A dinoflagellate under the ambit of Harmful Algal Blooms (HAB), the bioluminescent Noctiluca scintillans (NS), has been infesting the northern Arabian Sea increasingly over the last few decades during late winter. Their occurrence is found to be due to seasonal oscillations in the coastal currents. The physical and biogeochemical parameters associated with the seasonal blooms are reasonably well known. But accurate quantitative estimation capability using remote sensing sensors over the extensive oceanic regime is still lacking. This is especially due to a lack of information on bio-optical properties associated with cell density measurements. We attempted to show that remote sensing reflectance and chl-a show significant relationship e.g., Rᵣₛ(531)/Rᵣₛ(510) = 0.8261 + 6.06 × 10⁻⁶NS + 0.02323chl-a (N = 19, R²ₐdⱼ = 0.99, p = 2.5 × 10⁻¹⁷, RMSE = 0.1083) which is applicable over diverse areas of the northeastern Arabian Sea e.g., coastal, shelf and offshore regions. The model is supported by a second dataset with an RMSE of 0.022893 (N = 8) for the Rᵣₛ(531)/Rᵣₛ(510) ratio. The NS cell densities were derived from the Rrs(510)/Rrs(531) band ratio within reasonable error and accuracy limits. Including sensor capability at 510 nm is suggested in future satellite launches.

An assessment of quantity, composition and seasonal variation of fishing-related plastic debris was conducted in six beaches along the Kerala coast of India during 2017–2018. Plastic items were the most dominant type of waste constituting 73.8% by number and 59.9% by weight. In the total debris recorded, 5540 pieces (36%) weighing 198.4 kg (39.8%) were fishing related trash. On an average 14.4 ± 12 fishing related items/100 m², corresponding to mean weight of 0.55 ± 0.7 kg/100 m² was recorded from these beaches. Results indicated that the fishing-related plastic items were concentrated four times more in the beaches with higher fishing intensity, as compared to the other beaches. Also, the concentration of fishing-related plastic was recorded higher in the post-monsoon season compared to the lowest during monsoon, which was significant with p-value < 0.05. The results emphasize the role of fishing activities in the generation of marine litter.

Hemocyte parameters have been used as a proxy to characterize the health condition of marine bivalves, as the effects of external and internal stresses are reflected well in these parameters. Marine bivalve hemocyte functions are often depressed during the post-spawning period due to physiological stress and energy depletion. In this study, we analyzed temporal changes in hemocyte parameters of the oyster Saccostrea kegaki on Jeju Island, off the south coast of Korea, using flow cytometry. Total hemocyte count (THC), hemocyte types, hemocyte mortality, and phagocytosis capacity were analyzed. S. kegaki spawned during June and August, when the sea surface temperature increased from 18 to 23 °C. Most of the oysters were in the spent and resting phases from September to January. THC dropped dramatically from September to October, when most oysters completed spawning. Histology revealed that the residual eggs or sperm were actively resorbed through phagocytosis by hemocytes during the spent stage. Hemocyte mortality also showed its annual peak in October, possibly due to increased resorbing activities. The phagocytosis capacities of the granulocytes decreased dramatically from September to February. The level of energy reserves (glycogen) in post-spawning tissues was significantly lower than that prior to spawning. The low energy level reserve during the post-spawning period likely reduced the THC and immune capacities, as oysters may have been unable to acquire sufficient food from the ambient environment.

This study covers water and sediment chemical characteristics by the western shore of Admiralty Bay (King George Island, Antarctica) in 2016. Chemical processes between sediment and water have been described based on the determination of ions, metals, non-metals, and TOC concentrations. Rock weathering is an important source of Fe, Ni, Co, Al in the seashore area. The PCA shows the impact of acidification in the release metals from sediment. Our results indicate that riverine mineral fluxes need to be accounted for as the volume of melt increases in response to climate change. Based on geoaccumulation indexes (anthropogenic fingerprint), we observed an increased concentration of Pb (Igₑₒ = 1.643), in the lake near station facilities and Cd in the area of Ecology Glacier (Igₑₒ > 1.389). Taking into account climate change and the intensification of anthropopressure, our study indicates that Antarctica requires a special focus on the seasonal dynamics of mineral content and pollution assessment.

Coastal eutrophication and consequent oxygen depletion (hypoxia) occurs worldwide due to increased human activity. The paucity of genomic information of microbes in hypoxia prone coastal waters have hindered our understanding of microorganism related causation and adaption to the environment. Here, using metagenomic approach, we investigated microbial metabolic capability in heavily polluted Pearl River estuary. Our results highlighted the possible roles of microbial metabolic activity in the formation of bottom water hypoxia by revealing enriched organic degradation related microbial genes in the bottom layer beneath surface phytoplankton bloom. Microbial nitrate reduction in hypoxia layer was low, possibly due to the low pH and fluctuating oxygen level. On contrary, high abundance of sulfate-reducing, and antibiotic and metal resistance related genes were detected in bottom and surface layers, respectively, indicating microbial adaptation to oxygen depletion and pollution. Our study provides gene level information on the interactive relations between microbial functions and environmental stress.

Millions of recreational boats and ~ 65,000 ocean-going merchant ships anchor routinely. Anchor and chain scour associated with these vessels mechanically disturb the seabed having implications for marine environments globally. Our review summarises the scientific literature that examines the response of biota to anchor scour across five habitats; unvegetated sediments; seagrass; rhodolith beds; coral and rocky reefs. Forty-one studies met our criteria with >85% of articles targeting recreational-based disturbances, mostly focussed on seagrass. Investigations of anchor scour from ships comes almost exclusively from cruise ships anchoring on coral reef. All research examined reported biota responding negatively to anchor scour, either directly or indirectly. Effects to biota were dependent on the spatio-temporal scale of the perturbation or the life-histories of the organisms impacted. We highlight several key knowledge gaps requiring urgent investigation and suggest a range of management strategies to work towards sustainable anchoring practices and the preservation of valuable seabed environments.

The abundance and distribution of microplastics in estuaries have been barely documented, and generally without accounting for the vertical structure in the water column. This study presents the very first data on the occurrence and distribution of microplastics in the Adour Estuary, SW France. The experimental data set was complemented by numerical simulations to gain understanding of the behaviour of suspended microplastics. Microplastics were found throughout the water column with a mean abundance of 1.13 part/m³. Films and fragments were the most abundant types of particles collected. Numerical simulations demonstrated that vertical distribution of microplastics in the water column is highly dependent on particle characteristics and on the local hydrodynamics. The main trend is that neutrally-buoyant microplastics are easily flushed out while heavier microplastics are prone to entrapment in the estuary, in particular under low discharge conditions. The present study suggest that estuaries could be a sink of microplastics.

Toxic effects of heavy oiling to wildlife are well known from oil spills, although sublethal oil exposure effects are poorly understood. We used Niche Mapper™, to compute spatially and temporally specific energetic and behavioral impacts of repeated sublethal oil exposure to double-crested cormorants (Phalacrocorax auritus). During winter (October-March) cormorants exposed to 13 g, 39 g, and 65-78 g of oil, had on average a 31%, 59%, and 76% predicted increase in total resting energetic requirements (RMR) compared to unoiled birds, respectively. Increased RMR resulted in a mean (±SD) predicted increase in time spent foraging of 36 (±13) min·d⁻¹. During the breeding season (April-September), cormorants had on average a 29%, 57% and 73% increase in total RMR and the mean predicted increase in time spent foraging was 131 (±49) min·d⁻¹. Thermoregulatory effects of sublethal oil exposure may cause greater impacts to bird populations than is currently understood.