Arcuatula senhousia in the UK: evidence to inform current status and future invasive potential

Invasive non-native species proceed through the Invasion Process upon introduction to a new location, with stages comprising establishment, growth, spread, and invasive impact. High fecundity, driven by fast growth, short lifespan, and a long reproduction period, can lead to high population densities, facilitating stage progression. The Asian date mussel (Arcuatula senhousia) is a marine intertidal–subtidal species, recently established in the UK. Given its potential to impact ecosystem services in Northern Europe, understanding the Invasion Process stage it has reached is imperative for assessing potential invasiveness and informing management. Therefore, population parameters of subtidal A. senhousia in the UK were evaluated from April 2021 to March 2022 to assess invasion stage. Specimens were collected (n = 1,029) via dredging and processed for condition index, gonadosomatic index, gonad index, length-frequency distribution, and electronic length-frequency analyses. While densities were low (<1 individuals per m²), maximum lifespan was high (23 months) and growth rate was high (1.8 mm per month), relative to other populations within the species’ global range. Results confirmed June to October spawning as previously reported in the UK and France but also evidenced secondary spawning (in November) for the first time in Northern Europe. Successful recruitment from primary and secondary spawning in 2020 was also apparent. Findings indicate A. senhousia has reached the Growth stage, and that further spread within the UK and Northern Europe is likely. Climate change will likely increase larval survivorship and individual and population fecundity, facilitating progression to invasive impact, potentially within the next decade.