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.     

Determinants of some leaf characteristics of Australian mangroves

Leaf characteristics reflecting the size, lifespan (longevity), moisture content (degree of succulence) and complexity of structure of 20 mangrove species were studied over several years at 13 locations along the tropical and subtropical Australian coast. These characteristics were found to fall generally within the ranges of those for woody species from other ecosystems. With the exception of one species, it was found that leaf longevity was related inversely to leaf moisture content, increasing from nearly 6 months in more succulent species to over 2 years in less succulent species. This suggested that more succulent leaves are less complex in their structure because they have less well‐developed ability to compartmentalize salt. There was a tendency also for leaf longevity to increase in species with larger leaves. These findings were consistent with the general view for land plants that leaf longevity is greater in species that have developed tolerance to environmental stress, salt particularly in the case of mangroves. Leaf tissue in such species is more robust or complex and requires greater metabolic resources in its construction; the plant is then advantaged by retaining the tissue for longer periods. Classification of the species considered here, based on their leaf longevity, moisture content and complexity, identified phylogenetically related species groupings that reflected these leaf longevity effects.     

Role of crabs in the natural regeneration of mangroves in the Sundarbans forest of Bangladesh

Abstract A study in the Bangladesh Sundarbans forest observed the impact of crabs on mangrove regeneration. Crabs were not found to cause any damage to the seedlings of experimental plots. In addition, no morphological damage attributable to crabs was observed in Rhizophora propagules collected from the forest floor. Further studies covering other areas of the forests have been suggested.     

Photosynthesis and water-use efficiency of some mangroves from Sundarbans, India

We studied seasonal fluctuations in the rates of photosynthesis, transpiration, PAR, and stomatal conductance for 16 species of true mangroves from the Sundarbans region of West Bengal. Soil salinity and pH were also measured. Leaf temperatures were almost always higher than the ambient temperature. We observed considerable seasonal (summer vs winter) as well as interspecific variations in photosynthesis, with the highest rates occurring inHeritiera fomes (13.21 pmol m^-2s^-1) andAvicennia marina (11.8 mol m^-2s^-1), and the lowest inNypa fruticans (1.56 mol m^-2s^-1) andCeriops decandra (2.32 pmol m^-2s^-1), in many species, an abrupt rise in leaf temperature retarded the photosyn-thetic process. In winter, the rate of transpiration and stomatal conductance reached their maxima inA. marina (4.83 mmol ra^-2s^-1 and 124.23 m mol m^-2s^-1, respectively) and their mimima inExcoecaria agallocha (1.85 mmol m^-2s^-1 and 49.19 mmol m^-2s^-1, respectively). In contrast, the maximum summer readings were recorded in E.agallocha (6.07 mmol m^-2s^-1 and 192.74 mmol m^-2s^-1 respectively).     

RAPD and ISSR marker mediated genetic polymorphism of two mangroves Bruguiera gymnorrhiza and Heritiera fomes from Indian Sundarbans in relation to their sustainability

Physiology and Molecular Biology of Plants - Increased salinity distresses some key species severely in Indian Sundarbans. Geomorphic characteristics coupled with demographic obligations have...     

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.     

红树植物多样性及其研究进展

红树植物是分布于热带、亚热带海岸潮间的木本植物群落。因因适应海岸带和作的生长环境形成了独特的形态结构和生理生态特性。红树林是海岸有重要价值的湿地。论述了红树植物的物 多样性、适应多样性、物侯多样性以及分子水平的多样性及其研究进展。     

ISOLATION AND CHARACTERIZATION OF CYANOBACTERIA POSSESSING ANTIMICROBIAL ACTIVITY FROM THE SUNDARBANS,THE WORLD’S LARGEST TIDAL MANGROVE FOREST1

Eight obligately halophilic, euryhaline cyanobacteria from intertidal soil were isolated in artificial seawater nutrients III (ASN‐III) medium. Antimicrobial activity, 16S rRNA gene sequences, phenotypic characters as well as growth and antibiosis in response to variable salinity, temperature, phosphate concentration, and pH were studied. Minimum inhibitory concentrations (MIC) of the extracts against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa, and multiple drug‐resistant clinical isolates ranged between 0.25 and 0.5 mg · mL⁻¹. Cytotoxicity tests showed 73%–84% human colon adenocarcinoma (HT‐29/C1) cell survival at MIC values, indicating that the extracts were nontoxic. Morphologically, six cyanobacteria were assigned to the Lyngbya‐Phormidium‐Plectonema (LPP) group B, and one each was assigned to Oscillatoria and Synechocystis genera. Glycerol, mannitol, and starch supported better photoheterotrophic growth than simpler mono‐ and disaccharides. No heterocyst formation was observed when grown under nitrogen‐starved conditions. All isolates survived 7‰ salinity, grew at minimum 32‰ salinity, and showed sustained growth throughout 32‰–82‰ salinity but matured poorly in freshwater medium supplemented with 30.0 g · L⁻¹ NaCl. Antimicrobial production occurred only at 32‰ salinity. While four of the eight isolates demonstrated sustained growth at 37°C, maximum antimicrobial activity was obtained at 25°C. All strains showed maximum growth and antimicrobial elaboration at 0.04 g · L⁻¹ phosphate. All isolates thrived at pH 9.5; six grew at pH 4.5, though antimicrobial production occurred only at pH 7.5. Molecular phylogenetic analysis based on 16S rRNA gene sequences of the filamentous isolates validated the previous taxonomic affiliations established on morphological characteristics. This is the first study of antimicrobial‐producing halophilic cyanobacteria from the mangroves.     

红树植物淹水胁迫响应研究进展

潮汐淹水是红树植物面临的主要环境胁迫之一,也是导致目前红树林造林成活率低的一个关键因子。由于长期适应于水淹生境,红树植物发育出一套适应于潮间带生长的抗淹水机制。综述了与红树植物相关的抗淹水胁迫响应机制,包括了形态结构、生长、水分和光合作用、膜脂过氧化系统和根系脱氢酶系统、内源激素和胁迫多胺等5个方面。提出应用人工潮汐系统研究红树植物的淹水抗性机理是确定不同种类红树植物的耐淹水能力的有效手段。并指出生长的研究是淹水胁迫响应研究的基础,而与分子手段相结合的激素水平的研究将在红树植物抗性胁迫研究中得到重视。     

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.     

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.     

Ring width and vessel features of the mangrove Excoecaria agallocha L. depend on salinity in the Sundarbans,Bangladesh

The Bangladesh Sundarbans is the largest continuous mangrove in the world that providing crucial environmental services, particularly related to coastal protection and livelihoods of millions of people. However, anthropogenic disturbances, diseases infestation and environmental changes including sea level rise (SLR) and fresh-water flux into the delta are threatening the Sundarbans and other mangrove ecosystems worldwide. Protection of mangrove ecosystems requires knowledge on factors that mainly drive growth and vitality of tree species to evaluate which consequences can be expected from, mainly hydrology-related, environmental changes. In this study, we assessed the nature and periodicity of tree rings in Excoecaria agallocha, a wide spread mangrove species in the Bangladesh Sundarbans. We also analysed the influence of climatic factors, such as precipitation, temperature and vapor pressure deficit (VPD), and river discharge, as a proxy of salinity on ring width (RW) and vessel features, such as mean vessel area (MVA) and mean vessel density (MVD). E. agallocha forms distinct tree-ring boundary that characterized by a narrow (2–4 cells wide) band of radially flattened fibres. The RW as well as the MVA and MVD are crossdatable. The RW is mainly driven by salinity which is influenced by freshwater inputs through precipitation during monsoon along with river discharge January to April. The MVA and MVD responded to similar seasons and months as RW, but mostly with opposite signs in MVD. The results suggest that fresh water inputs through precipitation and river discharge positively influence the radial growth of E. agallocha in the Sundarbans. The RW and vessel features can be used as proxies to explore the growth dynamics of this species, especially in relation to global environmental changes.     

An investigation into the composition, complexity and functioning of snake communities in the mangroves of south-eastern Nigeria

The structure of the snake community was studied between 1996 and 2000 on a transect in the mangrove ecological zone of southern Nigeria, West Africa. In three major habitats, both taxonomical diversity and frequency of observations in relation to sampling effort were investigated. In general terms, the complexity of the snake community appeared less than in other habitats of the same geographic region (i.e. swamp forest and forest–plantation mosaics). In fact, only eighteen species were recorded, whereas 43 species are known to inhabit neighbouring habitats. A Principal Component Analysis allowed arrangement of the various species into two main groups in relation to the habitats of capture: (1) a group of species of rainforest biota (i.e. Toxicodryas blandingii, Thelotornis kirtlandii, Thrasops flavigularis, Rhamnophis aethiopissa, Gastropyxis smaragdina, Grayia smythii, Pseudohaje goldii, Python sebae), and (2) a group of species that, at least in Niger Delta, are typically linked to altered habitats, including derived savannas, plantations and suburbia (i.e. Psammophis cf. phillipsi, Philothamnus cf. nitidus, Hapsidophrys lineatus, Crotaphopeltis hotamboeia, Boaedon lineatus, Naja nigricollis, Python regius). The community structure in terms of food habits and body sizes appeared similar to those of other snake assemblages from different habitats of southern Nigeria. The conservation implications of our results are also discussed.     

Macrobenthic infauna of mangroves and surrounding beaches at Gazi Bay,Kenya

Twelve sites around Gazi Bay, Kenya, were examined for macrobenthic infauna. Stations differed in human disturbance, vegetation, and sediment type (sandflat, beach, denuded and virgin mangrove sites, with Sonneratia, Rhizophora, Avicennia, Ceriops or Bruguiera vegetation).Sixteen higher taxa were counted; Isopoda, Amphipoda, Polychaeta, Cumacea and Tanaidacea were determined to family level (sometimes to genus or species). Total densities of infauna ranged from 265 to 6025 ind m^–2.Gazi mangals had higher macrobenthos densities than other mangrove sediments described in literature and than the Gazi sandflats. The densities found in Gazi sandflats were comparable to similar habitats elsewhere.Virgin mangrove sediments were rich in mud and organic material, and were characterized by high densities of macro-Oligochaeta and Mollusca. Sandflats, beaches, exploited (denuded) and less dense mangroves or mangroves higher in the tidal zone (Bruguiera) were much more sandy and had a high abundance of Polychaeta and Nemertini.Structural patterns in the macrobenthos were only vaguely associated with vegetation type. Human impact (cutting) has resulted in a drastic decrease in densities of macro-infauna, possibly related to a reduction of organic material in the sediment.     

Conservation categories of siluroid fishes in North-East Sundarbans,India

In stock fishery of North-East Sundarbans, siluroid fishes hold a remarkable position owing to the culture potentiality of many of them. Scales in fishes play significant role in protection and resistance against environmental stresses and the lack of scalation in case of siluroid fishes is supposed to be one of the reasons for their decline in eco-degraded aquatic habitats. 11 species of fishes belonging to 9 genera, 8 families under the order Siluriformes have been recorded from different water bodies of North-East Sundarbans, India. Fish Magnitude Value (FMV) of those catfishes were recorded especially by information harvested from local fishermen community and stakeholders as well as from market survey on fish landing. The extensive damage to the population of catfishes in the area has placed the fishes under threat categories. Following the IUCN guidelines and also through Participatory Rural Appraisal (PRA) methods, an attempt has been made to assess the status of such fishes. Trend analysis, Fish Magnitude Value (FMV) and Rank Based Quotient (RBQ) revealed 1 catfish as Endangered, 5 as Vulnerable and 5 as Near Threatened species. The situation warrants immediate attention of ecologists, administrators, managers and entrepreneurs to propose remedial measures for revival of the fishes. The study also delineates distribution, present status and conservation measures for revival of the fishes in North-East Sundarbans wet-land environment of West Bengal, India.     

Taxonomic notes on some freshwater Gastrotricha from West Bengal,India

The present paper is a taxanomic account of seven species of gastrotrichs (Gastrotricha: Chaetonotidae) collected from Calcutta and its adjacent areas (Lower Bengal). All the reported species represent new records from the north-eastern region of this subcontinent and three of them are new records from India.     

The plankton ecology of some thermal springs in West Bengal,India

Estimates of planktonic growth kinetics in relation to the thermal environment were made over a two year period in three hot springs and one cold one located in West Bengal, India. A very characteristic feature of the Saubhagya Kund (43–49°C) and Papahara (46–51°C) was the abundance of phytoplankton, always dominated by blue-green algae. This situation changed in the other two springs where zooplankton was an essential component. The determination of the species diversity index indicated that the graph of cumulative species of plankton versus logarithm of individuals was roughly linear in Saubhagya Kund and Papahara, whereas in the other two a logistic curve was the result. The seasonal distribution of Myxophyceae/Phytoplankton was dependant upon the annual phosphorous cycle (P < 0.0001) in all the thermal waters studied. That the population dynamics of diatoms responded inversely to the level of phosphate (P < 0.05) has been clearly manifested in Swetganga (37–46°C). The variation in the silicate content of the water throughout the year has been found responsible for the seasonal succession of diatoms in some of the waters (P < 0.001). The multiple correlation between phosphate, silicate, dissolved oxygen and pH and Myxophyceae/Phytoplankton was significant in the case of Papahara (P < 0.01) and Swetganga (P < 0.05). Similarly, the multiple correlation between these factors and Bacillariophyceae was significant in Saubhagya Kund (P < 0.01). In the non-thermal water Jibatsa Kund (22–39°C), the multiple correlation between these factors and Phytoplankton was, however, not significant (P > 0.05).     

The mangroves of the north coast of Haiti

The study of five mangrove forests was undertaken during the summer of1998 on the north coast of Haiti. Photo-interpretation detected areachanges between 1978 and 1989; the areas were reduced by an averageof 43% each. Two of the sites, Salée River mangrove andHaut-du-Cap River mangrove, were characterized by means of a vegetationsurvey and water and soil analysis. Tree density averaged 58,750 stems/haand 114,250 stems/ha respectively, while tree height averaged 2 m.Interviews with villagers indicated that all the assessed mangroves areintensively harvested for charcoal and fuel wood. This extraction seems tobe the main human disturbance, resulting in changes in forest structure,although heavy fishing and conversion to residential sites constitutedisturbances in some mangroves. The situation is critical but probably notirreversible. However, the socio-economic and environmental conditionsprevailing in the country and the lack of basic information on Haitianmangroves are major obstacles to their preservation.     

Changes in the distribution of mangroves and saltmarshes in Jervis Bay,Australia

The decline of saltmarsh in Currambene Creek andCararma Inlet, in Jervis Bay, eastern Australia, inthe period 1944–1999 has been documented through photogrammetric analysis. The area of saltmarsh hasdeclined in Currambene Creek by approximately 52.5%and in Cararma Inlet by approximately 35%. InCurrambene Creek the decline of saltmarsh is primarilydue to the landward encroachment of mangroves, whilein Cararma Creek the seaward encroachment of Melaleuca and Casuarina have more significantlycontributed to losses of saltmarsh. Regional sea-levelrise is excluded as a primary cause of thistransgression. A more plausible hypothesis involvesan increase in the delivery of freshwater andnutrients to the intertidal environments in responseto higher rainfall and catchment modifications.