The disproportionately low presence of marine species in the list of invasive alien species (IAS) of Union concern of the European Union (EU) Regulation 1143/2014 does not fully acknowledge the threat they pose to the EU marine environment. In this study, the first EU‐scale Horizon Scanning (HS) focusing on marine alien species was performed, aiming to deliver a ranked list of species that should be of high priority for risk assessment (Article 5 of the EU IAS Regulation). Species absent from or with a limited distribution in EU marine waters were targeted. In total, 363 alien species were initially screened for HS by a panel of experts, including a broad range of taxonomic groups. Species were scored for their likelihood of arrival, establishment, spread, and impact in EU waters. A consensus workshop ranked 267 species, including a subset of 26 prioritized species. These species are considered to be mainly introduced by shipping (fouling and ballast water), via the Suez Canal, and aquaculture activities. The 26 priority species were also scrutinized in terms of feasibility of their management; 18 of them were suggested for performing risk assessments on the basis of the EU IAS Regulation. Since biological invasions are dynamic and connected with accelerated globalization and diversified human activities, we recommend HS to be repeated periodically to review the species already listed and assess new ones.

This collective article presents new information about 15 introduced taxa belonging to five phyla: one Rhodophyta, one Chlorophyta, one Mollusca, one Annelida, two Arthropoda, and nine Chordata (one Ascidiacea and eight Osteichthyes). The records refer to eight Mediterranean countries and extend from the Alboran Sea to the Levantine Sea as follows: Spain: first record of the African hind Cephalopholis taeniops for the Alboran Sea, and a further record of the Monrovia surgeonfish Acanthurus monroviae, extending its distribution northwards in the Western Mediterranean. Italy: an additional record of the squat lobster Scyllarus subarctus based on its nisto stage, new records of the lionfish Pterois miles in the north-western Ionian Sea, first records of the bivalve Fulvia fragilis for the Italian Adriatic coast, and a record of the amphipod Ptilohyale littoralis in the northern Adriatic Sea, also representing the first report for the Mediterranean Sea. Montenegro: first record of the non indigenous ascidian Ciona robusta. Albania: first record of the red cornetfish Fistularia petimba. Greece: first record of the cryptogenic polychaete Alitta succinea in association with ship fouling, suggesting the possibility of a non-indigenous origin of Mediterranean populations of this species, and first record of the Seychelles dragonet Synchiropus sechellensis for the Saronikos Gulf. Türkiye: first record of the red alga Womersleyella setacea, report of an abundant population of the Indian twospot cardinalfish Cheilodipterus novemstriatus in the Turkish Aegean Sea, and first record of Synodus randalli, also corresponding to the first report for the Mediterranean Sea. Syria: first record of the blenny Istiblennius cf. meleagris. Israel: report of an algal bloom of the green alga Codium parvulum, and first record of Synchiropus sechellensis.

This study was performed to analyse the genetic and morphological diversity of the sabellid annelid genus Branchiomma, with special emphasis on a taxon so far identified as Branchiomma bairdi. This species, originally described from Bermuda, has frequently been reported as an invader in the Mediterranean, the Atlantic and the Eastern Pacific, but recent observations have raised some taxonomic questions. Samples of this taxon were collected from five sites in the Mediterranean Sea, two sites in the original distribution area of B. bairdi in the Gulf of Mexico and four localities in the east Pacific and Atlantic Oceans where B. bairdi has been reported as invasive. The molecular results revealed a conspicuous genetic divergence (18.5% K2P) between the sampled Mediterranean populations and all the other ones that led to a re-evaluation of their morphological characters. The latter showed that the Mediterranean and extra-Mediterranean populations also differ in some discrete morphological and reproductive features. Consequently, the Mediterranean samples were re-designated as B. boholense, another non-indigenous species originally described from Philippines. Branchiomma bairdi and B. boholense differ in body size, development and shape of micro and macrostylodes, size of radiolar eyes and body pigmentation. Genetic diversity was high in B. boholense from the Mediterranean as well as in B. bairdi from the Gulf of Mexico, but low in B. bairdi populations outside their native range. The phylogenetic analysis revealed the presence of connections between the Mediterranean localities as well as between native and introduced B. bairdi populations that focus the attention on the Panama Canal as important passage for the introduction of the species from the Gulf of Mexico to the north-east Pacific Ocean.