Microplastics and food shortage impair the byssal attachment of thick-shelled mussel Mytilus coruscus.

Microplastics (MPs) have become a ubiquitous emerging pollutant in the global marine environment. The potential toxic effects of MPs and interactions of MP pollution with other stressors such as food limitation on marine organisms' health are not yet well understood. This study investigated the effects of three-week exposure to different MPs and food shortage on the physical defense mechanisms (byssus production and properties) of Mytilus coruscus. Starvation significantly reduced the number of byssus threads, and combined exposure to MPs and food shortage suppressed the adhesion ability and condition index of mussels. The length of the byssus threads was not affected by all experimental exposures. Transcript levels of genes encoding key proteins involved in byssus formation (the mussel foot proteins mfp-1, -2, -3, -4, -5 and -6, and prepolymerized collagen proteins preCOL-D, -P and -NG) were altered by interactions between the MPs and food shortage. These findings show that insufficient food supply can exacerbate the adverse effects of MPs on mussel defense which might have implications for survival and fitness of mussels under food limited conditions (e.g. in winter) in polluted coastal habitats.

Oxidative stress induced by nanoplastics in the liver of juvenile large yellow croaker Larimichthys crocea.

There are many toxicological studies on microplastics, but little is known about the effect of nanoplastics (NPs). Here, we evaluated the oxidative stress responses induced by NPs (10, 104 and 106 particles/l) in juvenile Larimichthys crocea during 14-d NPs exposure followed by a 7-d recovery. After exposure, the activities of antioxidant enzymes (SOD, CAT, GPx) and MDA levels increased in the liver of fish at the highest NPs concentration. SOD and CAT activities remained elevated above the baseline after recovery under high-concentration NPs but returned to the baseline in two other NP treatments. Although lipid peroxidation in liver was reversible, juvenile fish in NPs treatments exhibited a lower survival rate than the control during both exposure and recovery. Furthermore, IBR value and PCA analysis showed the potential adverse effects of NPs. Considering that NPs can reduce the survival of fish juveniles, impacts of NPs on fishery productivity should be considered.

Kelp cultivation effectively improves water quality and regulates phytoplankton community in a turbid, highly eutrophic bay.

Coastal eutrophication and its associated harmful algal blooms have emerged as one of the most severe environmental problems worldwide. Seaweed cultivation has been widely encouraged to control eutrophication and algal blooms. Among them, cultivated kelp (Saccharina japonica) dominates primarily by production and area. However, the responses of water quality and phytoplankton community to kelp farming remain unclear. Here, thirteen cruises were conducted in the kelp farms and control areas in the turbid, highly eutrophic Xiangshan Bay of the East China Sea from 2008 to 2015. Results indicated that kelp cultivation slightly increased dissolved oxygen and pH, but reduced dissolved inorganic nitrogen and phosphorus. We estimated that kelp harvesting would remove 297 t of nitrogen and 42 t of phosphorus from this bay annually. Because of decreased flow velocity, turbulence, and sediment resuspension, kelp farming greatly reduced suspended solids and increased transparency, resulting in increases in phytoplankton chlorophyll a and abundance. Additionally, kelp farming appreciably increased phytoplankton species number, Marglef richness, and Shannon-Wiener diversity indices by 51.6%, 40.1%, and 13.1%, respectively. Analysis of similarity and similarity percentages demonstrated that phytoplankton community composition differed significantly between the farm and control area, which was mostly attributed to long-chained diatoms and single-celled dinoflagellates. However, after the kelp harvesting, all measurements of water quality and phytoplankton biomass, diversity, and community composition exhibited no significant difference. Our study highlights that kelp cultivation alleviates eutrophication and acidification and enhances phytoplankton diversity, thus providing guidance for macroalgal aquaculture and remediation in eutrophic waters.