Microplastic size-dependent biochemical and molecular effects in alga Heterosigma akashiwo.

Micro- and nano-plastics (MNPs) are increasingly prevalent contaminants in marine ecosystems and have a variety of negative impacts on marine organisms. While their toxic impact on freshwater microalgae has been well-documented, limited research has been conducted on the influence of MNPs on marine red tide algae, despite their significant implications for human health and coastal ecological stability. This study investigated the physiological, biochemical and molecular reactions of the common harmful algal species, Heterosigma akashiwo, when exposed to polystyrene (PS) MNPs of 80 nm and 1 µm in size with the concentrations of 0, 1, 10, and 20 mg L-1 in 12 days. The results showed that 80 nm-sized MNPs (at concentrations of 10 mg L-1 and 20 mg L-1) inhibited algal growth. Despite the increased superoxide dismutase (SOD) activity and up-regulation of glutathione metabolism, exposure-induced oxidative stress remained the main cause of the inhibition. Up-regulation of aminoacyl-tRNA biosynthesis and amino acid biosynthesis pathways provide the necessary amino acid feedstock for the synthesis of antioxidant enzymes such as SOD. 1 µm sized PS MNPs increased chlorophyll a (Chl-a) content without significant effects on other parameters. In addition, H. akashiwo have an effective self-regulation ability to defend against two sized MNPs stress at concentrations of 1 mg L-1 by upregulating gene expression related to endocytosis, biotin metabolism, and oxidative phosphorylation. These results provided evidence that H. akashiwo was able to resist exposure to 1 µm MPs, whereas 80 nm NPs exerted a toxic effect on H. akashiwo. This study deepens our understanding of the interaction between MNPs and marine harmful algal at the transcriptional level, providing valuable insights for further evaluating the potential impact of PS MNPs on harmful algal blooms in marine ecosystems.

The inhibitory effects of the antifouling compound Irgarol 1051 on the marine diatom Skeletonema sp. across a broad range of photosynthetically active radiation.

The release of anthropogenic organic pollutants has resulted in extensive environmental risks to coastal waters. Among pollutants released, the most common antifoulant, Irgarol 1051, is an effective inhibitor of photosystem II of photoautotrophs; thus, the continuous release of this compound into surrounding seawater would potentially threaten marine algae. To investigate this, we grew the model marine diatom Skeletonema sp. at different concentrations of Irgarol 1051 and levels of photosynthetically active radiation (PAR). Irgarol did not affect the photochemical capacity when cells were incubated in the dark, but photochemical yields all significantly decreased, and relative inhibition by Irgarol increased once cells were exposed to even the lowest PAR, with lower photochemical yields observed under increased level of Irgarol. In addition, the rate of decrease in yield increased with Irgarol concentration but was unchanged among PAR treatments. The growth rates showed a similar pattern to photochemical yields, with lower values under higher Irgarol concentrations, but with no significant differences in the effect of Irgarol observed between the light levels employed. The ratio of repair to damage rates of PSII clearly shows that this ratio decreased with light intensity, largely due to increases in damage rates and that the PAR level at which repair balanced damage decreased under a high level of Irgarol. Our results suggest that the inhibitory effects of Irgarol become obvious after PAR exposure even at a relatively low light level, suggesting that Irgarol would affect phytoplankton throughout the daytime, and may therefore have a broad environmental risk, potentially limiting coastal primary production.