Development and Testing of Species-Specific Primers for Detecting the Presence of the Northern Pacific Sea Star (Asterias amurensis) from Environmental DNA.

The starfish Asterias amurensis, a well-known predator of molluscan species in intertidal ecosystems, has caused substantial ecological and economic losses in North China such as offshore Qingdao. Effective monitoring and prevention measures are urged to minimize its negative impacts. Compared with traditional biomonitoring methods, environmental DNA technology has emerged as a powerful and cost-efficient tool for inferring species' presence and abundance. In this study, we developed a pair of species-specific primers (i.e., Ast-F and Ast-R) for the A. amurensis mitochondrial COI gene and tested its utility in amplifying and quantifying the DNA fragments from environmental samples under both laboratory and field conditions. The results of controlled water tank experiments demonstrated that the amount of eDNA released by A. amurensis was positively related to its biomass; after the removal of the starfish, the eDNA degraded significantly in 24 h and remained detectable for 8 days. The number of eDNA copies enriched tended to increase with smaller pore size of filter membrane and larger volume of filtered water. For field tests, we confirmed the validation of our approach in six locations in Qingdao by filtering 1000 ml water per sample with a 0.45-µm pore size filtration. All the amplification products generated a single and bright band via gel electrophoresis, and the quantitative PCR results unveiled significant differences in eDNA copies. This study provided an eDNA-based approach for investigating the distribution and biomass of A. amurensis, which may help to formulate early warning and management strategies in coastal Qingdao and other regions.

Characterization and comparison of the mitochondrial genomes of the sea star Asterias amurensis (Echinodermata: Asteroidea) in East Asia.

The starfish Asterias amurensis is a marine pest native to the northwestern Pacific and has successfully invaded southern Australia. Asterias amurensis have caused substantial environmental and economic impacts in both native and non-native regions. However, little information is available about the genetic features of its native populations, especially for those in North China. Here we sequenced the complete mitochondrial genomes of five individuals from different locations in China and compared their characteristics with three mitogenomes available from Japan. Multiple analyses and comparisons revealed little difference in the gene composition, gene order, codon usage, and nucleotide content among the eight mitogenomes. However, intraspecific phylogenetic reconstruction unveiled two divergent lineages between specimens from North China plus Ushimado (Seto Inland Sea, Japan) and northern Japan (Asamushi and Onagawa). This conclusion was backed by an analysis of pairwise genetic distances, which showed that individuals from different lineages had relatively higher values (all above 2%). Based on knowledge of paleoenvironmental and tectonic activity in the northwestern Pacific, the two lineages might have originated during the Early Pliocene due to the isolation of the East China Sea from the Japan Sea/East Sea during that time, while the present-day distribution of these lineages have likely been influenced by the ocean current system.