To investigate toxic effects of microplastic on marine microalgae Skeletonema costatum, both algal growth inhibition test and non-contact shading test were carried out, and algal photosynthesis parameters were also determined. The SEM images were used to observe interactions between microplastic and algae. It was found that microplastic (mPVC, average diameter 1 μm) had obvious inhibition on growth of microalgae and the maximum growth inhibition ratio (IR) reached up to 39.7% after 96 h exposure. However, plastic debris (bPVC, average diameter 1 mm) had no effects on growth of microalgae. High concentration (50 mg/L) mPVC also had negative effects on algal photosynthesis since both chlorophyll content and photosynthetic efficiency (ΦPSⅡ) decreased under mPVC treatments. Shading effect was not one reason for toxicity of microplastic on algae in this study. Compared with non-contact shading effect, interactions between microplastic and microalage such as adsorption and aggregation were more reasonable explanations for toxic effects of microplastic on marine microalgae. The SEM images provided a more direct and reasonable method to observe the behaviors of microplastic.

Ocean acidification (OA) is a global problem to marine ecosystems. Cadmium (Cd) is a typical metal pollutant, which is non-essential but extremely toxic to marine organisms. The combined effects of marine pollution and climate-driven ocean changes should be considered for the effective marine ecosystem management of coastal areas. Previous reports have separately investigated the influences of OA and Cd pollution on marine organisms. However, little is known of the potential combined effects of OA and Cd pollution on marine diatoms. We investigated the sole and combined influences of OA (1500 ppm CO₂) and Cd exposure (0.4 and 1.2 mg/L) on the coastal diatom Skeletonema costatum. Our results clearly showed that OA significantly alleviated the toxicity of Cd to S. costatum growth and mitigated the oxidant stress, although the intercellular Cd accumulation still increased. OA partially rescued S. costatum from the inhibition of photosynthesis and pyruvate metabolism caused by Cd exposure. It also upregulated genes involved in gluconeogenesis, glycolysis, the citrate cycle (TCA), Ribonucleic acid (RNA) metabolism, and especially the biosynthesis of non-protein thiol compounds. These changes might contribute to algal growth and Cd resistance. Overall, this study demonstrates that OA can alleviate Cd toxicity to S. costatum and explores the potential underlying mechanisms at both the cellular and molecular levels. These results will ultimately help us understand the impacts of combined stresses of climate change and metal pollution on marine organisms and expand the knowledge of the ecological risks of OA.

Polystyrene nanoplastics (PS NPs), which are newly emerging as particulate pollutants, are one of the most abundant plastic types in marine debris. Although there has been extensive research on microplastics, the sorption behavior of PS NPs in surface waters remains unknown. In addition, in the previous joint toxicity studies, the concentration of organic pollutant in the joint system was based on the EC₅₀ of this pollutant, rather than the actually amount of this pollutant adsorbed on nanoplastics (NPs). In this study, the sorption behavior of PS NPs with different surface charges in the surface water of estuaries and joint toxicity of that absorbed tetracycline antibiotic in equilibrium were investigated for the first time. Because of the electrostatic repulsion, salting-out effect, and partition function, the sorption capacity of tetracycline antibiotic by differently charged PS NPs was enhanced with increasing salinity. The biological effects of exposure to tetracycline-saturated PS NPs were complicated, which can be attributed to the surface characteristics of mixtures such as hydrophobicity and charges. Thus, the role of NPs in the natural environment as a carrier of antibiotics may provide an alternative for antibiotic inputs from inland water to coastal marine water, which would not only change the environmental fate and ecotoxicology of antibiotics and NPs, but also pose challenges to the safety of coastal aquaculture and marine ecosystem.

Based on survey data from the Bohai Sea of China in autumn (October) and winter (December) 2019, the structural characteristics of phytoplankton communities and their relationship with environmental factors were analysed. A total of 114 species of phytoplankton belonging to 84 genera and 3 phyla were identified. Warm-water species occurred frequently but cold-water species decreased in the Bohai Sea. This was associated with global warming and rising water temperatures. By comparing with historical data, Paralia sulcata gradually flourished and became the dominant species in autumn and winter, whereas the dominance of Skeletonema costatum decreased. The marine environment of the Bohai Sea has improved significantly in recent years, and phytoplankton biodiversity has increased. In autumn, both total phytoplankton and dinoflagellates were negatively correlated with salinity, and Pseudo-nitzschia delicatissima was positively correlated with nitrite and ammonia nitrogen. In winter, Nitzschia spp. showed a positive correlation with nitrate and a negative correlation with salinity.

Dissolved organic nitrogen (DON) from terrestrial input exacerbates eutrophication and induces harmful algal blooms. We investigated the effects of hydrophilic (Hic) and low molecular weight (LMW) DON on the phytoplankton community in Jiaozhou Bay during autumn (October 2017) and spring (May 2018). Our results showed DON additions significantly increased algal growth while decreasing community biodiversity and provide a competitive advantage for Skeletonema costatum. These situations were further intensified by increasing temperature in autumn. Additionally, Hic DON had a higher bioavailability than LMW DON. Based on emission-excitation matrix spectra, we identified protein-like components as the main components of Hic DON whereas humus-like components were the principal components of LMW. Correlation analysis confirmed a positive correlation between DON bioavailability and protein-like components. Therefore, our results indicate DON from terrestrial input disrupts the structural stability of the phytoplankton community and increases the risk of harmful algal blooms, which in turn threaten coastal ecosystems.

Long-term effects of environmental factors on phytoplankton community in Deep Bay, Hong Kong, were investigated from 1994 to 2016. Phytoplankton community experienced three important shifts: small flagellates and Chroomonas spp. dominated from 1994 to 2006. Heavy blooms of diatoms Skeletonema costatum and Thalassiosira spp. occurred and became the dominant species between 2007 and 2009. Phytoplankton community was dominated by small flagellates and Chroomonas spp. from 2010 to 2015, and their abundance was much higher than earlier periods. Abundance of Chroomonas spp. decreased sharply in 2016, and Thalassiosira spp. became the dominant species. Phytoplankton community changed from consisting mainly of small flagellates and Chroomonas spp. to more diatoms, changing from ~90% to ~45% for other species abundance and from <10% to ~55% for diatoms. Nitrite, 5-day biochemical oxygen demand, salinity, suspended solids and turbidity were more influential on phytoplankton variation (23.65% explained by all the variables).

Spatial variations in summertime phytoplankton community structure from 1991 to 2017 in Daya Bay, China were investigated in this research. The abundance of total phytoplankton and diatoms significantly increased during the study period in all regions of the bay while an increase in dinoflagellates abundance was only significant in the inner and middle bay areas. Pseudo-nitzschia spp. were overwhelmingly dominant followed by Skeletonema costatum. Ceratium furca was the dominant dinoflagellate. Overall, species diversity and evenness indices showed downward trends during the study period. Moreover, the bloom frequency of Scrippsiella trochoidea (associated with red tides) has increased rapidly since the 2000s in the inner bay. These temporal dynamics are largely explained by enhanced dissolved inorganic nitrogen (DIN) concentrations, which increased by 64.58% during 2005–2017 relative to 1991–2004, induced by human activities, along with temperature reductions and salinity increases resulting from open oceanic seawater intrusion.

Ocean acidification (OA) and eutrophication intensifies in coastal sea under anthropogenic impact. OA coupled with the NH4-N source effect in coastal water is likely to affect the planktonic ecosystem. In this work, Skeletonema costatum and Nitzschia closterium were chosen as typical species of diatom in Chinese coastal ecosystems to test the potential effect of OA and NH4-N. Results showed that the growth and NH4-N uptake of S. costatum and N. closterium were significantly inhibited by pH decline. The maximum uptake rate is higher than the maximum growth rate, implying that NH4-N was assimilated faster for S. costatum and N. closterium with decreasing pH. Therefore, the inhibition rate of the growth of the two diatoms by the coupling effect of OA and eutrophication (pH7.45) is higher that than in the coastal sea by the end of the 21st century (pH7.71).

The Norwegian Authorities have classified 30 WWII shipwrecks to have a considerable potential for pollution to the environment, based on the location and condition of the wreck and the types and amount of fuel. Oil thus far has been removed from eight of these shipwrecks. The water accommodated fractions of oils from two British wrecks and two German wrecks have been studied with special emphasis on chemistry and biological effects (algae growth (Skeletonema costatum) and copepod mortality (Calanus finmarchicus)). Chemical analyses were also performed on three additional German wreck oils. The results from these studies show that the coal based oils from German WWII shipwrecks have higher toxicity to marine organisms than the mineral oils from the British shipwrecks. The potential for higher impact on the marine environment of coal based oils has resulted in an altering of the priority list for oil recovery from WWII wrecks by the authorities.

Dissolved organic nitrogen (DON) is an important nutrient in the aquatic environment. This study examined the influence of DON addition on the adsorption, absorption, and distribution in macromolecular forms of environmentally deleterious trace metal (Ni) in Prorocentrum donghaiense and Skeletonema costatum over eight days. Ni adsorption and absorption of two species increased with the addition of urea, while Ni adsorption and absorption of two species in the presence of humic substances (HS) decreased. Meanwhile, Ni adsorption and absorption of P. donghaiense were higher than that of S. costatum. Furthermore, Ni contents in the protein fraction of the cells, both in P. donghaiense and S. costatum, were increased with both urea and HS addition. Thus, urea and HS input could impact Ni biogeochemistry and bioavailability, and then affect the biodynamics thereafter.