Iron is recognized as an efficient method to alleviate sulfide stress. This study tested the response of Zostera marina plants to different levels of sedimentary sulfides (100.0–818.7 μmol L⁻¹) and iron inputs (590.0–825.3 μg L⁻¹) in a field experiment performed over an eighty-day period. We measured plant responses in terms of shoot density and plant morphology and productivity. The relationship between the propagation effort (PE, in %) and sulfide content (S, in μmol L⁻¹) was expressed as: PE = −14.01 × ln (S) + 86.86 (R² = 0.99, p < .01), which indicates that the toxic limit of the pore-water sulfide concentration for the survival of eelgrass is 493 μmol L⁻¹. The addition of iron can reduce the toxicity of sulfides to eelgrass beds, resulting in an increase in plant density and productivity, and can even reverse the decline of eelgrass beds exposed to high sulfide concentrations.

Microplastics (MPs) are present in fresh, brackish, or marine waters. Micro- and macroinvertebrates can mistake MPs or small microplastics (SMPs, <100 μm) to be food particles and easily ingest them according to the size of their mouthparts. SMPs may then block the passage of food through the intestinal tract (i.e. hepatopancreas), accumulate within the organism, and enter the food web. Pacific oysters (Crassostrea gigas) are allochthonous filter-feeding bivalve mollusks, which have been introduced in coastal seas around the world in both natural banks and farms. Considering their economic and ecological value, these bivalves have been chosen as a model to study the ingestion of SMPs. A novel method for the extraction and purification of SMPs in bivalves was developed. Quantification and simultaneous polymer identification of SMPs using Micro-FTIR (Fourier Transform Infrared Spectroscopy) were performed, with a limit of detection for the particle size of 5 μm.

Brunei Bay is one of the most important marine environments of East Malaysia (South China Sea), covering many productive ecosystems with activities including fisheries, tourism, and main shipping lanes for petroleum transfers. Evaluation of the sources and distributions of steroids in the surface sedimentary organic matter was carried out by gas chromatography–mass spectrometry (GC–MS). The concentrations of the total identified sterols (TIS) ranged between 0.81 and 12.69 μg g⁻¹ dry weight, and the total sterones were between 0.11 and 5.66 μg g⁻¹ dry weight. The coprostanol level was comparatively low (<0.10 μg g⁻¹), and the multi-biomarker proxies indicated that the region did not exhibit significant contamination from sewage effluents. Principal component analysis (PCA) revealed the coastal environment of the study area was dominated by allochthonous (mainly terrestrial) organic matter input.

Environmental contamination by organophosphate flame retardants (OPFRs) and plasticizers are environmental concerns. In this study, 18 OPFRs were analyzed in sediment and bivalves collected from 50 locations along the Korean coast to assess occurrence, geographical distribution, contamination source, and bioaccumulation potential. Tris(1-chloro-2-propanyl) phosphate (TCPP) and tris(2-ethylhexyl) phosphate (TEHP) were highly detected (>80%) OPFRs in sediment and bivalves. Total concentrations of OPFRs and plasticizers in sediment and bivalves ranged from 2.18 to 347 ng/g dry weight and from 6.12 to 206 ng/g dry weight, respectively, which were within the ranges reported for previous studies. Sedimentary organic carbon was a primary factor governing the OPFR distribution. Concentrations of OPFRs and plasticizers in sediments from harbor zones were significantly higher than non-harbor zones, indicating that shipping activity is a contamination source of OPFRs and plasticizers in coastal environments. Biota-sediment accumulation factors <1 for several OPFRs indicated limited potential for bioaccumulation.

Microbial mats may be an alternative tool for phosphorus (P) remediation of eutrophic coastal waters. The main objective of this work was to determine the importance that the living and non-living components of the mats have on P short-term sorption. Microbial mats were collected in the Paso Seco coastal flat, Argentina (40°38′3.32″S; 62°12′24.85″W), and incubated under controlled conditions in the lab. An adsorption curve was performed with the microbial mats. Active mats had a Freundlich constant 8.9-fold higher than underlying sandy sediments. Collected samples were then treated as follows: maintaining and disturbing their structural integrity (natural and autoclaved, respectively), and both conditions were incubated with filtered seawater, without and with phosphate addition (0 and 5 mg P L⁻¹, respectively). Natural mats had a significantly-higher phosphate removal percentage than autoclaved ones, suggesting that living microorganisms increase P short-term sorption efficiency by ~25%, while non-living matter may account for the rest.

Antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) are worldwide considered as emerging contaminants of large interest, and a primary threat to human health. It is becoming clear that the environment plays a central role in the transmission, spread, and evolution of antibiotic resistance. Although marine systems have been largely investigated, only a few studies have considered the presence of ARGs in meso- and bathypelagic waters. To date, no molecular based studies have yet been made to investigate the occurrence of ARGs in the Black Sea, the largest meromictic basin in the world, receiving water from a number of important European rivers and their residues of anthropogenic activities in permanently stratified mesopelagic water masses. In this study, we determined the presence and the abundance of five ARGs (blaCTXM, ermB, qnrS, sul2, tetA) and of the heavy metal resistance gene (HMRG) czcA, in different sampling sites in the eastern and western Black Sea, at several depths (up to 1000 m) and various distances from the shoreline. Three ARGs (blaCTXM, sul2, and tetA) and czcA were present in at least 43% of the analysed samples, whereas ermB and qnrS were never detected. In particular, sul2 abundances increased significantly in coastal location, whereas tetA increased with sampling depth. These findings point out the Black Sea as a source of ARGs and HMRGs distributed along the whole water column.

The aim of the present work was to unravel which environmental drivers govern the dynamics of toxic dinoflagellate abundance as well as their associated paralytic shellfish toxins (PSTs), diarrhetic shellfish toxins (DSTs) and pectenotoxin-2 (PTX2) in Ambon Bay, Eastern Indonesia. Weather, biological and physicochemical parameters were investigated weekly over a 7-month period. Both PSTs and PTX2 were detected at low levels, yet they persisted throughout the research. Meanwhile, DSTs were absent. A strong correlation was found between total particulate PST and Gymnodinium catenatum cell abundance, implying that this species was the main producer of this toxin. PTX2 was positively correlated with Dinophysis miles cell abundance. Vertical mixing, tidal elevation and irradiance attenuation were the main environmental factors that regulated both toxins and cell abundances, while nutrients showed only weak correlations. The present study indicates that dinoflagellate toxins form a potential environmental, economic and health risk in this Eastern Indonesian bay.

The Pearl River Estuary is an important sink of organochlorine compounds (OCs), and OC pollution levels in surface sediments remain largely unknown at present. We collected and analysed residual DDTs, HCHs and PCBs of 45 surface sediments from the Pearl River Estuary in 2017. The values of DDTs (1.83 to 6.98 ng·g⁻¹) and HCHs (0.43 to 2.14 ng·g⁻¹) were higher in the Humen outlet, and the values of PCBs (4.6 to 187.4 ng·g⁻¹) were higher in the coastal areas of Shenzhen. The DDTs and HCHs have generally decreased while the PCBs have been rapidly increasing in recent decades. The DDTs might originate from technical DDT and dicofol. The major source of HCHs was lindane. The main potential sources of PCBs were increased industrial products, ship painting, E-waste disassembly, maricultural and agricultural pollution. The total PCBs and DDTs had medium ecological risks according to the sediment quality guidelines.

Bulk sedimentary phosphorus (P) is studied to evaluate its source, distribution, preservation and enrichment in relation with organic carbon (OC), sediment textures and moisture contents in the northern Beibu Gulf. Approximately 80% of surface sediments in the investigated sites were composed of coarse sandy texture (>63 μm). Total P (TP), inorganic P (IP) and organic P (OP) contents were lower to medium range compared to the levels reported for other marginal seas. Sedimentary OC and P were derived from mixed sources, with high terrestrial influence in the coastal areas (molar OC/OP ratios >250:1). The distribution of P corroborated with the variation tendency of fine-grained sediments, moisture contents and OC. Both IP and OP may significantly influence the trophic state of seawater if released from surface sediments. Influenced by hydrodynamics, frequent resuspension and high abundance of sand, TP is less preserved, and shows low to moderate enrichment in surface sediments.

The Wetlands Reserve in Al Wusta Governorate on the Arabian Sea is important for internationally migrating birds and local wildlife, but data on marine litter in the reserve, and wider region, are rare. Seven beaches around the reserve were surveyed for litter in February 2020. Abundance and weight of litter were categorised along 100 m transects. Abundance ranged from 0.1 to 1.4 items m⁻² and weight ranged from 3.2 to 170.4 g m⁻². Plastic was the dominant material in abundance (84.4–97.7%) and weight (71.3–99.3%). Top categories in abundance and weight were fisheries-related, water bottles and caps, and food packaging. Fisheries-related litter comprised 19.6–36.7% of all in abundance, but 41.4–94.4% in weight. The high proportion of fisheries-related litter (by weight) indicates that providing practical disposal facilities for unwanted and broken fishing gear would substantially reduce the impact of litter on this vital wetlands reserve.