Below-ground biomass in healthy and impaired salt marshes

Twelve salt marshes in south Louisiana (USA) were classified as either impaired or healthy before a summer sample collection of above- and below-ground biomass and determination of sediment accretion rates. The above-ground biomass of plant tissues was the same at both impaired and healthy salt marshes and was not a good predictor of marsh health. However, below-ground root biomass in the upper 30cm was much lower in the impaired marshes compared to the healthy marshes. Compromises to root production apparently occur before there is an obvious consequence to the above-ground biomass, which may quickly collapse before remedial action can be taken. The subsequent change in vertical position of the marsh surface may be equivalent to many years of accretion, and be irreversible within decades without considerable effort. These results are consistent with the hypothesis that it is the plants below-ground accumulation of organic matter, not inorganic matter that governs the maintenance of salt marsh ecosystem in the vertical plane. Reversing the precursor conditions leading to marsh stress before the collapse of the above-ground biomass occurs is therefore a prudent management objective and could be easier than restoration.     

Cellulose-decomposing fungi of salt marshes in Egypt

Seventy-five species and three varieties which belong to thirty-four genera were identified from 74 soil samples collected from salt marshes in Egypt. The most frequent fungi wereAspergillus fumigatus, Aspergillus niger, Cladosporium herbarum andAlternatia alternata, followed byAspergillus terreus,Curvularia spicifera andPenicillium notatum. Six genera were of moderate occurrence:Penicillium, Futarium, Curvularia, Rhizopus, Stachybotrys, andChaetomium. Five genera were of low occurrence:Paecilomyces, Oephalosporium, Epicoccum, Mucor andMyrothecium.     

Restoration of salt marshes in the Netherlands

The conquest of land from the sea has been a long tradition in the Netherlands. When salt marshes were high enough, they were embanked when it was economically feasible, and transformed into intensively exploited agricultural land. This resulted in the transformation of halophytic communities to glycophytic communities. Often as an alternative, a low levee, a summerdike was built, which greatly reduced the flooding frequency of the landward summerpolder, hence creating a sedimentation deficit therein. Such summerpolders now cover 1200 ha in the Netherlands, 2100 ha in NW-Germany and small areas in England. Due to continuous embankments, the present salt-marsh area is relatively small with respect to the tidal basins. Discussions have been started how to increase the salt-marsh area. Two options will be discussed, firstly de-embankment of summerpolders and maintenance of the protective seawall, secondly increase of the effects of saline seepage behind the seawall by top soil removal. Both options include the restoration of salt-marsh communities (target communities) in intensively agriculturally exploited sites that have been salt marshes before. From the few examples abroad and experiments it is discussed (1) to which extent the sedimentation deficit in summerpolders could be compensated for, (2) if the soil seed bank is likely to contribute to re-establishment of salt-marsh communities, (3) if the dispersal of propagules of halophytic plants will be possible by hydrochory when the summerdike is breached, (4) to what extent is dispersal by endozoochory through waterfowl important in case re-establishment in a saline seepage area behind the seawall without open connection to the sea is envisaged. Two case studies of de-embanked summerpolders in the Netherlands revealed that the sedimentation deficit can be counteracted by rapid sedimentation, provided enough transport is possible from the foreshore. Dispersal by incoming tidal water from the nearby salt-marsh source area into the target area is possible for many salt-marsh plant species. The rate of success seems to depend on the relative position of source area and target area. A case study in a saline seepage area after top soil removal in the Netherlands, showed that the number of viable seeds dispersed by droppings from waterfowl is limited. Hence the possibilities for restoration of inland halophytic plant communities seem much lower than after de-embankment of summerpolders.     

The coastal salt marshes of California and Baja California

A comparative study of the North American salt marshes between Magdalena Plain (Baja California, 24° N)_and the north of San Francisco (California 38° N) is made in order to establish relationships between floristic and zonal gradients. The sigmatistic-phytosociological method along with Average Linkage Clustering are used to describe the zonation of these salt marshes and to define the optimum zone of several halophilous plants and communities.Abbreviations (As) Arthrocnemum subterminalis - (Ds) Distichlis spicata - (Fg) Frankenia salina - (Jc) Jaumea carnosa - (MI) Monanthochloe littoralis - (S1) Sarcocornia pacifica, prostrate biotype - (S2) Sarcocornia pacifica, erect biotype - (Sp) Spartina foliosa     

Zonation of shrubs in western Atlantic salt marshes

We explored the generality of the processes mediating shrub zonation in western Atlantic salt marshes by comparing the results of our experiments in Georgia, USA with previous studies from Rhode Island, USA. The shrub Borrichia frutescens dominates the terrestrial border of many Georgia salt marshes. Within the shrub zone, physical stress increased at lower elevations, shrubs at lower elevations were stunted, and experimentally reducing physical stress reduced shrub stunting. Below the shrub zone, physical stress increased further, and the grass Spartina alterniflora dominated. Transplant and neighbor-removal experiments indicated that the lower border of the shrub zone was set more by physical stress than by competition, but that the upper border of the grass zone was set primarily by competition with shrubs. Laboratory experiments indicated that S. alterniflora seedlings survived best and shrub seedlings worst in the flooded, salty treatment that mimicked low-marsh conditions. These processes are similar to those maintaining zonation patterns between the shrub Iva frutescens and the rush Juncus gerardi in Rhode Island salt marshes. However, markedly different processes appear to occur further to the north, where woody shrubs are absent from coastal marshes, and further to the south, where woody plants (mangroves) dominate coastal wetlands.     

Spatially heterogeneous refugia and predation risk in intertidal salt marshes

The effect of habitat structure on interactions between predators and prey may vary spatially. In estuarine salt marshes, heterogeneity in refuge quality derives from spatial variation in vegetation structure and in tidal inundation. We investigated whether predation by blue crabs on periwinkle snails was influenced by distance from the seaward edge of the salt marsh and by characteristics of the primary habitat structure, smooth cordgrass ( Spartina alterniflora ). Spartina may provide refuge for snails and interfere with foraging by crabs. Furthermore, predation risk should decline with distance from the seaward edge because landward regions require more travel time for crabs during tidal inundation. We investigated these processes using a comparative survey of snails and habitat traits, an experiment that assessed the crab population and measured predation risk, and a size-structured model that estimated encounter rates. Taken together, these approaches indicated that predation risk for snails was lower where Spartina was present and was lower in a landward direction. Furthermore, Spartina architecture and distance from the seaward edge interacted. The strength of the predation gradient between seaward and landward regions of the marsh was greater where Spartina was tall or dense. These predation gradients emerge because vegetation and distance inland decrease encounter rates between crabs and snails. This study suggests that habitat modification, a process not uncommon in salt marshes, may have consequences for interactions among intertidal fauna.     

Ecophysiological adaptations of coastal halophytes from foredunes and salt marshes

Ecophysiological strategies of coastal halophytes from foredunes and salt marshes are discussed. A comparison is made of the factors that limit growth in salt marshes and sand dunes. In salt marshes, zonation and succession are primarily governed by variation in soil salinity, which strongly depends on inundation with seawater. Results are described of experiments which aim at separating salinity and inundation effects on growth, osmotic and mineral relations in a comparison of salt-marsh halophytes. The growth response of plants cannot simply be correlated (and causally explained) with the concentration of Na, Cl, and K in the tissues. Also, the compatible osmotic solutes proline and methylated quaternary ammonium compounds may accumulate both in species with a positive response to increased salinity and in species with a growth reduction under seawater inundation. More likely inadequate adaptation of the plants water potential with these components is partly the cause of retarded growth. Disfunctioning of the plant in this respect may be at three levels: (a) total water potential of the plant, (b) (loss) of turgor pressure potential; (c) regulation at the cellular level. The ecological importance of some factors in seawater other than sodium chloride is considered. In coastal sand dunes airborne rather than soil salinity limits plant growth, together with the effects of abrasion, sand accretion, drought and the poor nutrient status of the dune sand. Adaptations of sand-dune species to these factors may consist of: large seeds with storage tissue germinating in the dark and seedling growth enough to emerge through the accreted sand. Aerial parts must be resistant to mechanical damage (high wind speed and abrasion), possibly by a sclerophyllous and tough structure. Efficient nutrient uptake, translocation and retranslocation seem to help survive sand-dune species in a nutrient-poor rooting medium.     

Environmental gradients and herbivore feeding preferences in coastal salt marshes

Current theories of plant-herbivore interactions suggest that plants may differ in palatability to herbivores as a function of abiotic stress; however, studies of these theories have produced mixed results. We compared the palatability of eight common salt marsh plants that occur across elevational and salinity stress gradients to six common leaf-chewing herbivores to determine patterns of plant palatability. The palatability of every plant species varied across gradients of abiotic stress in at least one comparison, and over half of the comparisons indicated significant differences in palatability. The direction of the preferences, however, was dependent on the plant and herbivore species studied, suggesting that different types of stress affect plants in different ways, that different plant species respond differently to stress, and that different herbivore species measure plant quality in different ways. Overall, 51% of the variation in the strength of the feeding preferences could be explained by a knowledge of the strength of the stress gradient and the type of gradient, plant and herbivore studied. This suggests that the prospects are good for a more complex, conditional theory of plant stress and herbivore feeding preferences that is based on a mechanistic understanding of plant physiology and the factors underlying herbivore feeding preferences.     

Osmophilous fungi in the salt marshes of Kuwait.

During an investigation of the mycoflora inhabiting saline soils in Kuwait, special attention was focused on osmophilous fungi. A total of 101 species belonging to 46 genera were encountered from 40 soil samples collected from salt marshes using Czapek's agar supplemented with 40% sucrose. Soil samples were collected from different habitats at different distances from the water edge. Soils near to the water edge were poor in their fungal content, while those taken from areas covered by Juncus arabicus contained highest fungal populations. The recorded genera were classified as follows: 7 were of high frequency of occurrence, 8 moderate, 17 low, and 13 were rare. The order of dominance was Aspergillus, Alternaria, Penicillium, Cephalosporium, Fusarium, Stachybotrys, and Drechslera. Comparison between our results and those in other studies showed that there is no fungal flora characteristic of saline soils.     

Methodology for studying exchanges between salt marshes and coastal marine waters

The salt marshes of the Mont St. Michel bay represent a complex system in continuous change, mostly due to the frequent exchanges with the coastal waters through tidal processes. In such ecosystems, water is an important element insofar as it represents the common vector of flows between and among several ecosystem compartments. The purpose of the approach discussed here is to estimate the volume of water coming in and out and to determine the variations of the water quality according to time and nutrients concentrations. The estimation of the water fluxes is dependent on the channel calibration downstream of the watershed. Among the different methods examined, the continuous integrals calibration appears as the best one because the water level changes very quickly.Up to now, estimations of nutrients exchanges in wetlands have been based on rigorously regular field sampling, in consideration of the fact that exchanges occurred mainly during annual spring tides or during spring tides of each cycle of the year. According to our results, it seems that every tide, and portion of a tide, of a monthly and seasonal cycle has some importance and variability, which suggests that all parts of a tide should be considered in estimations of exchanges between wetlands and coastal waters.Corresponding Editor: W. Mitsch     

Sounds recorded in salt marshes and attributed to the European eel

The sounds were recorded in coastal ponds off the French Atlantic coast. They are characterized by continuous series of regularly spaced sounds, each sound being composed of one to four pulses of 7.8-ms duration. The main frequencies of these sounds are under 350 Hz. Due to the special characteristics of these sounds, their temporal patterning, their coastal pond provenance and their close similarity to sounds made by the American eel (Anguilla rostrata), we attribute them to the European eel (Anguilla anguilla).     

Arbuscular mycorrhizal colonization of halophytes in Central European salt marshes

 Halophytes from both coastal and inland Central European salt marshes were examined for colonization by arbuscular mycorrhizal (AM) fungi. Plants from different families were strongly colonized but the degree of colonization varied with the individual plant and apparently during the vegetation period, too. Members of the typical non-mycorrhizal families like Armeria maritima of the Plumbaginaceae and Salicornia europaea of the Chenopodiaceae were found to be colonized, particularly in the drier salt marshes. High numbers of Glomus spores were found in the saline soils, especially those of the inland locations examined. Approximately 80% of these spores were from Glomus geosporum as shown by a typical restriction fragment length polymorphism (RFLP) pattern of the amplified internal transcribed spacer regions. The present study demonstrates that RFLP analysis is useful when screening habitats for the occurrence of mycorrhizal fungi which can be identified only with difficulty by morphological criteria. Accepted: 25 August 2000     

Trematodes associated with mangrove habitat in Puerto Rican salt marshes

Batillaria minima is a common snail in the coastal estuaries of Puerto Rico. This snail is host to a variety of trematodes, the most common being Cercaria caribbea XXXI, a microphallid species that uses crabs as second intermediate hosts. The prevalence of infection was higher (7.1%) near mangroves than on mudflats away from mangroves (1.4%). Similarly, there was a significant positive association between the proportion of a site covered with mangroves and the prevalence of the microphallid. The association between mangroves and higher trematode prevalence is most likely because birds use mangroves as perch sites and this results in local transmission to snails.     

Nitrogen sequestration capacity of two salt marshes from the Tagus estuary

The role of salt marshes as nitrogen sink is examined taking into consideration the seasonal variation of above and belowground biomass of Spartina martima and Halimione portulacoides in two marshes from Tagus estuary, Pancas and Corroios, and the degradation rates of belowground litter. Total nitrogen was determined in plant components, decomposing litter and sediment. Biomass was higher in Corroios, the saltier marsh, with 7190 g m⁻² y⁻¹ dw of S. maritima and 6593 g m⁻² y⁻¹ dw of H. portulacoides and the belowground component contributed to 96% and 90% of total biomass, respectively. In the other marsh, Pancas, belowground biomass contributed to 56% and 76% of total biomass for S. maritima and H. portulacoides, respectively. Litterbag experiment showed that between 25% and 50% of nitrogen is lost within the first month and remained relatively constant in the next four months. Slower decomposition is observed in sediments with higher nitrogen concentration (max. 0.7% N in the saltier marsh). Higher concentrations of N were found in the sediment upper layers. Considering the sediment-root system, most of the nitrogen is stored in the sediment compartment and only about 1–4% of the total N was found in the roots. Considering these results, Tagus salt marshes act as a sink for nitrogen.     

Latitudinal variation in plant–herbivore interactions in European salt marshes

Ecological interactions often vary geographically. Work in salt marshes on the Atlantic Coast of the United States has documented community-wide latitudinal gradients in plant palatability and plant traits that may be driven in part by greater herbivore pressure at low latitudes. To determine if similar patterns exist elsewhere, we studied six taxa of saltmarsh plants ( Atriplex , Juncus , Limonium , Salicornia , Spartina and Suaeda ) at European sites at high (Germany and the Netherlands) and low (Portugal and Spain) latitudes. We conducted feeding assays using both native and non-native consumers, and documented patterns of herbivore damage in the field. As in the United States, high-latitude plants tended to be more palatable than low-latitude plants when offered to consumers in paired feeding assays in the laboratory, although assays with grasshopper consumers were less consistent than those with crab consumers, and plants in the field at low-latitude sites tended to experience greater levels of herbivore pressure than plants at high-latitude sites. Similarly, high-latitude leaf litter was more palatable than litter from low-latitude plants when offered to consumers in paired feeding assays in the laboratory. Latitudinal gradients in plant palatability and herbivore pressure may be a general phenomenon, and may contribute to latitudinal gradients in decomposition processes.     

Flood tolerance and the distribution of Iva frutescens across New England salt marshes

Summary Tidal flooding is widely believed to be an important determinant of marsh plant distributions but has rarely been tested in the field. In New England the marsh elder Iva frutescens often dominates the terrestrial border of salt marshes and we examined its flood tolerance and distribution patterns. Marsh elders only occur at elevations where their roots are not subject to prolonged water table flooding. Consequently they are found on the terrestrial border of marshes and at lower elevations associated with drainage ditches and locally elevated surfaces. Marsh elders transplanted to elevations lower than they normally occur died within a year with or without neighbors and greenhouse tests revealed that I. frutescens is much less tolerant of flooded soil conditions than plants found at lower marsh elevations. We also manipulated the water table level of field plots and found that increasing or decreasing water table drainage led to enhanced and diminished I. frutescens performance, respectively. Our results demonstrate the importance of water table dynamics in generating spatial patterns in marsh plant communities and provide further evidence that supports the hypothesis that the seaward distributional limits of marsh plant populations are generally dictated by physical processes.     

The salt marshes of the Westerschelde and their role in the estuarine ecosystem

The salt marshes along the Westerschelde estuary have been influenced by various human activities of which reclamation has been a major cause for the loss of salt marsh area. The salinity gradient in the aquatic system is also mirrored in the vegetation of the salt marshes.The role of the salt marshes for the estuary as a whole is manifold but a major importance is their function as a sink for anthropogenic substances.The possible role as a carbon and mineral source for the estuary is discussed in this paper. It is estimated that the total area of salt marsh adds about 8% to the organic matter input in the estuary while the nutrient input may be as high as 25%.Communication nr. 403 of the Delta Institute, Yerseke.     

Patterns of reproduction and development of selected resident teleosts of Florida salt marshes

A wide variety of teleost fishes occur in tidal marshes of Atlantic and Gulf coasts of Florida, few of which breed in these habitats or remain there for extended periods of time. A significant fraction of teleosts that do so are members of one of five families. Eleven representative species belonging to these families, whose reproduction and development are considered here, include: Adinia xenica, Fundulus confluentus, F. grandis and F. similis (Fundulidae); Cyprinodon variegatus, Floridichthys carpio and Jordanella floridae (Cyprinodontidae); Gambusia holbrooki and Poecilia latipinna (Poeciliidae); Mugil cephalus (Mugilidae); and Dormitator maculatus (Eleotridae). Spawning or birth locations, patterns of growth and development, times of use of the salt marsh as a nursery area, and development of salinity tolerances/osmotic regulatory capabilities were evaluated for each, considering these in the context of variability of environmental conditions, especially of salinity. Five different patterns of reproduction are shown by these 11 species, and only A. xenica appears to be limited to reproducing in the salt marsh environment. Some of these species are capable of reproducing throughout the year. Several of the species are annuals, most others live only 2 or 3 years. Eight species (those other than M. cephalus, A. xenica and G. holbrooki) were found to show no size relationship, large juvenile to adult sizes, in osmotic regulatory capabilities.     

Biodiversity of arbuscular mycorrhizal fungi in roots and soils of two salt marshes

The occurrence of arbuscular mycorrhizal fungi (AMF) was assessed by both morphological and molecular criteria in two salt marshes: (i) a NaCl site of the island Terschelling, Atlantic Coast, the Netherlands and (ii) a K₂CO₃ marsh at Schreyahn, Northern Germany. The overall biodiversity of AMF, based on sequence analysis, was comparably low in roots at both sites. However, the morphological spore analyses from soil samples of both sites exhibited a higher AMF biodiversity. Glomus geosporum was the only fungus of the Glomerales that was detected both as spores in soil samples and in roots of the AMF-colonized salt plants Aster tripolium and Puccinellia sp. at both saline sites and on all sampling dates (one exception). In roots, sequences of Glomus intraradices prevailed, but this fungus could not be identified unambiguously from DNA of soil spores. Likewise, Glomus sp. uncultured, only deposited as sequence in the database, was widely detected by DNA sequencing in root samples. All attempts to obtain the corresponding sequences from spores isolated from soil samples failed consistently. A small sized Archaeospora sp. was detected, either/or by morphological and molecular analyses, in roots or soil spores, in dead AMF spores or orobatid mites. The study noted inconsistencies between morphological characterization and identification by DNA sequencing of the 5.8S rDNA-ITS2 region or part of the 18S rDNA gene. The distribution of AMF unlikely followed the salt gradient at both sites, in contrast to the zone formation of plant species. Zygotes of the alga Vaucheria erythrospora (Xanthophyceae) were retrieved and should not be misidentified with AMF spores.     

Bioinvasion by Spartina patens alters sediment biogeochemical functioning of European salt marshes

Biological Invasions - Bioinvasions pose undeniable threats and trigger changes in salt marsh ecosystem functioning. In Mediterranean and Atlantic marshes, the invasion by S. patens contributed to...