Intertidal Region Research Articles

The novel marine cyanobacterium Nunduva sanctimaloensis sp. nov. (Nostocales, Cyanobacteria) from rocky shores and its reproduction through modified monocytes

Rocky intertidal regions are diverse as they provide many unique habitats for the growth of cyanobacteria. From outcrops battered by waves, tidal pools, and periods of desiccations due to tides, these regions offer distinct environments and much of their cyanobacterial diversity remains unexplored. To help elucidate cyanobacteria from this habitat, one nostocalean cyanobacterium from Brittany, France was isolated and cultured. Typical morphological features including filaments with heteropolar trichomes, basal or intercalary heterocytes, false branching, and long hyaline apical hairs suggested the genus Nunduva. The combination of 16S rRNA gene and 16S-23S rRNA internal transcribed spacer (ITS), along with diagnosable morphological characteristics supports a distinct taxon from previously described species. Herein, the novel false branching cyanobacterium Nunduva sanctimaloensis sp. nov. is described along with its reproduction through modified monocytes.

Effect of cyclonic storm Vardah on the community structure and ecosystem functioning of macrobenthic fauna in the intertidal region of South Andaman Islands

An investigation was carried out to understand the effect of a cyclone Vardah on the functioning of macrobenthos. The assessment was accomplished by comparing before cyclone (BC) and after cyclone (AC) data of macrobenthos. Additionally, temporal changes in the faunal assemblages were evident through multivariate techniques. Five distinguished assemblages could be noticed through the Bray–Curtis similarity representing different phases of the cyclone. The cyclonic effect also resulted in the recruitment of some macrobenthic species and the loss of a few during the study period. Biological trait analysis identified subsurface deposit feeders, upward and downward conveyers, Ecological Group IV, mid-mobile macrobenthos and size class of 2–4 cm as the important groups that dominated the functioning of the macrobenthic community immediately after the cyclone. The resilience and recruitment of macrobenthos were explained using functional redundancy.

Validating ATLAS: A regional‐scale high‐throughput tracking system

Abstract Fine‐scale tracking of animal movement is important to understand the proximate mechanisms of animal behaviour. The reverse‐GPS system—ATLAS—uses inexpensive (~€25), lightweight (<1 g) and low‐power (~0.4 mJ/transmission) tags. Six systems are now operational worldwide and have successfully tracked over 50 species in various landscape types. The growing use of ATLAS to track animal movement motivates further refinement of best‐practice application and an assessment of its accuracy. Here, we test the accuracy and precision of the largest ATLAS system, located in the Dutch Wadden Sea, using concurrent GPS measurements as a reference. This large‐scale ATLAS system consists of 26 receivers and covers 1,326 km2 of intertidal region, with almost no physical obstacles for radio signals, providing a useful baseline for other systems. We compared ATLAS and GPS location estimates for a route (mobile test) and 16 fixed locations (stationary test) on the Griend mudflat. Precision was estimated using standard deviation during the stationary tests. We also give examples of tracked red knots Calidris canutus islandica to illustrate the use of the system in tracking small shorebirds (~120 g). ATLAS‐derived location estimates differed from GPS by a median of 4.2 m (stationary test) and 5.7 m (mobile test). Signals that were collected by more receiver stations were more accurate, although even three‐receiver localisations were comparable with GPS localisations (~10 m difference). Receivers that detected 90% of the 1 Hz transmissions from our test tag were within 5 km of their furthest detection but height of both receiver and tag seemed to influence detection distance. The test tag (1 Hz) had a fix rate of >90% at 15 of 16 stationary sites. Tags on birds (1/6 Hz) on the Griend mudflat had a mean fix rate of 51%, yielding an average sampling rate of 0.085 Hz. Fix rates were higher in more central parts of the receiver array. ATLAS provides accurate, regional‐scale tracking with which hundreds of relatively small‐bodied species can be tracked simultaneously for long periods of time. Future ATLAS users should consider the height of receivers, their spatial arrangement, density and the movement modes of their study species (e.g. ground‐dwelling or flying).

Reappearance of stomatopod Gonodactylus platysoma (Wood-Mason, 1895) after an era from the intertidal region of Chota Balu, South Andaman, India

Mantis Shrimp Gonodactylus platysoma was observed during a survey for seaweed-related macrofauna from the intertidal region of Andamans after a century. The specimen was collected using a scoop net, identified based on Kemp (1913) and Ahyong (2001). The detailed description, images and illustrations are given in this article. The reappearance of G. platysoma after a century highlights the potential of revealing the rich biodiversity in Andaman and the need to monitor stomatopods for a better overview of their ecological interactions and diversity.

High-resolution observations of lateral circulation at an inflection bend of the Oujiang River Estuary, China

Field observations were conducted at an inflection point of two bends of the Oujiang River Estuary, China, to investigate lateral circulation and its driving mechanisms, and the effect of stratification in a macrotidal estuary. Repeated cross-channel transect measurements of velocities were obtained by vessel-mounted acoustic Doppler current profiler at the inflection point during neap and spring tides. Conductivity, temperature, and depth were collected at both ends of the transects to estimate the lateral moment budget. We observed asymmetry of lateral circulation in intra-tidal and inter-tidal regions, with strong single-cell lateral circulation during the neap ebb tide. In contrast, during the flood, lateral circulation was weak but structurally complex. During the spring tide, lateral circulation only appeared at peak ebb and peak flood. This asymmetric variation in lateral circulation is induced by an asymmetric driving mechanism, investigated thoroughly and connected to water stratification. The significant effect of nonlinear advective acceleration in both highly stratified water and well-mixed water indicates the important influence of an inflection point of two bends on lateral circulation. Besides, the strong stratification plays a role to suppress the lateral circulation due to the tilted pycnocline spin opposite to lateral circulation. The Oujiang River Estuary is an important shipping area, and the results have practical significance for the development and utilisation of port and channel resources.

Transformation in the Stability of Tide‐Induced Upper Saline Plume Driven by Transient External Forcing

AbstractThe fluctuation in sea level induced by tides generates an upper saline plume (USP) in the intertidal region, which is closely related to groundwater flow and solute transport processes in coastal aquifers. Thus, a clearer understanding of the USP configuration is needed to accurately predict the extent of seawater intrusion and water chemical fluxes to the ocean. This study experimentally and numerically examined the effect of transient external forcing conditions on the stability of tide‐induced USP, represented as seasonal subsurface inflow. In contrast to earlier studies, the USP was not always stable or unstable, but experienced a dynamic transformation of stability‐instability as the seasonal subsurface inflow fluctuated. The same intensity of subsurface inflow caused a stable USP in the fixed cases but a dynamic USP state in the seasonal cases. The USP responded rapidly to the fluctuation of seasonal subsurface inflow and was drawn to expand into the intertidal zone. These features of the USP contributed to the increased potential for the onset of an unstable flow when the subsurface inflow varied seasonally. Therefore, ignoring the timescale changes on external forcing conditions may underestimate the generation of unstable USPs. The frequency contrast between seasonal subsurface inflow and tide also influenced the dynamic transformation process occurring in the intertidal region. There was an inverse relationship between the frequency contrast and the duration of the unstable flow. These findings provide a new understanding of the complex intertidal environment in coastal aquifers.

An RGB‐D framework for capturing soft‐sediment microtopography

Abstract Capturing sediment topography is one component in understanding how large animals in soft sediment ecosystems affect ecosystem processing. Traditional approaches for sampling soft‐sediment systems are too invasive and destructive for the fragile sediment structures. In contrast, non‐invasive approaches, such as LIDAR and monocular structure‐from‐motion (SfM) systems, can be expensive and cumbersome for data processing. We developed a low cost and practical framework for measuring morphological characteristics of soft sediment topography at the millimetre scale. Using an RGB‐D (red, green, blue and depth) device and a semi‐opaque container, the sediment surface can be imaged rapidly while operating in outdoor environments. The RGB‐D device imaged 0.3 m2 intertidal sediment surfaces, creating depth imagery over seven sites and 82 surfaces. First, using simulated surface data, we formulated and tested four variations of a geometrical detrending model to extract and measure the undulating surface microtopography. We then computed nine morphological characteristics, including arithmetic mean roughness, mean sediment peaks and rugosity, for the detrending models. We then used the two best performing models, linear and quadratic detrending models, to compare extracted morphological characteristics from the field data. We found a strong correlation between the models for extracted surface measures and similar extracted sediment trends. The results showed that RGB‐D real‐time imaging is a promising rapid scanning tool for collecting field data in intertidal regions and can be expanded to other fragile sediment surfaces outside the marine environment. The low costs and real‐time feedback makes it an attractive data collection tool for environments where data collection is challenging.

Biodegraders of Large Woody Debris Across a Tidal Gradient in an Indonesian Mangrove Ecosystem

There has been limited research on the breakdown, recycling, and flux of carbon from large woody detritus (LWD) in mangrove forests. The breakdown of LWD is caused by guilds of terrestrial and marine biodegrading organisms that degrade wood at a range of rates and efficiencies. Spatial variations in environmental factors within mangroves affect the distribution and community of biodegrading organisms, which, in turn, impacts carbon flow and sequestration. We reveal the role of biodegrading organisms in LWD breakdown and the environmental factors that influence the distribution of biodegrading guilds within a mangrove forest in South East Sulawesi that supports a diversity of mangrove species typical of Indonesian mangrove forests, which constitute 20% of Global mangrove cover. Within the high intertidal regions, terrestrial biodegradation processes dominated upon LWD. After 12 months exposure on the forest floor, experimental wooden panels in these areas remained unchanged in mass and condition. In the low intertidal region, marine wood-boring animals belonging to the family Teredinidae were the dominant biodegraders of LWD, and their activity reduces LWD volume and speeds up the loss of LWD volume. More than 50% of the experimental wooden panels’ weight in these areas was lost after 12 months exposure on the forest floor. Although different biodegrading guilds occupy the same LWD niche, their distribution throughout the mangrove forest is influenced by inundation time. The change of biodegrading guilds within LWD between the terrestrial and the marine organisms was distinct, creating a biodegradation boundary in a distance as narrow as 1 m on the mangrove forest floor. These results are important, as rising sea levels have crucial implications for biodegrading guilds. A full understanding of factors affecting the biodegradation processes of LWD in mangrove forests is critical to accurately assess mangrove carbon stores and the fate of mangrove derived carbon.

Effect of dissolved organic matter and heavy metals ions on sorption of phenanthrene at sedimentary particle scale

Human activities significantly increase the input of offshore heavy metals and organic pollutants. Although particle-scale and heterogeneous organic matters are fundamentally important to the fate of hydrophobic organic compounds (HOCs), deep understanding of the adsorption mechanism of HOCs on soil/sediment particles under the influence of heavy metal and organic pollution input is needed. This study investigates the effects of exotic DOM and heavy metals ions on the phenanthrene adsorption on sediment fractions. The adsorption experiments demonstrated that exotic DOM increased phenanthrene adsorption amount of sediment, with the greatest enhancement on clay particles (<2 µm). Nevertheless, the mechanism was differentiated accordingly to particle dimensions in terms of increased binding coefficients and mobility of phenanthrene. Furthermore, the introduction of heavy metals considerably enhanced the nonlinear sorption of phenanthrene. The Freundlich exponent N reduced by 0.01–0.24 when adding Cu2+, Zn2+ and Pb2+, especially for coarse particles (31–63 µm) fraction. In comparison, the enhancement of nonlinearity adsorption by Cu2+ and Zn2+ is significantly lower than Pb2+ ions. To our knowledge, the particle-scale study broadens the horizon of environmental fate and ecological risk of HOCs in intertidal regions, which is significantly affected by tidal action.

Dark survival in biofilm-forming microalgae: potential for colonizing benthic ecosystems.

The biofilm-forming microalgae are known to experience periods of continuous darkness (upto several days), in addition to the natural day-night cycle, especially in the intertidal sediment regions (when transported to deeper sediments) and the ships' ballast water tanks (during voyages). However, the information on community and physiological responses to different periods of darkness is limited. Here, the survival capability of biofilm-forming microalgae to varying periods of darkness (7-35 days) and the growth patterns upon resumption of normal 12 hlight:dark photocycle has been addressed through simulation experiments. Diatoms dominated the seawater biofilms, but the dark survival period varied and was species-specific. Of the 25 diatoms, only Amphora, potential toxin producer, followed by Navicula remained viable and photosynthetically healthy under darkness without undergoing asexual reproduction. Both diatoms are essential contributors to fouling and microphytobenthic community. Upon re-exposure of dark-adapted biofilms to 12 hlight:dark photocycle, the improvement in photosynthetic efficiency and resumption of growth via asexual-reproduction was observed. However, the lag-phase duration increased with a long dark history. Nevertheless, eurytolerant nature and high dark survival capability (with its quick response to light) of Amphora and Navicula indicated that they have the potential to colonize benthic-ecosystems thus impacting the benthic and fouling community.

Impact of multiple beach activities on litter and microplastic composition, distribution, and characterization along the southeast coast of India

A regional understanding of beach litter abundance, distribution, and composition is fundamental to formulate strategies to manage litter pollution in a particular area. The present study aimed to quantify and characterize the macro (2.5 cm to 1m), meso (5 mm–2.5 cm), and micro litter (≤5 mm) in the intertidal and backshore area of six sandy beaches utilized for various activities along the southeast coast of India. Macro litter was collected within 100m transects, while meso and micro litter was collected within 1 m2 quadrats (n = 5) from each beach's intertidal and backshore regions. In this study, the average beach litter concentrations were 0.24 ± 0.14 items/m2 (macro), 8.2 ± 5.6 items/m2 (meso), and micro litter was 505 ± 121 particles/kg of dry sediment. The backshore had a higher litter concentration than the intertidal area. Beaches closer to urban centers and multiple activities had higher litter abundance than more remote beaches. Using the Clean Coast Index (CCI), four beaches i.e., Neelankarai, Kovalam, Auroville, and Paradise are characterized as moderately clean beaches, whereas, the other two beaches i.e., Nemmeli and Palar are clean and very clean, respectively. Even though the beaches were found to be moderately clean, there is an urgent need to improve local waste management of beach litter. We suggest regular cleaning of river banks, a strict ban of single-use plastic in the beach area, and raising awareness e.g., by involving school and college students adopting a local beach.

Ecological value of the earliest human manipulated coastal habitats: Preliminary insights into the nursery function of a pre-colonial stonewalled fish trap in South Africa

Pre-colonial stonewalled fish traps, an ancient engineering feat in the intertidal region, represent the earliest proof of human manipulation of the coastline in Southern Africa, specifically by the First Indigenous Peoples of South Africa. We investigated the ecologically functioning of a fish trap located on the southeast coast of South Africa from a larval fish and invertebrate perspective. This research was done in collaboration with the Khoi traditional custodians of the area of study. Samples were collected using a light trap on four separate spring tide occasions, deployed for 3 consecutive nights during 2 full moon trips and 2 new moon trips during the known peak larval settlement period (November 2020–February 2021). Although time-dependent, the importance of this novel microhabitat for the development of coastal fishes and invertebrates was highlighted. Even with the high intertidal location of the stonewalled fish trap sampled at Cape Recife, the presence of a pool of permanent non-stagnant water within the fish trap, even during low spring tide, could provide protection to larvae, in the form of more stable environmental conditions, as well as less exposure to marine predators and harsh physical environmental conditions. This research aims to raise awareness of the stonewalled fish traps located on the southeast of South Africa with a view towards developing a more inclusive management of these marine cultural heritage sites, specifically involving the First Indigenous Peoples of South Africa.

An evaluation of the efficacy of shell hash for the mitigation of intertidal sediment acidification

AbstractOur objectives were twofold: (1) to determine whether the addition of shell hash to intertidal sediments would mitigate porewater acidification and (2) whether its effectiveness was dependent on the type of sediment as described by organic matter (OM) and particle grain size (PGS). Field experiments were conducted at two sites within Burrard Inlet, British Columbia; Maplewood Mudflats (MM), high in OM and silt and Whey‐ah‐Wichen/Cates Park (WAW), low in OM and an equal PGS among very coarse, coarse, fine sand, and silt. Shell hash was added to triplicate treatment plots matched with triplicate controls at each site and porewater pH measured at flood and ebb tide over eight tidal cycles. Sampling occurred during June and July when tidal cycles were at their maximum inundation and exposure. Porewater pH was significantly greater for ebb versus flood tide and also between sites with MM significantly lower (7.59) as compared to WAW (8.03). Although pH was not mitigated by the shell hash, for WAW, variation in pH was reduced as compared to MM, as indicated by coefficients of variation over the 6‐week sampling period. We suggest that the application of shell hash to reduce the impact of ocean acidification (OA) on intertidal sediments will be site dependent. The combined processes of eutrophication in sediments with high OM and respiration of infauna, especially at high densities, could act in concert with OA to create an intertidal region unsuitable for bivalve larvae settlement and development.

Abundant and rare microbiota assembly and driving factors between mangrove and intertidal mudflats

Abundant and rare microbiota both play crucial roles in sedimentary biogeochemical processes and have a profound influence on sediment functions. Uncovering the diversity patterns and assemblies of abundant and rare microorganisms is critical for understanding ecosystem diversity and function. We investigated the assemblies and diversity patterns of abundant and rare microbes in mangrove and intertidal mudflat sediments. Our results showed that the abundant and rare bacteria and fungi had distinct distribution patterns in diversity. The dispersal of abundant microbial taxa was less limited than that of rare taxa, and different variables drove their assemblies. The abundant taxa had significant responses to edaphic variables, but edaphic variables explained only a small proportion of the variation within the rare taxa, suggesting that there may be more complex unknown variables influencing the structure of rare taxa than abundant taxa. Cooccurrence network analysis revealed closer relationships between bacterial species and their enhanced effect in the community compared with fungal taxa and patterns wherein microorganisms in the mangrove regions had more interactions than those in the intertidal mudflat regions. Because rare microorganisms may be as important to sediment functions as abundant species, this patterned shift in microbial taxa is essential to take full advantage of their contributions to mangrove ecosystem services.

Heavy metals in surface sediments of the intertidal Thai Binh Coast, Gulf of Tonkin, East Sea, Vietnam: distribution, accumulation, and contamination assessment.

Heavy metals contamination in sediments may endanger ecosystems and human health via the food chain. In fact, there is little to no understanding about heavy metal accumulation in surface sediment of one of the most economically important marine bodies for Vietnam, the Thai Binh Coast, where five large rivers co-discharge into the Gulf of Tonkin. Twenty-seven surface sediment samples were collected from the intertidal regions and analyzed for: arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), and zinc (Zn) using inductively coupled plasma mass spectroscopy (ICP-MS). The studied area exhibited a large spatial variation in the concentration of heavy metals, e.g., the dry sediment concentration of Cd was the least (0.05-0.49mg.kg-1), whereas that of Zn was the greatest (45.4-252mg.kg-1). Based on the geoaccumulation index ([Formula: see text]), most of the studied heavy metals were accumulated at low pollution levels, except four locations exhibited moderately and highly polluted levels of Hg with [Formula: see text] Hg values from 1.92 to 2.66. However, the high contamination factor value implicated that not only Hg but also all other detected heavy metals in this area resulted from anthropogenic activities along the coast and the river upstream. This implied the need for quick action from the government. In addition, numerous analytical methods were used to see the association between metals, total organic carbon (TOC), and particle size distribution, including Pearson correlation coefficient (P) and principal component analysis (PCA). Hg demonstrates lowest connection with TOC (PHg-TOC ~ 0) but individual heavy metal correlations are largely positive, with many reaching 1.0 (e.g., PNi-Cr = 0.89, PCd-As = 0.72, PNi-Cu = 0.76, and PCu-Cr = 0.72). From the PCA diagram, we can observe that those sampling points in the positive direction of PC1 were expected to have a high concentration of Cu, Zn, As, Ni while having extremely little sand content.

Aggregatimonas sangjinii gen. nov., sp. nov., a novel silver nanoparticle synthesizing bacterium belonging to the family Flavobacteriaceae.

Microbially synthesized nanoparticles has received increasing attentions owing to the broad applications in biology and medicine. In this study, we report a novel bacterium that biologically generates silver nanoparticles (AgNPs). This bacterium, designated strain F202Z8T, was isolated from a rusty iron plate found in the intertidal region of Taean, South Korea. The morphological, biochemical and molecular characteristics predicted that strain F202Z8T belongs to the family Flavobacteriaceae. Phylogenetic analysis based on 16S rRNA gene sequence revealed that strain F202Z8T forms a distinct lineage with closely related genera Maribacter, Pelagihabitans, Pseudozobellia, Zobellia, Pricia, and Costertonia and showed the highest similarity to Maribacter aestuarii GY20T (94.5%). The digital DNA-DNA hybridization and average nucleotide identity values calculated from the whole genome-sequence comparison between strain F202Z8T and other members of the family Flavobacteriaceae were in the ranges of 12.7%-16.9% and 70.3%-74.4%, respectively, suggesting that strain F202Z8T represented a novel genus. The complete genome sequence of strain F202Z8T is 4,723,614bp, with 43.26% G + C content. Based on the COG, GO, KEGG, NR, and Swiss-Prot databases, the genomic analysis of F202Z8T revealed the presence of 17 putative genes responsible for the synthesis of AgNPs. Our polyphasic taxonomic results suggested that this strain represents a novel species of a novel genus in the family Flavobacteriaceae, for which the name Aggregatimonas sangjinii gen. nov., sp. nov. is proposed. The type strain of Aggregatimonas sangjinii is F202Z8T (= KCCM 43411T = LMG 31494T). Overall, our data provide fundamental information to potentially utilize this novel bacterium for synthesis of nanoparticles.

Assessment of Biochemical Constituents and Nutritional Aspects in Gracilariopsis persica and Hypnea flagelliformis

ABSTRACT In the present study, we assessed the nutritional composition and biochemical constituents of two Rhodophyta, Gracilariopsis persica and Hypnea flagelliformis, for their potential use as functional foods. Both species were collected from the intertidal regions of Bandar Abbas, Iran. The nutritional profile for H. flagelliformis consisted of ash (36% dw), crude protein (3% dw), lipids (2.1% dw), and phycobiliproteins (0.2% dw.). G. persica consisted of ash (31% dry weight), crude protein (4.4% dw), lipids (1.4% dw), and phycobiliproteins (0.2% dw). Leucine and phenylalanine were the most abundant amino acids in the assessed species. The samples were rich in essential amino acids (EAAs) and the obtained ratios of EAA/NEAA (non-essential amino acid) were 1.3. Palmitic acid was the predominant fatty acid in both species. The highest concentrations of polyunsaturated fatty acids were arachidonic acid and eicosapentaenoic acid. Recommended guidelines indicate an intake of omega-3 for each person that can be fully obtained by daily consumption of 130 g of dried G. persica or 100 g of dried H. flagelliformis. In conclusion, these two red seaweeds have good potential as nutritional sources for human and animal consumption.

Molecular and morphological evidence for the presence of a non-native oyster (genus Crassostrea) in the Persian Gulf

Oysters are widespread throughout the intertidal regions, and accurate identification and monitoring of their ecological status are still difficult due to their high level of plasticity. Anthropogenic activities facilitate oyster dispersal to new habitats through the shipping and elimination of existing barriers. In this study, a combination of morphological and molecular techniques was used to clarify the identity of an oyster species occurring along the Iranian coast of the Persian Gulf. Specimens were collected from the jetties of the ports and the rocky shores along the northern Persian Gulf. Oyster identification was carried out to the lowest possible taxonomic level based on shell morphology. The phylogenetic analysis was done using the cytochrome c oxidase subunit 1 (COI) fragments. Morphological results confirmed that studied samples belong to the genus Crassostrea and showed close to the Vietnamese (Crassostrea markushuberi) species. Molecular analysis reveals that species are a sister species to a clade containing Crassostrea zhanjiangensis and Crassostrea talonata. According to the relatively high genetic distances and lack of similarity in shell characteristics, the species is considered as distant sister species of C. zhanjiangensis and C. talonata. The results showed a non-native small size of oyster in the northern Persian Gulf, which might be a new species. The relative abundance of this species in the introduced location (Imam Khomeini port) may be linked to the high adaptation capability to the new environment.

Characteristics of Microbial Community and Function With the Succession of Mangroves.

In this study, 16S high-throughput and metagenomic sequencing analyses were employed to explore the changes in microbial community and function with the succession of mangroves (Sonneratia alba, Rhizophora apiculata, and Bruguiera parviflora) along the Merbok river estuary in Malaysia. The sediments of the three mangroves harbored their own unique dominant microbial taxa, whereas R. apiculata exhibited the highest microbial diversity. In general, Gammaproteobacteria, Actinobacteria, Alphaproteobacteria, Deltaproteobacteria, and Anaerolineae were the dominant microbial classes, but their abundances varied significantly among the three mangroves. Principal coordinates and redundancy analyses revealed that the specificity of the microbial community was highly correlated with mangrove populations and environmental factors. The results further showed that R. apiculata exhibited the highest carbon-related metabolism, coinciding with the highest organic carbon and microbial diversity. In addition, specific microbial taxa, such as Desulfobacterales and Rhizobiales, contributed the highest functional activities related to carbon metabolism, prokaryote carbon fixation, and methane metabolism. The present results provide a comprehensive understanding of the adaptations and functions of microbes in relation to environmental transition and mangrove succession in intertidal regions. High microbial diversity and carbon metabolism in R. apiculata might in turn facilitate and maintain the formation of climax mangroves in the middle region of the Merbok river estuary.

Occurrence, sources, and risk assessment of unconventional polycyclic aromatic compounds in marine sediments from sandy beach intertidal zones

This study investigated the concentrations of polycyclic aromatic compounds (PACs), including parent polyaromatic hydrocarbons (PAHs) and their nitrated and oxygenated derivatives, in 48 sediment samples from the intertidal region of sandy beaches in Baía de Todos os Santos (BTS), Salvador, State of Bahia, Brazil. The total PAH (∑PAH) concentration, total nitro-PAH (∑nitro-PAH) concentration, and total oxy-PAH (∑oxy-PAH) concentration ranged from 2.11 μg g−1 dry weight (dw) to 28.0 μg g−1 dw, 2.58 μg g−1 dw to 30.2 μg g−1 dw, and 0.34 μg g−1 dw to 3.65 μg g−1 dw, respectively. Elevated concentrations of parent PAHs and nitro-PAHs were found in samples from two sites in BTS, which were also characterized by high percentages of fine–medium sand and low organic matter contents. Potent mutagenic 3-nitrobenzanthrone (3-NBA) was found in 86% of the samples at concentrations ranging from 0.200 μg g−1 dw to 0.690 μg g−1 dw. Furthermore, calculations of the benzo[a]pyrene toxicity equivalency (BaPTEQ) indicated that three carcinogenic high-molecular-weight PAHs accounted for 98.7% of the total maximum PAH concentration. Finally, we assessed the possible environmental risks posed to benthic species living in the sediments of BTS. The results showed that the risk quotient for PAHs (RQPAHs) was ≥1. In turn, the summed RQ for all PACs (∑RQmixture) ranged from 1 to 30, but did not exceed the maximum allowable threshold; thus, the risks posed to benthic species were moderate for all sediment samples.