The effect of salinity on the reproduction of coastal submerged macrophytes in experimental communities

The effects of salinity on the reproduction of coastal submerged macrophyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/1 Cl^?1). In a companion paper (Grillas, van Wijck & Bonis 1993) three groups of species were distinguished on the basis of their biomass production over the salinity range 0 to 6 g/1 Cl^?1: (1) glycophytes (non-salt-tolerant species), (2) salt-tolerant species and (3) halo-phytes. This part of the study describes the impact of salinity on the reproduction of the individual species during the two experiments. The species differ in their capacity to reproduce in the autumn; only Zannichelliapedunculata and Tolypella hispánica were able to produce fruits in that season. For all species reproduction was greater in spring and strongly correlated with biomass, except for Chara canescens. Differences in reproductive effort over the salinity range amplified the halophytic nature of Ruppia marítima and Chara canescens and the intolerance of Callitriche truncata and Chara contraria. For the other species, reproductive effort did not differ significantly over the salinity range. Regarding the effect of salinity on biomass and reproductive effort of individual species, there were large differences in the total weight of propagules produced at the community level and in the relative contribution of individual species. The resulting quantitative changes in the species composition of the seed bank could affect the structure of the communities by their effects on the establishment and survival of species populations.     

Submerged macrophyte zonation in a Mediterranean salt marsh: a facilitation effect from established helophytes?

Abstract. The relationship between communities of submerged annual macrophytes (predominately Chara spp.) and environmental characteristics is studied in three habitats with different dominant perennial species (Arthrocnemum, Juncus, Scirpus) and areas of bare soil. The distribution of submerged annual macrophytes is significantly dependent on two independent environmental factors: a dominant gradient of flooding/salinity, and a secondary gradient of nutrients related exclusively to the combined abundance of helophytes of the genus Scirpus (S. maritimus and S. litoralis). The results suggest that these emergent helophytes (1) are able to modify water column parameters (such as concentration of nitrates, phosphates, potassium, and bicarbonates) which are important for the communities of submerged macrophytes, and (2) play a fundamental role in the generation of secondary sources of environmental variability which, superimposed on the main gradient of flooding/salinity, favours the appearance of new compositional equilibria in such communities. The existence of a process of facilitation is discussed by which the emergent helophytes induce changes in nutrient availability that would favour relatively nutrient‐demanding charophyte species (such as Chara connivens and Nitella hyalina), altering the established relationships with other coexisting charophytes (such as Chara canescens and C. galioides) that dominate in the absence of the facilitating species. Nevertheless, the increased nutrient concentration associated to the presence of helophytes would not introduce significant changes in the total biomass of submerged aquatic macrophytes.     

Community structure of endemic Mimosa species and environmental heterogeneity in a semi‐arid Mexican valley

Abstract. In this paper we analyse six communities with seven Mimosa species in the Tehuacán‐Cuicatlán valley, Mexico. All species are endemic to Mexico and four are endemic to the valley. Mimosa species are found in (1) the ‘matorral xerófilo’ (arid tropical scrub): Mimosa calcicola, M. lacerata, M. luisana, M. polyantha and M. purpusii, and (2) the ‘selva baja caducifolia’ (tropical deciduous forest): M. adenantheroides, Mimosa texana var. filipes. Most of them occur in similar soil environments, while M. polyantha and M. calcicola establish in particular soil conditions and only M. luisana establishes in two different sites showing a wider range of adaptation to soil characteristics. The communities studied include 24 plant families, 51 genera and ca. 70 species (5% of the total flora estimated in the valley). Heterogeneity was found among the communities. Our results point to the replacement of ‘matorral xerófilo’ and ‘selva baja caducifolia’ by ‘matorral espinoso’ (thorny scrub). Thorny species (e.g. Acacia cochliacantha, Mimosa spp.) are becoming the dominant/codominant elements in the communities. Within the communities, Mimosa species have a significant influence on soil pH, organic matter and electrical conductivity values. These species contribute to ameliorate soil nutrient conditions (OM, N_tot, P, Ca, Mg, Na and K contents) as well as other environmental factors (e.g. temperature, shade) under their canopy in degraded plant communities and may serve as ‘resource islands’.     

Opposing patterns of zooplankton diversity and functioning along a natural stress gradient: when the going gets tough,the tough get going

Salinity represents a major structuring factor in aquatic habitats which strongly affects species richness. We studied the relationships among species richness, density and phylogenetic diversity of zooplankton communities along a natural salinity gradient in astatic soda pans in the Carpathian Basin (Hungary, Austria and Serbia). Diversity and density showed opposing trends along the salinity gradient. The most saline habitats had communities of one or two species only, with maximum densities well above 1000 ind l^?1. Similarity of communities increased with salinity, with most of the highly saline communities being dominated by one highly tolerant calanoid copepod, Arctodiaptomus spinosus, which was at the same time the only soda‐water specialist. Salinity obviously constrained species composition and resulted in communities of low complexity, where few tolerant species ensure high biomass production in the absence of antagonistic interactions. The pattern suggests that environmental stress may result in highly constrained systems which exhibit high rates of functioning due to these key species, in spite of the very limited species pool.     

Population strategies in severe environments: alpine plants in the northwestern Caucasus

Abstract. This study attempts to show a differentiation into strategy types among plant species of four alpine communities in the northwestern Caucasus, Russia. Four groups of population characteristics (traits) were examined: above-ground biomass, seed size, seed yield and occurrence of a persistent seed bank. In addition, values for relative growth rate and a morphology index were estimated. Agglomerative Cluster Analysis and Principal Component Analysis were applied to a data set with 42 species from these communities and six species characteristics. In the Geranium gymnocaulon meadow, the most productive community, large gaps occur created by wild boars and bears. Here, the response of 13 species to disturbance was also analysed. Strategy types were approached both according to Grime: ‘competitive’, ‘ruderal’, ‘stress-tolerating’ and according to Ramensky, Rabotnov and Romanovsky: ‘violent’ ≈ dominant (V), ‘explerent’ ≈ explorative (E) and ‘patient’ ≈ endurant (P). Differentiation into strategy types was more obvious in productive alpine grasslands than in lichen heaths and snowbed communities. The grassland dominants Festuca varia, Geranium gymnocaulon and Hedysarum caucasicum showed a more or less ‘violent’ strategy. Species approaching an Estrategy, e.g. Matricaria caucasica, Sibbaldia procumbens and Gnaphalium supinum, were also found in the grasslands but prevailed in the snowbed communities. Species with a ‘patient’ strategy prevailed in the lichen heaths. We conclude that plant strategy types are well-differentiated, this is also seen in plant communities occurring under severe high-mountain conditions. We also suggest that the approaches by Grime and Ramensky/Rabotnov/Romanovsky are not so similar as has been assumed earlier and that the R/R/R types are better differentiated and ecologically better interpretable. We emphasize the gradient character of strategy ‘types’ and would characterize plant species by the degree of adaptation to conditions: (1) from small seed size and large persistent seed bank to large seed size and absence of a seed bank; (2) from high to low biomass and seed production, with relative growth rate as a less important partially correlated trait.     

Incorporating thresholds into understanding salinity tolerance: A study using salt‐tolerant plants in salt marshes

Although salinity in many ecosystems such as salt marshes can be extremely high, an asymmetry in salinity range between experimental studies (relatively narrow) and field conditions (potentially broad) has strongly affected current understanding of plant salinity tolerance. To improve understanding, it is thus important to examine plant tolerances over a broad range of salinities and identify potential tolerance thresholds. We examine tolerances of two widely distributed marsh plants, Suaeda salsa and Salicornia europaea, to salinities ranging from 0 to 100 g/kg, and determine survival, above‐ and belowground biomass after 8 weeks of salinity treatment. Both species, Sa. europaea in particular, have much broader salinity tolerances than other plants previously examined, (2) plant survival, above‐ and belowground biomass have remarkably different responses to salinity, and (3) there is a nonlinear, threshold response of S. salsa to salinity, above which S. salsa survivorship drastically decreases. These results provide multiple important insights. Our study suggests that the potential for using these halophytes to revegetate and restore salt‐affected land may be greater than previously thought, and highlights the importance of studying multiple plant responses. Importantly, our study calls for a better integration of thresholds into understanding plant salinity tolerances and their applications.     

AQUATIC MACROPHYTE COMMUNITIES OF THE WILDERNESS LAKES: COMMUNITY STRUCTURE AND ASSOCIATED ENVIRONMENTAL CONDITIONS

SUMMARY

The structure and summer biomass (g m^?2 dry mass) of the principal aquatic macrophyte communities of the Wilderness Lakes were measured. Both emergent and submerged communities were included in the study. Productivity estimates were made by multiplying biomass by production/biomass ratios for each species. Salinity gradients in the system are described and details of the different sediment types associated with the macrophytes are given. There was considerable variation in production rates between the different water bodies often coinciding with a salinity gradient. However, rapid, natural changes in the communities are described which also influence production rates in a given water body. Production rates (g dry mass m^?2 a^?1) were of the order: Typha latifolia > Phragmites australis > Scirpus littoralis > Potamogeton pectinatus > Chara qlobularis > Ruppia cirrhosa. The significance of the macrophyte rates is discussed in relation to Wilderness Lakes area as a whole.     

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

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

Distribution of submerged macrophytes in the Camargue in relation to environmental factors

Abstract. The species composition of stands of submerged macrophytes was studied in relation to the main environmental factors in oligohaline wetlands of the Camargue, southern France. Correlations were sought between the environmental factors and the abundance of the different species using canonical analysis. 24 species of submerged macrophytes, including 10 species of Charophyta, were recorded in the 60 sites studied. The hydrological regime and the salinity appeared to be the main factors controlling the abundance of the different species. This is related to the management of the marshes in the Camargue, which is carried out using these two controlling factors, particularly the hydrological regime, and also includes the destruction of emergent vegetation, mechanically or by grazing. The bivariate ecological amplitude of the individual species was calculated from field data along the gradients of flooding duration and conductivity of the water. My-riophyllum spicatum, Potamogetón pectinatus and Ruppia cirrhosa dominate permanent marshes along the conductivity gradient. In temporary marshes, all having a low conductivity, Zannichellia pedunculata, Ranunculus baudotii, Chara áspera and Callitriche truncata dominate.     

Ecological description of the sodium chloride mineral springs in the Kirenga River basin and the upper reaches of the Lena River: 1. General characteristics of the springs and their hydrofauna

The aquatic microecosystems and their environment have been studied in 12 mineral springs located in the Cis-Baikal Depression and in the basin of the upper reaches of the Lena River (Eastern Siberia). The hydrochemical characteristics of the springs, originating from the Cambrian salt deposits, are given. Their total mineralization varies from 1.1 to 123.0 g/L and the water is sodium chloride. The soils formed under the influence of the mineral waters (“para-soils”) are described. The data on the composition and quantitative abundance of aquatic fauna are presented. Six types of macroinvertebrate communities are described. The communities where Turbellaria, Gastropoda, and Psychodidae dominate are recorded in weakly mineralized waters (<3 g/L). The communities where Chironomidae dominate are found in waters characterized both by low and high (up to 28 g/L) salinity. In springs with a water salinity of 2.5–11 g/L, communities characterized by the dominance and high biomass of amphipods Gammarus lacustris Sars. are formed. A unique type of community where Ephydridae larvae dominate (>97% of the biomass) is described for the concentrated brines in Ust’-Kutskii spring. Halophilic species of crustaceans are recorded in the meiofauna. The presence of Foraminifera (marine organisms) in the two studied springs attracts specific interest.     

Vegetation communities in continental boreal wetlands along a salinity gradient: Implications for oil sands mining reclamation

Oil sands mining is a major disturbance to boreal landscapes in north-eastern Alberta, Canada. Freshwater peatlands dominate the landscape prior to mining, but the post-mining reclamation landscape will have wetlands that span a salinity gradient. Little is known about the native vegetation communities in subsaline and saline marshes in the boreal region, yet these communities offer the best potential for reclamation of wetlands after oil sands mining. The overall intent of this study is to provide information on natural wetland communities along a gradient of salinities that can be used to enhance oil sands wetland reclamation. Our specific study objectives were to: (1) characterize environmental conditions of industrial and natural wetlands, (2) characterize vegetation communities (composition and diversity) in these wetlands, (3) and explore how vegetation communities (composition and diversity) may be influenced by environmental conditions. We surveyed vegetation communities and environmental variables in 25 natural boreal wetlands along a salinity gradient and in 10 industrial marshes in the oil sands mining region. We observed an electrical conductivity (EC) range of 0.5-28 mS cm⁻¹ in the wetlands, indicating that salinity similar to or higher than anticipated for oil sands reclamation is naturally present in some boreal wetlands. We observed low species richness in both industrial and natural wetlands. There were 101 plant species observed in all the wetlands, with 82 species recorded in the natural wetlands and 44 species in industrial wetlands. At the plot level, richness decreased with increasing EC and pH, but increased with soil organic matter. Using Cluster Analysis and indicator species analysis we defined 16 distinct vegetation community types, each dominated by one or two species of graminoid vegetation. In general these communities resembled those of boreal or prairie marshes. Electrical conductivity, pH, and water depth were important factors correlating with community composition of the wetlands, however peat depth and soil organic content did not differ among community types. Not all community types were present in industrial wetlands, indicating that these communities may need to be planted to enhance overall diversity in future reclaimed oil sands wetlands.     

Phenotypic plasticity of four Chenopodiaceae species with contrasting saline–sodic tolerance in response to increased salinity–sodicity

It is unknown whether phenotypic plasticity in fitness‐related traits is associated with salinity–sodicity tolerance. This study compared growth and allocation phenotypic plasticity in two species with low salinity–sodicity tolerance (Chenopodium acuminatum and C. stenophyllum) and two species with high salinity–sodicity tolerance (Suaeda glauca and S. salsa) in a pot experiment in the Songnen grassland, China. While the species with low tolerance had higher growth and allocation plasticity than the highly tolerant species, the highly tolerant species only adjusted their growth traits and maintained higher fitness (e.g., plant height and total biomass) in response to increased soil salinity–sodicity, with low biomass allocation plasticity. Most plasticity is “apparent” plasticity (ontogenetic change), and only a few traits, for example, plant height:stem diameter ratio and root:shoot biomass ratio, represent “real” plasticity (real change in response to the environment). Our results show that phenotypic plasticity was negatively correlated with saline–sodic tolerance and could be used as an index of species sensitivity to soil salinity–sodicity.     

Host tolerance,not symbiont tolerance,determines the distribution of coral species in relation to their environment at a Central Pacific atoll

Tolerance of environmental variables differs between corals and their dinoflagellate symbionts (Symbiodinium spp.), controlling the holobiont’s (host and symbiont combined) resilience to environmental stress. However, the ecological role that environmental variables play in holobiont distribution remains poorly understood. We compared the drivers of symbiont and coral species distributions at Palmyra Atoll, a location with a range of reef environments from low to high sediment concentrations (1–52 g dry weight m⁻² day⁻¹). We observed uniform holobiont partnerships across the atoll (e.g. Montipora spp. with Symbiodinium type C15 at all sites). Multivariate analysis revealed that field-based estimates of settling sediment predominantly explained the spatial variation of coral species among sites (P < 0.01). However, none of the environmental variables measured (sedimentation, temperature, chlorophyll concentration, salinity) affected symbiont distribution. The discord between environmental variables and symbiont distributions suggests that the symbionts are physiologically tolerant of the variable environmental regime across this location and that the distribution of different host–symbiont combinations present is largely dependent on coral rather than Symbiodinium physiology. The data highlight the importance of host tolerance to environmental stressors, which should be considered simultaneously with symbiont sensitivity when considering the impact of variations in environmental conditions on coral communities.     

Changes in the species richness,spatial pattern and species frequency associated with the decline of oak forest

Nomenclature: follows Flora Europea (Tutin et al. 1964–1980). Since the extension of the irrigation system, the water regime of most of the permanent marshes of the Camargue (southern France) have been intensively controlled. Considerable quantities of nutrient rich Rhone water are pumped into these marshes, leading to lower salinities and a higher biomass production and consequently an increasing organic matter concentration of the sediments. Myriophyllum spicatum has become abundant in these permanent marshes since large quantities of freshwater entered these systems. It has displaced Potamogeton pectinatus in several of these marshes. The different factors likely to influence the distribution of P. pectinatus and M. spicatum were investigated experimentally. The impact of Cl^- concentrations between 0 and 6 g l^-1 on the biomass production of both species was tested. P. pectinatus appears to be more salt tolerant than M. spicatum. The influence of sediment quality on the biomass production of both species was investigated using six sediments differing in organic matter concentration. Compared to P. pectinatus, M. spicatum had a lower total biomass production when grown on sediments with low organic matter concentration (2–4% organic matter) and a higher biomass production on sediments with relatively high organic matter concentration (9–13% organic matter).Nitrogen addition to the sediments yielded an increased biomass production of P. pectinatus and M. spicatum. On some sediments M. spicatum needed higher concentrations of nitrogen than P. pectinatus to increase its biomass production.The creation of freshwater marshes by the introduction of irrigation water, resulting in lower salinities and an increase in sediment organic matter concentration, stimulates the biomass production of M. spicatum.As M. spicatum grows less well on poor sediments and at higher salinities it seems to be unable to displace P. pectinatus in more natural systems in the Camargue.     

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.     

Spatial and temporal variation in community composition and photosynthetic characteristics of phytoplankton in the upper Westerschelde estuary (Belgium,SW Netherlands)

Community composition, biomass and primary production of phytoplankton were studied in the east- ernmost section of the Westerschelde estuary in 1984. Photosynthetic characteristics were compared with distribution of some dominant phytoplankton species along a salinity gradient from 5 to 22 Spring phytoplankton, with Cyclotella meneghiniana (freshwater) and Skeletonema costatum (marine) as the dominant species grew faster than summer phytoplankton. In summer, biomass achieved its maximum, due to the riverine Scenedesmus species and the marine diatoms Thalassiosira levanderi and Ditylum brightwellii, as dominants. Growth conditions were more favourable to phytoplankton communities above 15%, than below this salinity. The data were compared with previous studies (1972) of species composition in the area.     

Distribution of algae in the San Joaquin River, California, in relation to nutrient supply, salinity and other environmental factors

1. The taxonomic composition and biomass of the phytoplankton and the taxonomic composition of the phytobenthos of the San Joaquin River and its major tributaries were examined in relation to water chemistry, habitat and flow regime. Agricultural drainage and subsurface flow contribute to a complex gradient of salinity and nutrients in this eutrophic, ‘lowland type’ river. 2. Because of light‐limiting conditions for growth, maintenance demands of the algae exceed production during summer and autumn in the San Joaquin River where there is no inflow from tributaries. In contrast to substantial gains in concentration of inorganic nitrogen and soluble reactive phosphorus during the summer of normal‐flow years, net losses of algal biomass (2–4 μg L^?1 day^?1 chlorophyll a) occurred in a mid‐river segment with no significant tributary inflow. However, downstream of a large tributary draining the Sierra Nevada, a substantial net gain in algal biomass (6–11 μg L^?1 day^?1) occurred in the summer, but not in the spring (loss of 1–6 μg L^?1 day^?1) or autumn (loss of 2–5 μg L^?1 day^?1). 3. The phytoplankton was dominated in summer by ‘r‐selected’ centric diatoms (Thalassiosirales), species both tolerant of variable salinity and widely distributed in the San Joaquin River. Pennate diatoms were proportionally more abundant (in biomass) in the winter, spring and autumn. Abundant taxa included the diatoms Cyclotella meneghiniana, Skeletonema cf. potamos, Cyclostephanos invisitatus, Thalassiosira weissflogii, Nitzschia acicularis, N. palea and N. reversa, and the chlorophytes Chlamydomonas sp. and Scenesdesmus quadricauda. Patterns in the abundance of species indicated that assembly of the phytoplankton is limited more by light and flow regime than by nutrient supply. 4. The phytobenthos was dominated by larger, more slowly reproducing pennate diatoms. Few of the abundant species are euryhaline. The diatoms Navicula recens and Nitzschia inconspicua and cyanophytes, Oscillatoria spp., were the principal late‐summer benthic species upstream in the mainstem and in drainages of the San Joaquin Valley. Many of the other abundant diatoms (Amphora veneta, Bacillaria paxillifer, Navicula symmetrica, Nitzschia amphibia, N. fonticola, N. palea, Pleurosigma salinarum) of late‐summer assemblages in these segments also are motile species. While many of these species also were abundant in segments downstream of confluences with rivers draining the Sierra Nevada, the relative abundance of prostrate (Cocconeis placentula var. euglypta, Navicula minima) and erect or stalked (Achnanthidium deflexum, Achnanthes lanceolata, Gomphonema kobayasii, G. parvulum var. lagenula) diatoms and Stigeoclonium sp. was greater in these lower San Joaquin River segments. 5. A weighted‐averaging regression model, based on salinity and benthic‐algal abundance in the San Joaquin River and segments of its major tributaries within the San Joaquin Valley, yielded a highly significant coefficient‐of‐determination (r²=0.84) and low prediction error between salinity inferred from the species and that observed, indicating that salinity tolerance is a primary constraint on growth and assembly of the phytobenthos. The same measures of predictability indicated poor performance of a model based on inorganic nitrogen. However, with a greater representation of tributaries (including segments within the Sierra Nevada foothills) in the sample set, an inorganic nitrogen model also yielded a highly significant coefficient‐of‐determination (r²=0.87) and low prediction error between the species‐inferred and the observed concentration. As with the salinity model (r²=0.94) for the enlarged data set, a systematic difference (increased deviation of residuals) existed at high inorganic nitrogen concentrations. These results indicate substantial interaction between salinity and inorganic nitrogen as constraints on the structure of benthic‐algal communities of the San Joaquin River basin.     

Effects of flooding, salinity and herbivory on coastal plant communities, Louisiana, United States

Flooding and salinity stress are predicted to increase in coastal Louisiana as relative sea level rise (RSLR) continues in the Gulf of Mexico region. Although wetland plant species are adapted to these stressors, questions persist as to how marshes may respond to changed abiotic variables caused by RSLR, and how herbivory by native and non-native mammals may affect this response. The effects of altered flooding and salinity on coastal marsh communities were examined in two field experiments that simultaneously manipulated herbivore pressure. Marsh sods subjected to increased or decreased flooding (by lowering or raising sods, respectively), and increased or decreased salinity (by reciprocally transplanting sods between a brackish and fresh marsh), were monitored inside and outside mammalian herbivore exclosures for three growing seasons. Increased flooding stress reduced species numbers and biomass; alleviating flooding stress did not significantly alter species numbers while community biomass increased. Increased salinity reduced species numbers and biomass, more so if herbivores were present. Decreasing salinity had an unexpected effect: herbivores selectively consumed plants transplanted from the higher-salinity site. In plots protected from herbivory, decreased salinity had little effect on species numbers or biomass, but community composition changed. Overall, herbivore pressure further reduced species richness and biomass under conditions of increased flooding and increased salinity, supporting other findings that coastal marsh species can tolerate increasingly stressful conditions unless another factor, e.g., herbivory, is also present. Also, species dropped out of more stressful treatments much faster than they were added when stresses were alleviated, likely due to restrictions on dispersal. The rate at which plant communities will shift as a result of changed abiotic variables will determine if marshes remain viable when subjected to RSLR. Received: 8 April 1998 / Accepted: 15 June 1998     

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 saltmarsh and brackish swamp vegetation of the Fife peninsula

Summary

A study of saltmarshes in Fife shows that they are far more widespread than previously thought. In this paper the saltmarsh and brackish swamp vegetation is described and classified at plant community level. Of particular interest are the small, rocky shore beach-head saltmarshes, which are often very species-rich and contain several plant communities having a predominantly north-western distribution in Britain. The Fife marshes are compared with those described from other regions, and it is suggested that the beach-head marshes are floristically more closely related to western Scottish marshes than those elsewhere on the east coast. However, some communities suggest certain affinities with the saltmarshes of south-eastern Britain, which lends weight to the view that the Firth of Forth lies on the boundary between ‘southern’ and ‘northern’ saltmarsh types in Britain.