Spread of the non-indigenous ascidian Aplidium accarense (Millar, 1953) in the Eastern Mediterranean Sea: morphological and molecular tools for an accurate identification

Abstract

The aplousobranch ascidian Aplidium accarense (Millar, 1953) was first described on the western coast of Africa, where it is considered native. Afterwards, this species was introduced along south-American Atlantic coasts, where it affected local shellfish farms through a massive colonization of both natural and artificial substrata. Aplidium accarense has been recently reported along Catalan coasts and in the Tyrrhenian Seas (Western Mediterranean) where it represents a non-indigenous species, only recorded in harbours and aquaculture farms thus far. These Mediterranean records support the hypothesis that A. accarense is currently expanding within the basin, representing a potential invasive species. In this study, several colonies of A. accarense were found for the first time on artificial substrata within the semi-enclosed basin of the Mar Piccolo of Taranto (Italy, Ionian Sea), in the Eastern Mediterranean. Here we provide an updated description of A. accarense combining both morphological and molecular approaches, in order to allow an accurate and reliable identification of this expanding species. Comparing the morphology of the specimens collected from Taranto with the previous descriptions, a slight intra-specific variability has been noticed. Therefore, we provide detailed comparisons of the specimens found in Taranto with all the other A. accarense sampled in other areas of the world, in order to highlight the intra-species variability. The correct identification of a potentially-dangerous species such as A. accarense, represents a needed step for environmental monitoring purposes and for implementing management strategies to mitigate the effects of non-indigenous species on natural ecosystems and human activities.

On some alien species from Emilia-Romagna harbors (northern Adriatic Sea, Italy)

“…This observation raises the possibility that A. accarense might exhibit an invasive tendency in the local area, posing potential ecological implications for the ecosystem. Aplidium accarense was identified according to Montesanto et al (2021).…”

Alien Species Associated with New Introductions and Translocations of Commercial Bivalves in Italian Marine Waters

“…Bacteria Francisella halioticida was associated with Mytilus spp. cultivation [26] and with consequent mass mortality events [31]; moreover, mussel farming (M) was identified as the possible vector of introduction for Pacific Bryozoa Tricellaria inopinata (d'Hondt and Occhipinti Ambrogi, 1985) ( [91] and references within) and one of the vectors of introduction and spread of African Ascidiacea Aplidium accarense (Millar, 1953) [92] into Atlantic and Mediterranean European waters.…”

Clogging nets-Didemnum vexillum (Tunicata: Ascidiacea) is in action in the eastern Mediterranean

“…Some of them are highly invasive, covering large areas and outcompeting native species (Ordóñez et al ., 2015; Stabili et al ., 2015; Çinar, 2016; Montesanto et al ., 2021a). They are frequently found on submerged ropes or tyres in harbour environments, but also occur in natural substrata like rocks (Çinar et al ., 2006; Ramos-Esplá et al ., 2020; Montesanto et al ., 2021b). Along the coasts of Turkey, 14 alien species have been reported up to date, with eight species being found in the Levantine Sea, and 11 species in the Aegean Sea (Çinar et al ., 2021).…”