Development of a sedimentary DNA detection assay for the invasive moon snail Laguncula pulchella preferentially preying on the Manila clam Ruditapes philippinarum

The moon snail Laguncula pulchella, native to China and the Korean Peninsula, has invaded Japan alongside the imported Manila clam Ruditapes philippinarum and is expanding its distribution. This species preferentially feeds on live R. philippinarum. Recently, the nationwide yield of Manila clams in Japan has declined significantly. Although the primary cause of this decline remains unclear, predation by L. pulchella is believed to be a contributing factor in northern Japan. Efficient eradication measures are essential to mitigate predation. However, this snail often burrows into sediment, making detection challenging and potentially leading to an underestimation of its presence and distribution in previous surveys. Analytical techniques for detecting environmental DNA present in water and sediment have advanced. Specifically, sedimentary DNA (sedDNA) can be used to estimate the distribution of target organisms using approximately 1 g of sediment. In this study, we aimed to estimate the presence of L. pulchella using sedDNA analysis, with the development of a detection assay. After evaluating the molecular phylogeny of this species, we designed primers and probes specific to all the haplotypes. Additionally, we performed tank experiments to confirm that the sedDNA of L. pulchella can be detected. The highest concentration detected was approximately 10⁸ copies/g of sediment, mainly from crawling traces. Since mucus is retained in the crawling traces, it may serve as a primary source of sedDNA. By applying the developed detection assay, it is anticipated that accurate estimates of the presence of L. pulchella will be possible, leading to efficient eradication efforts.