filling along margins).     

Wetland Loss Patterns and Inundation-Productivity Relationships Prognosticate Widespread Salt Marsh Loss for Southern New England

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

Growth and Movements of Mummichogs (<Emphasis Type="Italic">Fundulus heteroclitus</Emphasis>) Along Armored and Vegetated Estuarine Shorelines

Alteration of estuarine shorelines associated with increased urbanization can significantly impact biota and food webs. This study determined the impact of shoreline alteration on growth and movement of the estuarine fish Fundulus heteroclitus in a tributary of the Delaware Coastal Bays. Fundulus heteroclitus is abundant along the east coast of the USA, and is an important trophic link between marsh and subtidal estuary. The restricted home range of F. heteroclitus allowed discrete sampling, and fish growth comparisons, along 35–65-m long stretches of fringing Spartina alterniflora and Phragmites australis marsh, riprap, and bulkhead. Fundulus heteroclitus were tagged with decimal Coded Wire Tags. Of 725 tagged F. heteroclitus, 89 were recaptured 30–63 days later. Mean growth rate (0.06–0.15 mm day^?1 across all shoreline types) was greatest at riprap, lowest at Spartina and Phragmites, and intermediate at bulkhead, where growth was not significantly different from any other shoreline. This suggests that discernible environments exist along different shoreline types, even at the scale of tens of meters. No difference in movement distance was detected at different shoreline types; most individuals displayed a high degree of site fidelity. Forty-seven percent were recaptured within 5 m of their tagging location, although alongshore movements up to 475 m were recorded. Estimates of relative F. heteroclitus productivity, using relative density data from a concurrent study, were highest along Spartina and Phragmites, intermediate at riprap, and lowest at bulkhead. Therefore, despite greater growth rates along riprap than at vegetated shores, armoring reduces abundance sufficiently to negatively impact localized productivity of F. heteroclitus.     

Application of Species Distribution Models to Identify Estuarine Hot Spots for Juvenile Nekton

Modeling the distribution and habitat capacities of key estuarine species can be used to identify hot spots, areas where species density is significantly higher than surrounding areas. This approach would be useful for establishing a baseline for evaluating future environmental scenarios across a landscape. We developed species distribution models for early juvenile life stages of brown shrimp (Farfantepenaeus aztecus), white shrimp (Litopenaeus setiferus), blue crab (Callinectes sapidus), and spotted seatrout (Cynoscion nebulosus) in order to delineate the current coastal hot spots that provide the highest quality habitat conditions for these estuarine-dependent species in Louisiana. Response curves were developed from existing long-term fisheries-independent monitoring data to identify habitat suitability for fragmented marsh landscapes. Response curves were then integrated with spatially explicit input data to generate species distribution models for the coastal region of Louisiana. Using spatial autocorrelation metrics, we detected clusters of suitable habitat across the Louisiana coast, but only 1% of the areas were identified as true hot spots with the highest habitat quality for nekton. The regions identified as hot spots were productive fringing marsh habitats that are considered the most vulnerable to natural and anthropogenic impacts. The species distribution models identify the coastal habitats which currently provide the greatest capacity for key estuarine species and will be used in the Louisiana coastal planning process to evaluate how species distributions may change under various environmental and restoration scenarios.     

The Effects of Integrated Marsh Management (IMM) on Salt Marsh Vegetation,Nekton, and Birds

An integrated marsh management (IMM) project in an urbanized watershed on Long Island, New York, USA, aimed to mitigate salt marsh degradation and to reduce mosquito production by an innovative combination of restoration and open marsh water management methods. The grid ditch network at two treatment marshes was replaced with naturalized tidal channels and ponds. Effects of the hydrologic alterations were monitored utilizing a before–after–control–impact approach. The treatment marshes experienced a number of beneficial outcomes including a fourfold reduction in the invasive Phragmites australis and increased native vegetation cover in the most degraded portions of the marsh, increased abundance and diversity of marsh killifish and estuarine nekton species, higher shorebird and waterfowl densities, and increased avian species diversity. The successful implementation of IMM concept led to improved marsh health and diminished mosquito production. Therefore, this study may serve as a template for similar large-scale integrated salt marsh restoration projects.     

Effects of common reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>) expansions on nitrogen dynamics of tidal marshes of the northeastern U.S.

Several recent studies indicate that the replacement of extant species withPhragmites australis can alter the size of nitrogen (N) pools and fluxes within tidal marshes. Some common effects ofP. australis expansion are increased standing stocks of N, greater differentiation of N concentrations between plant tissues (high N leaves and low N stems), and slower whole-plant decay rates than competing species (e.g.,Spartina, Typha spp.). Some of the greater differences between marsh types involveP. australis effects on extractable and porewater pools of dissolved inorganic nitrogen (DIN) and N mineralization rates. Brackish and salt marshes show higher concentrations of DIN in porewater beneathSpartina spp. relative toP. australis, but this is not observed in freshwater tidal marshes whenP. australis is compared withTypha spp. or mixed plant assemblages. With few studies of concurrent N fluxes, the net effect ofP. australis on marsh N budgets is difficult to quantify for single sites and even more so between sites. The magnitude and direction of impacts ofP. australis on N cycles appears to be system-specific, driven more by the system and species being invaded than byP. australis itself. WhereP. australis is found to affect N pools and fluxes, we suggest these alterations result from increased biomass (both aboveground and belowground) and increased allocation of that biomass to recalcitrant stems. Because N pools are commonly greater inP. australis than in most other communities (due to plant and litter uptake), one of the most critical questions remaining is “From where is the extra N inP. australis communities coming?” It is important to determine if the source of the new N is imported (e.g., anthropogenic) or internallyproduced (e.g., fixed, remineralized organic matter). In order to estimate net impacts ofP. australis on marsh N budgets, we suggest that further research be focused on the N source that supports high standing stocks of N inP. australis biomass (external input versus internal cycling) and the relative rates of N loss from different marshes (burial versus subsurface flow versus denitrification).     

Impact of Armored Shorelines on Shore-Zone Fish Density in a Mid-Atlantic,USA, Estuary: Modulation by Hypoxia and Temperature

Anthropogenic modifications of estuarine environments, including shoreline hardening and corresponding alteration of water quality, are accelerating worldwide as human population increases in coastal regions. Estuarine fish species inhabiting temperate ecosystems are adapted to extreme variations in environmental conditions including water temperature, salinity, and dissolved oxygen across seasonal, daily, and hourly time scales. The present research utilized quantitative sampling to examine the spatiotemporal distribution of shore-zone estuarine fish species in association with four unique shoreline types across a range of water temperature and dissolved oxygen conditions. Fish were collected from the intertidal and shallow subtidal region of four shoreline types, Spartina alterniflora marsh, Phragmites australis marsh, riprap, and bulkhead, in the summer and fall of 2009 and 2010. Analyses were performed to (1) compare mean fish density among shoreline types across all water conditions and (2) explore relationships of the complete fish assemblage, three functional species groupings, and two fish species (Fundulus heteroclitus and Menidia menidia) to unique shoreline/water conditions. Significantly greater mean fish densities were found along S. alterniflora shorelines than armored shorelines. Several metrics including fish density, species richness, and occurrence rates suggest S. alterniflora shorelines may serve as a form of refuge habitat during periods of low dissolved oxygen and high temperatures for various species, particularly littoral-demersal species including F. heteroclitus. Potential mechanisms that could contribute to a habitat providing refuge during adverse water quality conditions include tempering of the adverse condition (decreased temperatures, increased dissolved oxygen), predation protection, and increased foraging opportunities.     

<Emphasis Type="Italic">Spartina alterniflora</Emphasis> Biomass Allocation and Temperature: Implications for Salt Marsh Persistence with Sea-Level Rise

To predict the impacts of climate change, a better understanding is needed of the foundation species that build and maintain biogenic ecosystems. Spartina alterniflora Loisel (smooth cordgrass) is the dominant salt marsh-building plant along the US Atlantic coast. It maintains salt marsh elevation relative to sea level by the accumulation of aboveground biomass, which promotes sediment deposition and belowground biomass, which accretes as peat. Peat accumulation is particularly important in elevation maintenance at high latitudes where sediment supply tends to be limited. Latitudinal variation in S. alterniflora growth was quantified in eight salt marshes from Massachusetts to South Carolina. The hypothesis that allocation to aboveground and belowground biomass is phenotypically plastic was tested with transplant experiments among a subset of salt marshes along this gradient. Reciprocal transplants revealed that northern S. alterniflora decreased allocation to belowground biomass when grown in the south. Some northern plants also died when moved south, suggesting that northern S. alterniflora may be stressed by future warming. Southern plants that were moved north showed phenotypic plasticity in biomass allocation, but no mortality. Belowground biomass also decomposed more quickly in southern marshes. Our results suggest that warming will lead northern S. alterniflora to decrease belowground allocation and that belowground biomass will decompose more quickly, thus decreasing peat accumulation. Gradual temperature increases may allow for adaptation and acclimation, but our results suggest that warming will lower the ability of salt marshes to withstand sea-level rise.     

<Emphasis Type="Italic">Deepwater Horizon</Emphasis> Oil Spill Impacts on Salt Marsh Fiddler Crabs (<Emphasis Type="Italic">Uca</Emphasis> spp.)

The Deepwater Horizon oil spill was the largest marine oil spill in US waters to date and one of the largest worldwide. Impacts of this spill on salt marsh vegetation have been well documented, although impacts on marsh macroinvertebrates have received less attention. To examine impacts of the oil spill on an important marsh invertebrate and ecosystem engineer, we conducted a meta-analysis on fiddler crabs (Uca spp.) using published sources and newly available Natural Resources Damage Assessment (NRDA) and Gulf of Mexico Research Initiative (GoMRI) data. Fiddler crabs influence marsh ecosystem structure and function through their burrowing and feeding activities and are key prey for a number of marsh and estuarine predators. We tested the hypothesis that the spill affected fiddler crab burrow density (crab abundance), burrow diameter (crab size), and crab species composition. Averaged across multiple studies, sites, and years, our synthesis revealed a negative effect of oiling on all three metrics. Burrow densities were reduced by 39 % in oiled sites, with impacts and incomplete recovery observed over 2010–2014. Burrow diameters were reduced from 2010 to 2011, but appeared to have recovered by 2012. Fiddler crab species composition was altered through at least 2013 and only returned to reference conditions where marsh vegetation recovered, via restoration planting in one case. Given the spatial and temporal extent of data analyzed, this synthesis provides compelling evidence that the Deepwater Horizon spill suppressed populations of fiddler crabs in oiled marshes, likely affecting other ecosystem attributes, including marsh productivity, marsh soil characteristics, and associated predators.     

Vegetation Dynamics in Rhode Island Salt Marshes During a Period of Accelerating Sea Level Rise and Extreme Sea Level Events

Sea level rise is a major stressor on many salt marshes, and its impacts include creek widening, ponding, vegetation dieback, and drowning. Marsh vegetation changes have been associated with sea level rise across southern New England, but most of these studies pre-date the current period of rapidly accelerating sea level rise coupled with episodic events of extreme increases in water levels. Here, we combine data from two salt marsh monitoring and assessment programs in Rhode Island that were designed to assess marsh responses to sea level rise and use these data to document temporal and spatial patterns in marsh vegetation during the current period of extreme water level increases. Vegetation monitoring at two Narragansett Bay salt marshes confirms the ongoing decline of the salt meadow species Spartina patens during this period as it becomes replaced by Spartina alterniflora. Bare ground resulting from vegetation dieback was significantly related to mean high water levels and led to the rapid conversion of mixed Spartina assemblages to S. alterniflora monocultures. A broader spatial assessment of RI marshes shows that S. alterniflora dominance increases at lower elevation marshes toward the mouth of Narraganset Bay. Our data provide additional evidence that S. patens continues to decline in southern New England marshes and show that losses can accelerate during periods of extreme high water levels. Unless adaptive management actions are taken, we predict that marshes throughout RI will continue to lose salt meadow habitat and eventually resemble lower elevation marshes that are already dominated by S. alterniflora monocultures.     

Predation by the black-clawed mud crab,<Emphasis Type="Italic">Panopeus herbstii</Emphasis>, in Mid-Atlantic salt marshes: Further evidence for top-down control of marsh grass production

Although top-down control of plant growth has been shown in a variety of marine systems, it is widely thought to be unimportant in salt marshes. Recent caging experiments in Virginia and Georgia have challenged this notion and shown that the dominant marsh grazer (the periwinkle,Littoraria irrorata) not only suppresses plant growth, but can denude marsh substrate at high densities. In these same marshes, our field observations suggest that the black-clawed mud crab,Panopeus herbstii, is an abundant and potentially important top-down determinant of periwinkle density. No studies have quantitatively examinedPanopeus distribution or trophic interactions in marsh systems, and its potential impacts on community structure remained unexplored. We investigated distribution and feeding habits ofPanopeus in eight salt marshes along the Mid-Atlantic seashore (Delaware-North Carolina). We found that mud crabs were abundant in tall (4–82 ind m^?2), intermediate (0–15 ind m^?2), and short-form (0–5 ind m^?2)Spartina alterniflora zones in all marshes and that crab densities were negatively correlated with tidal height and positively correlated with bivalve density. Excavation of crab lairs r?utinely produced shells of plant-grazing snails (up to 36 lair^?1) and bivalves. Lab experiments confirmed that mud crabs readily consume these abundant marsh molluscs. To experimentally examine potential community effects of observed predation patterns, we manipulated crab and periwinkle densities in a 1-mo field experiment. Results showed thatPanopeus can suppress gastropod abundance and that predation rates increase with increasing snail density. In turn, crab suppression of snail density reduces grazing intensity on salt marsh cordgrass, suggesting presence of a trophic cascade. These results indicate that this previously under-appreciated consumer is an important and indirect determinant of community structure and contribute to a growing body of evidence challenging the long-standing notion that consumers play a minor role in regulating marsh plant growth.     

Development of a Multimetric Index for Integrated Assessment of Salt Marsh Ecosystem Condition

Tools for assessing and communicating salt marsh condition are essential to guide decisions aimed at maintaining or restoring ecosystem integrity and services. Multimetric indices (MMIs) are increasingly used to provide integrated assessments of ecosystem condition. We employed a theory-based approach that considers the multivariate relationship of metrics with human disturbance to construct a salt marsh MMI for five National Parks in the northeastern USA. We quantified the degree of human disturbance for each marsh using the first principal component score from a principal components analysis of physical, chemical, and land use stressors. We then applied a metric selection algorithm to different combinations of about 45 vegetation and nekton metrics (e.g., species abundance, species richness, and ecological and functional classifications) derived from multi-year monitoring data. While MMIs derived from nekton or vegetation metrics alone were strongly correlated with human disturbance (r values from ?0.80 to ?0.93), an MMI derived from both vegetation and nekton metrics yielded an exceptionally strong correlation with disturbance (r = ?0.96). Individual MMIs included from one to five metrics. The metric-assembly algorithm yielded parsimonious MMIs that exhibit the greatest possible correlations with disturbance in a way that is objective, efficient, and reproducible.     

Anthropocene Survival of Southern New England’s Salt Marshes

In southern New England, salt marshes are exceptionally vulnerable to the impacts of accelerated sea level rise. Regional rates of sea level rise have been as much as 50 % greater than the global average over past decades, a more than fourfold increase over late Holocene background values. In addition, coastal development blocks many potential marsh migration routes, and compensatory mechanisms relying on positive feedbacks between inundation and sediment deposition are insufficient to counter inundation increases in extreme low-turbidity tidal waters. Accordingly, multiple lines of evidence suggest that marsh submergence is occurring in southern New England. A combination of monitoring data, field re-surveys, radiometric dating, and analysis of peat composition have established that, beginning in the early and mid-twentieth century, the dominant low-marsh plant, Spartina alterniflora, has encroached upward in tidal marshes, and typical high-marsh plants, including Juncus gerardii and Spartina patens, have declined, providing strong evidence that vegetation changes are being driven, at least in part, by higher water levels. Additionally, aerial and satellite imagery show shoreline retreat, widening and headward extension of channels, and new and expanded interior depressions. Papers in this special section highlight changes in marsh-building processes, patterns of vegetation loss, and shifts in species composition. The final papers turn to strategies for minimizing and coping with marsh loss by managing adaptively and planning for landward marsh migration. It is hoped that this collection offers lessons that will be of use to researchers and managers on coasts where relative sea level is not yet rising as fast as in southern New England.     

Reproductive success of wading birds using<Emphasis Type="Italic">Phragmites</Emphasis> marsh and upland nesting habitats

Colonial nesting of long-legged wading birds (Ciconiiformes) in the coastal northeastern U.S. is limited primarily to islands, which provide isolated habitats that are relatively free of ground predators. Estuarine wetlands in this heavily developed region, including foraging wetlands and fringe marshes surrounding nesting islands, are often dominated byPhragmites australis. On Pea Patch Island in Delaware Bay, site of one of the largest and most enduring mixed-species heron colonies on the East Coast, wading birds nest inPhragmites marsh habitat as well as in adjacent upland shrubs and trees. BecausePhragmites is aggressively managed in Delaware Bay, we investigated the relative habitat value of marsh and upland nesting sites for the purpose of developing recommendations for marsh and wildlife management. Utilization of marsh habitat by nesting birds ranged from 27–82% during 1993–1998. Two species (great blue heronArdea herodias and great egretA. alba) never nested inPhragmites, four species (little blue heronEgretta caerulea, snowy egretE. thula, cattle egretBubulcus ibis, and black-crowned night-heronNycticorax nycticorax) nested in approximately equal proportions in both habitats, and one species (glossy ibisPlegadis falcinellus) was largely confined to marsh nesting. Productivity (egg and nestling production) varied between habitats for some species. Cattle egrets produced larger clutches and had higher hatching rates inPhragmites compared to upland habitat. Little blue herons were more successful in the uplands. Managers should retainPhragmites marsh at colony sites, such as Pea Patch Island, where it provides critical habitat for nesting wading birds both as substrate for nesting and buffer habitat to control human disturbance.     

Growth of the marsh elder<Emphasis Type="Italic">Iva frutescens</Emphasis> in relation to duration of tidal flooding

Iva frutescens is a common shrub at the upland fringe of salt marshes throughout the East and Gulf Coasts of North America. Within a marsh, its location and relative size are governed largely by the degree of flooding by seawater.Iva’s wide distribution and restricted location within salt marshes may make it a useful indicator of overall conditions of the marshes. This work was designed to provide basic information on the age and growth ofI. frutescens, especially as they relate to the degree of flooding that is needed in order to investigateIva’s potential as an indicator. Cross-sections of older stems (living and standing dead) from salt marshes in Rhode Island, United States, were examined in order to age stems and estimate their growth rate from cumulative increase in woody tissue. Most stems were six yr old or less, suggesting that aboveground structures live for only a few years. Stem diameter correlated with growth rate and aboveground biomass. Elevation at the root zone was used to estimate the duration that plants were flooded, which was negatively correlated with stem diameter. The most robust plants came from sites that were flooded only up to 6–7% of the total time during the growing season. No plants were found in areas flooded more than 30% of the time.     

Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone

Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.     

Tropicalization of the Northern Gulf of Mexico: Impacts of Salt Marsh Transition to Black Mangrove Dominance on Faunal Communities

The tropically associated black mangrove (Avicennia germinans) is expanding into salt marshes of the northern Gulf of Mexico (nGOM). This species has colonized temperate systems dominated by smooth cordgrass (Spartina alterniflora) in Texas, Louisiana, Florida and, most recently, Mississippi. To date, little is known about the habitat value of black mangroves for juvenile fish and invertebrates. Here we compare benthic epifauna, infauna, and nekton use of Spartina-dominated, Avicennia-dominated, and mixed Spartina and black mangrove habitats in two areas with varying densities and ages of black mangroves. Faunal samples and sediment cores were collected monthly from April to October in 2012 and 2013 from Horn Island, MS, and twice yearly in the Chandeleur Islands, LA. Multivariate analysis suggested benthic epifauna communities differed significantly between study location and among habitat types, with a significant interaction between the two fixed factors. Differences in mangrove and marsh community composition were greater at the Chandeleurs than at Horn Island, perhaps because of the distinct mangrove/marsh ecotone and the high density and age of mangroves there. Infaunal abundances were significantly higher at Horn Island, with tanaids acting as the main driver of differences between study locations. We predict that if black mangroves continue to increase in abundance in the northern GOM, estuarine faunal community composition could shift substantially because black mangroves typically colonize shorelines at higher elevations than smooth cordgrass, resulting in habitats of differing complexity and flooding duration.     

Foraminiferal evidence of basin submergence in part of Sundarban mangrove delta,India

Sundarban is a largest mangrove forest delta developed along the NE-SW direction covering parts of India and Bangladesh. Little work has been done on Indian part of Sundarban in respect of heterogeneity in channel morphology which could be mostly due to the effect of tilting and basin subsidence. These changes might have played a major role on development of high marshes, which offers a congenial environment for survival of Haplophragmoides wilberti, Jadammina macrescens, Trochammina inflata, and Miliammina fusca. These marsh benthonic foraminiferal assemblages provide a direct evidence of recent past sea level changes. To establish the depositional pattern and their effects rendered by merciless changing environment, 11 pit sections have been excavated along three E-W transects from Indian Sundarban. Depth of these pit sections varies from 2 to 3 m. Generally, top 20 cm sediment (in pit section W-1 to W-11) deposited under the intertidal environment, as indicated by the presence of Ammonia tepida. However, sediment below 20 cm in some of the pit sections (W-3 and W-5) exhibits fresh water signatures as indicated by the presence of Charophytes algae. In other pit sections (W-1, W-2, W-6, W-7, W-8, W-9 and W-11), the intertidal assemblage is noticed just above the upper marshes assemblage and vice versa, signifying that depositional environment is in proximity to the mangrove dominated area as indicated by the presence of marsh benthonic foraminiferal assemblage containing T. inflata, H. wilberti, Haplophragmoides sp., J. macrescens and M. fusca. Bottom sediment in most of the pit sections from south to north have different depositional environment with alternate presence of intertidal to subtidal faunal assemblages. The peculiar presence of intertidal assemblage above the upper marshes assemblages in recent sediment points towards the theory of submergence due to relative rise in the sea level. But the effect of relative sea level rise is not uniform throughout the area because of differential subsidence due to varied rate of sediment supply (0.5 to 3.3 cm/year) and eastward tilting of the basin. Based on the upper marshes benthonic foraminiferal assemblage and radiocarbon age (in W-1 at 100 cm ~?150 years age), the average subsidence rate as recorded is approximately 0.3 to 0.5 cm/year. Hence, such depositional sequence conjectures that the Indian part of Sundarban is undergoing a phase of submergence concomitant to basin subsidence.     

Comparison of fish and macroinvertebrate use of<Emphasis Type="Italic">Typha angustifolia,Phragmites australis</Emphasis>, and treated<Emphasis Type="Italic">Phragmites</Emphasis> marshes along the lower Connecticut River

Since 1965 large areas of lower Connecticut River tidelands have been converted from high diversity brackish meadow andTypha angustifolia marsh to near monocultures ofPhragmites australis. This study addresses the impact ofPhragmites invasion on fish and crustacean use of oligohaline high marsh. During spring tides from early June through early September 2000, fishes and crustaceans leaving flooded marsh along 3 km of the Lieutenant River, a lower Connecticut River tributary, were captured with Breder traps at 90 sites, equally distributed amongPhragmites, Typha, and treated (herbicide and mowing)Phragmites areas. Pit traps, 18 per vegetation type in 2000 and 30 each inPhragmites andTypha in 2001, caught larvae and juveniles at distances of up to 30 m into the marsh interior. There were no significant differences in fish species compositions or abundances among the vegetation types. Size distributions, size specific biomasses, and diets ofFundulus heteroclitus, the numerically dominant fish, were also similar. The shrimpPalaemonetes pugio was more abundant inPhragmites than in other types of vegetation, whereas the fiddler crabUca minax was least numerous inPhragmites. Mean numbers ofF. heteroclitus andP. pugio caught per site event were positively correlated with increasing site hydroperiod. Significantly moreF. heteroclitus were captured along the upper reach of the river where marsh elevations were lower than farther downstream. MoreF. heteroclitus and fewerP. pugio andU. minax were captured during the day than at night. A relatively small number of larval and juvenileFundulus sp. were captured in pit traps, but consistently fewer inPhragmites than inTypha, suggesting thatTypha and brackish meadow marshes may provide better nursery habitat. Vegetation was sampled along a 30 m transect at each trap site in 2000. Plant species diversity was greatest in treatedPhragmites areas and lowest inPhragmites sites.     

Effects of Local Shoreline and Subestuary Watershed Condition on Waterbird Community Integrity: Influences of Geospatial Scale and Season in the Chesapeake Bay

In many coastal regions throughout the world, there is increasing pressure to harden shorelines to protect human infrastructures against sea level rise, storm surge, and erosion. This study examines waterbird community integrity in relation to shoreline hardening and land use characteristics at three geospatial scales: (1) the shoreline scale characterized by seven shoreline types: bulkhead, riprap, developed, natural marsh, Phragmites-dominated marsh, sandy beach, and forest; (2) the local subestuary landscape scale including land up to 500 m inland of the shoreline; and (3) the watershed scale >500 m from the shoreline. From 2010 to 2014, we conducted waterbird surveys along the shoreline and open water within 21 subestuaries throughout the Chesapeake Bay during two seasons to encompass post-breeding shorebirds and colonial waterbirds in late summer and migrating and wintering waterfowl in late fall. We employed an Index of Waterbird Community Integrity (IWCI) derived from mean abundance of individual waterbird species and scores of six key species attributes describing each species’ sensitivity to human disturbance, and then used this index to characterize communities in each subestuary and season. IWCI scores ranged from 14.3 to 19.7. Multivariate regression model selection showed that the local shoreline scale had the strongest influence on IWCI scores. At this scale, percent coverage of bulkhead and Phragmites along shorelines were the strongest predictors of IWCI, both with negative relationships. Recursive partitioning revealed that when subestuary shoreline coverage exceeded thresholds of approximately 5% Phragmites or 8% bulkhead, IWCI scores decreased. Our results indicate that development at the shoreline scale has an important effect on waterbird community integrity, and that shoreline hardening and invasive Phragmites each have a negative effect on waterbirds using subestuarine systems.