Oligohaline Marshes Research Articles

Marsh Vegetation Types of the Chenier Plain, Louisiana, USA

The Chenier Plain of Louisiana contains 3.085 km2 of coastal marshes and stretches from the Texas border to Vermilion Bay at approximately 91°30′W. The objective of this study was to describe the vegetation types of the Chenier Plain in 1997, compare the vegetation types of the Chenier Plain with those described previously for the Mississippi River Deltaic Plain, and compare the distribution and composition to previous descriptions of vegetation types in the region. Two-way Indictor Species Analysis (TWINSPAN) revealed seven major vegetation types that occurred in the region in 1997: fresh bulltongue, fresh maidencane, oligohaline bulwlwhip, oligohaline paspalum, oligohaline wiregrass, mesohaline wiregrass, and mesohaline mixture. These vegetation types are a logical expansion of the habitats previously described for the region. Five of the seven vegetation types were also identified by similar analyses and descriptions for the Mississippi River Deltaic Plain. Vegetation in the fresh marsh substantially changed since it was first described by O’Neil in the 1940s. The largest change was the disappearance of the sawgrass habitat, although this change occurred before 1968. We show a continued trend in increase of oligohaline marsh at the expense of mesohaline wiregrass marsh, although it is not clear if this change is genuine or arises from the difference in classification methods among years. The mesohaline mixture, labeled saline marsh in previous studies, has remained relatively stable over time.

Salinity as a constraint on growth of oligohaline marsh macrophytes. I. Species variation in stress tolerance

The effects of increased salinity on plant growth were examined in a greenhouse experiment with four species common to oligohaline marshes of the northern Gulf of Mexico: Eleocharis palustris, Panicum hemitomon, Sagittaria lancifolia, and Scirpus americanus. Effects of final salinity reached (6 or 12 g/L), salinity influx rate (3 d or 3 wk), and duration of exposure (1, 2, or 3 mo) were investigated. Sagittaria lancifolia was the first species to show visible signs of stress, with browning and curling of older leaf edges. The salt effect was delayed for 6-8 wk in P. hemitomon, but this species had the highest aboveground tissue mortality rate at 12 g/L as exposure continued. Final salt concentration affected all species to a greater degree than did salinity influx rate. No aboveground mortality occurred at 6 g/L, but growth suppression was apparent and varied with species. The magnitude of growth suppression in response to salinity increased for all species as the duration of exposure increased. Overall, we ranked the species as follows, in order from least to most salt tolerant: Panicum hemitomon < Sagittaria lancifolia < Eleocharis palustris < Scirpus americanus. This ranking reflects the field occurrence of these species along a gradient of increasing salinity in northern Gulf of Mexico coastal habitats from freshwater wetlands through oligohaline areas to mesohaline wetlands.

Salinity as a constraint on growth of oligohaline marsh macrophytes. II. Salt pulses and recovery potential

The ability of common oligohaline marsh macrophytes of the northern Gulf of Mexico coast to recover from pulses of increased salinity was investigated in a greenhouse experiment with Eleocharis palustris, Panicum hemitomon, Sagittaria lancifolia, and Scirpus americanus monocultures. Components of salinity pulses applied were final salinity reached (6 or 12 g/L), salinity influx rate (3 d or 3 wk), and duration of exposure (1, 2, or 3 mo). After each exposure period, we placed plants into freshwater until the end of the 120-d experiment to determine recovery potential. The four species varied in their ability to recover from the salinity pulses. Within a species, recovery varied with final salinity level and duration of exposure, and to a lesser extent with salinity influx rate. Scirpus americanus, growth of which was stimulated by <3 mo of exposure to 6 g/L, was able to recover even under the most extreme conditions of exposure to 12 g/L salinity for 3 mo. Ability to recover decreased with increased salinity and increased duration of exposure for the remaining three species. Recovery of specific aspects of growth was also suppressed in these species by a rapid salinity influx rate compared to a slow influx rate. The complex variations in recovery patterns displayed by the different species may lead to changes in species dominance following the short-term salinity pulses that can occur during storm events, which in turn may affect marsh plant community composition and structure.

Response of two oligohaline marsh communities to lethal and nonlethal disturbance.

Severity is recognized as an important attribute of disturbance in many plant communities. However, the effects of disturbances of different severity on patterns of regeneration in oligohaline marsh vegetation have not been experimentally examined. In these communities, a critical difference in the effects of disturbance severity may be whether the vegetation dies as a result of the disturbance or is merely damaged and hence capable of resprouting. We described the regeneration of vegetation in two Louisiana marsh community types, one dominated by Sagittaria lancifolia L. and the other by Spartina patens (Ait.) Muhl., following three levels of disturbance: no disturbance, a nonlethal disturbance, and a lethal disturbance. In the nonlethal disturbance, aboveground vegetation was clipped to simulate common disturbances such as fire and herbivory that remove aboveground vegetation but leave rhizomes intact. In the lethal disturbance vegetation was killed using herbicide to simulate disturbances causing plant mortality such as wrack deposition, sedimentation, scouring, and flooding following fire or herbivory. Regeneration was assessed over a 2-year period by measuring plant species richness, relative abundance, relative dominance, cover, and final biomass. To elucidate mechanisms for observed responses of vegetation, the species composition of the seed bank, light penetration, water level, salinity, and soil redox potential were evaluated. Despite differences in the structure of undisturbed vegetation in the two community types, they exhibited the same overall pattern of regeneration. Following nonlethal disturbance, the dominant species resprouted and quickly reestablished the structure of the vegetation. In contrast, recolonization following lethal disturbance occurred primarily via seedling recruitment, which resulted in marked shifts in community structure that persisted throughout the study. While the two communities responded similarly overall to disturbance, the response of individual species was not uniform; abundance, dominance, biomass, or cover increased for some species but decreased for others in response to disturbance. Seed bank species occurred in the vegetation following lethal disturbance in the Spartina community and in both disturbed and undisturbed plots in the Sagittaria community, indicating that the seed bank is a source of propagules for regeneration and maintenance of oligohaline marshes. Of the environmental variables measured, light level was most closely related to the effect of disturbance severity on community structure. Our results suggest that lethal and nonlethal disturbances have differential effects on regeneration of vegetation that can create pattern in oligohaline marshes communities.

Effects of salinity and water level on coastal marshes: an experimental test of disturbance as a catalyst for vegetation change

Wetlands in many coastal areas are threatened by sea level rise. Higher sea level will increase the frequency and duration of inundation in coastal areas and, in some systems, result in higher salinity as well. While the effects of salinity and water level on coastal marsh vegetation have been widely investigated, the role of disturbance in causing shifts in vegetation due to changes in salinity or water level has received little attention. We examined interactions of disturbance (clipping of aboveground vegetation) with salinity and water level treatments in a factorial arrangement using oligohaline marsh mesocosms. The mesocosms all contained soil and vegetation from two adjoining plant communities, one dominated by Spartina patens (Ait.) Muhl. and the other by Sagittaria lancifolia L. We assessed vegetation responses quarterly for 1 year and related responses to soil redox potential ( E h), sulfide concentration, salinity, and pH. We found that salinity and water level had significant effects on species richness only following disturbance and that similar patterns occurred for aboveground biomass of dominant and subdominant species. Following disturbance, aboveground biomass of Sagittaria lancifolia was significantly reduced by salinity but not by flooding (due to a capacity for seed germination under flooded conditions and rapid vegetative growth following disturbance), while the more salt-tolerant Spartina patens was eliminated by flooding but not affected by salinity. Disturbance led to almost complete eradication of vegetation under flooded, saline conditions. In the absence of disturbance, Sagittaria lancifolia biomass increased while Spartina patens was not affected in response to flooding, and neither species was significantly affected by salinity. Responses of vegetation corresponded with lower E h in flooded and saline treatments and higher sulfide concentration in saline treatments. Our results suggest that disturbance is an important component of vegetation change in response to rising sea level, catalyzing rapid shifts in vegetation structure or accelerating wetland loss.

The relative importance of sulfate availability in the growth of Spartina alterniflora and Spartina cynosuroides

The marsh cordgrass Spartina alterniflora Loisel. dominates temperate coastal marshes on the Atlantic coast of North America, and it is an aggressive invader in other coastal wetlands around the world. However, it also flourishes at much lower salinities, extending well into the mesohaline region of major estuaries such as Chesapeake Bay. This species survives even in oligohaline marshes, usually disappearing in the natural environment at salinities below about 2‰ The possibility that this distribution is related to sulfate limitation was investigated in a long-term greenhouse experiment. Sulfate uptake kinetics were first determined for S. alterniflora. The long-term growth response to four different concentrations of sulfate was then evaluated for S. alterniflora and for Spartina cynosuroides (L.) Roth, a low salinity species of overlapping distribution. Growth indices included the total number of leaves, total leaf length, and the relative growth rate of shoots and of whole plants. Spartina alterniflora responded positively to increasing sulfate concentration; however, S. cynosuroides did not exhibit a growth response. These results suggest that S. alterniflora distribution in oligohaline marshes is limited by sulfate supply, and that the plant may have an uncommonly high sulfate requirement.

The influence of vines on an oligohaline marsh community: results of a removal and fertilization study.

The effects of competitive suppression by vines on the non-vine plant community have received little attention in temperate habitats. This study investigated the impact vines have on their herbaceous hosts in a wetland community at two soil fertility levels. Plots in an oligohaline marsh were treated in a 2 × 2 factorial design with vine removal and fertilization over two growing seasons. There was no significant interaction between removal and fertilization treatments on any of the measured variables. Vine removal initially caused an increase in light penetration through the canopy, but by the end of the study, plots with vines removed had less light due to a 25% increase in biomass by the plants released from competition with vines. For plots with vines removed, species richness was higher during a brief period in the spring of the second year, but by the end of the study, richness in removal plots decreased relative to controls. Fertilization caused a 40% increase in biomass overall, although only two species, Sagittaria lancifolia L. and Polygonum punctatum Ell., showed dramatic increases. Despite fertilization causing a 40% decrease in light penetration to the ground, no change in species richness was observed. Overall, these results show that vine cover in this wetland suppresses non-vine species and reduces community biomass. Removal of vines increased biomass of non-vine dominants but resulted in only an ephemeral change in species richness. Fertilization did not increase the effects of vines on the non-vine community.

Erratum: Factors Affecting vegetation Dieback of an Oligohaline Marsh in Coastal Louisian: Field Manipulation of Salinity and Submergence

Erratum: Factors Affecting vegetation Dieback of an Oligohaline Marsh in Coastal Louisian: Field Manipulation of Salinity and Submergence

Factors affecting vegetation dieback of an oligohaline marsh in coastal Louisiana: Field manipulation of salinity and submergence

Vegetation dieback is an important component of wetland loss in low salinity marshes of coastal Louisiana. A field experiment was conducted to determine the factors responsible for vegetation dieback within oligohaline marshes of Louisiana. Sections of marsh, dominated by Sagittaria lancifolia L., were transplanted into one of four locations depending on the treatment: (1) increased submergence—sods were lowered 15 cm below the donor marsh surface, (2) increased salinity—sods were transplanted into a higher salinity marsh and adjacent dieback pond, (3) increased salinity and submergence—sods were transplanted into a higher salinity marsh and adjacent dieback pond at 15 cm below the marsh surface, and (4) control—sods were exhumed and replaced at the ambient elevation of the donor marsh. Plant biomass and edaphic characteristics were measured after 5 mo. An increase in submergence caused decreased plant growth of the S. lancifolia‐dominated marsh community. An increase in salinities to 4–5 g/kg were not detrimental to plant growth. Although saltwater intrusion alone did not cause decreased growth of the S. lancifolia‐dominnled plant community, the combination of saltwater intrusion and increased plant submergence caused the greatest decrease in plant growth due to increased toxic sulfides and a likely reduction in the uptake of NH4‐N by the wetland vegetation. This illustrates that the dieback of oligohaline marsh vegetation can be alleviated by decreasing plant submergence even at salinities as high as 4.6 g/kg.

Factors Affecting Vegetation Dieback of an Oligohaline Marsh in Coastal Louisiana: Field Manipulation of Salinity and Submergence

Factors Affecting Vegetation Dieback of an Oligohaline Marsh in Coastal Louisiana: Field Manipulation of Salinity and Submergence

The influence of vegetation, salinity, and inundation on seed banks of oligohaline coastal marshes

Sea level rise may alter salinity and inundation regimes and create patches of open water in oligohaline coastal marshes, potentially affecting the composition and germination of seed bank species. We conducted seedling emergence experiments to: (1) examine the effects of standing vegetation on the seed banks of three oligohaline marsh communities in coastal Louisiana (dominated by Paspalum vaginatum Sw., Sagittaria lancifolia L., or Spartina patens (Ait.) Muhl., respectively); and (2) investigate the effects of salinity and inundation regime on germination of seed bank species. We also studied the effect of a temporary increase in salinity (to simulate a salt water intrusion event) on the viability of buried seeds. We found that the presence or absence of vegetation within a community affected the abundance of some species in the seed bank but had little effect on species composition. Also, the seed banks of the three communities exhibited considerable overlap in species composition and had similar species richness (10–11) and diversity (antilog Shannon‐Weaver diversity index = 6.5–7.1), despite differences in vegetation type. Higher salinities and flooding reduced seedling emergence for most species; few species emerged at salinities above four parts per thousand (ppt), and only Sagittaria lancifolia and Eleocharis parvula germinated well under flooded conditions. A temporary increase in salinity did not affect species richness or seedling emergence of most species. Our results suggest that differences in vegetation may have little effect on the composition of seed banks of oligohaline marshes. However, higher salinities and greater depth and duration of inundation (anticipated as global sea level continues to rise) may decrease recruitment of seed bank species, reducing their abundance in oligohaline marsh communities.

The interactive effects of herbivory and fire on an oligohaline marsh, Little Lake, Louisiana, USA

Herbivory and fire have been shown to affect the structure and composition of marsh communities. Because fire may alter plant species composition and cover, and these alterations may have an effect on herbivore populations or foraging patterns, an interactive effect of herbivory and fire may be expected. In this study, the effects of fire and vertebrate herbivory in a Louisiana oligohaline marsh were studied using small, controlled burns and animal exclosures. Mean total biomass was nearly 2 times greater in the plots protected from herbivory than in the plots subject to natural herbivory. Additionally, mean total biomass was over 1.5 times greater in the plots that remained unburned than in those that were burned. Two dominant perennial species,Spartina patens andScirpus olneyi, were negatively affected by herbivory, but two annual sedges,Cyperus flavescens andCyperus odorata, were positively affected. Burning reduced the aboveground biomass ofSpartina patens andBacopa monnieri. No species increased in biomass as a result of fire. No significant differences were found in species richness between herbivory treatments or between fire treatments. Although both herbivory and fire were found to cause significant changes in the vegetation, the interaction between herbivory and fire was not found to produce any significant effects in any test conducted.

Transferring sediment containing intact seed banks: a method for studying plant community ecology

The experimental study of the ecology of natural plant communities is necessary to demonstrate the effects of environmental factors on plant growth. It allows one to make predictions of the likely effects of environmental changes on plant communities. Manipulating an entire ecosystem is complicated, and is rarely attempted. An alternative method is applied here for the submerged plant communities of the seasonally-flooded oligohaline marshes of the Camargue. It consists of collecting undisturbed sediment samples with their contained intact seed bank, and submitting them to different salinities. The study of total biomass and of the biomass of the more frequent species was carried out using parametric tests. The precision of the results depended on the frequency of the species in the replicates. When the frequency was low, non-parametric statistics were necessary. The method seems to be particularly suitable for the study of communities of annual species in aquatic environments.

Differential length-weight relations among centrarchids (Pisces: Centrarchidae) from tidal freshwater and oligohaline wetland habitats

Use of tidal-freshwater and oligohaline wetlands by centrarchid fishes along a coastal river-estuarine gradient is partially controlled by salinity. I examined length-weight relationships between tidal-freshwater and oligohaline populations ofMicropterus salmoides, M. punctulatus, Lepomis microlophus, L. punctatus andL. macrochirus, species that commonly use saline wetlands. Analysis of covariance (ANCOVA) documented significantly heavier specimens ofMicropterus salmoides andLepomis microlophus in tidal-freshwater (P 0.05) in length-weight patterns. Specimens ofL. macrochirus andM. punctulatus were heavier at a given length in tidal-freshwater than oligohaline marshes, but direct comparisons were not possible because of violation of the parallel slope assumption of ANCOVA. Data on some species examined contradict previous laboratory physiological data which suggested that salinity and its rate of change control use of saline habitats by centrarchids. These data support the hypothesis that use of habitat is a multidimension function of abiotic and biotic factors and that laboratory physiological studies based on abiotic factors alone may not provide all the answers to questions centered around life-history consequences of using various habitats.

The impact of three‐spined sticklebacks on the Zooplankton of a previously fish‐free pool

SUMMARY. In the Camargue (southern France), most invertebrates inhabiting temporary shallow oligohaline marshes and pools are large‐bodied, conspicuous and defenceless taxa that are restricted to fish‐free environments. Management practices, by creating drainage canals, strongly affect the invertebrate community by allowing colonization by fish. Sticklebacks colonizing the study pool were sampled daily and Zooplankton sampling was carried out at weekly intervals. From early October until the pool dried in June, 1365 sticklebacks entered and only 139 stickleback's fry and seven adults left the pool. Zooplankton abundance was high during the whole study period with a mean density of 1360 ind. 100cm−2. Larger forms (Daphnia magna, Simocephalus vetulus, Arctodiaptomus wierzejskii) quickly disappeared after the first wave of sticklebacks entered the pool in November. Subsequently, smaller species (Diacyclops bicuspidatus odessanus, Chydorus sphaericus and ostracods) replaced the larger ones until the pool dried. Food selectivity of sticklebacks and daily Zooplankton consumption were investigated under experimental conditions within the pool in spring. After introduction of sticklebacks, densities of Zooplankton species dropped quickly (D. b. odessanus, C. sphaericus) with the exception of Ostracoda. Estimates of daily Zooplankton consumption by adult sticklebacks varied between 2.8 and 10.7% of fish body weight. Examination of gut contents showed that fry mainly ingested Chydorus sphaericus. Given that the stickleback is an annual species in the Camargue, and that few fry are able to leave the pool due to the early drying out, the colonization of such a former fish‐free pool is not beneficial for the stickleback population. However, a more serious effect of such colonization is the progressive local extinction of the most typical Zooplankton species inhabiting these formerly fish‐free environments.

Spatial Distributions of the Softstem Bulrush, Scirpus validus, across a Salinity Gradient

Spatial distribution patterns ofScirpus validus were studied in tidal marshes of the lower Savannah River. The hypothesis that changes in spatial pattern forS. validus would accompany differences in environmental parameters was tested by sampling densities and biomass along environmental gradients of salinity and elevation. Coefficients of dispersion were calculated forS. validus and used to compare spatial patterns among freshwater, midly oligohaline, strongly oligohaline, and mesohaline tidal marshes. Results indicated significantly greater clumping ofS. validus in mesohaline marsh than in freshwater marsh. Only the mildly oligohaline site supported a random population ofS. validus, while the strongly oligohaline marsh supported a uniform spatial distribution. Spatial pattern and relative importance ofS. validus, as well as composition of co-occurring species, changed significantly with changing salinity. The relations between changes in relative importance ofS. validus and differences in soil organic matter and elevation were also significant.

A Comparative Study of the Mollusc Communities of Two Oligohaline Intertidal Marshes: Spatial and Temporal Distribution of Abundance and Biomass

Molluscs were collected monthly for a year from two low salinity (0–9‰) intertidal marshes dominated by the macrophytesJuncus roemerianus orSpartina cynosuroides in St. Louis Bay, Mississippi. TheJuncus marsh had lower soil organic matter, higher pH and was more frequently inundated than theSpartina marsh. Eight species of gastropods were abundant and dominated in the higherSpartina marsh, while three bivalve species were dominant in theJuncus marsh. Of the common species,Succinea ovalis, Vertigo ovata andDeroceras laeve are gastropods of terrestrial origins;Geukensia demissa granosissima (bivalve) andMelampus bidentatus (gastropod) are euryhaline estuarine species and the remaining gastropods (Detracia floridana, Littoridinops palustris, Onobops jacksoni) and bivalves (Polymesoda caroliniana, Cyrenoida floridana) are brackish species. Most species were capable of continuous recruitment (based on size class analysis), but exhibited peak activity in particular seasons. Bivalve abundance correlated to temperature, and gastropod abundance was negatively correlated to soil pH. These correlations reflect the influence of flooding regime at the two sites. Biomass was greater in theJuncus marsh because of the increased presence of the large-bodiedPolymesoda. Polymesoda represented >90% and >50% of the total biomass in theJuncus andSpartina (except summer) marshes respectively but always <-5% of the individuals collected. Gastropod biomass was the same in both marshes. Species diversity (H′) was greater inSpartina except for summer months. TheJuncus marsh always exhibited greater species richness. Evenness (J′) determined seasonal changes in diversity (H′). Similarity values (Cz) were always quite low, with highest values in spring In contrast to faunal studies from Gulf and East Coast salt marshes, we found 1) fewer species, 2) communities comprised of unique species combinations, 3) greatest mean densities in summer, and 4) potentially less productivity by the molluscs of our sites. These mollusc communities exhibit structural characteristics that emphasize the unique ecotonal nature of the oligohaline marshes within which they are found.

Orientation behaviour of Lepomis macrochirus Rafinesque to salinity fluctuations

The impact of the rate of salinity change has never been studied in primary freshwater fish occupying oligohaline marshes, where they are near their upper physiological limits. We conducted experiments on the bluegill sunfish, Lepomis macrochirus Rafinesque, to examine their orientation to salinity changes under winter temperature and photoperiod. We found significant difference in behavioural responses to rates of salinity change. The responses to the two flow rate changes indicate orthokinesis for ± 1.0‰ and −12.0‰ change h −1 treatments; however, a ‘closure’ type of response is apparent during +12.0‰ change h −1 treatment. These results indicate that bluegill sunfish respond behaviourally to salinity change, but reduce all overt activity when rate changes are unnatural and potentially lethal. It is apparent that behavioural and physiological responses are synergistic when the salinity exceeds a critical rate of change, which presumably is based upon the species' recent acclimatization history. Moreover, an orthokinetic response to the rate of salinity change may allow bluegill sunfish to move into and out of oligohaline marshes.

Use of Oligohaline Marshes by Fishes and Macrofaunal Crustaceans in North Carolina

Fishes and invertebrate macrofauna (nekton) inhabiting three low salinity, intertidal rivulets were sampled biweekly from July 1981 through June 1982. Twenty-nine species of fishes (24,335 individuals, 9.671 kg wet weight) representing 19 families and four species of invertebrates (6,812 individuals, 4.708 kg wet weight) were collected. The most abundant species were spot (Leiostomus xanthurus), grass shrimp (Palaemonetes pugio), bay anchovy (Anchoa mitchilli) and Atlantic menhaden (Brevoortia tyrannus). Only a few large predacious fish (e.g., largemouth bass,Micropterus salmoides) were collected in the rivulets although largemouth bass and longnose gar (Lepisosteus osseus) were abundant in a nearby permanently flooded area. The number of species was greatest during the warmer months and lowest, during the winter. There were three seasonal peaks of numerical abundance: spring peak attributed to the influx of junvenile spot Atlantic menhaden, Atlantic croaker (Micropogonias undulatus), and southern, flounder (Paralichthys lethostigma); summer peak due to grass shrimp; and fall peak to bay anchovy and grass shrimp. The occurence of these species was not correlated with salinity in the study area. Average densities of spot and Atlantic menhaden in the oligohaline rivulets at the peak of juvenile recruitment were similar to the average densities of these species reported for salt marshes. The results suggest that oligohaline estuarine areas contain important nursery habitat for some euryhaline species.

The transport of bacteria in the sediments of a temperate marsh

The number of bacteria in sediments, interstitial water and overlying tidal water of an oligohaline marsh system are about 10 9, 10 6 and 10 6 cells cm −3, respectively. Average cell size in the overlying water (about 0·06 μm 3), is much smaller than that in sediments and interstitial water (about 0·18 μm 3). Most bacterial cells in sediments are bound to sediment particles and less than 1% of the cells were displaced by percolating water through sediment columns. Concentration of bacteria in flooding tidal waters is generally higher than that in ebbing waters. Movement of bacterial biomass does not appear to be a significant mechanism of particulate organic transport in marsh sediments and marsh sediments do not appear to be a source of suspended bacteria for estuaries.