Salinity drives growth dynamics of the mangrove tree Sonneratia apetala Buch. -Ham. in the Sundarbans,Bangladesh

Mangroves throughout the world are threatened by environmental changes apart from anthropogenic disturbances. Many of these changes may inhibit the growth and survival of mangrove species. To understand and predict the effects of global change on mangrove forests, it is necessary to obtain insights on the growth dynamics of mangroves in relation to environmental factors. This study was conducted on Sonneratia apetala, a mangrove species which grows under a range of salinity conditions across the Sundarbans in Bangladesh. We studied trees growing under respectively high, medium, and low salinity conditions based on the influence of freshwater discharge. First, the periodicity of radial growth across the year was detected by applying cambial analyses. Based on tree-ring analyses, we calculated the growth response of S. apetala to monthly variation in precipitation and temperature as well as river discharge, as a proxy for salinity. We found the cambium of S. apetala being active during the monsoon and post-monsoon period whereas it was dormant in the pre-monsoon. This periodicity in radial growth leads to the formation of distinct annual rings with ring boundaries being marked by radially flattened fibres. S. apetala trees growing under low salinity conditions generally show higher growth rates indicating the positive impact of river discharge, i.e. freshwater input on mangrove growth. Wet and warm conditions during the monsoon period positively affected S. apetala growth, especially in the low salinity zone. Our results show that salinity is the primary driver of growth dynamics of S. apetala in the Sundarbans. A gradual or seasonal increase in salinity, e.g. as a consequence of sea-level rise may therefore importantly alter the growth of this species, possibly leading to changes in mangrove forest dynamics and zonation.     

Allometry, above-ground biomass and nutrient distribution in Ceriops decandra (Griffith) Ding Hou dominated forest types of the Sundarbans mangrove forest, Bangladesh

The Sundarbans, the world??s largest single expanse of natural mangroves located in southern Bangladesh, is the most productive mangrove ecosystem in the world. Ceriops decandra (Griff.) Ding Hou is the dominant shrub in the strong saline zone of the Sundarbans and is mainly extracted for fuel wood, charcoal and tannin. The harvest of C. decandra has decreased by about 50?% in the Sundarbans during the last 10?years creating a major concern. This study derived allometric models of above-ground biomass and estimated of above-ground standing and harvestable biomass and nutrient stock in C. decandra in dominant forest types (C. decandra and C. decandra?CExcoecaria agallocha) in the Sundarbans. Allometric relationships between collar girth (CG) and biomass of plant parts (leaf, branch and stem) were tested using linear, power and logarithmic equations. The power equation was found to be most suitable. The density and the estimated total aboveground biomass of C. decandra in C. decandra and C. decandra?CE. agallocha forest types were 33,237 and 965?stems/ha (density) and 33.49 and 14.36?t/ha (biomass), respectively. Also, 13.56 and 6.61?t/ha of harvestable biomass were estimated, from C. decandra and C. decandra?CE. agallocha forest types, respectively. Nitrogen, potassium and phosphorus concentrations in the leaves, branches and stems showed significant (p?<?0.05) variation. The findings of the present study will help to quantify the impact of present harvesting techniques and alteration of different silvicultural intervention like fixation of felling cycle, felling criterion, and regeneration and slash treatment.     

Climatic Signals in Tree Rings of Heritiera fomes Buch.-Ham. in the Sundarbans,Bangladesh

Mangroves occur along the coastlines throughout the tropics and sub-tropics, supporting a wide variety of resources and services. In order to understand the responses of future climate change on this ecosystem, we need to know how mangrove species have responded to climate changes in the recent past. This study aims at exploring the climatic influences on the radial growth of Heritiera fomes from a local to global scale. A total of 40 stem discs were collected at breast height position from two different zones with contrasting salinity in the Sundarbans, Bangladesh. All specimens showed distinct tree rings and most of the trees (70%) could be visually and statistically crossdated. Successful crossdating enabled the development of two zone-specific chronologies. The mean radial increment was significantly higher at low salinity (eastern) zone compared to higher salinity (western) zone. The two zone-specific chronologies synchronized significantly, allowing for the construction of a regional chronology. The annual and monsoon precipitation mainly influence the tree growth of H. fomes. The growth response to local precipitation is similar in both zones except June and November in the western zone, while the significant influence is lacking. The large-scale climatic drivers such as sea surface temperature (SST) of equatorial Pacific and Indian Ocean as well as the El Niño-Southern Oscillation (ENSO) revealed no teleconnection with tree growth. The tree rings of this species are thus an indicator for monsoon precipitation variations in Bangladesh. The wider distribution of this species from the South to South East Asian coast presents an outstanding opportunity for developing a large-scale tree-ring network of mangroves.     

Vegetation dynamics in the Bangladesh Sundarbans mangroves: a review of forest inventories

The Sundarbans, the largest contiguous mangrove forest in the world, covers 6,017 km² of the coastal zone of Bangladesh. Heritiera fomes Buch.-Ham., Excoecaria agallocha L. and Ceriops decandra (Griff.) Ding Hou jointly cover 95% of the forest area. In this study, the results of four forest inventories have been analyzed to understand observed vegetation dynamics of the Sundarbans from 1926 to 1997. The diversity of forest types has been gradually reduced over time, but H. fomes and E. agallocha have maintained their dominance over large portions of the forest. H. fomes is spread over 67% of the vegetated area of the forest, concentrated mostly in the northeastern area, and constitutes 75% of the density of trees with >15 cm dbh. The distribution and stem density of H. fomes show negative relationships with that of E. agallocha and C. decandra. In terms of coverage, E. agallocha is the most common species, spread over 74% of the vegetated area of the forest, and constitutes 39% of the density of trees with >2.5 cm dbh. On a longer timeframe (1926–1997), the dominance (coverage and density of larger diameter trees) of H. fomes as well as that of E. agallocha is declining. Even on parameters such as density of trees with >15 cm dbh, the dominance of E. agallocha is declining at a much greater rate than H. fomes. This observation contradicts the successional schemes proposed by different authors. This might indicate that theorizing successional schemes based on short-term observations on vegetation dynamics is not sufficient. The effect of human interference, changes in hydroedaphic condition and species interaction should be taken into consideration during explaining observed vegetation dynamics. Moreover, the need to understand vegetation trajectories at the micro-scale should be emphasized.     

Leaf morphological plasticity in three dominant tree species in the Sundarbans mangrove forest of Bangladesh in different salinity zones

Mangrove tree species show plasticity in their leaf morphological traits in different salinity zones. However, leaf morphological plasticity and its causes in different salinity zones are incompletely understood. To understand the mechanism of plasticity, this study investigated the responses of three dominant tree species Sundri (Heritiera fomes), Gewa (Excoecaria agallocha) and Goran (Ceriops decandra) of the Sundarbans to the salinity gradients. A total of 17 leaf parameters were measured and quantified. All collected data were analyzed using univariate and multivariate statistical tools to investigate leaf morphological plasticity. A wide range of phenotypic plasticity was observed in all leaf parameters studied among the salinity zones of the Sundarbans. One-way ANOVA and Tukey’s posthoc test revealed significant differences (P?<?0.05) in all leaf parameters among the salinity zones and confirming that there was a high degree of phenotypic plasticity among the salinity zones of the Sundarbans. Petiole length (PL), leaf area (LA) and leaf length/petiole length (LL/PL) showed high level of plasticity among the salinity zones of the Sundarbans for each species of Sundri, Gewa and Goran. Plasticity index (PI) was developed in this study for each species studied. High level of phenotypic plasticity in these leaf traits reflects fitness of these species to different saline environments. Our results provide clear evidence that all the leaf parameters measured for three tree species viz., Sundri, Gewa and Goran effectively utilizes a plastic strategy in different salinity zones in the Sundarbans. Morphological trait plasticity could serve as powerful biological indicators to predict the shift of leaf morphology in upcoming environmental change events like sea level rise and reduction of fresh water flow from upstream.

     

Abundance and seasonal distribution of Penaeus monodon postlarvae in the Sundarbans mangrove,Bangladesh

We record the decline of Penaeus monodon postlarvae (PL) in five rivers of the world's largest mangrove ecosystem, the Sundarbans, from 1992 to 1999. Shrimp aquaculture in the coastal belt of Bangladesh is dependent on the collection of P. monodon PL from the coastal rivers, and horizontal expansion of shrimp farming has resulted in a severe decline of this wild resource in the Sundarbans. Abundance of P. monodon PL was significantly (P<0.05) reduced in 1999 compared to the previous two-year studies (1992 and 1995) in the rivers. About 12–551 postlarvae of other shrimps, 5–152 finfish postlarvae and 26–1636 other macro-zooplankters are wasted during the collection of a single P. monodon PL. Water temperature and salinity of the river systems are correlated with P. monodon PL abundance. Besides P. monodon PL, inshore fishery of Hilsa ilisha, catfishes and Scylla serrata are also overexploited. The management practices and conservation of fishery resources of Sundarbans are reviewed in the context of its world heritage status.     

Do rivers influence fine-scale population genetic structure of tigers in the Sundarbans?

Global tiger Panthera tigris populations mostly survive within the geographically fragmented forest patches, thereby limited genetic exchange between isolated populations. Assessing the genetic status of these populations can reveal the effects of dispersal barriers and provide critical insights to guide future conservation actions. Using non-invasively collected biological samples, we investigated fine-scale genetic structure of tigers in the Sundarbans mangrove forests intersected by the complex river systems, and which holds one of the largest global tiger populations. We genotyped 52 tiger samples at 10 polymorphic microsatellite loci, and sequenced 33 of them for a total of 1263 base-pairs at four mitochondrial gene fragments. Microsatellite analyses exhibit a signature of fine-scale genetic structure, which might have been the consequence of limited tiger dispersal due to wide rivers across the Sundarbans. Similarly, mitochondrial data show a historic pattern of population isolation that might be due to wider rivers across the entire Sundarbans shared by Bangladesh and India. Given the intrinsic nature of the mangrove habitat embedded with numerous rivers, increased commercial traffic and human activities may further impede tiger dispersal across wide rivers, escalating further genetic isolation of the Sundarbans tigers.     

Hydrographic Status of Sundarbans Mangrove, Bangladesh with Special Reference to Post-larvae and Juveniles Fish and Shrimp Abundance

Environmental factors, including water parameters were correlated with assemblages of shell and finfish post-larvae and juveniles in the 5 rivers of Sundarbans mangrove for 2 years, located in the south-west of Bangladesh. Fifteen species of shellfish belonging to 6 families and 37 species of finfish belonging to 27 families were recorded. Four species of shrimp (Metapenaeus monoceros, M. brevicornis, Macrobrachium villosimanus and Acetes spp.) and megalopa of crabs (79.3–96.83%), and 4 species of finfish (Panchax melastigma, Liza parsia, L. tade and Gobidae) (40–76%) were the most abundant species. Significant (p<0.05) inter-month variations in temperature, transparency and chlorophyll-a; inter-month and inter-river variations in salinity, conductivity and TDS were observed in the Sundarbans water. Ordination on correlation coefficients between temperature and salinity with the abundance of dominant species showed that Acetes spp. and Gobidae were abundant in high salinity and high temperature areas; Stolephorus tri in low salinity and high temperature areas; Macrobrachiun villosimanus, Leiognathus spp. and Liza tade in low salinity and low temperature areas, however, other species showed variations among 2 years of study. Out of 7 dominant shellfishes, 4 species showed positive correlation to temperature, pH and TDS; 3 species to salinity, transparency, conductivity and chlorophyll-a in the river water. Among 8 dominant fish species, 4 species were found to positively correlate with temperature and pH; 3 with salinity, conductivity and chlorophyll-a; 6 with transparency and 5 species showed positive correlation to TDS in Sundarbans water. Abundance of Penaeus monodon also showed positive correlation to observed water parameters except chlorophyll-a.     

Stable soil pH of thai mangroves in dry and rainy seasons and its relation to zonal distribution of mangroves

Soil characteristics of mangrove forests at Amphur Laemngob, Trat Province, east Thailand were investigated in both dry andrainy seasons. Sonneratia alba, Avicennia alba andRhizophora mucronata mainly grew as seaward mangroves.Rhizophora apiculata, Ceriops tagal, Excoecaria agallocha andBruguiera gymnorrhiza grew as meso mangroves in most cases.Lumnitzera racemosa was found as a landward mangrove. The salinity of the soil in which these 8 species grew was significantly higher in the dry season than in the rainy season. Soil pH did not change irrespective of the season. Each species seemed to grow at inherent soil pH. Bruguiera gymnorrhiza, Sonneratia alba andAvicennia marina were found both in Japan and Thailand. The soil pH of each mangrove species was similar in Japan and Thailand. The soil salinity of each mangrove species in Japan was similar to that in Thailand in the dry season. It was suggested that soil pH and salinity in the dry season are the important factors governing the zonal distribution of mangroves.     

Importance of mangrove plantations for climate change mitigation in Bangladesh

Mangroves have been identified as blue carbon ecosystems that are natural carbon sinks. In Bangladesh, the establishment of mangrove plantations for coastal protection has occurred since the 1960s, but the plantations may also be a sustainable pathway to enhance carbon sequestration, which can help Bangladesh meet its greenhouse gas (GHG) emission reduction targets, contributing to climate change mitigation. As a part of its Nationally Determined Contribution (NDC) under the Paris Agreement 2016, Bangladesh is committed to limiting the GHG emissions through the expansion of mangrove plantations, but the level of carbon removal that could be achieved through the establishment of plantations has not yet been estimated. The mean ecosystem carbon stock of 5–42 years aged (average age: 25.5 years) mangrove plantations was 190.1 (±30.3) Mg C ha⁻¹, with ecosystem carbon stocks varying regionally. The biomass carbon stock was 60.3 (±5.6) Mg C ha⁻¹ and the soil carbon stock was 129.8 (±24.8) Mg C ha⁻¹ in the top 1 m of which 43.9 Mg C ha⁻¹ was added to the soil after plantation establishment. Plantations at age 5 to 42 years achieved 52% of the mean ecosystem carbon stock calculated for the reference site (Sundarbans natural mangroves). Since 1966, the 28,000 ha of established plantations to the east of the Sundarbans have accumulated approximately 76,607 Mg C year⁻¹ sequestration in biomass and 37,542 Mg C year⁻¹ sequestration in soils, totaling 114,149 Mg C year⁻¹. Continuation of the current plantation success rate would sequester an additional 664,850 Mg C by 2030, which is 4.4% of Bangladesh's 2030 GHG reduction target from all sectors described in its NDC, however, plantations for climate change mitigation would be most effective 20 years after establishment. Higher levels of investment in mangrove plantations and higher plantation establishment success could contribute up to 2,098,093 Mg C to blue carbon sequestration and climate change mitigation in Bangladesh by 2030.     

Climate change impacts on Indian Sunderbans: a time series analysis (1924–2008)

Climate change induced sea level rise (SLR) added with anthropogenically altered environment leads to rapid land dynamics in terms of erosion and accretion; and alteration in species diversity and productivity, more pronouncedly in sensitive ecosystems such as river deltas. Here, we tried to analyze the historical records to understand the SLR with respect to hydrological conditions, sedimentation and morphological processes. We analyzed the land transformation of few islands in Indian Sunderbans using maps and satellite images in increasing order of temporal frequency between 1924 and 2008, which revealed that both the erosion and accretion processes go hand in hand. Increase of downstream salinity due obstruction in upstream has led to decrease in transparency of water causing decrease in phytoplankton and fish, density and diversity in the central sector of Indian Sunderbans. Analysis of the above ground biomass of three dominant mangrove species (Sonneratia apetala, Avicennia alba and Excoecaria agallocha) revealed better growth in the western sector compared to the central sector. The study reveals the cumulative effect of climate change and anthropogenic disturbance on the diversity and productivity in World’s largest ecosystem; and advocates mangrove plantation and effective management of freshwater resources for conservation of the most vulnerable and sensitive ecosystem.     

Cambial dormancy induced growth rings in <Emphasis Type="Italic">Heritiera fomes</Emphasis> Buch.- Ham.: a proxy for exploring the dynamics of Sundarbans,Bangladesh

Key message

Cambial marking experiment and cambial activity analysis offer strong evidence on existence of annual growth rings in Heritiera fomes and revealing the potential of dendrochronological applications in Bangladesh mangroves.

Abstract

Despite enormous significance in coastal protection, biodiversity conservation and livelihood support to the local communities, mangrove ecosystems have been continuously degrading mainly due to anthropogenic disturbances and climate change. Time series based on dated tree ring is an option to identify the causes of forest dilapidation. In this study, we investigated the structure and periodicity of the growth ring in Heritiera fomes, the flagship tree species of the Bangladesh Sundarbans, combining cambial marking experiment and cambial activity analysis. Distinct growth rings were found which are delineated by a band of marginal parenchyma, predominantly one cell wide but up to three and occasionally interrupted with fiber. Of the 13 trees with cambium marking experiment, one growth ring was found in each tree during a year. The dormant cambium was characterized by the abrupt boundary between xylem and cambial zone, absence of enlarging or differentiating cambial derivatives, lower number of cambial cells and thicker radial walls in cambial cells. Growth ring anomalies, i.e., wedging and partially missing rings were also found. In most of the cases, the lower part of the eccentric discs had low radial increment (<0.75 mm) and therefore the growth ring in that area merged with previous one and produced wedging or partially missing ring. However, the existence of annual rings suggests its great potential for future dendrochronological applications to reveal the dynamics of vegetation and climate in Sundarbans.

     

Testing patterns of zonation in mangroves: scale dependence and environmental correlates in the Sundarbans of Bangladesh

Summary 1  Associations between abiotic variables and patterns of species distribution and abundance are a major preoccupation of community ecologists. In many habitats, this association is manifest in discrete zones of vegetation.
2  We used statistical methods to examine tree species distribution patterns in relatively undisturbed regions of the Sundarbans of Bangladesh. We tested the hypothesis that mangroves occur in discrete zones with respect to elevation. These data were gathered with explicit attention to local and regional differences in edaphic characteristics so that species-environment relationships could be analysed at several spatial scales.
3  Correlations were also assessed between mangrove species composition and edaphic variables that co-vary with elevation, i.e. salinity, field capacity, cation exchange capacity, percentage silt, and mangrove physiognomic category (slope, basin, levee and flat).
4  Quantitative statistical analysis using randomization techniques failed to detect species zonation along any of 33 individual 200-m transects, within 1-km² blocks, or within 1200-km² regions.
5  Canonical correspondence analysis relating edaphic variables to species distributions accounted for a total of only 24% of the variance in species composition.
6  Our data suggest that the absence of zonation in the Bangladesh Sundarbans reflects the underlying biology of the system and is not an artefact of long-term human disturbance.     

Salinity mediated biochemical changes towards differential adaptability of three mangroves from Indian Sundarbans

Cellular ion homeostasis through osmotic adjustment and efficient free radical scavenging ability are considered as fundamental salt tolerance determinants of plants. Increased salinity (~30 ppt) in Indian Sundarbans has incurred detrimental impact on vegetation pattern, and leading to the precarious existence of some taxa. A comparative account on some physiological and biochemical determinants towards salt stress were assayed in order to focus on the extent of adaptability among the three true mangroves. An in vitro experiment was carried out with mangrove seedlings of Avicennia marina, Bruguiera gymnorrhiza and Heritiera fomes in differential NaCl treatments. Among the five sets of treatment (0, 100, 200, 300 and 400 mM), leaf osmotic potential (ψ) shows consistent hike in A. marina and B. gymnorrhiza along the salinity gradient, at least up to 300 mM (77 and 58 % respectively over control) and comparatively poor in 400 mM. On the other hand, H. fomes reaches its maximum OP value in 200 mM NaCl treatment (64 % increment from control). Thin layer Chromatography was employed for assessing seven free amino acids and spectrophotometric quantification of them from leaf tissues grown in different salinity gradients were performed. The two antioxidative enzymes (Peroxidase and Superoxide dismutase) were estimated qualitatively and quantitatively in three taxa at different salinity level. As compared to other two taxa, H. fomes depicted fewer numbers of isoforms of two enzymes in PAGE analysis, and less enzyme activity across the salinity gradients. Considering the studied parameters, H. fomes might be endorsed towards the feeble adaptability in the present day’s elevated salinity of Indian Sundarbans.     

Protein and enzymes regulations towards salt tolerance of some Indian mangroves in relation to adaptation

Elevated substrate salinity and anthropogenic impulse are the major threat to the mangrove ecosystem. In the Indian subcontinent, Sundarbans have the richest mangrove species diversity. Due to geomorphic characteristics and unplanned management, the elevated salinity prevails in the western part and that has direct impact on vegetation. Seven mangrove taxa were examined, of which four (Aegialitis rotundifolia, Heritiera fomes, Xylocarpus granatum, and X. mekongensis) were considered as degrading and three (Bruguiera gymnorrhiza, Excoecaria agallocha, and Phoenix paludosa) were considered as natural control. The targeted taxa were collected from five different islands and were selected on the basis of increasing salinity gradient. As salinity increased from site I to V (11.76–15.2 ppt), the amount of total leaf proteins decreased in all the targeted species and ranged between 5.67 and 25.23%. The percentage of protein depletion was less in Aegialitis, Heritiera, and Xylocarpus than the other three taxa in higher salinity that pointed out their less adaptability, as degradation of protein may be essential for efficient stress management. Two antioxidative (peroxidase and superoxide dismutase) and two hydrolyzing (acid phosphatase and esterase) enzymes showed a positive correlation with salinity. In four degrading taxa, the percentage of enzyme increment was less than those of their natural control taxa. Salinity imposed increment of antioxidant enzymes facilitate ROS scavenging, which is an inevitable elevated byproduct during photo-inhibition. Lower amount and number of isoforms in higher salinity indicated towards less suitability of Aegialitis rotundifolia, Heritiera fomes, Xylocarpus granatum, and X. mekongensis in increased salinity level of western Sundarbans.     

漳江口红树植物群落周转对大型底栖动物群落结构的影响

在城市化的背景下,探明不同大型底栖动物群落对植物群落变化的响应,对红树林生态系统的健康评价和退化生态系统的修复具有重要意义。以福建漳江口国家级红树林自然保护区为研究对象,揭示红树植物群落周转对不同大型底栖动物群落结构（蟹类和软体动物）的影响,并分析其与环境参数的关联性。结果表明：在1.6 km的地理尺度上,漳江口红树林湿地的环境变化较大,表现出7.19个环境梯度。在此地理尺度的环境梯度上,红树植物群落由5种红树植物组成,其平均周转率为76%;软体动物群落由12种软体动物以模块化和非随机的方式聚集,其平均周转率为83%,并随红树植物群落周转出现显著非线性增加,盐度和老鼠簕（Acanthus ilicifolius）周转是其主要影响因素;蟹类群落则由20种蟹类以更高的模块化和非随机的方式分散,平均周转率为89%,并随红树植物群落周转而呈线性增加,主要受pH和白骨壤（Avicennia marina）周转的影响。研究揭示了大型底栖动物与植物群落和环境之间的关系,为城市化背景下红树林生态系统的保护和恢复提供基础资料。     

Effects of Salinity and Nutrient Addition on Mangrove Excoecaria agallocha

Effects of salinity on seed germination and growth of young (1 month old) and old (2-year old) seedlings of Excoecaria agallocha were investigated. Combined effects of salinity and nutrient level were also examined on old seedlings. Seed germination was best at 0 and 5 psu salinity. 15 psu salinity significantly delayed root initiation and decreased final establishment rate. All seeds failed to establish at 25 psu salinity. Young seedlings performed best at 0 and 5 psu, but growth was stunned at 15 psu, and all seedlings died within 90 days at 25 psu. Old seedlings grew best at salinities below 5 psu and they survived the whole cultivation at 25 psu. This indicated that E. agallocha increased salt tolerance over time. Gas exchange was significantly compromised by salinities above 15 psu but evidently promoted by high nutrient. Proline accumulated considerably at high nutrient, and its contents increased from 0 to 15 psu but decreased at 25 psu salinity. Lipid peroxidation was aggravated by increasing salinity beyond 15 psu but markedly alleviated by nutrient addition. These responses indicated that E. agallocha was intolerant to high salinity but it can be greatly enhanced by nutrient addition.     

Development of a salinity-secondary flow-approach model to predict mangrove spreading

This paper presents a new salinity-secondary flow-approach (SSA) model for identifying areas likely to be colonized by mangrove species based on two indices: water salinity concentration and river secondary flow intensity, R/W (the ratio of radius of curvature to river width). The mangrove Kandelia obovata is spreading rapidly in the Tanshui River system and therefore resulting in flooding impact to riparian wetlands; however, few studies have examined the dispersal characteristics of this species on the reach scale. According to the literature review and our observation, the salinity is the major factor in determining the spreading capabilities of mangroves. In addition, the effect of secondary flow can also facilitate mangrove invasion through the creation of bare mudflats.The case study of the Tanshui River system shows that the SSA model can be used for the determination of the habitat requirements and thus the dispersal capabilities of K. obovata. The results of the study show that the optimum conditions for the growth and dispersal of K. obovata exist in waters with mean annual salinity levels that are higher than 5 ppt (parts per thousand). Although K. obovata can survive in brackish wetlands with mean annual salinity levels lower than 5 ppt, its spreading capability is impaired. In tidal freshwater wetlands with mean annual salinity levels that are lower than 0.1 ppt, K. obovata cannot survive. The study also found that the R/W lower than 3 led to large mudflats, which provide an ideal environment for the growth of mangroves, due to the secondary flow.It shows that the SSA model can identify the potential habitat of mangrove in tidal region, so it might help with not only estuarine wetland management but also mangrove restoration project, especially for the sea level rise effect and its impact on potential mangrove invasion.     

<Emphasis Type="Italic">Daphnia galeata</Emphasis> in the deep hypolimnion: spatial differentiation of a “typical epilimnetic” species

One of the most serious threats to tropical mangrove ecosystems caused by shrimp farming activities is the poor management of pond waste materials. We hypothesise that mangroves can tolerate chemical residues discharged from shrimp farms and can be used as biofilters, but the capability of mangroves to cope with solid sediments dredged from shrimp ponds is limited. Our study in Pak Phanang, Thailand, confirmed that the excess sediments discharged from nearby shrimp ponds reduced mangrove growth rates and increased mortality rates. A series of transformed multi-temporal satellite images was used in combination with the field data to support this claim. In addition, a comparison between four dominant mangrove species revealed that Avicennia marina could tolerate sedimentation rates of >6 cm year⁻¹, while Bruguiera cylindrica tolerated sedimentation rates of 5 cm year⁻¹ (total sediment depth = 25 cm) before dying, while Excoecaria agallocha and Lumnitzera racemosa performed intermediate. This outcome implied that in our situation A. marina and to lesser extent E. agallocha and L. racemosa could be more effective as biofilters than B. cylindrica, as they may survive the sedimentation longer in the disposal areas. Further studies on the impact of sedimentation and chemical pollution of shrimp farm wastes on mangrove mortality and growth are required.     

Modern pollen rain in mangroves from San Andres Island, Colombian Caribbean

The precise characterisation of present-day mangrove ecosystems from modern pollen rain facilitates the accurate use of fossil pollen data for late Quaternary sea level and environmental reconstructions. Here, we investigate whether the analysis of pollen rain data corroborates existing floristic and structural characterisation of different mangrove types at the Caribbean island of San Andrés, Colombia. At 82 plots along 20 transects of four distinct mangrove types, samples were obtained of (i) surface sediments for pollen analysis, and (ii) a range of environmental parameters (including inundation levels, salinity and pH). This information was compared to previously sampled mangrove composition and tree basal area. In surface sediment samples 82 pollen taxa were found, from which 19 were present in the vegetation plots. However, because pollen may be transported by wind and/or watercourses, the overall floristic composition of the different forest types may not necessarily be reflected by the pollen spectra. Local vegetation (i.e. mangroves and beach) represented > 90% of the pollen spectra, while the regional one (i.e. hinterland forests) represented < 5% of it. Unlike the four mangrove types that were previously described in the vegetation, the analysis of pollen samples suggested only three distinct types of forest.The groups were characterised based on (i) the dominance of at least one of the true mangrove species from pollen data ordination and the presence of associated species, and (ii) their relationship with environmental parameters. Rhizophora was present in all plot samples, but did not contribute to forest type separation. In fact, just three true mangrove species proved reliable indicators of (i) high salinity and fringe mangroves (i.e. Avicennia), (ii) high pH levels and landward mangroves (i.e. Conocarpus), and (iii) natural or anthropogenic caused disturbance of forest stands (Laguncularia and associated Acrostichum fern). Hence our study confirms that mangrove pollen spectra can be accurately used to describe different mangrove environments for fossil based palaeoecological reconstructions.