Mytella strigata (Bivalvia: Mytilidae): an alien mussel recently introduced to Singapore and spreading rapidly

Abstract

ABSTRACTThe American brackish-water mussel Mytella strigata is reported from Singapore for the first time. In 2016 a survey of intertidal hard structures in the Johor Straits revealed its almost ubiquitous presence in high mean densities, up to 124 ± 32 individuals 25 cm−2 along the shoreline. Subtidal nets employed by floating fish farms were also fouled with this species. Densities exceeding 10,000 individuals 100 cm−2 were observed, to the exclusion of its relative Perna viridis, the Asian green mussel. Size-frequency analyses of shells indicated the presence of both juveniles and adults. Juveniles have an extremely variable shell surface pigmentation. The adults, reaching 5 cm in shell length, generally have a thick dark greenish brown to almost black periostracum, but bright green and olive green individuals, some with distinctive brown streaks, have also been observed. However, sequences of the mitochondrial COI gene were consistent with mussels from Brazil, Colombia and Ecuador, where they are natively distributed, while shells were reconcilable with type material. The species may have been transported in ballast water and/or with fouling directly from its native provinces, or spread from the Philippines where there are already established populations of M. strigata, possibly since the nineteenth century.