During the COVID-19 pandemic, face masks became a common type of litter invading many different environments, including tourist beaches. However, the presence of face masks on beaches threatens the marine environment with a new form of plastic pollution. In this study, we monitored the occurrence and density of face masks on five tourist beaches along the Moroccan Mediterranean during five months starting from February until June 2021. A total of 321 face masks were recorded on the five beaches, 96.27% of which were single use. The mean density of face masks was 0.0012 ± 0.0008 m⁻². Recreational beaches were the most polluted in the study area. This is related to the important influx of beachgoers on urban beaches compared to resort beaches. With the large number of masks introduced on the beach, we hypothesize that microplastic pollution could increase drastically in the Moroccan Mediterranean in the coming years. Significant efforts are required to reduce this type of waste.

Laboratory exposure studies allow to investigate the impact of microplastics on marine biota, but commonly lack a procedural control, i.e. assessing the effects of natural microparticles. In two experiments with the mussel Semimytilus algosus, we compared the effects of clay vs. polyvinyl chloride (PVC) and celite vs. polymethyl-methacrylate (PMMA), respectively, at concentrations of 1.5, 15 and 150 mg l⁻¹. After more than 60 days, no effects on respiration and clearance rates, mortality and byssus strength were observed. However, in mussels exposed to PVC the Body Condition Index was 34% lower at 150 mg l⁻¹ than at 1.5 mg l⁻¹. Furthermore, at 15 mg l⁻¹, mussels exposed to microplastics produced over 40% less byssus than those exposed to natural microparticles. This suggests that mussels react differently to natural microparticles and to microplastics, but only at high particle loads that exceed current environmental microplastic concentrations by orders of magnitude.

The construction of world-class Bay makes the marine ecology in Guangdong-Hong Kong-Macao Great Bay Area in risk. Based on the DPSIR index framework, Lotka-Volterra symbiosis model is applied to calculate symbiosis degree between coastal socio-economic system and marine ecosystem in 9 coastal cities. It is found that the marine ecological pressure in this area have not been reversed in recent 20 years. Most cities are in the stage that socio-economic development and marine ecological damage coexist. In Shenzhen, Guangzhou, Dongguan and Zhongshan, the damaged marine ecology has begun to restrain the further expansion of economy and society. The massive population agglomeration in Hong Kong, Macao and other places has caused serious marine ecological stress. It is urgent to improve the marine ecological security by cultivating ecological industrial system and industrial clusters, establishing a land-sea ecological restoration, promoting joint-protection and co-governance across different administrative regions.

The structural characteristics of phytoplankton communities and their relationship with environmental factors were analysed based on survey data from the central South China Sea in summer 2020. A total of 416 separate taxa from 90 genera and 4 phyla were identified, with an average cell abundance of 572.98 cells/L. The dominant phytoplankton species were Nitzschia spp., Gyrodinium spp., Synedra spp. and Navicula spp. The Shannon-Wiener index ranged from 2.25 to 4.98, and the evenness index varied from 0.48 to 0.93. Correlation analysis showed that total cell abundance was negatively correlated with salinity, nitrate and silicate and was positively correlated with nitrite. Compared with the historical data, Thalassionema nitzschioides was cited repeatedly in previous researches as the dominant species. In addition, the Shannon–Wiener index showed an overall increasing trend over time, and the community structure is becoming more stable.

This baseline study describes the microplastic (MPs) problem on seven beaches located on Agadir, central Atlantic coast of Morocco. Microplastics abundances (densities) ranged from 7680 MPs/kg to 34,200 MPs/kg above other world beaches. The following shapes were found: fibers, fragments, films, and pellets. Fibers were the dominant typology with a 73%. Polyethylene (PE) was the predominant polymer in all beaches with an average percentage of 59%, followed by Polypropylene (PP - 18%), Polystyrene (PS - 9%), Polyvinyl chloride (PVC - 8%), and Ethylene-vinyl acetate (EVA - 6%). Microplastics abundances presented in this work suggest continuous inputs of plastics of all sizes and types. Also, all observed shapes highlight a combination of sources (primary and secondary). Central Atlantic Moroccan beaches are currently affected by extreme values of MPs that demand urgent interventions to restore environmental quality.

Foamed litter comprise a significant amount of the pollution at beaches globally. This group represents a variety of foamed items and fragments originating from different applications and sources. Although foamed plastic contributes importantly to the marine environmental pollution, there is generally limited knowledge of the composition of this litter pool. The aim of this study was to characterize item types and polymer materials of foamed litter from six Danish reference beaches during the period 2018–2021. The foamed litter were classified into ten categories, including identifiable items, as well as fragments of foamed PS, or pieces of other foamed polymers of rigid or flexible sponges. Foamed PS (42%) and PUR (49%) were identified as the dominant polymers by FTIR analysis. Multivariate exploratory analysis was performed to investigate PUR foam, and specific spectra features for rigid and flexible foam were demonstrated. Furthermore, we assessed different correlation methods for identification of PUR foams.

Between 2017 and 2022, sediment labile organic matter, physico-chemical and nutrient content of the water column, biomass and C, N, P, S content of Sphaerococcus coronopifolius, a Rhodophyta that produced vegetative blooms in an area of the Orbetello lagoon (Italy) not far from the effluents of two land-based fish-farms, were examined and compared with an area even further away from that source where the species was not found. In order to understand the reasons for an important mat development in only one specific area, microcosm experiments were also carried out. Results suggest the species developed in dense and extensive mats under high orthophosphate and nitrate nitrogen ion concentrations conditions, behaving as an opportunistic species.

The pollution status of polycyclic aromatic hydrocarbons (PAHs) in seawater, surface sediment, and marine organisms was investigated in Haizhou Bay, which is a traditional marine fish farming region in China. The total concentrations of PAHs in seawater, surface sediment, and marine organisms were 12.4–40.3 ng/L (average 24.8 ng/L), 183.2–496.6 ng/g (average 293.5 ng/g), and 228.1–679.9 ng/g (average 392.6 ng/g), respectively. Source analysis results showed that the PAH sources for seawater and marine organisms were coal and biomass combustion (66.53%), petroleum (28.94%), and traffic (4.52%), while those for the surface sediment were traffic (48.14%), coal and biomass combustion (40.56%). The lifetime cancer risk increment (ILCR) values of marine organisms in the Haizhou Bay were less than 10⁻⁶, indicating no carcinogenic risk. In the future, this study can be used as a reference to understand the distribution and interrelation of PAHs in other semi-enclosed bays in the world.

For the first time, this study explored the dominant features of Marine HeatWaves (MHWs) in the Persian Gulf and Oman Sea (1982–2020). The spatial extent of MHWs has nearly doubled in the last 24 years. Since 1997, the average number of MHW days in the central parts of the Persian Gulf has increased about 19 times compared to the period 1982–1997. The average number of the detected MHW events has increased by about three times. Simultaneously with the increase in MHWs frequency trend, the trend in the average number of MHW days has also increased. Since 1997, the average number of MHW days in the study area has almost increased by 10 times. The mean duration of the detected MHWs ranged from 5 to10 days. On average, in a major part of the Persian Gulf, about 1–2 MHW events occur annually.

Biotic resistance is considered an important driver in the establishment of non-indigenous species (NIS), but experiments in the marine environment have led to contradictory results. In this context, a transplant experiment of fouling communities was carried out over five months. Settlement panels were moved from low impact (species-rich native communities) to high impact sites by NIS in two Italian areas to test the biotic resistance hypothesis. Fouling communities displayed significant differences among treatments before and after the transplant, thus indicating the maintenance of a peculiar fouling community in transplanted panels. On the other hand, newly recruited species were similar between treatments and neither a facilitation nor a mitigation role from native fouling communities on NIS was observed. Our results highlight the importance to better investigate the factors affecting the high variability obtained in experiments testing this hypothesis, with the aim to identify potential solutions for NIS management in ports.