Experimental salt marsh islands: a model system for novel metacommunity experiments

Shallow tidal coasts are characterised by shifting tidal flats and emerging or eroding islands above the high tide line. Salt marsh vegetation colonising new habitats distant from existing marshes are an ideal model to investigate metacommunity theory. We installed a set of 12 experimental salt marsh islands made from metal cages on a tidal flat in the German Wadden Sea to study the assembly of salt marsh communities in a metacommunity context. Experimental plots at the same elevation were established within the adjacent salt marsh on the island of Spiekeroog. For both, experimental islands and salt marsh enclosed plots, the same three elevational levels were realised while creating bare patches open for colonisation and vegetated patches with a defined transplanted community. One year into the experiment, the bare islands were colonised by plant species with high fecundity although with a lower frequency compared to the salt marsh enclosed bare plots. Initial plant community variations due to species sorting along the inundation gradient were evident in the transplanted vegetation. Competitive exclusion was not observed and is only expected to unfold in the coming years. Our study highlights that spatially and temporally explicit metacommunity dynamics should be considered in salt marsh plant community assembly and disassembly

Salt marsh harvest mouse abundance and site use in a managed marsh

The salt marsh harvest mouse (Reithrodontomys raviventris) is a federal and California listed endangered mammal endemic to the San Francisco Bay. The objectives of this research were to determine habitat use of endangered salt marsh harvest mice in a managed marsh in Fremont California, and to evaluate whether managed flooding of the marsh provides favorable habitat conditions for the mice. In addition, this research explores the effectiveness of using mark-recapture model selection analysis to estimate capture probability, survival, and population growth rate for salt marsh harvest mice. Mice were captured for four nights per month between May and August, 2008. Thirty-six unique salt marsh harvest mice were captured for a catch per 100 nights of trap effort of 1.9. The sex ratio of male to female mice was skewed towards males with a sex of 2.3:1. Salt marsh harvest mice were distributed randomly throughout the marsh and no relationships were found between mice distribution and pickleweed salinity, pickleweed height, distance to levees, distance to dry or filled water bodies, percent cover of vegetation, or sympatric rodents. The findings of this study indicate that catch-per-trap-effort, the current standard method to estimate salt marsh harvest mice populations, may not be accurate. The results of this study can be used by managers of salt marsh harvest mice habitat to manage and estimate mouse populations

Remote sensing of tidal networks and their relation to vegetation

The study of the morphology of tidal networks and their relation to salt marsh vegetation is currently an active area of research, and a number of theories have been developed which require validation using extensive observations. Conventional methods of measuring networks and associated vegetation can be cumbersome and subjective. Recent advances in remote sensing techniques mean that these can now often reduce measurement effort whilst at the same time increasing measurement scale. The status of remote sensing of tidal networks and their relation to vegetation is reviewed. The measurement of network planforms and their associated variables is possible to sufficient resolution using digital aerial photography and airborne scanning laser altimetry (LiDAR), with LiDAR also being able to measure channel depths. A multi-level knowledge-based technique is described to extract networks from LiDAR in a semi-automated fashion. This allows objective and detailed geomorphological information on networks to be obtained over large areas of the inter-tidal zone. It is illustrated using LIDAR data of the River Ems, Germany, the Venice lagoon, and Carnforth Marsh, Morecambe Bay, UK. Examples of geomorphological variables of networks extracted from LiDAR data are given. Associated marsh vegetation can be classified into its component species using airborne hyperspectral and satellite multispectral data. Other potential applications of remote sensing for network studies include determining spatial relationships between networks and vegetation, measuring marsh platform vegetation roughness, in-channel velocities and sediment processes, studying salt pans, and for marsh restoration schemes

Impact of sheep grazing on juvenile sea bass, Dicentrarchus labrax L., in tidal salt marshes

The diet of young of the year sea bass, Dicentrarchus labrax L., from sheep grazed and ungrazed tidal salt marshes were com-pared qualitatively and quantitatively in Mont Saint-Michel Bay. In areas without grazing pressure, the vegetation gradient changes from a pioneer Puccinellia maritima dominated community at the tidal ¯at boundaries through a Atriplex portulacoides dominated community in the middle of the marsh to a mature Elymus pungens dominated community at the landward edge. The A. portula-coides community is highly productive and provides important quantities of litter which provides a habitat and good supply to substain high densities of the detrivorous amphipod Orchestia gammarellus. In the grazed areas, the vegetation is replaced by P. maritima communities, a low productive grass plant, and food availability and habitat suitability are reduced for O. gammarellus. Juvenile sea bass colonise the salt marsh at ¯ood during 43% of the spring tides which inundate the salt marsh creeks. They forage inside the marsh and feed mainly on O. gammarellus in the ungrazed marshes. In grazed areas, this amphipod is replaced by other species and juvenile sea bass consume less food from the marsh. This illustrates a direct effect of a terrestrial herbivore on a coastal food web, and suggests that management of salt marsh is complex and promotion of one component of their biota could involve reductions in other species

Environmentally determined spatial patterns of annual plants in early salt-marsh succession versus stochastic distribution in old salt-marsh conditions

It is generally accepted that in terrestrial ecosystems the occurrence and abundance of plant species in late succession stages can be well predicted from prevailing soil conditions whereas in early succession their presence is much more influenced by chance events (e.g. propagule availability). In other words late successional vegetation stages would be deterministically structured, while early succession stages would be of a more stochastic nature.To test this hypothesis, we compared the effect of abiotic environmental factors on vegetation composition and probability of occurrence of single species in two adjacent saltmarshes, differing in age (successional stage). A new salt-marsh of about 14ha was created in 2002 by removing a several meters thick layer of sand and slurry which was deposited on the major part of the salt-marsh along the IJzer estuary in the 1960s. From 2002 onwards, primary colonization started on that sterile substrate by hydrochoric seed dispersal, induced by tidal water currents from an adjacent 4ha old salt-marsh and the latter remained untouched as saltmarsh for more than two hundred years. Between mid August and the end of September 2005, three years after the start of the colonization in the new salt-marsh, vegetation and three abiotic environmental factors (soil texture, salinity and elevation) were described in a set of 155 plots (2m × 2m), distributed over the new and the old salt-marsh.In contrast to the general rule for terrestrial ecosystems, the vegetation composition of the early succession stage of the new salt-marsh appears to be at least as much determined by the combined effect of the measured abiotic factors as that of the old salt-marsh. As revealed by logistic regression the presence/absence of perennial species as well as annual species of the young salt-marsh can be well predicted by the measured abiotic environment. For the old salt-marsh, this also holds for the perennials, but not for the annuals. The stochastic appearance of gaps in the perennial vegetation cover appears to be important for the establishment of annuals in the older salt-marsh

Indications of dynamic effects on scaling relationships between channel sinuosity and vegetation patch size across a salt marsh platform

Salt marshes are important coastal areas that consist of a vegetated intertidal marsh platform and a drainage network of tidal channels. How salt marshes and their drainage networks develop is not fully understood, but it has been shown that the biogeomorphic interactions and feedbacks between vegetation development and channel formation play an important role. We examined the relationships among tidal channel sinuosity, marsh roughness, vegetation type (pioneer, Elymus athericus or Phragmites australis), and patch size at different spatial scales using a high-resolution vegetation map (derived from aerial photography) and lower-resolution satellite imagery processed with linear spectral mixture analysis. The patch-size distribution in all vegetation types corresponded to a power law, suggesting the presence of self-organizational processes. While small vegetation patches are more dominant in pioneer vegetation, they were present in all vegetation types. The largest patch size is restricted to E. athericus. We observed an inverse logarithmic relationship between channel sinuosity and vegetation patch size in all vegetation types. The fact that this relationship is observed in both pioneer and later successional stages suggests that after the establishment of a drainage network in the dynamic pioneer stages of salt marsh development, the later stages of salt marsh succession largely inherit the meandering pattern of the early successional stages. Our study confirms recent evidence that no significant changes in the specific features of tidal channel networks (e.g., channel width, drainage density, and efficiency) take place during the later stages of salt marsh development

Development and Monitoring of Revegetation Methods: Connecting Students with Restoration Activities at Awcomin Marsh

Five classes in a local elementary school participated in an effort to grow and plant high marsh and upper border vegetation at a salt marsh restoration site in spring 2005. Seeds of six marsh upper edge species were successfully germinated and grown into seedlings by third graders. The seedlings were planted by the students in late spring 2005, but only switchgrass and quackgrass plants appeared to have established and survived after one year. Mature shoots of three high marsh species planted by the third graders (salt hay, salt grass and black grass) established successfully and continue to proliferate. In addition, we assessed an experiment of cordgrass plantings performed by community volunteers in 2002. The experiment was designed to test the effectiveness of three planting techniques at a salt marsh restored by the excavation of old dredge spoil that had been colonized by common reed. After four growing seasons, Plug, Bare Root Shoot, and Seed Head planting techniques exhibited greater cover of cordgrass and total cover of vascular plants when compared with unplanted areas. Cover of perennial plants (e.g., cordgrass), which contributes directly to belowground soil development in salt marshes, dominated the planted plots. Cover of annual species dominated the unplanted plots. Planting cordgrass in areas where dredge spoils and common reed had been excavated from a historic marsh accelerated the development of native vegetation compared with unplanted areas. Performance and evaluation of the two sets of plantings has provided information about appropriate planting techniques for our region and has involved and educated the local community about the values of salt marsh to promote stewardship. Recommendations included the use of bare root shoot and seed head planting techniques where cordgrass is desired. Outside plots or a greenhouse may be needed for successful propagation of upper edge marsh species from seed, and a planting program that includes mature plants as well as seedlings is recommended to ensure success

The effect of successional stage and salinity on the vertical distribution of seeds in salt-marsh soils

Seed bank density and similarity between seed bank and above-ground vegetation along depth were compared between two salt-marshes different in age. In addition, the effect of salinity on the variation in seed bank density and similarity between seed bank and aboveground vegetation along depth was investigated. The study was conducted in an euhaline saltmarsh that contained both old and newly created habitats. In addition, two other old saltmarshes were selected to study the effect of salinity on the distribution pattern of seed bank and similarity between seed bank and above-ground vegetation at different soil depths. One of them was mesohaline, the other euhaline.Ten plots of 2m × 2m were situated in the new salt-marsh (existing since 2002) and 80 plots in the three old salt-marshes. Soil samples were collected at three different depths (0- 5cm, 5-10cm and 10-15cm) in spring 2006. After washing by fresh water, the soil samples were spread in the greenhouse to allow viable seeds to germinate. Germination experiments lasted 6 months and all seedlings were identified and removed after identification. Aboveground vegetation composition was determined during the growing season in all plots. Viable seed density was calculated for each plot and for the three different depths; the similarity between seed bank and floristic composition of the above-ground vegetation was calculated. A general linear model was used to investigate the effect of soil depth, age and salinity of the salt-marsh on density and similarity between seed bank and above-ground vegetation.The results showed that seed density decreased with depth in all salt-marshes irrespective of their age and soil salinity. Seed density and similarity between seed bank and above-ground vegetation were higher in the new salt-marsh than in the old one in the same study area. This is because in young as well as in old successional stages, the seed bank was mostly composed of new colonizers, while most perennial species were absent from the soil seed bank, although they were dominant in the above-ground vegetation of the old salt-marsh.The characteristics of the seed bank of a mesohaline salt-marsh were found not to be fundamentally different from that of both euhaline salt-marshes

Wave attenuation at a salt marsh margin: A case study of an exposed coast on the Yangtze estuary

To quantify wave attenuation by (introduced) Spartina alterniflora vegetation at an exposed macrotidal coast in the Yangtze Estuary, China, wave parameters and water depth were measured during 13 consecutive tides at nine locations ranging from 10 m seaward to 50 m landward of the low marsh edge. During this period, the incident wave height ranged from <0.1 to 1.5 m, the maximum of which is much higher than observed in other marsh areas around the world. Our measurements and calculations showed that the wave attenuation rate per unit distance was 1 to 2 magnitudes higher over the marsh than over an adjacent mudflat. Although the elevation gradient of the marsh margin was significantly higher than that of the adjacent mudflat, more than 80% of wave attenuation was ascribed to the presence of vegetation, suggesting that shoaling effects were of minor importance. On average, waves reaching the marsh were eliminated over a distance of similar to 80 m, although a marsh distance of >= 100 m was needed before the maximum height waves were fully attenuated during high tides. These attenuation distances were longer than those previously found in American salt marshes, mainly due to the macrotidal and exposed conditions at the present site. The ratio of water depth to plant height showed an inverse correlation with wave attenuation rate, indicating that plant height is a crucial factor determining the efficiency of wave attenuation. Consequently, the tall shoots of the introduced S. alterniflora makes this species much more efficient at attenuating waves than the shorter, native pioneer species in the Yangtze Estuary, and should therefore be considered as a factor in coastal management during the present era of sea-level rise and global change. We also found that wave attenuation across the salt marsh can be predicted using published models when a suitable coefficient is incorporated to account for drag, which varies in place and time due to differences in plant characteristics and abiotic conditions (i.e., bed gradient, initial water depth, and wave action).

Wetlands and coastal water quality: Should wetland size matter?

Generally, wetlands are thought to perform water purification functions, removing contaminants as water flows through sediment and vegetation. This paradigm was challenged when Grant et al. (2001) reported that Talbert Salt Marsh (Figure 1.) increased fecal indicator bacteria (FIB) output to coastal waters, contributing to poor coastal water quality. Like most southern California wetlands, Talbert Salt Marsh has been severely degraded. It is a small (10 ha), restored wetland, only 1/100th its original size, and located at the base of a highly urbanized watershed. Is it reasonable to expect that this or any severely altered wetland will perform the same water purification benefits as a natural wetland? To determine how a more pristine southern California coastal wetland attenuated bacterial contaminants, we investigated FIB concentrations entering and exiting Carpinteria Salt Marsh (Figure 2.), a 93 ha, moderate-sized, relatively natural wetland.(PDF contains 4 pages