This study aimed to investigate the spatial and temporal distribution as well as the partitioning behavior of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) during the summer and autumn seasons of 2020. It was found that the average concentration of PAHs in surface seawater was significantly higher in autumn (58.16ngL-1) than in summer (40.47ngL-1) due to a large amount of input in autumn and more photodegradation and biodegradation affected by higher temperatures in summer. The spatial distribution indicated that the river had a significant dilution effect on PAHs in summer and became a significant input source in autumn. In addition, a large number of oil and gas development platforms were distributed throughout the Bohai Bay, and the discharge of production and domestic sewage contributed to the PAHs pollution level. As a semi-enclosed bay, the water exchange capacity of Bohai Bay was poor, leading to a greater accumulation of PAHs in the marine environment. The diagnostic ratios and PCA-MLR indicated that petroleum was the most important source of PAHs with a contribution of 45%, followed by fuel combustion (39%) such as coal and oil. Photooxidation in seawater resulted in a reduction of BaP/BeP, indicating that seasonal variations in photooxidation had a significant impact on the composition of PAHs (summer: 1.49, autumn: 2.96). The concentration of particulate PAHs was correlated with the concentration of dissolved PAHs and SPM, and the proportion of 3-rings (43.8%) and 4-rings (49.8%) PAHs was significantly higher on SPM. The distribution coefficients Log Kd and φspm-water showed a trend of increasing and then decreasing as the number of rings increased, with the 4-rings Pyr exhibiting the highest value. According to the ecological risk assessment, the ecological risk of total PAHs was low (RQNCs<800, RQMECs<1), but the ecological risk of individual PAHs and the carcinogenicity of high-ring PAHs could not be ignored (＞96.5%). This study is significant for investigating the "sources and sinks" of PAHs in the complex marine environment by analyzing the partitioning behavior of PAHs in different phases.

A 45-day trial was conducted to study the effect of seawater total alkalinity (TA) level up- and downregulation on the growth performance and calcification of Haliotis discus hannai Ino, while seawater pH was maintained at pHNBS=8.1. Although seawater was not acidified, the results showed that TA downregulation caused a significant reduction (P<0.05) in the somatic tissue growth of juvenile abalone, while TA upregulation significantly increased growth performance (P<0.05). Similar to the impacts of pH reduction, TA downregulation also induces a decline in CO2 buffering capacity, which may be the reason why somatic tissue growth was reduced, as lowered CO2 buffering capacity was reported to shift the acid-base balancing of abalone. Parts of the periostracum layer weremissing and exposed the inner shell layers of the individuals from the TA-downregulated group. Scanning electron microscopy (SEM) results showed calcium carbonate densely deposited onto the inner shell in the control and TA-upregulated groups, while sparsely deposited calcium carbonate was observed in the TA-downregulated group. The C: N ratio in the shell of individuals from the TA-downregulated group was significantly lower than that of the other two groups, indicating that less inorganic carbon was added to the shell. As a result, abalone grew lighter and thinner shells in TA-downregulated seawater. Although seawater was not acidified, TA downregulation also caused a reduction in the calcium carbonate saturation state (Ω), which induced the erosion of the surface shell and the interruption of calcium carbonate generation. In conclusion, although seawater pH remained at ambient levels, the lowered CO2 buffering capacity and Ω induced by seawater TA downregulation also showed a detrimental effect on the growth and calcification of Pacific abalone. The impact of ocean acidification on the growth of abalone should not be assessed using only seawater pH and/or pCO2 but rather taking into account all of carbonate chemistry, particularly the CO2 buffering capacity. Abalone cultivation is suggested to be carried out in seawater with a higher level of CO2 buffering capacity and Ω, which can be achieved through integrated culture with seaweed or increasing the seawater TA level.

The interpretation of δ13C values in trophic ecology requires standardization of the lipid content of organisms estimated through their C:N ratio. To avoid time-consuming lipid extractions, the use of mathematical corrections has been developed for many years, and the conclusions generally point in the direction of species-specific adjustment of the models. This study aimed at defining the maximum taxonomic level required to obtain the best corrected δ13C values in small pelagic fish of the order Clupeiformes. δ13C values of six species were analyzed bulk and lipid-free, and were used to fit and validate linear and mass-balance models at different taxonomic levels. Despite a species effect combined with the C:N ratio effect, the corrected δ13C values produced by a global model for the Clupeiformes were as good as or better when compared to lipid-free samples than those produced by species-specific models, paving the way for possible generalization to other species in this order. At the order level, the linear model outperformed the mass-balance model.

A trophic model was constructed for the Poonthura Estuary, a small, anthropogenically impacted estuary along the south-western coast of India. An Ecopath with Ecosim based trophic modelling approach, based on observations made between 2016 and 2020, revealed that the Poonthura Estuary had a low total system throughput (3044.2tkm-2 year-1), low ascendancy (15%), high Finn's cycling index (17.9%), low primary production/total biomass (5.2tkm-2 year-1), high mean transfer efficiency (12.4%), and low eco-exergy (14,455.46gm detritus equivalent m-2). These values indicated that the estuary is an immature, less organized, and unhealthy system. The evaluation of Ecological Network Analysis, and ecosystem health indices revealed that the ecological structure and functioning of the estuary are impaired to a large extent from multiple anthropogenic stressors. The Poonthura Estuary trophic model revealed the total primary production/respiration value as 0.46, indicative of the massive pollution that the system is subjected to, particularly from organic sources. Small benthic carnivores were the most important keystone groups recorded from the Poonthura Estuary, despite their low biomass. The comparison of ecological indices of Poonthura Estuary, with those recorded for other small estuaries from various geographical locations, suggested dissimilar trophic functioning and food web structures from estuaries with similar physical features. Our study is a pioneering step to reveal the ecosystem status and functioning of small, anthropogenically disturbed estuaries, besides offering theoretical and scientific basis for the management, supervision and restoration of the Poonthura Estuary as well as other small estuaries, around the world.

Atlantification, known as impacts of high-latitude Atlantic water inflows on the Arctic Ocean has strengthened owing to climate change, corresponding to the rapid ice retreat in the Arctic. The relationship between phytoplankton and environmental changes in the Arctic on the interannual scale is unclear because of the lack of long-time series data. In this study, we discuss the ecological response to Atlantic water intrusion in the Kongsfjorden,Svalbard. We measured chlorophyll a and photosynthesis pigments for the water column samples from a fixed section along the Kongsfjorden to study the response of phytoplankton biomass and communities to Atlantic water intrusion in the summer season from 2007 to 2018. The results showed that dinoflagellates, prasinophytes, cryptophytes, and chlorophytes consistently accounted for over 50% of the total biomass, with the distinct annual variation of chlorophyll a. Bioavailable nitrogen was the main limiting factor on phytoplankton growth in the study area, as inferred by its concentration and nutrients ratios. The relationship between phytoplankton and water mass analysis suggested that the intrusion of Atlantic water in Kongsfjorden may cause interannual variability of the phytoplankton biomass and community structure by influencing the nutrient supply and water stratification in the fjord region. Our study provides insights into the ongoing impact of Atlantification on the phytoplankton community in the Arctic fjord.

Temperature plays an important role in affecting the physiological traits of marine plankton. In this study, we conducted an outdoor incubation experiment to investigate the effects of elevated temperature on Chl a, photosynthetic carbon fixation and the composition of plankton communities in the surface seawater around Pingtan Island, the northwest Taiwan Strait in Autumn 2022. After 3-4 days of incubation, elevated temperature (1-4°C higher than ambient temperature) led to a decrease in Chl a concentration across all three stations, did not result in significant increases in the particulate organic carbon (POC) and nitrogen (PON) concentrations in seawater with high nitrate concentrations, whereas increased POC and PON concentrations in nitrate-limited seawater. These findings suggest that the effect of temperature on the POC and PON contents of plankton is affected by the availability of nitrate. Diatoms were the dominant phytoplankton group in all three stations. Our results indicate that ocean warming has a potential to increase the POC contents of marine plankton per volume of seawater, which may increase the ability of phytoplankton to absorb atmospheric CO2 and to alleviate global warming.

Marine bivalves in intertidal zones and land-based seawater ponds are constantly subjected to a wide range of salinity fluctuations due to heavy rainfall, intense drought, and human activities. As osmoconformers, bivalves rely primarily on rapid release or accumulation of free amino acids (FAAs) for osmoregulation. Euryhaline bivalves are capable of withstanding hyposaline and hypersaline environments through regulation of physiology, metabolism, and gene expression. However, current understanding of the molecular mechanisms underlying osmoregulation and salinity adaptation in euryhaline bivalves remains largely limited. In this study, RNA-seq, WGCNA and flow cytometric analysis were performed to investigate the physiological responses of hard clams (Mercenaria mercenaria) to acute short-term hyposalinity (AL) and hypersalinity (AH), and chronic long-term hyposalinity (CL) and hypersalinity (CH) stress. We found that amino acids biosynthesis was significantly inhibited and aminoacyl-tRNA biosynthesis was augmented to decrease intracellular osmolarity during hyposaline exposure. Under CH, numerous autophagy-related genes (ATGs) were highly expressed, and the autophagy activity of gill cells were significantly up-regulated. A significant decrease in total FAAs content was observed in gills after NH4Cl treatment, indicating that autophagy was crucial for osmoregulation in hard clams during prolonged exposure to hypersaline environments. To prevent premature or unnecessary apoptosis, the expression of cathepsin L was inhibited under AL and AH, and inhibitors of apoptosis was augmented under CL and CH. Additionally, neuroendocrine regulation was involved in salinity adaption in hard clams. This study provides novel insights into the physiological responses of euryhaline marine bivalves to hyposaline and hypersaline environments.

Marine fungi are widely distributed in the ocean, playing an important role in the ecosystems, but only little information is available about their occurrence and activity. Seagrass bleaching is also a neglected phenomenon that seems to be linked to warm environments, even though the causes are still to be defined. In this study, the cultivable mycoflora associated to the leaf conditions (bleached, necrotic and live) and section (from the base to the tip) in the seagrass Posidonia oceanica was investigated in a Mediterranean warm-edge location (Cyprus). A total of 17 Ascomycota species/taxon were identified and results highlighted that mycoflora composition changed significantly in relation to both the leaf condition and section. A few known pathogens of terrestrial plants were detected only on bleached leaves, but it remains unknown whether they have any direct connections with P. oceanica bleaching phenomenon.

In this study, we investigated the taxonomic composition of the bacteria and phytoplankton communities in the Pearl River Estuary (PRE) through Illumina sequencing of the V3-V4 region of the 16S rRNA gene. Furthermore, their relationships as well as recorded environmental variables were explored by co-occurrence networks. Bacterial community composition was different in two size fractions, as well as along the salinity gradient across two seasons. Free-living (FL) communities were dominated by pico-sized Cyanobacteria (Synechococcus CC9902) while Exiguobacterium, Halomonas and Pseudomonas were predominantly associated with particle-associated (PA) lifestyle, and Cyanobium PCC-6307 exhibited seasonal shifts in lifestyles in different seasons. In wet season, bacterial community composition was characterized by abundance of Cyanobacteria, Actinobacteria, and Bacteroidetes, which were tightly linked with high riverine inflow. While in dry season, Proteobacteria increased in prevalence, especially for Psychrobacter, NOR5/OM60 clade and Pseudomonas, which were thrived in lower water temperature and higher salinity. Moreover, we discovered that differences between PA and FL composition were more significant in the wet season than in the dry season, which may be due to better nutritional conditions of particles (indicated by POC%) in the wet season and then attract more diverse PA populations. Based on the analysis of plastidial 16S rRNA genes, abundant small-sized mixotrophic phytoplankton (Dinophyceae, Euglenida and Haptophyta) were identified in the PRE. The complexity of co-occurrence network increased from FL to PA fractions in both seasons, which suggested that suspended particles can provide ecological niches for particle-associated colonizers contributing to the maintenance of a more stable community structure. In addition, the majority of phytoplankton species exhibited positive co-occurrences with both other phytoplankton species and bacterial counterparts, indicating the mutual cooperation between phytoplankton assemblages and specific bacterial populations e likely benefited from phytoplankton-derived organic compounds. This study enhances our understanding of the seasonal and spatial dynamics of bacterial communities and their potential relationship with phytoplankton assembly in estuarine waters.