Grey Mangrove Research Articles

Unveiling the Healing Potential of Avicennia marina: A Mini Review on its Medicinal Marvels

This mini review delves into the therapeutic attributes of Avicennia marina, commonly known as the Grey Mangrove, situated within mangrove ecosystems. Characterized by unique biochemical features, A. marina has captured the attention of the scientific community for its potential medicinal applications. Thriving in intertidal zones amidst salinity fluctuations and environmental stressors, this resilient mangrove species has evolved adaptive mechanisms, leading to the synthesis of secondary metabolites with recognized pharmacological properties. Beyond its immediate relevance in medical research, A. marina emerges as a significant player in environmental health, especially in the context of escalating climate change challenges. The intertidal zones it inhabits face increasing vulnerability to rising sea levels and temperature fluctuations, emphasizing the importance of understanding its adaptive mechanisms for both medicinal and ecological insights. Moreover, A. marina serves as a testament to the intricate interplay between nature and human health. Bioactive compounds found in this mangrove not only hold promise for pharmaceutical applications but also contribute to the burgeoning field of herbal medicine. Integrating traditional knowledge with modern scientific approaches provides a holistic understanding of the Grey Mangrove’s therapeutic spectrum, unveiling potential herbal remedies with relevance to contemporary healthcare practices. This dual perspective positions A. marina as a subject of interdisciplinary research, where botanical pharmacology intersects with ecological resilience, addressing both medical and environmental challenges.

Investigating the bacterial community of gray mangroves (Avicennia marina) in coastal areas of Tabuk region.

Mangrove vegetation, a threatened and unique inter-tidal ecosystem, harbours a complex and largely unexplored bacterial community crucial for nutrient cycling and the degradation of toxic pollutants in coastal areas. Despite its importance, the bacterial community composition of the gray mangrove (Avicennia marina) in the Red Sea coastal regions remains under-studied. This study aims to elucidate the structural and functional diversity of the microbiome in the bulk and rhizospheric soils associated with A. marina in the coastal areas of Ras Alshabaan-Umluj (Umluj) and Almunibrah-Al-Wajh (Al-Wajh) within the Tabuk region of Saudi Arabia. Amplicon sequencing targeting the 16S rRNA was performed using the metagenomic DNAs from the bulk and rhizospheric soil samples from Umluj and Al-Wajh. A total of 6,876 OTUs were recovered from all samples, of which 1,857 OTUs were common to all locations while the total number of OTUs unique to Al-wajh was higher (3,011 OTUs) than the total number of OTUs observed (1,324 OTUs) at Umluj site. Based on diversity indices, overall bacterial diversity was comparatively higher in rhizospheric soil samples of both sites. Comparing the diversity indices for the rhizosphere samples from the two sites revealed that the diversity was much higher in the rhizosphere samples from Al-Wajh as compared to those from Umluj. The most dominant genera in rhizosphere sample of Al-Wajh were Geminicoccus and Thermodesulfovibrio while the same habitat of the Umluj site was dominated by Propionibacterium, Corynebacterium and Staphylococcus. Bacterial functional potential prediction analyses showed that bacteria from two locations have almost similar patterns of functional genes including amino acids and carbohydrates metabolisms, sulfate reduction and C-1 compound metabolism and xenobiotics biodegradation. However, the rhizosphere samples of both sites harbour more genes involved in the utilization and assimilation of C-1 compounds. Our results reveal that bacterial communities inhabiting the rhizosphere of A. marina differed significantly from those in the bulk soil, suggesting a possible role of A. marina roots in shaping these bacterial communities. Additionally, not only vegetation but also geographical location appears to influence the overall bacterial composition at the two sites.

Evaluation of the Antibacterial Activities of Mangrove Honeybee Propolis Extract and the Identification of Transpeptidase and Transglycosylase as Targets for New Antibiotics Using Molecular Docking.

Developing new antibiotics is a critical area of research that grows as a result of the increasing problem of antibiotic resistance. Scientists search for new antibiotics by screening natural sources such as soil, plants, and marine environments. One of the iconic plants in the marine environment is the mangrove, which is a source of honeybee propolis. Propolis collected from the grey mangrove Avicennia marina on Tarout Island, the Eastern Province of Saudi Arabia, was used to evaluate antibacterial activities against three pathogenic bacteria: gram-negative Enterobacter cloacae (RCMB 001(1) ATCC® 23355TM), gram-positive methicillin-resistant Staphylococcus aureus (clinical isolate), and Streptococcus mutans Clark (RCMB 017(1) ATCC® 25175TM). The results indicate the effectiveness of the methanolic extract of such propolis. The chemical composition of this extract was analyzed using LC-MS, and four compounds were identified (alginic acid, carrageenan, fucoxanthin, cycloeudesmol). Their modes of action were evaluated against bacterial cell walls. Bacterial transpeptidase and transglycosylase on the surface are basic for cell divider amalgamation, and numerous antimicrobials have been created to target these compounds. Molecular docking was employed to predict the interactions of four compounds and S. aureus to predict interaction. Alginic acid was found to be the best interaction with a score of -7.44 Kcal/mol with distance ranges between 2.86 and 3.64 and RMSD refined below 2 Å. Carrageenan with -6.64 Kcal/mol and a distance of 3.05 and 2.87 came second. Then, fucoxanthin with -6.57 Kcal/mol and a distance of 1.4. Finally, cycloeudesmol with a score of -4.6 Kcal/mol and a distance of 2.87 showed the least activity. The first three compounds interacted effectively and could form very promising chemicals that could be used one day against pathogenic bacteria in the future.

Distribution, speciation, and bioaccumulation of potentially toxic elements in the grey mangroves at Indian Sundarbans, in relation to vessel movements

Sundarban is the world's largest mangrove wetland and home of 4.6 million people (Indian part), whose principal mode of communication is motorized boats (ferries). This study shed light on the role played by ferry movement in the speciation (following the BCR three-step sequential extraction method), ecological impact and bioaccumulation of potentially toxic elements (PTEs) in plant tissues (root and lamina) of grey mangrove (Avicennia marina) found near the five ferry ghats (ports). One-way ANOVA showed variation in major soil parameters (silt, clay, organic carbon, pH, Electrical conductivity) and PTEs (As, Cd, Cr, Cu, Hg, and Pb) between sites. Sequential extraction revealed that Cd was present in the ‘exchangeable’ form across the sites, Pb was in the ‘reducible’ form, and the rest of the PTEs were majorly found in ‘residual’ phase. Pollution indices revealed moderate to heavy contamination and considerable potential ecological risk due to Cd. Pearson correlation statistics and concentration variations indicate a relation between Pb and ferry movement frequency in the sites. Higher bioconcentration of Pb in the roots of A. marina, indicates phytostabilization action. Translocation factor for Cd in the leaves, indicates phytoextraction by A. marina. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a close association between vehicle movement and Hg, Pb, Silt fraction, electrical conductivity, Cr, and As. This study recommends regular pollution monitoring across Sundarbans, as the PTEs in sediment-plant matrix can impact the higher trophic levels, human health through possible biomagnification in the detritus food chain, and can adversely impact the existing conservation initiatives.

Sediment CO2 Flux from a Mangrove in Southern China: Is It Controlled by Spatiotemporal, Biotic or Physical Factors?

Carbon gas flux is important for studies on carbon dynamics in mangroves, but the controlling factors have not always been sufficiently understood. In this study, it is suggested that sediment carbon dioxide (CO2) fluxes in a natural mangrove in Southern China are controlled by tidal positions, seasons, species, the densities of crab burrows and pneumatophores, light conditions and sediment temperature. All these factors account for 51.47% variation in CO2 flux from the sediment–air interface. CO2 flux generally decreased along the tidal position from landward to seaward, and was higher in the dry season than in the wet season. CO2 flux was highest in Avicennia marina (grey mangrove) in comparison with Aegiceras corniculatum (river mangrove) and Kandelia obovata. Pneumatophores and crab burrows promoted sediment CO2 flux in the mangrove at a rate of 18.29 and 15.52 mmol m−2 d−1. Dark flux was higher than light flux. Sediment temperature has a negative influence on CO2 flux. Pneumatophores explain the most variation (13.9%) in CO2 flux among the above factors. Our study suggests that the photosynthesis activity of microphytobenthos is an important factor driving the change of CO2 emissions in this natural mangrove. This is of great significance for the study and for the full exploitation of the carbon sink potential of mangroves.

Potential of nitrification rate: in sediments of grey mangrove (Avicennia marina) located at different stations along Karachi coast, Pakistan

Potential of nitrification rate: in sediments of grey mangrove (Avicennia marina) located at different stations along Karachi coast, Pakistan

Effects of salinity and iron deficiency on growth and physiological attributes of Avicennia marina (Forssk.) Vierh

ABSTRACT The grey mangrove, Avicennia marina, grows in coastal zones in which salinity is frequently associated with iron deficiency. Its response to these combined stresses has not yet explored. The current study aims to assess the physiological and biochemical effects of iron deficiency (ID), salt stress (SS) and their combination (ID + SS) on A. marina seedlings. Iron deficiency reduced growth at non-saline treated plants by 27% while its deleterious effect was mitigated by the supply of 600 mM NaCl, mainly through the increase of photosynthetic pigment contents, iron accumulation in leaves, and intrinsic water use efficiency (iWUE), and the maintain of iron use efficiency (FeUE). Iron deficiency restricted iron accumulation in leaves (31%), iron absorption efficiency (FeAE) (38%), photosynthetic activity and pigment contents, and enhanced FeUE (48%) at saline treated plants. Otherwise, salinity enhanced growth (47%), root volume (20%), Fe accumulation in leaves (8%), and pigment contents at Fe-deficient plants. However, it reduced their FeAE (18%), transpiration rate (77%) and stomatal conductance (86%). Equally, it increased Na and Cl accumulation, the net photosynthetic assimilation rate and iWUE at Fe-deficient. Interestingly, the combined stresses had no additive effects and stressed plants (ID +SS) had comparable biomass to that of the control.

Isolation and Characterization of Dehydrin Gene from Egyptian Gray Mangrove in Nabq Protectorate

ABSTRACT: Dehydrins have a key role in protecting plants, especially in the grey mangrove tree Avicennia marina (Forssk.) Vierh. from salt stress. Understanding the mangrove plants at the molecular level will be necessary for developing such highly salt-tolerant crops. The full-length cDNA of the DHN gene sequence AmDHN was isolated from Avicennia marina and contained a 588bp open reading frame (ORF) encoding a 195 amino acid protein with a molecular weight of about 19.746k Da. As well as, multiple alignment sequences and phylogenetic relationships were analyzed for sequences using MEGA7 software revealing that AmDHN has a high identity with other DHNs plants and suggesting that AmDHN belongs to group II (LEA) proteins. Using bioinformatics analysis tools, we have investigated characterize and gene expression to better understand the structure and function analysis prediction of the AmDHN protein. AmDHN protein contains motifs (SYK2), Sn, Yn segment, and at least one copy of a lysine-rich conserved sequence known as K-segment (consensus EKKGIME/DKIKEKLPG) near the C terminal, the 3D predicted the structure protein sequence of the secondary structure, the top 5 final models using by I-TASSER server and several parameters computed by the software were obtained. Our results indicate that the AmDHN gene plays an essential role in salt stress remediation in the Avicennia marina. They could be used for further studies to understand the molecular mechanisms of salinity tolerance in plants and can be potentially utilized in transforming other plants to improve tolerance to salinity stress.

Uptake and Accumulation of Zinc by Grey Mangrove at Wonorejo Mangrove Forest, Surabaya, Indonesia

Heavy metals have non-biodegradable, toxic and accumulative properties in the environment. Heavy metals that enter water bodies will be carried by the flow towards the coast. Zinc (Zn) is one of the metals found polluting the waters in the city of Surabaya, Indonesia. One of the efforts to overcome this problem is the use of mangroves as phytoremediation agents. The purpose of the study was to determine the ability of Avicennia marina (Forssk.) Vierh in the Wonorejo Ecoforest to accumulate Zn by determining the bioconcentration factor (BCF) and the translocation factor (TF). Determination of the sampling points of this study using the transect method. Samples were taken in the form roots, stems, and leaves of mangrove plants and those were analyzed for Zn concentration using an atomic absorption spectrophotometer (AAS). Based on the result, A. marina showed the immobilized of Zn in root due to the BCF value was higher than 1. In conclusion, A. marina have potential to be phytoremediation plants in coastal area.

Reforestation of grey mangroves (Avicennia marina) along the northern coasts of the Persian Gulf

Every ecosystem supports the living organisms by providing direct and indirect benefits and services. Among these areas, mangrove forests are one of the most fertile ecosystems in the intertidal zones. These natural forests are one of the coastal ecosystems that not only provide a source of food for humans and animals, but also play a major role in protecting and stabilizing coastlines and controlling climate. Mangroves are a breeding ground and a safe habitat for a variety of marine vertebrates and invertebrates. This study explains the experienced methods of propagation and foresting of Avicenna marina species. For the first time in the Persian Gulf, we reported a 5-year evaluation of reforestation method of grey mangrove. Reforestation in the highest latitude of natural forests in the Persian Gulf did not have any side effects on growing of Grey mangrove in the selected sites. As a result, increasing the area of Grey mangrove forests in the Persian Gulf improves the ecosystems of the tidal area. Increasing the chances of fishing and improving the economic conditions of the local communities around this bay will be some of the results of mangrove forestation. Furthermore, this is the first report of a simple method to train all the steps of grey mangrove reforestation.

Foliar water uptake enables embolism removal in excised twigs of Avicennia marina.

Embolism refilling is thought to require relaxation of xylem tension, and it is unclear whether and how tall trees or plants growing in arid or saline soils recover from embolism. We tested whether foliar water uptake could enable embolism refilling in dehydrated twigs of the grey mangrove (Avicennia marina). Four dehydrated twigs were imaged by laboratory-based micro-computed tomography before and after wetting leaves. Emboli were observed in dehydrated stems and leaves. Embolism decreased with increasing distance from the cut end of stems, suggesting that stem emboli were caused by cutting. A significant (P=0.026) c. 80% reduction in the embolised area was observed in leaves between the start and the end of the experiment (29 ± 10 h after wetting). Embolus diameter was unaffected by wetting. Embolism refilling occurred slowly, in stems embolised by cutting and leaves embolised by cutting and/or dehydration. The lack of response of embolus diameter to wetting suggests that capillarity was not the main mechanism for refilling. Results show that excised twigs of A. marina are able to recover from embolism by absorption of atmospheric water and call for studies under natural conditions.

Metallic mangroves: Sediments and in situ diffusive gradients in thin films (DGTs) reveal Avicennia marina (Forssk.) Vierh. lives with high contamination near a lead‑zinc smelter in South Australia

From 1889, aerial emissions and effluent from a coastal lead‑zinc smelter at Port Pirie, South Australia, have led to the accumulation of lead (Pb), zinc (Zn), arsenic (As), cadmium (Cd) and copper (Cu) in the surrounding marine environment. Despite this, extensive stands of grey mangrove (Avicennia marina) inhabit coastal areas at Port Pirie, right up to the smelter's boundary. To understand the contamination level the mangroves are living in there, elemental concentrations were measured in mangrove sediments, leaves, pneumatophores and fruits at sites 0.30–43.0 km from the smelter. Plant health was assessed via leaf chlorophyll content at four sites with contrasting contamination, as well as in situ labile elemental concentration using diffusive gradients in thin films (DGT). Sites < 1.7 km of the smelter exceeded Australian and New Zealand Environment and Conservation Council (ANZECC) & Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) (2000) sediment quality guideline values for As (78.3–191 mg/kg), Cd (5.17–151 mg/kg), Cu (80.7–788 mg/kg), Pb (2,544–14,488 mg/kg) and Zn (281–62,097 mg/kg), while sites further away showed less enrichment above background. Similarly, elevated elemental concentrations in leaves and pneumatophores occurred closer to the smelter (up to 319 mg/kg Pb; 1,033 mg/kg Zn), while fruits had little contamination of non-essential elements (≤ 5.23 mg/kg). Relationship between sediment and leaf elemental concentration was isometric for Pb and anisometric for others. Labile As, Cd, Cu, Pb and Zn exceeded the 95% and 80% level of species protection in marine water by ANZECC & ARMCANZ (2000) near the smelter, but chlorophyll content did not vary significantly among sites (p > 0.05). These results reveal that A. marina tolerate high elemental contamination at Port Pirie, contributing to lesser but still high contamination in plants, warranting further investigation into non-lethal impacts on mangroves or additional biota inhabiting this ecosystem.

Simulated digestion, dynamic changes during fecal fermentation and effects on gut microbiota of Avicennia marina (Forssk.) Vierh. fruit non-starch polysaccharides.

Grey mangrove (Avicennia marina (Forssk.) Vierh.) fruit is a traditional folk medicine and health food consumed in many countries. In this study, its polysaccharides (AMFPs) were obtained and analyzed by chemical and instrumental methods, with the results indicating that AMFPs consisted of galactose, galacturonic acid, arabinose, and rhamnose in a molar ratio of 4.99:3.15:5.38:1.15. The dynamic changes in AMFPs during the digestion and fecal fermentation processes were then investigated. The results confirmed that AMFPs were not depolymerized by gastric acid and various digestive enzymes. During fermentation, 56.05 % of the AMFPs were utilized by gut microbiota. Galacturonic acid, galactose, and arabinose from AMFPs, were mostly consumed by gut microbiota. AMFPs obviously decreased harmful bacteria and increased some beneficial microbiota, including Megasphaera, Mistuokella, Prevotella, and Megamonas. Furthermore, AMFPs obviously increased the levels of various short-chain fatty acids. These findings suggest that AMFPs have potential prebiotic applications for improving gut health.

Marine ecosystem restoration and aquaculture-based stock enhancement for fishery resource conservation in Abu Dhabi Emirate, United Arab Emirates

There is a necessity to protect and manage the marine ecosystem towards the conservation of the ecological equilibrium and in turn the sustainability of the fishery resources in Abu Dhabi, UAE. Marine stock enhancement (MSE) proved that releasing hatchery fingerlings of marine animals can improve the abundance of harvest beyond the level supported by natural recruitment. For such programme to be beneficial and economical, considerable investment and scientific efforts are required. Among the concerned entities in the United Arab Emirates, the Aquaculture and Marine Studies (AMSC) in Abu Al Abyad Island successfully released 59 million of juveniles of different finfish species and 96 million juveniles of prawn species in Abu Dhabi waters. In the context of conserving the ecological equilibrium, the AMSC was able to plant an area of 5,026 ha in various areas of Abu Dhabi Emirate with grey mangrove, Avicennia marina; culturing over 21,290 corals of Acropora sp., Porites sp., Cyphastrea sp and Psammocora sp. in an area of 0.5 ha nurseries in Abu Al Abyad and Yasat Islands which will later be transplanted in the degraded reef sites in both islands; and a well-established seagrass coverage of 2500 m2 was achieved in affected areas in Abu Al Abyad Island.

Life on the Edge: A Powerful Tsunami Overwhelmed Indian Ocean Mangroves One Millennium Ago

In this paper, we demonstrate how subfossil mangrove wood can be used to elucidate the timing of past tsunami events. Although tsunamis generated by submarine earthquakes along the Makran subduction zone in the Arabian Sea are not unusual, rigorous age documentation is generally lacking. The best known is the only instrument-recorded tsunami, which affected the coastlines of Iran, Pakistan, India, and Oman in November 1945. Eyewitness accounts of the effect along the Oman coastline assert that this tsunami was not destructive. However, a 25-cm-thick shell layer in the lagoon adjacent to the city of Sur was attributed to the 1945 tsunami, although dating of the shell deposit proved difficult, and the radiocarbon dates of mollusk shells were regarded as unreliable. Here, we reinterpret the age of this tsunamigenic layer based on the new discovery of parallel-oriented woody axes in the sedimentological context of the tsunami shell layer in the Sur lagoon. The woody axes were analyzed anatomically and identified as pertaining to the gray mangrove Avicennia. Radiocarbon dating of the wood (905–722 cal BP), along with sedimentological investigations, suggests that the deposition of the woody axes should be attributed to an older tsunami event that occurred ca. 1000 years ago, which has been documented at other locations along the Arabian Sea coastline. From this, we conclude that mangroves grew in this lagoon at that time. Very little is known about ancient mangrove distribution in this region and, so far, no records have been provided for this time window at this site. We also deduce that the tsunami event that occurred one millennium ago must have been substantially more severe than the one in 1945. More accurate dating of tsunamigenic events will aid in calculating the recurrence intervals and magnitude of tsunamis generated along the Makran subduction zone.

Anatomical Adaptation of Grey Mangrove (Avicennia marina) Leaf in the Pond and Coast Located in Mangunharjo, Semarang, Central Java

Mangrove is a brackish plant that can live in habitats with extreme environmental conditions. For instance, the grey mangrove (Avicennia marina) is a mangrove species that can adapt anatomically in habitats with a wide range of salinity, such as ponds and coasts. This study examines the forms of anatomical adaptation of A. marina by comparing the anatomical structure of A. marina leaves that live in two different habitats, namely pond, and coast in the Mangunharjo area, Semarang, Central Java. The third leaf from the tip of the tree branches was used as samples and taken from three different trees in each habitat. Cross-section prepared microscope slides of the leaves were made using the embedding method and observed using a photomicrograph. The quantitative data were analyzed using the T-test at a 90% confidence level, while the qualitative data were analyzed descriptively. The results showed that different environmental conditions do not cause differences in the anatomy of A. marina leaves, but there are some histological modifications as a form of adaptation. These modifications are differences in the thickness of the cuticle, adaxial epidermis, parenchymal palisade tissue, spongy parenchyma, and the number of xylem cells in one vascular bundle. This research might initiate more advanced studies regarding the correlation between mangroves’ anatomical structure and anatomical adaptation towards diverse environmental conditions. The results of this study are expected to provide information about the anatomical structure of A. marina leaves that live in two habitats with different environmental conditions.

Assessing the spatiotemporal changes, associated carbon stock, and potential emissions of mangroves in Bahrain using GIS and remote sensing data

The gray mangrove (Avicennia marina (Forssk) Vierh) constructs one of Bahrain’s most critical ecosystem, severly deteriorating, which has been severely deteriorated by increasing anthropogenic pressures. This study aimed to assess the spatiotemporal changes in the mangrove habitat around Tubli Bay, Kingdom of Bahrain, over the last 50 years through achieving the following: (1) detect the progressive reduction in the mangrove cover using Geographic Information Science and Systems (GISs) techniques and remote sensing data, (2) estimate the changes of above–below ground (AGB-BGB) carbon sequestered in the mangroves using a GIS-based spatial analysis approach, and (3) estimate the potential carbon emission changes from the loss of original mangrove habitats. Various GIS and remotely sensed data were employed in the study, including high-resolution satellite images from Worldview-3, Worldview-2, IKONOS, and QuickBird, coupled with true-color orthorectified aerial photographs. Additional data was acquired from fieldwork and the ancillary GIS maps. Image processing of the satellite data was conducted using ENVI 5.5 Software. ArcGIS 10.8 was used for digitizing the mangrove areas in all satellite imagery. The final maps were used to calculate mangrove area changes and carbon loss due to land reclamation activities. Our results indicated that Bahrain lost more than 95% of the natural mangrove cover from 1967 to 2020. The mangrove extent area’s net loss reached 280 ha during 1967–2020, as it declined from 328 ha in 1967 to 48 ha in 2020. The primary cause of the decline was land reclamation associated with urban development. The rates and causes of the loss varied both spatially and temporally. Due to land clearing, the total carbon stored in the mangrove habitats declined from 34,932.2 Mg C ha−1 in 1967 to 5112 Mg C ha−1 in 2020. Consequently, the potential carbon Sequestration decreased from 128,200.44 Mg CO2e ha−1 in 1967 to 18,761.04 Mg CO2e ha−1 in 2020. Our study urges for more efficient conservation of the remaining mangroves in Bahrain to sustain their valuable ecosystem services particularly carbon sequestration.

Metal(loid) accumulation in the leaves of the grey mangrove (Avicennia marina): Assessment of robust sampling requirements and potential use as a bioindicator

This study assessed the appropriate sampling design required for quantifying variability in metal accumulation in the leaf tissues of A. marina, a dominant mangrove inhabiting Australian estuaries, by applying a hierarchical nested sampling design to sample mangroves at various levels of biological and spatial hierarchies (leaf, branch, tree, site). It was revealed that most variation in metal accumulation occurred among trees and branches, with insignificant variation between sites and among leaves. We also examined the accumulation of metal (loid)s in the leaf tissues collected from six locations across the Georges River estuary in southern Sydney, which differ in metal contamination history. Prospect Creek and Salt Pan Creek were the most contaminated locations, which exceeded sediment quality guideline values for Cu (66.71 ± 2.18 μg/g), Zn (317.14 ± 46.14 μg/g) and Pb (81.02 ± 2.79 μg/g). All metal(loid) concentrations in leaf tissues were much lower than their concentrations in sediment, but essential metals exhibited greater mobility. Out of 10 metal(loid)s, Mn, Co and Pb in leaves showed linear relationships (R2 = 0.28–0.47) with sediment, indicating that mangrove leaves may be used as a bioindicator of environmental loads for these metals.

Larval habitats of Culicoides ornatus Taylor, 1913 (Diptera: Ceratopogonidae) within the mangroves of Darwin Harbour in the wet‐dry tropics of northern Australia

AbstractLarval habitats of the pest biting midge Culicoides ornatus were identified and characterised in a macrotidal mangrove creek system in Darwin Harbour in the wet‐dry tropics of northern Australia. Sampling was undertaken during the mid to late dry season using submersible emergence traps to indicate larval activity. Substantial emergence was found in two well separated and distinctly different habitats: open creekbanks covered in Avicennia marina (Grey Mangrove) pneumatophores in the upper reaches of small tidal creeks and broad relatively flat areas dominated by Sonneratia alba (Mangrove Apple) at the mouth of the creek system. Intervening areas along creeklines were lined by Camptostemon schultzii (Kapok Mangrove) and did not support emergence activity. Adults emerging from each habitat were conspecific, based on comparison of mitochondrial COI gene sequences and a range of morphological characters. Nine different haplotypes were identified from 26 adults, with four haplotypes common to both habitats. Neighbour‐joining analysis resolved all the haplotypes as a single highly supported clade with an average sequence difference of 1.6%. Features common to the two habitats included occurrence in sheltered mangrove‐lined estuaries; occurrence in soft, fine, silt mud; presence of mangrove pneumatophores; and an open vegetation structure providing partial shade. Dense vegetation appeared to be a limiting factor. The tidal creek habitat was similar to C. ornatus habitats previously described from the east coast of Australia, but neither the Sonneratia zone nor other habitats at such a low tidal elevation have been previously associated with C. ornatus. This is the first detailed account of the larval biology of this important mangrove breeding pest species. The identification of likely C. ornatus breeding sites in Darwin Harbour and other similar ria coastlines of northern Australia should be possible from aerial photographs using the habitat descriptions presented in this paper.

Hydroclimate proxies for eastern Australia using stable isotopes in grey mangroves (Avicennia marina)

The development of high-resolution terrestrial palaeoclimate records in Australia is hindered by the scarcity of tree species suitable for conventional dendrochronology. However, novel analytical techniques have made it possible to obtain climate information from tree species that do not reliably form annual growth rings. In this paper we assess the potential of stable carbon and oxygen isotopes in the xylem wood of grey mangroves (Avicennia marina (Forssk.) Vierh.) as hydroclimate proxies for eastern Australia. Bomb-pulse radiocarbon dating and simple age models were used to estimate the age of the growth layers in radial sequence in stems from four grey mangrove trees in two adjacent estuaries in New South Wales, Australia. Stable isotope data measured from the xylem wood of the four stems were composited to yield mean δ18O and δ13C series for the 1962–2016 period. Significant negative Spearman correlations were found between δ18O and rainfall, sea level, instrumental Palmer Drought Severity Index (scPDSI) and the El Niño Southern Oscillation (ENSO), while δ13C was positively correlated with temperature, vapour pressure and evapotranspiration. The results demonstrate that stable oxygen isotopes in grey mangroves have the potential to yield valuable information about pre-instrumental hydroclimate. Grey mangroves can survive with intact centres for an estimate of >250 years based on observed growth rates, are widespread along northern Australian and tropical coastlines and could provide important information regarding pre-instrumental climate in regions currently lacking high-resolution (i.e., near annual) centennial scale climate proxy records.