Coastal wetland sediments are vital to the global carbon cycle as they represent large sinks of blue carbon – carbon from atmospheric and oceanic sources – which are threatened by ecosystem loss. The forms of sequestered carbon and the sequestration capability are affected by many bio- and geochemical factors that change unpredictably along coastal locales. In the present study, we investigated three unique coastal sites – a coastal mangrove and two sabkhas with contrasting geology and tidal influence in the Qatar peninsula – for their carbon capture ability to determine how biogeochemical indices affect their blue carbon sequestration potential. We applied a suite of biological and geochemical tools, collecting the sediment cores of approximately 40 cm depth; analysed sediment porewater; performed depth-profiling of the organic matter, sedimentary minerals, microbial community and analysis of sediment surface for pH, oxygen (O2); redox potential and hydrogen sulfide (H2S) by microsensors. High-resolution transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDXS) and scanning transmission X-ray microscopy (STXM) revealed templating effects that promoted Mg-carbonate nucleation in coastal hypersaline environments. Microsensing reveals the intricacy of the oxic/anoxic transition at the sediment surface. Microbial DNA sequencing at various sediment depths shows the occurrence of microbial genera, whose functions explain the geochemical trends and carbon sequestration pathways observed at each site. Notably, we found that carbon sequestration in the mangrove and carbonate-sand sabkha was correlated with organic matter degradation and inorganic carbon content, while in the siliciclastic sabkha it was solely influenced by sediment density and depth.

We measured the concentrations of antifouling biocides in sediment, mangrove leaves and seagrasses from Merambong and Tinggi Island, Johor, Malaysia to evaluate their contamination levels. Although the concentrations of tributyltin (TBT) in mangrove leaves in Merambong in 2013 were significantly lower than those in 2012, the Sea-Nine 211 concentration in 2013 was significantly higher than that in 2012, suggesting that the use of antifouling biocides changed from TBT to Sea-Nine 211. The concentration of each BT (butyltin) and PT (phenyltin) in the mangrove area was significantly higher than the corresponding concentration in the seagrass area in Merambong, but the concentrations of Sea-Nine 211, diuron, chlorothalonil, Irgarol 1051 and M1 in seagrasses were significantly higher than those in mangrove leaves. There were differences in the accumulation profiles of OTs (organotins) and alternative biocides between the seagrass shoots and roots. The concentration of OTs in the seagrass roots was almost the same or higher than those in the shoots, whereas those of alternative biocides shows the opposite pattern to the OTs. Significant high relationships were observed between stable carbon isotope (δ13C) and OTs, Sea-Nine 211 and Irgarols in mangrove leaves. The concentrations of these compounds increased along with the δ13C values of the mangroves. These results suggest that mangroves take up the bicarbonate ions and nutrients in sediment and/or seawater through their roots, along with OTs, Sea-Nine 211 and Irgarols which were accumulated in sediment.

Coastal vegetation includes unique species with adaptations to the specific conditions of this environment, and in the Mediterranean region urban development of coastal areas has severely affected coastal ecosystems. Astragalus berytheus Boiss. & Blanche is a narrow endemic plant of the eastern Mediterranean coast, occurring in Lebanon and Palestine/Israel; its Red List status has not been previously assessed. As a result of the effects of urban sprawl in coastal areas A. berytheus is one of the most threatened plant taxa in Lebanon. We assess the conservation status of this taxon and propose conservation measures. Only one population of A. berytheus is extant in Lebanon, in the Tyre Coast Nature Reserve. We recommend that A. berytheus should be categorized as Endangered globally and as Critically Endangered at the national level in Lebanon. Unless adequate conservation measures are implemented A. berytheus is likely to go extinct in Lebanon in the near future.

To elucidate the details of both the current status of contamination and the accumulation of organotin compounds (OTs) in mangroves in coastal ecosystems, we determined the concentrations of butyltin compounds (BTs) and phenyltin compounds (PTs) in sediment and mangrove leaves collected from mangrove forests in Merambong and Tinggi Island, Malaysia. Butyltins were detected in all sediment samples collected from both regions, whereas PTs were not detected. The levels of tributyltin (TBT) compounds in the sediment samples were lower than those from previous studies conducted in Malaysia and at other sites in South-east Asia. In both Merambong and Tinggi Island, the average proportions of dibutyltin (DBT) and monobutyltin (MBT), which are degradation products of TBT, were ~70%. This result suggests that the input of TBT has decreased in Malaysia. The proportions of DBT and MBT in the sediment from Merambong were higher than those from Tinggi Island. The concentrations of TBT in mangrove leaves from Tinggi Island were significantly higher than those from Merambong. MBT was the most dominant type among the BTs in mangrove leaves from both Merambong and Tinggi Island. The ratios of the BTs burden in mangrove leaves to the BTs concentration in sediment from Merambong and Tinggi Island averaged 3.1 and 6.2, respectively. Among the values of BTs, the MBT values were found to be the highest in both regions.

The variation in CO2 flux from the forest floor is important in understanding the role of mangrove forests as a carbon sink. To clarify the effects of soil temperature and tidal conditions on variation in CO2 flux, sediment–atmosphere CO2 fluxes were measured between June 2012 and May 2013. We used the closed chamber method for two plots, with a 0.5 m difference in elevation (B, high elevation; R-B, low elevation), in a mangrove forest in south-western Japan. CO2 fluxes were highest in the warm season and showed a weak positive correlation with soil temperature in both forests. Estimated monthly CO2 flux showed moderate seasonal variation in accordance with the exposure duration of the soil surface under tidal fluctuation. Additionally, measured CO2 flux and soil temperature were slightly higher in the R-B plot than the B plot, although estimated annual CO2 flux was higher in the B plot than the R-B plot due to different exposure durations. These results suggest that variation in the exposure duration of the forest floor, which changes seasonally and microgeographically, is important in evaluating the annual CO2 flux at a local scale and understanding the role of mangrove ecosystems as regulators of atmospheric CO2.

The temporal variation in the taxonomic distinctness of biofilm-associated diatom microflora within the colonization process was studied in coastal waters of the Yellow Sea, northern China from May to June 2014. Samples were collected at depths of 1 and 3 m, using glass slides as an artificial substratum. The colonization dynamics of diatom microflora showed similar species composition at both depths. In the young communities (1–7 days), the taxonomic patterns showed high variability compared with those in the mature ones (10 days and more). However, taxonomic distinctness indices at the two depths differed during early stages (e.g. 1–3 days). The taxonomic diversity (Δ) represented a high variability (coefficients of variation >10%) over all colonization periods, whereas the taxonomic distinctness (Δ*), average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) showed high stability (coefficients of variation <10%) after 7 days. Based on these findings, we suggest that the exposure time of more than 7 days may be sufficient to identify the taxonomic distinctness of biofilm-associated diatom microflora for both community research and monitoring programmes in marine ecosystems.

Sanya Bay lies at the southern part of Hainan Island, 18°15′N 109°28′E. The seawater in the bay has been catastrophically polluted during the past two decades with urban sewage from the rapidly developing Sanya City. The marine flora research in Sanya Bay was started at the beginning of the 1930s and the most detailed studies were performed by two German-Chinese expeditions in 1990 (October–December) and in 1992 (March–April). In April, October, November and December 2008–2010 the marine flora of Sanya Bay was studied by the authors at three localities: Luhuitou Peninsula, Xiaodong Hai and Dadong Hai. Marine algae were sampled in the intertidal and upper subtidal zones (to 4–5 m depth). The list of species (including varieties and forms) of the marine algae for Sanya Bay sampled during the period from 2008 to 2010 is compared with those collected at the same localities in 1990/1992. Comparative analysis of the floristic composition of the marine red, brown and green algae (found during different time periods) revealed that considerable changes have taken place between 1990/1992 and 2008–2010 at Sanya Bay. There was an increase in filamentous, tubular and fine blade-like green and red algae (mainly epiphytes with a high surface to volume ratio) and a displacement of upright-growing fleshy, foliose and other large green, brown and red algae with a low surface to volume ratio. It is assumed that the changes reflect mainly increased pollution by urban sewage and mariculture pond wastes and probably by coral bleaching events of 1998.