Emergence of an invasive ascidian in Canary Islands (Eastern Atlantic): Tracking the arrival and spread of Cnemidocarpa irene

This study documents the first occurrence and rapid expansion of the solitary ascidian Cnemidocarpa irene in natural marine habitats of Tenerife (Canary Islands). Native to the Indo-Pacific, C. irene had previously been introduced to the Caribbean, Brazil, and Cape Verde. It was first observed in Tenerife in 2020, though retrospective records through citizen science tools date its presence back to 2018. A total of 74 sightings along the island’s coasts were reported between 2018 and 2024, when it reached densities of ca. 2 individuals/aggregates per square metre in the initial introduction area. Thus, the species is undergoing a clear proliferation and a spatial expansion. Morphological and genetic analyses confirmed the identity of C. irene and its phylogenetic placement, closely related to other Cnemidocarpa and related genera such as Asterocarpa . This species shows concerning invasive characteristics, such as a fast expansion, abundance in natural habitats, and aggregative behaviour, suggesting potential threats to native biota. Due to its limited natural dispersal capacity, the introduction of C. irene to Tenerife is attributed to anthropogenic vectors, particularly oil platforms arriving at major Canary Island ports. The proximity of the initial records to port areas supports this hypothesis. Given the potential species’ ecological risks, the authors recommend close monitoring, manual removal where feasible, and strengthened involvement of citizen science. This case highlights the vulnerability of oceanic islands to marine biological invasions and the importance of ports and marinas as critical entry points, underscoring the need for proactive surveillance and early intervention strategies.