Yi Zhu

Food safety concerns affect life health. Mussels are a significant source of high-quality marine protein in China, but their ability to bioaccumulate heavy metals raises concerns regarding food safety, warranting further investigation. This study compares the concentrations of seven trace elements include six heavy metals (Cd, Cr, Hg, Pb, Cu, Zn) and harmful element inorganic arsenic (iAs) in the soft tissues of two mussel species, i.e. the invasive Mytella strigata (Hanley, 1843) and the native, commercially important Perna viridis (Linnaeus, 1758), collected from same habitats of Haikou, Shanwei, and Zhanjiang, China. The results revealed species-related variations in trace elements concentrations. Zinc (Zn) exhibited the highest concentration, while cadmium (Cd) and mercury (Hg) had the lowest levels in both mussel species. M. strigata was more proficient in accumulating iAs, Cu, and Pb than P. viridis, but was less efficient in accumulating Cd. Correlation analysis showed significant positive correlations between iAs-Pb and iAs-Zn (p < 0.05). Heavy metal pollution and food safety evaluations indicated that iAs had the highest single-factor pollution index in both species across all locations. The Nemerow comprehensive indices for M. strigata from both Shanwei and Zhanjiang, and P. viridis from Zhanjiang, exceeded 3, indicating severe pollution. Target hazard quotient analysis of iAs suggested a potential health risk for M. strigata from Shanwei. Therefore, the trace elements and food safety of wild mussels, especially invasive mussels, should draw more attention.

Native to tropical America, the charru mussel, Mytella strigata, has been spreading rapidly in the West Pacific Ocean, including the South China Sea. In order to study the adaptive evolution of M. strigata and examine the present status of invasion in China, the mitochondrial nad2 gene fragment was employed to analyze the genetic variations of seven populations sampled in both spring and autumn 2023. Results showed that all the populations had high haplotype diversity (>0.5) and low nucleotide diversity (M. strigata population expansion in China.

Biological invasion is a primary direct driver of biodiversity loss. Recently, owing to exploitation competition with an invasive mussel, Mytella strigata (Hanley, 1843), there has been a drastic decrease in the population of native Perna viridis (Linnaeus, 1758) in several western Pacific regions. In the present study, intestinal microbiota, metabolome, and key digestive enzyme activities were compared between the two competing mussels, M. strigata and P. viridis, to elucidate the differences in intestinal microbiota and metabolic points. We observed that Proteobacteria, Firmicutes, and Bacteroidota were the three predominant bacterial phyla in the two species. The relative abundance of Bacteroidota related to carbohydrate-degrading ability was significantly higher in M. strigata than in P. viridis. Compared to P. viridis, different metabolites including maltose and trehalose were enriched in M. strigata. Lastly, higher carbohydrases activities of alpha-amylase, cellulase, and xylanase were observed in M. strigata than in P. viridis. These differences might play an important role in the adaptation process of M. strigata to the new environment. This study provides important basic knowledge for investigating the competition between M. strigata and P. viridis in terms of food resources utilization.

Mytella strigata is a highly adaptable invasive alien species that has been established in coastal China since 2014. Mitochondrial DNA (mtDNA) is an important tool for studying the evolution and population genetics of invasive species. In this study, the mitochondrial genome of M. strigata from China was sequenced by Illumina high-throughput sequencing and characterized with 13 protein-coding genes (PCGs). By assessing the selective pressure of 13 PCGs, the nad2 gene had the fastest evolutionary rate and was finally selected for population genetic analysis. A total of 285 nad2 sequences from seven M. strigata populations in China were analyzed and showed obviously T-rich and C-rich characteristics. According to population genetic diversity analysis, all the seven populations had haplotype (gene) diversity (Hd) ≥ 0.5 and nucleotide diversity (Pi) < 0.005. Haplotype networks showed a “star” distribution. Population historical dynamic analyses showed that Fu’s Fs and Tajima’s D values of all populations were negative except the Qukou (QK) and Beihai (BH) populations. The Zhangzhou (ZJ) and Xiamen (XM) populations were unimodal while the other populations were multimodal. These results suggested that the population of M. strigata in China may have passed the bottleneck period and is currently in a state of population expansion.