Estuaries are one of the most valuable biomes on earth. Although humans are highly dependent on these ecosystems, anthropogenic activities have impacted estuaries worldwide, altering their ecological functions and ability to provide a variety of important ecosystem services. Many anthropogenic stressors combine to affect the soft sedimentary habitats that dominate estuarine ecosystems. Now, due to climate change, estuaries and other marine areas might be increasingly exposed to the emerging threat of megafires. Here, by sampling estuaries before and after a megafire, we describe impacts of wildfires on estuarine benthic habitats and justify why megafires are a new and concerning threat to coastal ecosystems. We (1) show that wildfires change the fundamental characteristics of estuarine benthic habitat, (2) identify the factors (burnt intensity and proximity to water's edge) that influence the consequences of fires on estuaries, and (3) identify relevant indicators of wildfire impact: metals, nutrients, and pyrogenic carbon. We then discuss how fires can impact estuaries globally, regardless of local variability and differences in catchment. In the first empirical assessment of the impact of wildfires on estuarine condition, our results highlight indicators that may assist waterway managers to empirically detect wildfire impacts in estuaries and identify catchment factors that should be included in fire risk assessments for estuaries. Overall, this study highlights the importance of considering fire threats in current and future estuarine and coastal management.

Plastic pollution continues to seep into natural and pristine habitats. Emerging laboratory-based research has evoked concern regarding plastic’s impact on ecosystem structure and function, the essence of the ecosystem services that supports our life, wellbeing, and economy. These impacts have yet to be observed in nature where complex ecosystem interaction networks are enveloped in environmental physical and chemical dynamics. Specifically, there is concern that environmental impacts of plastics reach beyond toxicity and into ecosystem processes such as primary production, respiration, carbon and nutrient cycling, filtration, bioturbation, and bioirrigation. Plastics are popularly regarded as recalcitrant carbon molecules, although they have not been fully assessed as such. We hypothesize that plastics can take on similar roles as natural recalcitrant carbon (i.e., lignin and humic substances) in carbon cycling and associated biogeochemistry. In this paper, we review the current knowledge of the impacts of plastic pollution on marine, benthic ecosystem function. We argue for research advancement through (1) employing field experiments, (2) evaluating ecological network disturbances by plastic, and (3) assessing the role of plastics (i.e., a carbon-based molecule) in carbon cycling at local and global scales.

The effects of dike construction on the geomorphology and sedimentary processes of tidal flats were investigated using high-precision topographic profiling, short cores, and unmanned aviation vehicle (UAV)-assisted photogrammetry to understand their adverse consequences on the benthic ecosystem. Tidal flats at the south of Shinsi Island near one of the two sluice gates of the Saemangeum dike, display prominent morphologic features known as shelly sand ridges or cheniers (sensu Otvos, 2000) that have migrated landward about 5 m in a year. The tidal flats were dominated by erosion from winter to spring and by deposition during the remainder of the year except for the periods of heavy precipitation when tidal drainage channels became larger and deeper by headward erosion. With overall coarser-grained surface sediments, the presence of actively migrating wave-built cheniers are in stark contrast to muddy tidal flats with a monotonous morphology before the completion of the Saemangeum dike in 2006. Southeasterly waves reflected from the dike during winter to spring when north to northwesterly winds prevail account for the wave-induced onshore sediment transport and rapid morphologic changes in the tidal flats despite their location protected from offshore waves. The diversity and biomass of major macrofauna species tend to increase during rapid erosion and decrease during rapid deposition, highlighting the anthropogenic effect of dike-induced physical disturbance on the benthic ecosystem in the otherwise sheltered tidal flats.

The eastern part of the Bay of Seine (English Channel) is highly impacted by harbour activities and the dumping of dredged sediment by the port authorities of Le Havre (GPMH) and Rouen (GPMR). Sediment dredged by the GPMH (2–2.5 millions of m³ per year) has been disposed at the subtidal Octeville site since 1947. Since the 2000s, mainly fine sediment (80% of fine particles <63 μm) has been disposed using alternate mosaic boxes with limited thickness (0.2 to 0.6 m per box per year), preventing the accumulation of disposed sediment in some parts of the dumping site. During the period August 2016 to September 2017, an experimental study was set up to identify the spatio-temporal changes of the macrobenthos collected at ten stations on six dates: three stations where different volumes of sediments were dumped (from 41,000 to 186,000 m³), two stations located within the Octeville site but without dumping operations during the study and five stations outside the disposal site (northern and southern zones). The Taxonomic Richness, total abundance and abundances of the polychaete Owenia fusiformis show negative correlations with the volumes of deposited sediment, whereas use of the AMBI (AZTI's Marine Biotic Index) and B2OA (Benthic Opportunist Annelids Amphipods) indices does not allow us to distinguish the impacted zone. Our study shows that the impact of dumping remains local and the benthic habitats display a high degree of resilience with rapid recovery of the community after the cessation of disturbance. Recommendations on the future long-term strategy are proposed to improve assessment and minimise the impact of dumping sediment on this benthic habitat.

Characterizing benthic habitat sensitivities of rapidly-developing countries is of paramount importance. Recent efforts defining the benthic habitat of Qatar's coastal zone with a high-resolution, ground-truthed benthic habitat map has provided a framework on which to develop a habitat sensitivity map. Here we present a sensitivity analysis catered towards identifying habitats with varying sensitivities to natural and anthropogenic stressors on a quantitative scale from 1 to 5, low to high. We have identified that the majority of the coastal area is low risk habitat (i.e. sandflats). However, there are six areas which are assigned as high risk by virtue of their rich occurrences of seagrass meadows, mangrove forests, and coral reefs - [1]. The reefs offshore of Al Zubarah on the west coast of the peninsula; [2] The Al Ruwais fringing reef on the northern tip of the peninsula; [3] The east-coast bays of Al Khor and Al Dhakira; [4] The shore-attached reef complex off Mesaieed (east coast); [5] The Jazirat al Bushayriyah offshore high; and, [6] The entire shelf of Halul Island. The sensitivity analysis presented here builds on a recently-developed benthic habitat map of Qatar's coastal zone and covers a total are of 4500km². Results gleaned from this analysis can be used to support marine spatial planning objectives and ecosystem-based management decision making.

Non-biodegradable marine debris such as derelict fishing gears and their parts, polythene covers, carry bags, synthetic packaging materials etc., cause serious damages to the benthic ecosystem including the marine biota. We report here the monthly variation in the marine plastic litter (MPL) and its relative percentage to the quantity of fish caught from the trawling grounds off Cochin, Ratnagiri, Mumbai and Veraval along the west coast as well as Visakhapatnam from the east coast of India. The mean values of MPL from the fishing grounds registered the maximum of 55.2 ± 16.52 kg/km² off Veraval and the minimum of 2.11 ± 0.55 kg/km² off Visakhapatnam, registering a national average of 10.95 ± 3.05 kg/km². The relative percentage of MPL over the fish catch remained highest (3.83%) at Veraval and lowest from Visakhapatnam (0.33%) while, the national average was 1.89 ± 0.28. Monsoon season registered maximum MPL in the fishing grounds of all the coastal regions we studied. Depth of the trawling grounds also influenced the quantity of MPL that 20 m depth registered quantity (24.25 ± 9.16 kg/km²) and the overall mean at 10 m and 40 m depth zone are significantly different from that of 20 m. The database created through this study are discussed in the light of increasing deleterious effects of plastic pollution in the active fishing areas in coastal region and the urgent need to save the sea for sustainable use of its resources.

Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) can pose serious threats to the marine benthic ecosystem as it results in a deposition of oil contaminated marine snow on the sediment surface. In a microcosm experiment we investigated the effects of oil in combination with artificial marine snow or kaolin clay on two benthic invertebrate species and benthic meiofauna. The amphipod showed a dose-dependent decrease in survival for both oil-contaminated clay and oil-contaminated marine snow. The gastropod was only affected by the highest concentration of oil-contaminated marine snow and had internal concentrations of PAHs with a similar distribution as oil-contaminated marine snow. Benthic copepods showed higher survival in presence of marine snow. This study revealed that marine snow on the sediment after oil spills affects organisms in a trait-dependent way and that it can be a vector for introducing oil into the food web.

This study investigated the structure and function of macrobenthic community in Bohai Bay upon improvement of water quality due to pollution abatement. A total of 166 species were collected in the summer and autumn sampling, with an increase in sensitive species recorded as compared to data from previous studies. While historical variations in species richness indicated signs of improvement in community structure, results of functional diversity indices revealed that the macrobenthic community in Bohai Bay was still in an early stage of recovery. From BIO-ENV analysis, habitat instability may hinder how community responded to water quality improvement. Results of the benthic habitat quality assessment also indicated that the ecological status in most areas of Bohai Bay was classified as good, while a few estuarine regions were categorized in a poor status.

To evaluate the impact of bottom aquaculture on benthic ecosystems, characteristics of benthic food web were studied using stable isotope techniques during four seasons in a Manila clam (Ruditapes philippinarum) bottom aquaculture area in a semi-enclosed bay, China. Results showed that although nitrogen stable isotope values of food sources (particulate organic matter and phytoplankton) had significant seasonal differences, there were no significant seasonal changes for benthic food web structure. Manila clam bottom aquaculture can enhance the secondary productivity and improve the basic trophic pathways by providing bio-deposits. Besides particulate organic matter and phytoplankton, Manila clam could feed on self-generated feces with high nitrogen stable isotope values, and benthic micro- and macroalga with high carbon stable isotope values. Secondary productivity of the stations with a high degree of aquaculture was higher than that of stations with a low degree. Bivalve bottom culture may have a positive impact on benthic ecosystem functioning.

The Sanchi oil tanker collision has attracted worldwide attention for its uniqueness in history. This study investigates the contamination level, spatial distribution, sources, and ecological risk level of polycyclic aromatic hydrocarbons (PAHs) present in the surface sediments collected from around the sunken tanker. The results indicated that the total PAH contents in the study area were in the range of 26.42–226.94 ngˑg⁻¹, with an average of 106.86 ngˑg⁻¹. The highest PAH concentration was observed at the station closest to the Sanchi wreckage, indicating potential PAH contamination due to the accident. The PAH ratios and statistical analysis revealed that the PAHs were mainly generated by coal and fuel oil combustion, with certain petrogenic inputs. The ecological risk assessment results suggested that adverse ecological effects to the benthic ecosystem due to PAH contamination was rare. However, long-term monitoring of the local sedimentary environment is highly recommended because of the prominent presence of high molecular weight PAHs.