Grey Mangrove Research Articles

Inverse relationship between salinity and n-alkane δD values in the mangrove Avicennia marina

Hydrogen isotope ratios in lipids derived from mangroves have the potential to be used for paleohydrologic reconstructions and could serve as a much needed tool for establishing past climate variability in the tropics. We assessed the effect of salinity on the apparent fractionation factor, αa, between mangrove derived n-alkanes and their source water for Avicennia marina (gray mangrove) specimens collected along a 28PSU salinity gradient in the Brisbane River Estuary. Our results indicate that there is an inverse relationship between the apparent fractionation factor and salinity. This salinity effect is large enough to override variability in the isotopic composition of source water, which plays a dominant role in determining the hydrogen isotope ratio of leaf waxes in other vascular plants. We suggest that this relationship may be due to (i) increased discrimination against deuterium during water uptake at high salinity, (ii) increased production of compatible solutes from D enriched pyruvate at high salinity, resulting in more hydrogen from D depleted NADPH being incorporated in leaf waxes, and/or (iii) increased secretion of salty brine by leaves at high salinity, resulting in (iii.a) higher relative humidity at the leaf surface, and (iii.b) introducing the possibility that D depleted water of hydration is absorbed by the leaf. Our results indicate that hydrogen isotope ratios of mangrove lipid biomarkers can be developed as a paleosalinity indicator. They also imply that care must be taken when interpreting hydrogen isotopic variations in non-source specific higher plant lipids in sediments where both mangrove and non-mangrove plants contribute organic material.

Nutrient and nitrogen isotope monitoring of an aquaculture fishery in North Queensland, Australia

A one-time monitoring event was initiated by an aquaculture fishery in North Queensland to assess if the discharges from the aquaculture fishery were increasing nutrient input into the Great Barrier Reef Marine Park. Leaf samples from Avicennia marina (grey mangrove) were used to compare the nitrogen (N) and phosphorous (P) concentrations, and δ15N values in the receiving waters of the adjacent creeks and a set of reference sites established in a neighbouring creek. The same indicators were also measured in macroalgae from the nutrient extraction ponds. The mangrove leaves in the Mixing Zone of the receiving creek were slightly elevated in N concentrations (22 mg g−1 compared to 17.5 mg g−1 at the Reference sites) and δ15N values (6.5 compared to 4.5 at the Reference sites) showing there was an influence from the outputs of the aquaculture fishery. However, P concentrations were the same in the Mixing Zone and Reference sites. Downstream of the Mixing Zone, the concentration of N and P, and the δ15N values in the Receiving Waters were the same as the Reference sites, at levels considered normal in other studies. These results show that aquaculture fisheries can be managed to maintain nutrients at reference levels in mangrove foliage in estuaries of the receiving zones.

Expression of a cloned sweet potato catalase SPCAT1 alleviates ethephon-mediated leaf senescence and H 2O 2 elevation

In this report a full-length cDNA, SPCAT1, was isolated from ethephon-treated mature L3 leaves of sweet potato. SPCAT1 contained 1479 nucleotides (492 amino acids) in its open reading frame, and exhibited high amino acid sequence identities (ca. 71.2–80.9%) with several plant catalases, including Arabidopsis, eggplant, grey mangrove, pea, potato, tobacco and tomato. Gene structural analysis showed that SPCAT1 encoded a catalase and contained a putative conserved internal peroxisomal targeting signal PTS1 motif and calmodulin binding domain around its C-terminus. RT-PCR showed that SPCAT1 gene expression was enhanced significantly in mature L3 and early senescent L4 leaves and was much reduced in immature L1, L2 and completely yellowing senescent L5 leaves. In dark- and ethephon-treated L3 leaves, SPCAT1 expression was significantly enhanced temporarily from 0 to 24 h, then decreased gradually until 72 h after treatment. SPCAT1 gene expression levels also exhibited approximately inverse correlation with the qualitative and quantitative H 2O 2 amounts. Effector treatment showed that ethephon-enhanced SPCAT1 expression was repressed by antioxidant reduced glutathione, NADPH oxidase inhibitor diphenylene iodonium (DPI), calcium ion chelator EGTA and de novo protein synthesis inhibitor cycloheximide. These data suggest that elevated reactive oxygen species H 2O 2, NADPH oxidase, external calcium influx and de novo synthesized proteins are required and associated with ethephon-mediated enhancement of sweet potato catalase SPCAT1 expression. Exogenous application of expressed catalase SPCAT1 fusion protein delayed or alleviated ethephon-mediated leaf senescence and H 2O 2 elevation. Based on these data we conclude that sweet potato SPCAT1 is an ethephon-inducible peroxisomal catalase, and its expression is regulated by reduced glutathione, DPI, EGTA and cycloheximide. Sweet potato catalase SPCAT1 may play a physiological role or function in cope with H 2O 2 homeostasis in leaves caused by developmental cues and environmental stimuli.

Has the Herbicide Diuron Caused Mangrove Dieback? A Re-Examination of the Evidence

ABSTRACT The claim that the herbicide Diuron in agricultural runoff caused dieback of the grey mangrove (Avicennia marina) in Central Queensland, Australia, has influenced government policies including programs to save the Great Barrier Reef. Several investigations on mangrove dieback in Central Queensland river estuaries have been published during the past decade. However, proof of a causal link between mangrove dieback and Diuron remains inconclusive. This study presents a systematic review of the evidence using Hill's Criteria of Causation. Our review shows that using concentrations of the chemical bound to sediment as a measure for biological availability in either glasshouse or field studies is inappropriate. The appropriate measure is Diuron concentration in solution and this parameter bears no simple relationship to concentration bound to sediment, and is not strongly correlated with mangrove health. Only when the herbicide is applied in experimental investigations at many orders of magnitude higher than measured in rivers has an impact on A. marina been demonstrated. Evidence from field studies suggests burial of pneumatophores, the plant's breathing roots, following flood events is a more likely causal factor in mangrove dieback, whereas any contribution from Diuron remains unproven.

Effect of runoff from acid-sulfate soils on pneumatophores of the grey mangrove, Avicennia marina

Runoff from acid-sulfate soils (ASS) is increasingly threatening the structure and function of estuarine ecosystems worldwide. Along the eastern coast of Australia, sulfuric acid is known to affect the growth and survival of mangrove saplings; however, impacts of ASS runoff on the structure and function of established mangrove trees are unclear. Pneumatophores, the aerial roots produced by some species of mangrove, are critical sites of gas exchange, allowing these species to persist in waterlogged soils. They also provide physical structure in estuarine sediments, facilitating communities of algae, invertebrates and, at high tide, fish. We tested the hypotheses that Avicennia marina (Forsk.) Vierh. pneumatophores would be less abundant, shorter, thinner and weaker close to major ASS outflow drains. Sampling at sites close to and away from drains within each of two estuaries of New South Wales, Australia, showed no effect of exposure to runoff on pneumatophore density or thickness. Pneumatophores were, however, shorter (~2 cm) and weaker (up to two-fold) at ASS-affected than reference sites. Although the reduced length and strength of pneumatophores at acidified sites may limit the number of epifaunal molluscs they can support, the persistence of dense pneumatophores indicates that the capacity to benefit invertebrates and fish remains.

Bioavailability and Concentration of Heavy Metals in the Sediments and Leaves of Grey Mangrove, Avicennia marina (Forsk.) Vierh, in Sirik Azini Creek, Iran

The concentration and bioavailability of Ni, Cu, Cd, Zn, and Pb in the sediments and leaves of grey mangrove, Avicennia marina, were studied throughout Sirik Azini creek (Iran) with a view to determine heavy metals bioavailability, and two methods were used. Results show that Zn and Ni had the highest concentrations in the sediments, while Cd and Cu were found to have the lowest concentrations in the sediments. Compared to the mean concentrations of heavy metals in sedimentary rock (shales), Zn and Cu showed lower concentration, possibly indicating that the origin of these heavy metals is natural. A geo-accumulation index (Igeo) was used to determine the degree of contamination in the sediments. Igeo values for Zn, Cu, Pb, and Ni showed that there is no pollution from these metals in the study area. As heavy metal concentrations in leaves were higher than the bioavailable fraction of metals in sediments, it follows that bioconcentration factors (leaf/bioavailable sediment) for some metals were higher than 1.

The influence of nutrient enrichment upon mangrove seedling establishment and growth in the Hawkesbury River Estuary, New South Wales, Australia

The hypothesis that mangrove exclusion from saltmarsh is attributable to nutrient deficiency is experimentally tested on the Hawkesbury River estuary. Survivorship and growth of seedlings of the grey mangrove Avicennia marina were followed for a sixteen month period, in an experiment in which half of all seedlings were treated with a slow-releasing source of phosphorus, nitrogen and potassium. While fertilisation substantially increased growth rate, this occurred in the second summer of growth and fertilisation did not improve the low survivorship of A. Marina at the mangrove-saltmarsh boundary. Fertilisation has no influence on the root/shoot ratio where measured. It is postulated that factors other than nutrient deficiency are primarily responsible for determining the upslope distribution of mangroves in temperate Australian estuaries.

Changes in the distribution of mangroves in the Port Jackson-Parramatta River Estuary from 1930 to 1985.

The Division of Fisheries is mapping the historical distribution of estuarine vegetation in a number of estuaries as part of an Estuarine Inventory of New South Wales. This preliminary report outlines the changes in distribution of mangroves in the Port Jackson-Parramatta River Estuary from 1930 to 1985. The Port Jackson-Parramatta River estuary is a ria (drowned river valley) on the coast of NSW, surrounded by the cities of Sydney and Parramatta. It is composed of three arms – Middle Harbour, the Lane Cove River, and Parramatta River/Duck Creek, and a deep harbour in which they converge (see fig. 1). Two species of mangrove grow in this estuary, Avicennia marina, the grey mangrove, and Aegiceras corniculatum, the river mangrove.

Potential biological indicators of heavy metal stress in mangrove ecosystems

The effects of heavy metals Cu, Pb, and Zn on a number of biological structural components of Avicennia dominated mangrove ecosystems is reviews and their potential as biological indicators of metal stress discussed. Three main taxa groups were chosen for examination, representing key structural components of Avicennia systems at different trophic levels. As the primary producer, Avicennia marina (Forsk.) Vierh, the grey mangrove, was studied most intensely. Heloecious cordiformis (Milne Edwards, 1852), the semaphore crab, was chosen as a higher level consumer. A suite of benthic organisms were also studied, representing a range of trophic associations at the community level. Potential biological indicators of metal stress were investigated in each group, at various organisational levels. A combination of laboratory and field based experiments have shown that most biological indicators investigated have merit in terms of reflecting exposure and effect of heavy metal stress in Avicennia systems. Avciennia marina was found to be highly tolerant to Cu, Pb and Zn. Both field and laboratory studies revealed the three metals were accumulated in root tissue in proportion to sediment metal loadings, and Cu and Zn showed some limited mobility to leaf tissue. Zn was the only metal in leaf tissue. Zn was the correlated with sediment loadings. All metals in root tissue and Zn in leaves were appropriate for accumulative indication. In both field and laboratory studies, increases in peroxidase activity and decreases in photopigments (most notably the chlorophyll a/b ratio) were found with increasing Cu and Zn. Significant relationships with peroxide ase activity only, were found for Pb. Both peroxidise activity and photopigment may be employed as sensitive early warning biomarkers of metal stress in A. Marina. For H. Cordiformis, Cu and Zn were regulated in the hepatopancreas. Lead was accumulated in the hepatopancreas in proportion to sediment Pb levels, and Pb was the main metal loadings tended to support lower numbers of crabs, greater proportions of females with purple chelae (rather than orange) and less females in the population, and thus may be employed as population level indicators of metal stress. Monitoring of macrobenthic community assemblage diversity and abundance along with natural variables and low-level anthropogenic contaminnts including Cu, Pb, Zn, revealed no significant pollutant related patterns. Natural physiochemical sediment differences were found to be the main determinants in species assemblage patterns among sites. An integrated approach of both field and laboratory based testing, with a range of species measured at various organisational hierarchies, is most instructive in the assessment of metal impacts on mangrove ecosystems.

Nitrogen fertilization enhances water-use efficiency in a saline environment

Effects of salinity and nutrients on carbon gain in relation to water use were studied in the grey mangrove, Avicennia marina, growing along a natural salinity gradient in south-eastern Australia. Tall trees characterized areas of seawater salinities (fringe zone) and stunted trees dominated landward hypersaline areas (scrub zone). Trees were fertilized with nitrogen (+N) or phosphorus (+P) or unfertilized. There was no significant effect of +P on shoot growth, whereas +N enhanced canopy development, particularly in scrub trees. Scrub trees maintained greater CO(2) assimilation per unit water transpired (water-use efficiency, WUE) and had lower nitrogen-use efficiency (NUE; CO(2) assimilation rate per unit leaf nitrogen) than fringe trees. The CO(2) assimilation rates of +N trees were similar to those in other treatments, but were achieved at lower transpiration rates, stomatal conductance and intercellular CO(2) concentrations. Maintaining comparable assimilation rates at lower stomatal conductance requires greater ribulose 1.5-bisphosphate carboxylase/oxygenase activity, consistent with greater N content per unit leaf area in +N trees. Hence, +N enhanced WUE at the expense of NUE. Instantaneous WUE estimates were supported by less negative foliar delta(13)C values for +N trees and scrub control trees. Thus, nutrient enrichment may alter the structure and function of mangrove forests along salinity gradients.

Decomposition of Avicennia marina on an iron-smelting slag substrate

The present study, conducted near Newcastle, Australia, used a blocked analysis of variance experimental design to compare initial nutrient concentrations and decomposition rates of Avicennia marina (grey mangrove) grown on sand and rock blast furnace slag. There were no significant differences ( ANOVA; P > 0.05) in mean initial nutrient concentrations of total C, N and P for plants grown on the sand and slag substrates. A litterbag technique was used to estimate decomposition rates. After 360 days of incubation, repeated measures analysis did not identify significant differences between the substrates for the interaction term ‘substrate × time’ or the term ‘substrate’ for percentage weight loss or for C, N and P remaining. Avicennia marina on both substrates had nutrient characteristics and decomposition rates comparable to those found in the literature. Results suggest that initial nutrient concentration and decomposition rates are not dramatically influenced by the presence of slag.

The glutathione antioxidant system as a biomarker suite for the assessment of heavy metal exposure and effect in the grey mangrove, Avicennia marina (Forsk.) Vierh

Alterations in the glutathione antioxidant system and lipid peroxidation in Avicennia marina were studied under laboratory and field conditions. The activity of glutathione peroxidase (GPx) was found to respond to Zn exposure, and a significant positive relationship between leaf Zn concentration and GPx activity was observed after 96 h and 8 weeks. Lipid hydroperoxides increased proportionally with increasing leaf Zn concentration after 2 and 8 weeks, while no changes in total glutathione were observed. Induction of GPx at 96 h predicted effects at the individual level at a later time interval (reduced biomass at 8 weeks). Results from the field revealed that increasing leaf metal concentration (Zn, Cu or Pb) produced a proportional increase in GPx activity whereas lipid hydroperoxides and total glutathione were not affected. The utility of GPx as an early warning biomarker is suggested, since GPx activity increases in a dose-dependant fashion in response to accumulated leaf metals, and is predictive of later effects on growth.

Field records of painted apple moth (Teia anartoides Walker: Lepidoptera: Lymantriidae) on plants and inanimate objects in Auckland, New Zealand

Abstract As part of an eradication program, field searches were conducted to verify the geographical extent of the painted apple moth (PAM; Teia anartoides Walker: Lepidoptera: Lymantriidae) incursion and to determine which plants were being attacked. Most PAM were found on the wattle species, in particular Paraserianthes lophanta and Acacia mearnsii. Other species with large numbers of PAM included the native Corynocarpus laevigatus (karaka) and Avicennia marina (grey mangrove). The large number of PAM on these New Zealand species would not have been predicted from the known unrelated Australian hosts. The relatively high number of PAM found on inanimate objects demonstrated the mobility of PAM larvae and that plants upon which few larvae were found may not be suitable hosts for PAM.

Seasonal and spatial variation in the distribution of mangrove macroalgae in the Clyde River, Australia

The objective of this study was to determine whether there was significant spatial and temporal variation in macroalgae epiphytic on pneumatophores of the Grey Mangrove, Avicennia marina (Forsk.) Vierh., in the Clyde River, located 280 km south of Sydney, Australia. Three estuarine sites in the Clyde River were surveyed seasonally on four occasions over a two-year period, and algal distribution and abundance assessed in respect to temporal, inter-site, intertidal (from front to back of mangrove stand) and vertical (from bottom to top of pneumatophores) variation. Sediment and water characteristics, including nutrient levels, were also assessed in order to examine all variables of potential influence on algal distribution and abundance. The results indicated that intertidal position within sites, and vertical height along the length of the pneumatophore, were the greatest influence on algal frequency and biomass. Individual species dominated in different intertidal and vertical zones. These observations, together with the identification of three species of macroalgae that fulfil the criteria for bioindicators/biomonitors of environmental impacts are discussed.

Spatial and temporal variation of nitrous oxide and methane flux between subtropical mangrove sediments and the atmosphere

We quantified spatial and temporal variations of the fluxes of nitrous oxide (N 2O) and methane (CH 4) and associated abiotic sediment parameters across a subtropical river estuary sediment dominated by grey mangrove ( Avicennia marina). N 2O and CH 4 fluxes from sediment were measured adjacent to the river (“fringe”) and in the mangrove forest (“forest”) at 3-h intervals throughout the day during autumn, winter and summer. N 2O fluxes from sediment ranged from an average of −4 μg to 65 μg N 2O m −2 h −1 representing N 2O sink and emission. CH 4 emissions varied by several orders of magnitude from 3 μg to 17.4 mg CH 4 m −2 h −1. Fluxes of N 2O and CH 4 differed significantly between sampling seasons, as well as between fringe and forest positions. In addition, N 2O flux differed significantly between time of day of sampling. Higher bulk density and total carbon content in sediment were significant contributors towards decreasing N 2O emission; rates of N 2O emission increased with less negative sediment redox potential ( E h). Porewater profiles of nitrate plus nitrite (NO x −) suggest that denitrification was the major process of nitrogen transformation in the sediment and possible contributor to N 2O production. A significant decrease in CH 4 emission was observed with increasing E h, but higher sediment temperature was the most significant variable contributing to CH 4 emission. From April 2004 to July 2005, sediment levels of dissolved ammonium, nitrate, and total carbon content declined, most likely from decreased input of diffuse nutrient and carbon sources upstream from the study site; concomitantly average CH 4 emissions decreased significantly. On the basis of their global warming potentials, N 2O and CH 4 fluxes, expressed as CO 2-equivalent (CO 2-e) emissions, showed that CH 4 emissions dominated in summer and autumn seasons (82–98% CO 2-e emissions), whereas N 2O emissions dominated in winter (67–95% of CO 2-e emissions) when overall CO 2-e emissions were low. Our study highlights the importance of seasonal N 2O contributions, particularly when conditions driving CH 4 emissions may be less favourable. For the accurate upscaling of N 2O and CH 4 flux to annual rates, we need to assess relative contributions of individual trace gases to net CO 2-e emissions, and the influence of elevated nutrient inputs and mitigation options across a number of mangrove sites or across regional scales. This requires a careful sampling design at site-level that captures the potentially considerable temporal and spatial variation of N 2O and CH 4 emissions.

Purification and Partial Characterization of an Acidic Polysaccharide with Complement Fixing Ability from the Stems of Avicennia Marina

An acidic polysaccharide fraction that had high anticomplementary activity was isolated from the stems of Grey Mangrove in 0.15% yield. The final fractions was designated HAM-3-IIb-II. The polysaccharide fraction appeared to be homogenous by high performance size exclusion chromatography with an estimated molecular weight of 105 kDa. The isolated polysaccharide is more effective than polysaccharide K (PSK) in its anticomplementary activity at 58 microg/ml of PSK and 23 microg/ml of HAM-3-IIb-II that inhibit 50% of complement activity in the complement fixation assay. Structural studies indicated that HAM-3-IIb-II was rich in galacturonic acid along with arabinose, galactose and rhamnose, characterizing a pectin-type polysaccharide, which was also confirmed by FT-IR spectrum. The presence of rich neutral sugar side chains of arabinogalactans may have contributed to the expression of high activity. Traditionally, this mangrove plant is used for medicinal purposes and it appears to have some scientific applications.

Monitoring expression profiles of antioxidant genes to salinity, iron, oxidative, light and hyperosmotic stresses in the highly salt tolerant grey mangrove, Avicennia marina (Forsk.) Vierh. by mRNA analysis

Plant photosynthesis results in the production of molecular oxygen. An inevitable consequence of this normal process is the production of reactive oxygen species (ROS) by the transfer of electrons to molecular oxygen. Plants are adequately protected by the presence of multiple antioxidative enzymes in different organelles of the plant such as chloroplasts, cytosol, mitochondria and peroxisomes. Under high light and CO(2) limiting conditions caused by environmental stress like salinity, these antioxidative enzymes play an important role in scavenging toxic radicals. To investigate the functions of antioxidative enzymes in a mangrove plant, we isolated three cDNAs encoding cytosolic Cu-Zn SOD (Sod1), catalase (Cat1) and ferritin (Fer1) from Avicennia marina cDNA library. Sod1, Cat1 and Fer1 cDNA encoded full-length proteins with 152, 492 and 261 amino acids respectively. We studied the expression of these antioxidant genes in response to salt, iron, hydrogen peroxide, mannitol and light stress by mRNA expression analysis. Cat1, Fer1 showed short-term induction while Sod1 transcript was found to be unaltered in response to NaCl stress. A decrease in mRNA levels was observed for Sod1, Cat1 while Fer1 mRNA levels remained unaltered with osmotic stress treatment. Sod1, Cat1 and Fer1 mRNA levels were induced by iron, light stress and by direct H(2)O(2) stress treatment, thus confirming their role in oxidative stress response.

Zonal and seasonal variation in the distribution and abundance of mangrove macroalgae in the Parramatta River, Australia

The purpose of this study was to examine the spatial and temporal variation of macroalgae epiphytic on pneumatophores of the Grey mangrove, Avicennia marina (Forsk.) Vierh., in the Parramatta River, the major estuarine system flowing into Sydney Harbour. No previous studies have examined algal distribution in three spatial dimensions (along the mid-saline length of a river, from front to back of mangrove stand, and from bottom to top of pneumatophores), simultaneously with their temporal variation within mangrove stands. Three sites in the Parramatta River, Australia, were surveyed seasonally on four occasions over a two-year period, and algal distribution and biomass assessed with respect to temporal, site, intertidal and vertical variation. Sediment and water characteristics, including nutrient levels, were also assessed in order to examine all variables that may be influencing algal distribution and abundance. The results indicated that intertidal position within sites (front, middle and back zones of the intertidal mangrove stands) was the factor of greatest influence on algal frequency and biomass, with individual species dominating in different zones. This observation together with the identification of four species of macroalgae that fulfill the criteria for bioindicators of environmental impacts are discussed.

Study of gray mangrove (Avicennia marina) afforestation for greening of desert coasts : Gray mangrove afforestation on banks of artificial channel across a sabkha and the established biotic community

Study of gray mangrove (Avicennia marina) afforestation for greening of desert coasts : Gray mangrove afforestation on banks of artificial channel across a sabkha and the established biotic community

Changes in the distribution of the grey mangrove Avicennia marina (Forsk.) using large scale aerial color infrared photographs: are the changes related to habitat modification for mosquito control?

Runnelling, a method of habitat modification used for mosquito management in intertidal saltmarshes in Australia, alters marsh hydrology. The objective of this research was to assess if runnelling had affected the distribution of the grey mangrove ( Avicennia marina (Forsk.)) at a study site in southeast Queensland. Since runnelling is carried out in diverse marshes a second aim was to assess differences in mangrove colonisation in the two main saltmarsh species in the area. These are marine couch [ Sporobolus virginicus (L.) Kunth.] and samphire [ Sarcocornia quinqueflora (Bunge ex Ung.-Stern.)]. Runnels at the study site were in an area dominated by Sporobolus. The mangrove area was measured by classifying digital color infrared (CIR) data obtained from aerial photographs acquired in 1982, which was 3 years before runnelling, and in 1987, 1991 and 1999, 2–14 years after. Changes in the spatial extent of A. marina were identified using difference images produced from post-classification change detection. The results showed that runnels did not significantly influence the distribution of A. marina at the study site. At a more detailed level differences in A. marina establishment in the Sporobolus and Sarcocornia areas were determined from counts of trees on the aerial photographs. There was a greater proportion of mangroves in Sarcocornia than Sporobolus and this increased over time. This may be related to differences in density between the plant species, to grapsid crab activity or to other edaphic conditions. There may be implications for runnelling in Sarcocornia marshes. The large increase observed in A. marina in the area generally is likely to be related to factors such as catchment modification or tidal/sea-level changes. It is concluded that runnelling has not led to mangrove establishment in the Sporobolus dominated saltmarsh.