Revealing polychaetes invasion patterns: Identification, reproduction and potential risks of the Korean ragworm, Perinereis linea (Treadwell), in the Western Mediterranean Andrés Arias a, * , Alexandra Richter a , Nuria Anadón a , Christopher J. Glasby b a Department of Biology of Organisms and Systems (Zoology), University of Oviedo, Oviedo 33071, Spain b Museum and Art Gallery of the Northern Territory, GPO Box 4646, NorthernTerritory 0801, Australia article info Article history: Received 31 October 2012 Accepted 7 August 2013 Available online xxx Keywords: Nereididae baitworm alien epitokal transformation Mar Menor lagoon Euplotes abstract An established population of the polychaetous annelid Perinereis linea (Treadwell) is reported for the first time outside its native distribution range (NW Pacific). This exotic worm has reached the Western Mediterranean (Mar Menor lagoon) via importing live fishing-bait as it is commonly used by anglers in Mar Menor lagoon, an area largely used for recreational fishing. To avoid confusion with other related species, and because the scientific name has been in synonymy for many years, P. linea is redescribed and illustrated. We focus on the reproductive biology and ecology of P. linea to help to understand its introduction, naturalization and spread along this coastal lagoon. Comparison between the Mediterra- nean population with a native population from South Korea revealed that the species exhibits a great reproductive plasticity and adaptability, which depends on the environmental conditions. Perinereis linea can reproduce after acquiring the epitokous form or prior to complete epitokal modification. In the Mar Menor lagoon population females release eggs asynchronically without completing epitokal modifica- tions. However, under particular laboratory conditions females produce eggs synchronically and release them after complete epitokal transformations. Fertilization can occur internally in the female coelom, and females release zygotes and larvae through openings in their body walls; they are then incubated in gelatinous masses attached to the female parapodia. The sperm morphology is of the ent-aquasperm type. The eggs and larvae are attacked by symbiotic ciliate protozoa that feed on their yolk reserves. These foreign ciliates may act as carriers of disease in native beachworms and constitute an important risk for the ecosystem health. Finally, we provide recommendations on the prevention of the adverse effects that this exotic ragworm can cause in receiving ecosystems. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Introductions of non-native species are threatening the eco- nomic and ecological well-being of coastal marine ecosystems. The vectors of introduction of alien species to the Mediterranean sea are diverse: migration through the Suez Canal ‘Lessepsian migration’ (Por, 1978), migration through the Gibraltar Strait (Vietti and Thompson, 1989), transport on vessel hulls or with ballast waters, intentional introductions (mariculture) and accidental in- troductions accompanying intentionally introduced species (Arias and Anadón, 2013), market discards and escapees from aquaria (Zibrowius, 1992). Potential transport vectors of non-native species need to be identified and evaluated in order to help environmental managers to reduce introductions of non-native species, which is often a considerably less expensive strategy than attempting to restore an area after a non-native introduction (Ricciardi and Rasmussen, 1998; Olenin et al., 2011). Indeed, most non-native introductions in marine ecosystems are irreversible e one of the only successful attempts at eradicating a non-native marine species is that of the bivalve Mytilopsis halei (Recluz, 1849) in Cullen Bay Marina, Darwin Harbour in 1999 (CG pers. obs.). The Suez Canal has been the largest pathway for the entry of invaders into the Mediterranean Sea and more than 300 Erythrean species e principally molluscs, fish, decapod crustaceans, poly- chaetes and algae e have become established in the Eastern Mediterranean, primarily in the Levantine Basin. The rate of these Abbreviations: BOS, Biology of Organism and Systems e Zoology e University of Oviedo; Phy, Phyllodocida; NTM, Museum and Art Gallery of the Northern Territory (formerly Northern Territory Museum), Darwin, Australia. * Corresponding author. E-mail addresses: ariasandres.uo@uniovi.es, andres404ar@gmail.com (A. Arias). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ecss.2013.08.017 Estuarine, Coastal and Shelf Science xxx (2013) 1e12 Please cite this article in press as: Arias, A., et al., Revealing polychaetes invasion patterns: Identification, reproduction and potential risks of the Korean ragworm, Perinereis linea (Treadwell), in the Western Mediterranean, Estuarine, Coastal and Shelf Science (2013), http://dx.doi.org/ 10.1016/j.ecss.2013.08.017