Harbor networks as introduction gateways: contrasting distribution patterns of native and introduced ascidians

16 páginas, 6 tablas, 4 figurasHarbors and marinas are well known gateways for species introductions in marine environments but little work has been done to ascertain relationships between species diversity, harbor type, and geographic distance to uncover patterns of secondary spread. Here, we sampled ascidians from 32 harbors along ca. 300 km of theNWMediterranean coast and investigated patterns of distribution and spread related to harbor type (marina, fishing, commercial) and geographic location using multivariate techniques. In total, 28 ascidians were identified at the species level and another 9 at the genus level based on morphology and genetic barcoding. Eight species were assigned to introduced forms, 15 were given native status and 5 were classified as cryptogenic. Aplidium accarense was reported for the first time in the Mediterranean Sea and was especially abundant in 23 of the harbors. Introduced and cryptogenic species were abundant in most of the surveyed harbors, while native forms were rare and restricted to a few harbors. Significant differences in the distribution of ascidians according to harbor type and latitudinal position were observed. These differences were due to the distribution of introduced species. We obtained a significant correlation between geographic distance and ascidian composition, indicating that closely located harbors shared more ascidian species among them. This study showed that harbors act as dispersal strongholds for introduced species, with native species only appearing sporadically, and that harbor type and geographic location should also be considered when developing management plans to constrain the spread of nonindigenous species in highly urbanized coastlines.This study was funded by the Marie Curie International Reintegration Grant FP7-PEOPLE-2010-RG 277038 and by the COCONET project #287844, both within the 7th European Community Framework Program, by the Spanish Government project CTM2013-48163, and by the Catalan Government Grant 2014SGR-336 for Consolidated Research Groups.Peer reviewe