Edaphic diatom communities associated with Spartina alterniflora and S. patens in New Jersey

Edaphic diatoms inhabiting the sediments beneath dwarf Spartina alterniflora Loisel. and S. patens (Ait.) Muhl. in Great Bay salt marsh, Tuckerton, New Jersey were collected from 24 September 1974 through 20 August 1975. Of the 91 taxa encountered, 8 were endemic to the dwarf S. alterniflora habitat and 42 endemic to the S. patens habitat. The edaphic diatom community associated with S. patens was comprised of a much greater number of taxa and possessed higher values for species diversity (H') and evenness (J') than the community associated with dwarf S. alterniflora. The salinity of the marsh surface showed a completely opposite trend, being greatly reduced at the S. patens habitat. A highly significant relationship (P < 0.001) between the number of diatom taxa and marsh surface salinity at the S. patens habitat was demonstrated by a least squares regression. This finding led to the conclusion that the dissimilarity in the structure of the two edaphic diatom communities was primarily due to the very low marsh surface salinities at the S. patens habitat from January through June, and that this sustained. low-salinity regime allowed a very large number of taxa to coexist only in the S. patens community. Comparison of the diatom flora of Great Bay salt marsh with that of a Delaware marsh studied previously by the author showed that 67.0% of the 91 taxa encountered in New Jersey also occur on the Delaware marsh.     

Quantifying Vegetation and Nekton Response to Tidal Restoration of a New England Salt Marsh

Tidal flow to salt marshes throughout the northeastern United States is often restricted by roads, dikes, impoundments, and inadequately sized culverts or bridge openings, resulting in altered ecological structure and function. In this study we evaluated the response of vegetation and nekton (fishes and decapod crustaceans) to restoration of full tidal flow to a portion of the Sachuest Point salt marsh, Middletown, Rhode Island. A before, after, control, impact study design was used, including evaluations of the tide‐restricted marsh, the same marsh after reintroduction of tidal flow (i.e., tide‐restored marsh), and an unrestricted control marsh. Before tidal restoration vegetation of the 3.7‐ha tide‐restricted marsh was dominated by Phragmites australis and was significantly different from the adjacent 6.3‐ha Spartina‐dominated unrestricted control marsh (analysis of similarities randomization test, p < 0.001). After one growing season vegetation of the tide‐restored marsh had changed from its pre‐restoration condition (analysis of similarities randomization test, p < 0.005). Although not similar to the unrestricted control marsh, Spartina patens and S. alterniflora abundance increased and abundance and height of Phragmites significantly declined, suggesting a convergence toward typical New England salt marsh vegetation. Before restoration shallow water habitat (creeks and pools) of the unrestricted control marsh supported a greater density of nekton compared with the tide‐restricted marsh (analysis of variance, p < 0.001), but after one season of restored tidal flow nekton density was equivalent. A similar trend was documented for nekton species richness. Nekton density and species richness from marsh surface samples were similar between the tide‐restored marsh and unrestricted control marsh. Fundulus heteroclitus and Palaemonetes pugio were the numerically dominant fish and decapod species in all sampled habitats. This study provides an example of a quantitative approach for assessing the response of vegetation and nekton to tidal restoration.     

DECOMPOSITION DYNAMICS OF SPARTINA ALTERNIFLORA AND SPARTINA PATENS IN A NEW JERSEY SALT MARSH

Decomposition dynamics of two salt marsh species, Spartina alterniflora tall (SAT) form and Spartina patens (SP), were investigated at Mud Cove, near Manahawkin, Ocean County, New Jersey. Decomposition rates were determined monthly over 371 days by measuring the amount of material lost from plastic net litter bags. Litter bags containing SP material were placed in both SP and SAT vegetation zones; litter bags containing SAT material were also placed in both of these zones. The material was analyzed for ash content, total carbon, Kjeldahl nitrogen, caloric content, fat, and crude fiber. Final weight loss values were as follows: SAT in SAT zone 72.4%, SP in SAT zone 56.9%, SAT in SP zone 46.7%, and SP in SP zone 26.4%. When SAT and SP material were placed in the same location (SAT or SP sites), the SAT material decomposed at a greater rate. If the same vegetation type (SAT or SP) were placed in both SAT and SP locations, the material at the SAT location decomposed at a greater rate than similar material in the SP location. The results indicate that while environmental characteristics (e.g., flooding) at a site influence the rate at which these two species will decompose, Spartina patens is inherently more resistant to decomposition.     

Fifteen Years of Vegetation and Soil Development after Brackish-Water Marsh Creation

Aboveground biomass, macro‐organic matter (MOM), and wetland soil characteristics were measured periodically between 1983 and 1998 in a created brackish‐water marsh and a nearby natural marsh along the Pamlico River estuary, North Carolina to evaluate the development of wetland vegetation and soil dependent functions after marsh creation. Development of aboveground biomass and MOM was dependent on elevation and frequency of tidal inundation. Aboveground biomass of Spartina alterniflora, which occupied low elevations along tidal creeks and was inundated frequently, developed to levels similar to the natural marsh (750 to 1,300 g/m²) within three years after creation. Spartina cynosuroides, which dominated interior areas of the marsh and was flooded less frequently, required 9 years to consistently achieve aboveground biomass equivalent to the natural marsh (600 to 1,560 g/m²). Aboveground biomass of Spartina patens, which was planted at the highest elevations along the terrestrial margin and seldom flooded, never consistently developed aboveground biomass comparable with the natural marsh during the 15 years after marsh creation. MOM (0 to 10 cm) generally developed at the same rate as aboveground biomass. Between 1988 and 1998, soil bulk density decreased and porosity and organic C and N pools increased in the created marsh. Like vegetation, wetland soil development proceeded faster in response to increased inundation, especially in the streamside zone dominated by S. alterniflora. We estimated that in the streamside and interior zones, an additional 30 years (nitrogen) to 90 years (organic C, porosity) are needed for the upper 30 cm of created marsh soil to become equivalent to the natural marsh. Wetland soil characteristics of the S. patens community along upland fringe will take longer to develop, more than 200 years. Development of the benthic invertebrate‐based food web, which depends on organic matter enrichment of the upper 5 to 10 cm of soil, is expected to take less time. Wetland soil characteristics and functions of created irregularly flooded brackish marshes require longer to develop compared with regularly flooded salt marshes because reduced tidal inundation slows wetland vegetation and soil development. The hydrologic regime (regularly vs. irregularly flooded) of the “target” wetland should be considered when setting realistic expectations for success criteria of created and restored wetlands.     

How will warming affect the salt marsh foundation species Spartina patens and its ecological role?

Foundation species structure environments and create refuge from environmental stress. In New England high salt marsh, the grass Spartina patens is a foundation species that reduces salinity, anoxia, desiccation, and thermal stresses through canopy shading and root proliferation. In a factorial S. patens-removal and warming field experiment, foundation species removal strongly impacted every aspect of the community, reiterating the important role of the foundation species S. patens in the high marsh. Given this central role, we hypothesized that facilitation by the foundation species would be even more important under warmer conditions by ameliorating more severe thermal stress. However, the ecological role of S. patens was unaffected by experimental warming, and, independent of the presence of the foundation species, warming had only weak effects on the salt marsh ecological community. Only the foundation species itself responded strongly to warming, by significantly increasing aboveground production in warmed plots. Apparently, amelioration of thermal stress is not as important for salt marsh ecosystem function as S. patens’ moderation of salinity and desiccation stresses. From these experimental results, we anticipate that climate change-associated thermal stress will not greatly affect S. patens-dominated high marsh communities. In contrast, foundation species loss, an emergent conservation issue in Atlantic salt marshes, represents a critical threat to salt marsh ecosystem function.     

Effects of regular salt marsh haying on marsh plants, algae, invertebrates and birds at Plum Island Sound, Massachusetts

The haying of salt marshes, a traditional activity since colonial times in New England, still occurs in about 400 ha of marsh in the Plum Island Sound estuary in northeastern Massachusetts. We took advantage of this haying activity to investigate how the periodic large-scale removal of aboveground biomass affects a number of marsh processes. Hayed marshes were no different from adjacent reference marshes in plant species density (species per area) and end-of-year aboveground biomass, but did differ in vegetation composition. Spartina patens was more abundant in hayed marshes than S. alterniflora, and the reverse was true in reference marshes. The differences in relative covers of these plant species were not associated with any differences between hayed and reference marshes in the elevations of the marsh platform. Instead it suggested that S. patens was more tolerant of haying than S. alterniflora. Spartina patens had higher stem densities in hayed marshes than it did in reference marshes, suggesting that periodic cutting stimulated tillering of this species. Although we predicted that haying would stimulate benthic chlorophyll production by opening up the canopy, we found differences to be inconsistent, possibly due to the relatively rapid regrowth of S. patens and to grazing by invertebrates on the algae. The pulmonate snail, Melampus bidendatus was depleted in its δ¹³C content in the hayed marsh compared to the reference, suggesting a diet shift to benthic algae in hayed marshes. The stable isotope ratios of a number of other consumer species were not affected by haying activity. Migratory shorebirds cue in to recently hayed marshes and may contribute to short term declines in some invertebrate species, however, the number of taxa per unit area of marsh surface invertebrates and their overall abundances were unaffected by haying over the long term. Haying had no impact on nutrient concentrations in creeks just downstream from hayed plots, but the sediments of hayed marshes were lower in total N and P compared to references. In sum, haying appeared to affect plant species composition but had only short-term affects on consumer organisms. This contrasts with many grassland ecosystems, where an intermediate level of disturbance, such as by grazing, increases species diversity and may stimulate productivity. From a management perspective, periodic mowing could be a way to maintain S. patens habitats and the suite of species with which they are associated.     

Palatability of salt marsh forbs and grasses to the purple marsh crab (Sesarma reticulatum) and the potential for re-vegetation of herbivory-induced salt marsh dieback areas in cape cod (Massachusetts, USA)

Intense herbivory by a growing population of intertidal burrowing crabs Sesarma reticulatum (purple marsh crabs) has denuded large areas of salt marsh on Cape Cod (Massachusetts, USA). Spartina alterniflora (smooth cordgrass) and, to a lesser extent, S. patens (salt marsh hay) have been the primary taxa affected while halophytic forb populations of Salicornia spp. (pickleweed), Suaeda maritima (sea-blite), and Limonium carolinianum (sea lavender), that normally constitute a relatively low proportion of marsh vegetation, have remained intact. In addition, these forb species appear to be colonizing some of the marsh grass dieback areas. Because the loss of vegetation results in considerable subsidence and erosion, the objective of this study was to (1) confirm whether certain taxa are unpalatable to S. reticulatum and (2) determine whether unpalatable species could be used to re-vegetate dieback areas as an interim measure to control marsh sediment and elevation loss. The results suggest that S. reticulatum prefers Spartina alterniflora over forbs and that one or all of these forb species are good candidates for vegetation restoration in dieback areas.     

Dissolved Inorganic Nitrogen Pools and Surface Flux under Different Brackish Marsh Vegetation Types,Common Reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>) and Salt Hay (<Emphasis Type="Italic">Spartina patens</Emphasis>)

The current expansion of Phragmites australis into the high marsh shortgrass (Spartina patens, Distichlis spicata) communities of eastern U.S. salt marshes provided an opportunity to identify the influence of vegetation types on pools and fluxes of dissolved inorganic nitrogen (DIN). Two brackish tidal marshes of the National Estuarine Research Reserve system were examined, Piermont Marsh of the Hudson River NERR in New York and Hog Island in the Jacques Coustaeu NERR of New Jersey. Pools of DIN in porewater and rates of DIN surface flux were compared in replicated pairs of recently-expanded P. australis and neighboring S. patens-dominated patches on the high marsh surface. Both marshes generally imported nitrate (NO₃⁻) and exported ammonium (NH₄⁺), such that overall DIN was exported. No differences in surface exchange of NO₃⁻ or NH₄⁺ were observed between vegetation types. Depth-averaged porewater NH₄⁺ concentrations over the entire growing season were 56% lower under P. australis than under S. patens (average 1.4 vs. 3.2 mg NH₄⁺ L⁻¹) with the most profound differences in November. Porewater profiles showed an accumulation of NH₄⁺ at depth in S. patens and constant low concentrations in P. australis from the soil surface to 50 cm depth, with no significant differences in porewater salinity. Despite these profound differences in porewater, NH₄⁺ diffusion from soils of P. australis and S. patens were not measurably different, were similar to other published rates, and were well below estimated rates based on passive diffusion alone. Rapid adsorption and uptake by litter and microbes in surface soils of both communities may buffer NH₄⁺ loss to flooding tides in both communities, thereby reducing the impact of P. australis invasion on NH₄⁺ flux to flooding waters.     

Ecological significance of wing polymorphism in Fulgoroidea which inhabit tidal salt marshes

• 1 The vegetation of New Jersey tidal salt marshes is composed primarily of two grasses, Spartina patens, which occupies a narrow elevational zone of high marsh and varies little in structure from site to site, and Spartina alterniflora, an intertidal species which occurs as two spacially separated growth forms (tall and short). Fulgoroids, polymorphic for wing length, inhabit these grasses.
• 2 Populations of the common fulgoroid inhabiting short form S.alterniflora were composed of equal numbers of macropters and brachypters. Mesothoracic wings of brachypters were subequal in length to the abdomen allowing for short but inefficient flights compared to macropters.
• 3 Fulgoroids residing in S.patens produced mostly brachypters having small meso-and vestigial metathoracic wings and were incapable of flight.
• 4 Brachypter density of all fulgoroids was correlated with the seasonal increase in biomass of the host grass, while macropter density was not.
• 5 Peak macropter density occurred shortly before maximum biomass of the host grass was attained.
• 6 The production of macropterous forms was correlated with high levels of crowding incurred during nymphal stages.
• 7 Spatial and temporal variation in the structure of the host grasses and habitat reliability are suggested as important factors dictating the wing-polymorphism strategies of fulgoroids.

     

Success criteria and adaptive management for a large-scale wetland restoration project

We are using a 20+ year photographic history of relatively undisturbed and formerly diked sites to predict the restoration trajectories and equilibrium size of a 4,050 ha salt marsh on Delaware Bay, New Jersey (USA). The project was initiated to offset the loss of finfishes from once-through cooling at a local power plant. We used a simple food chain model to estimate the required restoration size. This model assumed that annual macrophyte detritus production and benthic algal production resulted in production of finfishes, including certain species of local interest. Because the marsh surface and intertidal drainage system are used by many finfishes and are the focal points for exchange of detrital materials, the restoration planning focused on both vegetational and hydrogeomorphological parameters. Recolonization bySpartina spp. and other desirable taxa will be promoted by returning a natural hydroperiod and drainage configuration to two types of degraded salt marsh: diked salt hay (Spartina patens) farms and brackish marsh dominated byPhragmites australis. The criteria for success of the project address two questions: What is the bound of expectation for restoration success, and how long will it take to get there? Measurements to be made are macrophyte production, vegetation composition, benthic algal production, and drainage features including stream order, drainage density, channel length, bifurcation ratios and sinuosity. A method for combining these individual parameters into a single success index is also presented. Finally, we developed adaptive management thresholds and corrective measures to guide the restoration process.Corresponding editor: R.E. Turner     

Success criteria and adaptive management for a large-scale wetland restoration project

We are using a 20+ year photographic history of relatively undisturbed and formerly diked sites to predict the restoration trajectories and equilibrium size of a 4,050 ha salt marsh on Delaware Bay, New Jersey (USA). The project was initiated to offset the loss of finfishes from once-through cooling at a local power plant. We used a simple food chain model to estimate the required restoration size. This model assumed that annual macrophyte detritus production and benthic algal production resulted in production of finfishes, including certain species of local interest. Because the marsh surface and intertidal drainage system are used by many finfishes and are the focal points for exchange of detrital materials, the restoration planning focused on both vegetational and hydrogeomorphological parameters. Recolonization bySpartina spp. and other desirable taxa will be promoted by returning a natural hydroperiod and drainage configuration to two types of degraded salt marsh: diked salt hay (Spartina patens) farms and brackish marsh dominated byPhragmites australis. The criteria for success of the project address two questions: What is the “bound of expectation” for restoration success, and how long will it take to get there? Measurements to be made are macrophyte production, vegetation composition, benthic algal production, and drainage features including stream order, drainage density, channel length, bifurcation ratios and sinuosity. A method for combining these individual parameters into a single success index is also presented. Finally, we developed adaptive management thresholds and corrective measures to guide the restoration process.     

Microclimate and substrate quality controls on nitrogen mineralization in a New England high salt marsh

New England high salt marsh primary productivity is limited by N, but variation in plant N availability across salt marsh vegetation zones has not been quantified. To investigate this, we measured in situ net N mineralization rates throughout the growing season in three zones of a Maine high salt marsh, Juncus gerardii, Spartina patens, and mixed perennial forb. We also measured microclimate factors (soil temperatures and moistures) and substrate quality parameters (soil organic matter, soil total nitrogen, soil C:N ratio) to see if either related to differences in net N mineralization. To determine the relative importance of substrate quality and microclimate, we measured N mineralization of the different soil types in the laboratory, holding microclimate parameters constant. We also investigated the relative importance of microclimate and substrate statistically, with principal components analysis and multiple regression. In situ net N mineralization rates were significantly higher in the forb zone than in graminoid zones, but graminoid zone N mineralization rates did not vary significantly from each other. Soil temperatures, moistures, carbon, and nitrogen were all significantly higher in the forb zone than in graminoid zones, but C:N ratio did not vary significantly across zones. Principal components analysis and multiple regression revealed that microclimate was a more significant predictor of total N mineralized over the course of the growing season than was substrate quality. In contrast, when microclimate conditions were held constant, forb zone N mineralization was still significantly higher than that of graminoid zones, suggesting that substrate quality does exert some control on this process. Thus, both microclimate and substrate quality appear to influence N mineralization rates across vegetation zones of this Maine salt marsh.     

RECOLONIZATION OF SMALL DISTURBANCE PATCHES IN A NEW ENGLAND SALT MARSH

Availability of colonizers and edaphic conditions were tested in relation to rates of recolonization of open patches in salt marsh vegetation. The density of buried viable seeds was estimated by counting seedlings in undisturbed vegetation and germinating seeds in the laboratory. A low density of viable seeds (<50 per m²) found in these salt marsh soils indicated the absence of an important viable seed bank in this system. Rates of recolonization in natural open patches were monitored for three years. Vegetative expansion of Spartina alterniflora, at approximately 12 cm per year, accounted for most of the recolonization of open patches, although some colonization of annual Salicornia spp. occurred from seeds. Salinity and sulfide and ammonium concentrations were measured in pore water samples from depths of 2–7 cm and 10–15 cm of soil. Comparison of the concentrations from disturbed and undisturbed plots in the marsh did not show significant differences, indicating that none of the edaphic conditions measured would be more inhibitory to plant growth in the disturbed than the undisturbed plots. Therefore, the rate at which small open patches become recolonized is primarily controlled by proximity of Spartina alterniflora and its capacity for vegetative expansion.     

Sea level rise may increase extinction risk of a saltmarsh ontogenetic habitat specialist

Specialist species are more vulnerable to environmental change than generalist species. For species with ontogenetic niche shifts, specialization may occur at a particular life stage making those stages more susceptible to environmental change. In the salt marshes in the northeast U.S., accelerated sea level rise is shifting vegetation patterns from flood‐intolerant species such as Spartina patens to the flood‐tolerant Spartina alterniflora. We tested the potential impact of this change on the coffee bean snail, Melampus bidentatus, a numerically dominant benthic invertebrate with an ontogenetic niche shift. From a survey of eight marshes throughout the northeast U.S., small snails were found primarily in S. patens habitats, and large snails were found primarily in stunted S. alterniflora habitats. When transplanted into stunted S. alterniflora, small snails suffered significantly higher mortality relative to those in S. patens habitats; adult snail survivorship was similar between habitats. Because other habitats were not interchangeable with S. patens for young snails, these results suggest that Melampus is an ontogenetic specialist where young snails are habitat specialists and adult snails are habitat generalists. Temperature was significantly higher and relative humidity significantly lower in stunted S. alterniflora than in S. patens. These data suggest that thermal and desiccation stress restricted young snails to S. patens habitat, which has high stem density and a layer of thatch that protects snails from environmental stress. Other authors predict that if salt marshes in the northeast U.S. are unable to migrate landward, sea level rise will eliminate S. patens habitats. We suggest that if a salt marsh loses its S. patens habitats, it will also lose its coffee bean snails. Our results demonstrate the need to consider individual life stages when determining a species’ vulnerability to global change.     

Blocking Phragmites australis reinvasion of restored marshes using plants selected from wild populations and tissue culture

This study tested a vegetation strategy for controlling Phragmites australis invasion into brackish marshes as an alternative to the current technique of repeated herbicide sprays followed by burning. This strategy involves blocking P. australis by planting desired plants selected from wild populations and/or tissue culture regenerants at key points on the major routes of P. australis invasion. The planting of native species was conducted at three sites in a herbicide-treated P. australis marsh near Salem, NJ. Wild population selections of three upland marsh shrubs, Myrica cerifera, Baccharis halimifolia, and Iva frutescens, as well as two grass species, Spartina alterniflora and Spartina patens, and two rushes, Juncus gerardi and Juncus roemerianus, were planted according to their normal zonation positions. Tissue culture regenerated plants of the two grasses and two rushes, and the sedge species Scirpus robustus, were also planted. Plant growth at each site was monitored each year after planting for up to 3 years. Most plants of B. halimifolia, I. frutescens, J. roemerianus, and S. patens demonstrated a consistent vigorous growth at all three sites, whether or not the plants were collected from wild populations or were tissue culture regenerants. These multi-layered walls of plants demonstrated effectiveness in controlling the P. australis by restricting or inhibiting its spread. Upon screening 48 regenerated plants of S. patens at one of the three sites, we found that some regenerants showed enhanced characteristics for blocking P. australis, such as greater expansion and a high stem density. The availability of the tissue culture-regenerated plants of the native marsh species makes it possible to select lines from local genotypes that have desirable characteristics for wetland restoration projects, such as blocking P. australis reinvasion.     

Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon,Florida (USA)

Salt marshes of the Indian River Lagoon, Florida (USA) were once prolific producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the infrequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16.200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes. However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation from the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped from 16 to 5 after impounding. Wetland vegetation within some impoundments was totally eliminated; other impoundments developed into freshwater systems. When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began almost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped mullet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic. Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of the year. Culverts are typically opened when the fall sea level rise first floods the high marsh. Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRL system. One stumbling block is private ownership of many of the remaining isolated impoundments.     

Sensitivity of US Gulf of Mexico coastal marsh vegetation to crude oil: Comparison of greenhouse and field responses

Greenhouse and field studies were conducted to evaluate the effect of crude oil on selected US Gulf of Mexico coastal marsh species. Species showed different levels of sensitivity to oiling between greenhouse and field conditions. In greenhouse studies, two crude oils were used: South Louisiana crude oil (SLC) and Arabian Medium crude oil (AMC). The majority of Spartina patens plants died within one month following oiling with little or no recovery after three months. Panicum hemitomon and Spartina alterniflora were also adversely affected by oiling under greenhouse conditions but to a lesser extent than S. patens. The SLC or AMC oiling led to biomass reductions in S. alterniflora and S. patens. The dry biomass was not affected by oiling in P. hemitomon, Sagittaria lancifolia, Typha latifolia, and Scirpus olneyi. Results showed that S. patens plants were more sensitive to SLC as compared to AMC oil. Gross CO₂-C fixation data collected in the greenhouse indicated no differences in recovery among species across oiling treatments for S. lancifolia, S. olneyi, and T. latifolia. Field studies with S. alterniflora, S. patens and S. lancifolia demonstrated initial sensitivity of these species to oiling, and recovery following oiling with SLC. Our data also showed that caution must be employed whenever results from greenhouse studies are extrapolated to predict oil impact on vegetation under field conditions. Development of any sensitivity index of plant responses to oiling should not be based on greenhouse experiments only. Field evaluations should be included which best depict plant responses to oiling. Thus, restoration measures of US Gulf of Mexico coastal marshes following oiling should rely primarily on field studies. The field research suggests that the US Gulf of Mexico coastal marsh vegetation are likely to recover from oil spills naturally without the need for remediation procedures.     

Physiological Integration among Clonal Ramets during Invasion of Disturbance Patches in a New England Salt Marsh

Resource sharing between ramets growing across environmentalresource gradients may have important consequences for clonalplant populations and community dynamics. As the clonal saltmarsh grasses, Spartina patens and Distichlis spicata, vegetativelycolonize disturbance-generated bare patches, they span steepgradients in soil salinity and available sunlight. Examinationof water relations and carbon translocation in the field andgreenhouse revealed that connected ramets of these marsh grassesshare water and carbon in response to gradients in resourceavailability. Ramets colonizing disturbance patches rely uponphysiological integration with connected parent ramets to overcomewater stress associated with hypersaline patch environments.In addition, upon establishment inside a bare patch, daughterramets may translocate carbon back to shaded parent ramets inthe surrounding vegetation outside of patches. Physiological integration of ramets colonizing disturbance-generatedbare patches and parent ramets outside of patches may explainthe predominance of vegetative invasion over sexual recruitmentin marsh succession. Hypersaline soil conditions, which inhibitseedling recruitment into patches, have little effect on thesuccess of clonal colonizers that can import water from parentramets. This success appears to be due to the ability of clonalmarsh grasses to translocate water and carbon products betweenramets growing across opposing gradients in resource availability.Copyright1995, 1999 Academic Press Clonal integration, Distichlis spicata, halophytes, salt marsh ecology, secondary succession, Spartina patens     

Interactions between C3 and C4 salt marsh plant species during four years of exposure to elevated atmospheric CO2

Elevated atmospheric CO2 is known to stimulate photosynthesis and growth of plants with the C₃ pathway but less of plants with the C₄ pathway. An increase in the CO₂ concentration can therefore be expected to change the competitive interactions between C₃ and C₄ species. The effect of long term exposure to elevated CO₂ (ambient CO₂ concentration +340 µmol CO₂ mol^-1) on a salt marsh vegetation with both C₃ and C₄ species was investigated. Elevated CO₂ increased the biomass of the C₃ sedgeScirpus olneyi growing in a pure stand, while the biomass of the C₄ grassSpartina patens in a monospecific community was not affected. In the mixed C₃/C₄ community the C₃ sedge showed a very large relative increase in biomass in elevated CO₂ while the biomass of the C₄ species declined.The C₄ grassSpartina patens dominated the higher areas of the salt marsh, while the C₃ sedgeScirpus olneyi was most abundant at the lower elevations, and the mixed community occupied intermediate elevations.Scirpus growth may have been restricted by drought and salt stress at the higher elevations, whileSpartina growth at the lower elevations may be affected by the higher frequency of flooding. Elevated CO₂ may affect the species distribution in the salt marsh if it allowsScirpus to grow at higher elevations where it in turn may affect the growth ofSpartina.     

Rehabilitation of impounded estuarine wetlands by hydrologic reconnection to the Indian River Lagoon, Florida (USA)

Salt marshes of the Indian River Lagoon, Florida (USA) were once prolific producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the infrequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16.200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes.However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation from the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped from 16 to 5 after impounding. Wetland vegetation within some impoundments was totally eliminated; other impoundments developed into freshwater systems.When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began almost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped mullet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic.Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of the year. Culverts are typically opened when the fall sea level rise first floods the high marsh.Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRL system. One stumbling block is private ownership of many of the remaining isolated impoundments.University of Florida, IFAS, Journal Series No. R-05201.Harbor Branch Contribution Number 1152.Corresponding editor: R.E. Turner