Adjacent Marsh Research Articles

Salt Marsh Mosquito-Control Ditches: Sedimentation, Landscape Change, and Restoration Implications

Corman, S.S.; Roman, C.T.; King, J.W., and Appleby, P.G., 2012. Salt marsh mosquito-control ditches: sedimentation, landscape change, and restoration implications. Mosquito ditches are a prolific physical feature of Atlantic coast salt marshes, dug most intensely since the 1930s to control the breeding of salt marsh mosquitoes. Removal of ditches by filling or other methods is under consideration as a restoration alternative at a Fire Island, New York, salt marsh. This study evaluated sediment dynamics and marsh landscape structure of the ditched marsh, thereby providing information to better support efforts to predict marsh responses to restoration alternatives. Field surveys, historic and recent aerial photography analysis, and radiometric dating techniques were used. The estimated average natural sedimentation rate within the ditches was 0.52 cm y−1, a rate greater than the accretion rate of the adjacent marsh surface. The average time for a Fire Island ditch to naturally fill would be 175 years from present, but spatially this is highly variable, with some ditches completely filled and others showing no evidence of natural filling. Active filling of ditches may be a feasible restoration alternative, pending the findings of pilot studies, but given concerns for marsh submergence with accelerated rates of sea level rise, restoration design should provide a hydrologic network to facilitate adequate marsh drainage.

Mesoscale geomorphic change on low energy barrier islands in Chesapeake Bay, U.S.A.

This paper presents an analysis of decadal (mesoscale) geomorphic change on sandy barrier islands in the fetch-limited environment of Chesapeake Bay. Low energy barrier islands exist in two settings: on the fringe of marshes and in open water and this analysis shows the various types of barrier island to be genetically related. Barrier islands that face the dominant wind and wave direction (E or W) retreat via barrier translation, preserving the barrier island volume. Those that exist in re-entrants are dominated by longshore transport processes, are strongly affected by sediment supply and are subject to disintegration.Marsh fringe barrier islands are perched on or draped over the surface of the underlying marsh. They migrate landwards via barrier translation during periodic high water events accompanied by large waves (hurricanes and northeasters). The underlying marsh surface erodes under all water levels and the rate of retreat of the barrier island and underlying marsh may take place at different rates, leading to various configurations from perched barrier islands several metres landward of the marsh edge, to barrier islands that have a sandy shoreface extending into the subtidal zone. The coastal configuration during landward retreat of marsh fringe barrier islands is subject to strong local control exerted by the underyling marsh topography. As erosion of marsh promontories occurs and marsh creeks are intersected and bypassed, the configuration is subject to rapid change.Periodic sediment influxes cause spits to develop at re-entrants in the marsh. The spits are initiated as extensions of adjacent marsh fringe barrier islands, but as the sediment volume is finite, the initial drift-aligned spits become sediment-starved and begin to develop a series of swash-aligned cells as they strive for morphodynamic equilibrium. The individual cells are stretched until breaches form in the barrier islands, creating inlets with tidal deltas. At this stage the low energy barrier islands closely resemble open ocean barrier islands. Continued reworking leads to widening of the inlets with consequent loss of constriction of tidal flow. The tidal deltas are, thus, no longer maintained and ultimately the island system disintegrates through inlet widening and is transformed to subtidal shoals. Barrier islands at various stages in this evolutionary cycle can be observed around the bay.Mid-bay barrier islands are affected by wave processes from both sides. This helps maintain the barrier island form and enables barrier islands to persist as sediment is exchanged between both sides of the island.Rates of barrier island translation are extremely high (up to 30m/year over a 12year period). This is attributed to the low volume of sand, which facilitates complete rollover in short periods. Accelerated sea level rise is likely to hasten the translation rates of marsh fringe barrier islands. The rapid disintegration of most spits compared to the persistence of marsh fringe barrier islands points to a reliance on the marsh as a stabilising point. If the marshes are overstepped by rising sea level as appears to be happening, the complete disintegration of the barrier islands is highly likely.

Using Multitemporal Remote Sensing Imagery and Inundation Measures to Improve Land Change Estimates in Coastal Wetlands

Remote sensing imagery can be an invaluable resource to quantify land change in coastal wetlands. Obtaining an accurate measure of land change can, however, be complicated by differences in fluvial and tidal inundation experienced when the imagery is captured. This study classified Landsat imagery from two wetland areas in coastal Louisiana from 1983 to 2010 into categories of land and water. Tide height, river level, and date were used as independent variables in a multiple regression model to predict land area in the Wax Lake Delta (WLD) and compare those estimates with an adjacent marsh area lacking direct fluvial inputs. Coefficients of determination from regressions using both measures of water level along with date as predictor variables of land extent in the WLD, were higher than those obtained using the current methodology which only uses date to predict land change. Land change trend estimates were also improved when the data were divided by time period. Water level corrected land gain in the WLD from 1983 to 2010 was 1 km2 year−1, while rates in the adjacent marsh remained roughly constant. This approach of isolating environmental variability due to changing water levels improves estimates of actual land change in a dynamic system, so that other processes that may control delta development such as hurricanes, floods, and sediment delivery, may be further investigated.

Long-Term Impacts of Draining a Watershed Wetland on a Downstream Lake, Lake Kinneret, Israel

During the 1950s, the shallow Lake Hula and its adjacent marshes, located in the watershed of Lake Kinneret (LK), were drained in order to increase arable land. The drainage resulted in increasing loads of nutrients in the Jordan River and in oxidative degradation of the underlying peat, followed by Aeolian (mostly) and riverine transport to LK. Peat had been accumulating in LK bed sediments since the 1950s, with peak deposits recorded in the mid-1970s. The routine monitoring of Norg and Corg, associated with the peat, in the watershed streams and in LK water (initiated in 1970) also showed the highest levels in the mid-1970s. During the 1980s, a succession of dense natural vegetation inhibited soil surface erosion and a decline in Aeolian transport of peat to LK was recorded. Inversed temporal patterns appear for oxygen and pH, and this is suggested to result from the dependence of these parameters on the magnitude of respiratory process, induced by peat availability. During the 1970s allochthonous peat resources supported about half of the zooplankton activity in LK and therefore the decline in peat availability during the 1980s was accompanied by a two-fold decline in zooplankton biomass. The subsequent lessening of grazing pressure together with the elevated inflows of bio-available P resulted in a significant rise in LK phytoplankton biomass. The 1980s decline in Norg associated with the peat led to lower N/P ratios in the external sources of nutrients to LK. These conditions may have favored the appearance of N2 fixing cyanobacteria noted in the lake since 1994.

An Evaluation of Boat Basin Dredging Effects: Response of Fishes and Crabs in a New Jersey Estuary

AbstractDredging is one of the most common human modifications of estuaries and although its effects have often been studied, there has been little effort in evaluating the effects on mobile macrofauna, such as fishes and crabs. We evaluated the response of fishes and crabs to 4 d of dredging in a small boat basin within a polyhaline marsh creek of a New Jersey estuary. We used several measures, including fish and crab species composition, abundance, and size from trap collections and movements of marked mummichogs Fundulus heteroclitus before, during, and after dredging. In general, the fauna changed little during the 4 d of dredging relative to the 1.5‐month sampling period. Species composition variations that did occur may have been due to seasonal changes that are typically observed during the fall based on annual sampling at this site. The movement of tagged mummichogs was minimal, with most recaptures taking place in the boat basin. Individuals that left the boat basin moved into pools in an adjacent marsh for the winter. These results suggest that the short‐term effect of this low‐sediment‐volume dredging project was negligible for the benthic fishes and crabs studied, which we believe are representative of the high‐salinity portions of estuaries in the northeastern United States.

Modeling anthropogenic substances in coastal wetlands: Application to herbicides in the Camargue (France)

The purpose of this work was to develop a coupled hydrological and chemical model that can simulate time-dependent concentrations of pesticides and their degradation products in shallow coastal water bodies of variable volumes. The model was applied to simulate the exposure of two herbicides, oxadiazon and MCPA, in three interconnected lagoons which form the coastal wetlands of the Camargue. These shallow lagoons and adjacent marshes are of international importance for the preservation of biodiversity. The chemical fugacity and reactivity are modeled in these complex ecosystems as in classical fate models for well-mixed lakes, but additionally water exchanges between the lagoons, seawater intrusion, variable evaporation rates and fluctuating water volumes of the lagoons are incorporated. Analytical solutions for coupled differential equations for the water volumes of the lagoons, the salinities, and the concentrations of pesticides were derived and evaluated using the software Maple. The model was calibrated using salinity data and was able to simulate measured concentrations of oxadiazon and MCPA and two subsequent degradation products of MCPA in the main lagoon in Camargue. Interestingly, model simulations differed from real observations in the two smaller lower lagoons, and the model served tracking so far unknown entry paths of herbicides into these lagoons.

Nekton Density Patterns in Tidal Ponds and Adjacent Wetlands Related to Pond Size and Salinity

We examined the distribution of nekton across the marsh landscape using a 1-m2 drop sampler to compare nekton densities across three different salinity zones (intermediate, brackish, saline), three pond sizes (diameter 750 m = large), and two habitat types (pond, adjacent marsh) in the Barataria Bay Estuary, Louisiana. Nekton assemblages of ponds and the adjacent marsh appeared to be structured by the responses of individual species to the estuarine salinity gradient at the landscape scale and to pond habitat attributes locally. Our results indicate that ponds in the brackish and saline zones are more important nursery areas for most fishery species than ponds in the intermediate zone. Medium and large ponds supported higher densities of most species than small ponds. Most species of nekton were associated with vegetation structure, and individuals of these species were either concentrated among plant stems at the marsh edge or within submerged aquatic vegetation in ponds.

Sediments and water fluxes in a muddy coastline: interplay between waves and tidal channel hydrodynamics

AbstractTidal channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of intertidal landforms. In muddy coastlines, the morphology of tidal channels and adjacent marshes strongly depends on the supply of fine sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fluxes in muddy coastlines, we measured tidal velocity and sediment concentration in Little Constance Bayou, a tidal channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the channel, thus allowing the quantification of feedbacks between waves and sediment fluxes. Results indicate that the sediment concentration in the channel is directly related to the wave height in the adjacent bay during flood and high slack water, whereas the concentration during ebb depends on local channel velocity. Moreover, the sediment flux during ebb is of the same order of magnitude as the sediment flux during the previous flood, indicating that only a small fraction of transported sediments are stored in the marsh during a tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean. Copyright © 2010 John Wiley & Sons, Ltd.

A New Juncus Sect. Ozophyllum (Juncaceae) from Peninsular Florida, U.S.A

Juncus paludosus E. L. Bridges & Orzell is described and illustrated as a new species from peninsular Florida, U.S.A., occurring primarily in hardwood and cypress swamps and adjacent ditches and marshes. Although closest in diagnostic characters to J. megacephalus M. A. Curtis, it has been confused with J. polycephalus Michaux of section Iridifolii Snogerup & Kirschner based on its overall size, gross morphology, and floral characteristics. Differences between J. paludosus and other closely related species of section Ozophyllum Dumortier are discussed, and a key is provided to the group within section Ozophyllum that includes J. paludosus.

HIGHLAND BAYOU: APPROVED DESTRUCTION OF A MARSH

ABSTRACT On December 18, 2004 the Texas General Land Office Oil Spill Prevention and Response Program was notified of a spill originating from an abandoned tank battery located in the marsh of Highland Bayou near Galveston, Texas. The discharge of 9460 gallons of crude oil into the bayou and adjacent marsh resulted from lack of maintenance to the tank battery. A vertical pipe attached to one of the tanks rusted through, allowing the tank to drain. The oil did not flow over the secondary containment, but seeped underneath it and spread through the marsh. This flow-path complicated the response by concentrating the spill in the subsurface, thereby impacting the roots system of the marsh plants, and rendering response techniques such as underflow dams, low water flushing, and in-situ burning either minimally effective or not viable. Aggressive tactics such as trenching and digging of holes in combination with massive water flushing were used to remove the oil. Short and long term consequences from these aggressive tactics were clearly evident in the trampling of the marsh grasses and changing of the local hydrology during clean-up operations. Initial trustee assessments determined the heaviest area impacted had died and was to be tilled. This provided a valuable learning opportunity for area responders and saved the surrounding acres of marsh.

Physical variation of non-vegetated marsh edge habitats, and use patterns by nekton in Barataria Bay, Louisiana, USA

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 356:51-61 (2008) - DOI: https://doi.org/10.3354/meps07256 Physical variation of non-vegetated marsh edge habitats, and use patterns by nekton in Barataria Bay, Louisiana, USA Megan K. La Peyre1,*, Timothy Birdsong2,3 1US Geological Survey, Louisiana Fish and Wildlife Cooperative Research Unit, School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803, USA 2School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803, USA 3Present address: Coastal and Inland Fisheries Division, Texas Parks and Wildlife Department, 4200 Smith School Road, Austin, Texas 78744, USA *Email: mlapey@lsu.edu ABSTRACT: While the ecological importance of vegetated marsh edge habitats for many estuarine-dependent nekton is well documented, less is known about nekton use of the non-vegetated, water edge adjacent to marsh habitats and how physical variation of these habitats affects habitat use. The effects of morphological variation of these edge habitats on nekton communities were studied in Barataria Bay, Louisiana, USA. Monthly seining in fall 2003 (September, October, November) and spring 2004 (March, April, May) was conducted at 75 marsh edge study sites <10 m from the water-vegetation interface. Morphological variation in edge habitats (i.e. elevation, slope, irregularity) was quantified concurrent with nekton sampling at each sample site. Nekton assemblages were analyzed seasonally as different community assemblages were present in fall and spring, although consistent patterns emerged. Temperature and salinity were the dominant factors influencing nekton assemblages. Edge habitats with shallower slopes and greater marsh inundation supported more organisms and more resident species; in contrast, edges with steeper slopes supported more diverse and species-rich assemblages, possibly providing greater niche availability due to larger water depth gradients and increased edge irregularity, particularly when the adjacent marsh is not flooded. Use of the gently sloped sites by organisms probably reflects increased access to the marsh when flooded, and may provide shallow water refuge for many smaller species. Non-vegetated marsh edge provides valuable habitat for species, and the physical variation that exists within this habitat helps support a high species diversity. KEY WORDS: Non-vegetated marsh edge · Nekton · Nekton community · Louisiana · Edge habitat Full text in pdf format PreviousNextCite this article as: La Peyre MK, Birdsong T (2008) Physical variation of non-vegetated marsh edge habitats, and use patterns by nekton in Barataria Bay, Louisiana, USA. Mar Ecol Prog Ser 356:51-61. https://doi.org/10.3354/meps07256 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 356. Online publication date: March 18, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Litter decomposition promotes differential feedbacks in an oligotrophic southern Everglades wetland

The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P), nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr−1). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands, and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands (r 2 = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems. Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization, further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state.

NMR and mass spectrometry of phosphorus in wetlands

SummaryThere is at present little information on the long‐term stability of phosphorus sequestered in wetlands. Phosphorus sequestered during high loading periods may be relatively unstable and easily remobilized following changes in nutrient status or hydrological regime, but the chemical forms of sequestered phosphorus that do remobilize are largely unknown at this time. A lack of suitable analytical techniques has contributed to this dearth of knowledge regarding the stability of soil organic phosphorus. We analysed phosphorus in soils from the ‘head’ of Rescue Strand tree island and an adjacent marsh in the Florida Everglades by 31P nuclear magnetic resonance (NMR) spectroscopy and high‐resolution mass spectrometry. Tree islands are important areas of biodiversity within the Everglades and offer a unique opportunity to study phosphorus sequestration because they are exposed to large phosphorus loads and appear to be natural nutrient sinks. The 31P NMR profiling of extracts from surface and sediment samples in the tree island indicates that phosphorus input to Rescue Strand tree island soils is mostly in the form of inorganic ortho‐phosphate and is either refractory when deposited or rapidly recycled by the native vegetation into a stable phosphorus pool largely resistant to re‐utilization by plants or microbes. Mass spectrometry revealed the presence of inositol hexakisphosphate, a common organic monophosphate ester not previously observed in Everglades’ soils.

Solar and Tidal Modulations of Fecal Indicator Bacteria in Coastal Waters at Huntington Beach, California

The coastal waters at many beaches in California and the United States are afflicted with fecal pollution, which poses a health risk for people exposed to the water through recreational activities such as swimming, surfing, and diving. Identifying sources of pollution is complicated by oceanographic transport/mixing processes and the nonconservative behavior of microorganisms exposed to sunlight and hostile marine conditions. This article investigates the variation of fecal indicator bacteria (FIB) concentrations in the surf zone and the adjacent coastal marsh by applying autocorrelation and cross-correlation analyses that illustrate solar and tidal modulations. A steady state bioreactor model was developed to explain solar inactivation in the surf zone, whereas a dynamic model was applied to explain tidally influenced disturbances in the coastal marsh. These models applied to intensive monitoring datasets on FIB and environmental variables have provided insights into the biologic and physical processes controlling coastal water quality, specifically the influence of sunlight and tides on bacterial levels.

Effectiveness of Atimycin‐A as a Toxicant for Control of Invasive Asian Swamp Eels

AbstractThe Asian swamp eel Monopterus albus is native to southeast Asia but has established populations in several locations within the United States. These eels grow up to 1 m long and may prey on or compete with native fishes and amphibians. Additionally, these eels are obligate air‐breathers, can survive long periods out of water, and will travel over land in search of new habitats when necessary. As early as 1990, Asian swamp eels were introduced to several ponds at a local nature center near Atlanta, Georgia, within the Chattahoochee River drainage basin; individuals have since migrated to an adjacent marsh of the Chattahoochee River. Because this population is relatively contained, several methods for control, containment, and possible eradication are being investigated. Juvenile and adult swamp eels primarily obtain oxygen through surface air, although very young eels absorb oxygen directly through their skin. Because they are obligate air‐breathers, standard piscicides (e.g., rotenone and antimycin‐A) that are transmitted across the gill membrane may not be effective. Nonetheless, we tested the effectiveness of antimycin‐A on 2–3‐week‐old Asian swamp eels in case transmission occurred across the epidermis. We tested antimycin‐A concentrations of 2, 5, 10, and 100 nL/L (ppb). No concentration was effective at killing Asian swamp eels, although golden shiners Notemigonus crysoleucas were susceptible at 10 nL/L. Eels that have not undergone metamorphosis (&lt;10 d old) may be susceptible to piscicides such as antimycin‐A, but the lack of effectiveness at the early life stage we tested indicates that eradication through such toxicants probably is not a feasible control method.

Assessing the net effect of anthropogenic disturbance on aquatic communities in wetlands: community structure relative to distance from canals

Anthropogenic alterations of natural hydrology are common in wetlands and often increase water permanence, converting ephemeral habitats into permanent ones. Since aquatic organisms segregate strongly along hydroperiod gradients, added water permanence caused by canals can dramatically change the structure of aquatic communities. We examined the impact of canals on the abundance and structure of wetland communities in South Florida, USA. We sampled fishes and macroinvertebrates from marsh transects originating at canals in the central and southern Everglades. Density of all aquatic organisms sampled increased in the immediate proximity of canals, but was accompanied by few compositional changes based on analysis of relative abundance. Large fish ( >8 cm), small fish ( <8 cm) and macroinvertebrates ( >5 mm) increased in density within 5 m of canals. This pattern was most pronounced in the dry season, suggesting that canals may serve as dry-down refugia. Increases in aquatic animal density closely matched gradients of phosphorus enrichment that decreased with distance from canals. Thus, the most apparent impact of canals on adjacent marsh communities was as conduits for nutrients that stimulated local productivity; any impact of their role as sources of increased sources of predators was not apparent. The effect of predation close to canals was overcompensated by increased secondary productivity and/or immigration toward areas adjacent to canals in the dry season. Alternatively, the consumptive effect of predatory fishes using canals as dry-season refuges is very small or spread over the expanse of marshes with open access to canals.

Interannual variation in stable carbon and nitrogen isotope biogeochemistry of the Mattaponi River, Virginia

Seasonal and interannual variation of the stable carbon (C) and nitrogen (N) isotope composition of suspended particulate organic matter (POM) was measured in the brackish and tidal freshwater regions of the Mattaponi River, a tributary of the York River, Virginia, and a pristine end member on a continuum of anthropogenic modification within Chesapeake Bay. A principal components analysis indicated that seasonal variation was related to physical mixing and river discharge. Freshwater POM had high C : N (.12), depleted particulate organic carbon isotopic composition (d13CPOC, 226% to 230%), and depleted particulate nitrogen isotopic composition (d15NPN, 2–10%) compared to brackish water POM, which had lower C : N and enriched d13CPOC (224% to 227%) and d15NPN (7–15%). During high discharge events, the d13CPOC was enriched, the d15NPN depleted, and the C : N high relative to low discharge periods, indicating a large contribution from terrestrial-derived material. Within tidal freshwater, POM was comprised of humic-rich sediment, vascular plant matter, and phytoplankton produced in situ. Nonconservative mixing behavior was observed. Endogenously produced phytoplankton increased POC concentrations in tidal freshwater and oligohaline portions during base flows. Where estuarine and riverine POM mixed, the isotopic composition of the POM was homogenized, blurring source-specific characters observed upriver and thereby emphasizing the need to characterize the freshwater end member of estuaries carefully in order to identify POM sources. In estuaries, identifying the origin of particulate organic matter (POM) is difficult because POM is received from multiple sources, including riparian vegetation, adjacent marsh vegetation, submerged and emergent aquatic vegetation and associated epiphytes, and phytoplankton produced in situ. Early research using the stable isotope composition of estuarine POM to identify its dominant origins and fates led investigators to conclude that estuarine phytoplankton and terrestrial material were the major contributors to estuarine organic matter (OM; dissolved and particulate fractions) and that these sources

Trophic relationships of juvenile blue crabs (Callinectes sapidus) in estuarine habitats

Salt marshes and shallow-water macroalgal beds are known to provide nursery habitat for many species of fish and invertebrates. The role of these habitats as refuge from predation is well established, but the degree to which indigenous primary production within the nursery provides food for growth and development of estuarine species remains unresolved. In this study, we tested the hypothesis that juvenile blue crabs depend on indigenous primary production, directly or indirectly, during their entire stay within the nursery. To test this hypothesis, we conducted isotopic studies and stomach content analyses of juveniles from habitats near the mouth of Delaware Bay and from an adjacent lagoonal estuary (ca. 39.5° N, 75.1° W). Primary producers, marsh detritus, various life-history stages of blue crabs and potential prey species were sampled in the main estuary and in an adjacent marsh during the summer and early fall of two consecutive years. Newly settled juveniles ( 60 mm were enriched in δ13C (−14.7 ± 0.1‰) compared to small crabs, suggesting a gradual shift in diet from a planktonic to a detritus-based food web with increasing size. As with crabs from Delaware Bay, the δ13C signature of juvenile crabs sampled from macroalgal beds in the lagoonal estuary (Rehoboth Bay) changed as a function of size. Also, δ13C ratios of crabs varied among the various species of macroalgae. The δ15N composition of primary producers in the marsh and main estuary also was reflected in the δ15N values of crabs and other benthic consumers in the respective habitats. Results of stomach-content analysis in this study were consistent with isotope data. Observed changes in prey preferences were related to changes in size of juvenile crabs and also differed among habitats. Gut content analyses of the three size classes of juveniles in macroalgal beds from Rehoboth Bay indicated that the crabs depend heavily on various amphipod species that occur on the seaweeds. These amphipods graze directly on the macroalgae and are among the most abundant invertebrates in the macroalgal beds. This implies a direct trophic relationship between the juvenile crabs and the macroalgae. In summary, our study provides strong evidence that the value of nursery areas such as salt marshes and macroalgal beds goes beyond that of providing refuge from predation, and that species using these nurseries (e.g. juvenile blue crabs) are ultimately dependent on primary production originating in benthic plants indigenous to the nursery.

Anthropogenic Sulfur Effects on Marshland Sulfate Sources

Human activity can have measurable impacts on sulfur levels in the world's water bodies. Atmospheric sulfur dioxide pollution and the resulting acid rain increases freshwater sulfate levels, and individual pollution sources deposit organic sulfur compounds in river sediments. Since the affected water bodies can be the primary sources of sulfur in adjacent marsh environments, anthropogenic pollution may influence the sulfur cycling of nearby marshes. Appropriate levels of plant-available sulfur are necessary for plant growth in marshes, though too much sulfur can damage plants. Saline marshes are often high-sulfur environments due to the steady sulfur inputs that come from seawater present in saline estuaries. Sulfur content is more variable in less saline environments, where primary inputs are rainfall and freshwater runoff. The link between human activity and sulfur levels in marsh soils has not yet been established, since research has not clearly demonstrated the effects of human activity on sulfur in saline water bodies and has generally not sought to link water-body sulfur levels to plant-available sulfur levels or area marsh health.

Post-construction Effects of an Urban Development on Migrating, Resident, and Wintering Birds

Many urban areas contain forest remnants and city parks that may be used by birds as stopover and wintering sites. We conducted a case study on how construction of a new apartment complex in Gainesville, FL, affected avian communities both in a forest site and in a portion of a marsh in an adjacent city park. In fall and winter, 1995–1999, we conducted point count surveys of migrant, resident, and wintering birds and compared 1 year of pre-construction survey data to 2 years of post-construction survey data. We conducted analyses to explore changes in: 1) abundance and richness by residency status (resident and migrant guilds), and 2) individual species abundance. Combining pre- and post-construction surveys, we sighted 71 bird species in the developed site and adjacent marsh during the fall and 46 species during the winter. Resident and migrant guild abundance and species richness were not different before versus after construction on the forest site or in the marsh for both seasons. Several individual species did decline in post-construction years, most notably the ovenbird (Seiurus aurocapillus) during the fall migration period that went from 32 to 3 sightings, pre- to post-construction. Results suggest that within the timeframe of this study, the remnant forest patch and adjacent marsh continued to attract migrating and resident species, even after development. On-site preservation of tree canopy and natural buffer areas, in combination with existing vegetative features in the surrounding landscape matrix, may explain why development had a minimal impact on avian richness and abundance.