Abstract

Research and monitoring of coastal habitats and biodiversity is increasingly contributing to the discovery of new alien species, which highlights the use of long-term monitoring for timely assessment and management due to marine environmental changes. Research work undertaken through coastal snorkelling surveys and working with fishermen allow for additional monitoring effort to record biodiversity changes and new alien species presence. One such new alien fish species was observed during spring snorkelling research while a specimen was collected in August 2016 to undertake detailed morphological, meristic and genetic analyses. Mitochondrial DNA barcoding analyses were undertaken to confirm the species' identity as the family Holocentridae is composed of a number of species that have very similar and overlapping morphological characters which may lead to misidentification. This research led to the identification of the first record of a specimen of Longjaw squirrelfish, Holocentrus adscensionis (Osbeck, 1765), in the Mediterranean Sea. This is a subtropical reef-associated species native to the Atlantic Ocean and may compete with native Mediterranean reef species.