Leech breach: a first record of the invasive freshwater leech Helobdella europaea (Hirudinea: Glossiphoniidae) in Fiji

Context. The freshwater flat leech Helobdella europaea Kutschera, 1987 is a small annelid indigenous to South America. This invasive species feeds on the haemolymph of host aquatic invertebrates, with occurrences reported from Europe, USA, Taiwan, North Africa, Hawai'i, Australia and New Zealand. A large number of individuals were discovered in the Ba River catchment, Fiji, during a 2015-2020 freshwater biodiversity survey, raising concerns of potential impacts on endemic Fijian aquatic invertebrate fauna and ecosystem integrity. Aims. To facilitate assessments of its spread and ethology, this study employed morphological and phylogenetic analyses for verification of taxonomic identity. Methods. Phylogenetic trees were constructed using a 658 bp fragment of the mitochondrial DNA cox1 (COI) gene. The first complete mitochondrial genome sequence of H. europaea was also determined using selective multiple displacement amplification and Oxford Nanopore Technology to provide a reference for future comparative analyses and source tracking of spread to other regions. Key results. Morphological and COI analyses identified all Fijian leech specimens collected (n = 16) as H. europaea, reporting the first occurrence of this species on a south-west Pacific Island. The complete mitochondrial genome was sequenced. Conclusions. Confirmation of its presence in Fiji is a national biosecurity concern and will guide the Biosecurity Authority of Fiji and national agencies in further ecosystem assessment and response strategies. Implications. With the complete mitochondrial genome of H. europaea now available, transmission pathway traceability is possible in other regions where this species may be detected.