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A new invasive snapping shrimp from the Alpheus lobidens De Haan, 1849 species complex has become one of the most frequently observed crustaceans in certain saltmarshes along the southwestern Spanish coast. The first place in Europe where this invasion has occurred is reported in this study; however, little is known about this species, even within its undetermined native range. Here, the population structure, density, sex ratio, sexual dimorphism, reproductive period, and relative growth of this nonnative shrimp are reported for an intertidal saltmarsh in SW Spain based on monthly data collection over a year. Ovigerous females were collected during all months of the year. This population trait is not found in any native crustacean in the temperate zone of Europe. The sex ratio showed a similar proportion of male and female individuals, 0.88:1 (F:M), throughout the year. Sexual dimorphism was evident in the growth characteristics of body structures and implications are discussed. These results highlight the successful establishment of this shrimp in the Mediterranean climate area of Spain and have implications on marine fauna conservation and management. These findings also provide a basis for future comparative research in the shrimp native regions and enhance understanding of the species population dynamics.

One specimen of the shortfin neoscopelid Neoscopelus microchir Matsubara, 1943, has been recorded for the first time on the Porcupine Bank, southwestern Ireland, providing a new northern limit of distribution for the eastern Atlantic. Morphometric and meristic parameters confirm the taxonomic identification. However, DNA barcoding shows deficiencies in current taxonomy and the potential occurrence of cryptic species. On this basis, the specimen is cautiously reported as Neosopelus cf. microchir pending a taxonomic revision of the genus.

One specimen of the shortfin neoscopelid Neoscopelus microchir Matsubara, 1943, has been recorded for the first time on the Porcupine Bank, southwestern Ireland, providing a new northern limit of distribution for the eastern Atlantic. Morphometric and meristic parameters confirm the taxonomic identification. However, DNA barcoding shows deficiencies in current taxonomy and the potential occurrence of cryptic species. On this basis, the specimen is cautiously reported as Neosopelus cf. microchir pending a taxonomic revision of the genus.

Since its first record in Europe as an exotic species back in 2009 at the Schelde estuary (Belgium), the weakfish Cynoscion regalis -native from North America East coast- has increased its presence in the Iberian Peninsula waters. Identified for the first time in the Guadalquivir River estuary (2011) and later in the Sado estuary (2014), C. regalis population is increasing in the Gulf of Cadiz and is becoming a fisheries resource. Its introduction into Europe probably occurred through maritime transatlantic trade. Morais et al (2017) suggested that weakfish could have been introduced through multiple independent ballast water release events. The Guadalquivir, Sado and Schelde estuaries show similar transoceanic ship traffic to upstream important commercial ports, supporting multiple direct or secondary transatlantic introductions among European ports. The first genetic studies suggest that C. regalis populations in southern European estuaries are connected and come from a single transoceanic commercial route. Currently, the Gulf of Cadiz maintains a well-established population with frequent catches by artisanal fishing, especially in coastal waters and the estuary, where it is sold in local markets of the surrounding cities. The population in the area is constituted by mature specimens (ranging from 234 to 453 mm) that are using the estuary as a spawning area, where larvae and juvenile have also been found. In recent years, an increase in the abundance of larvae and juvenile has been observed through monthly samplings in the estuary, which indicates the culmination of the complete life cycle in the Gulf of Cadiz. These findings represent new evidence that the Guadalquivir estuary constitutes a remarkable nursery habitat for this species. This could have effects on native fauna and the ecosystem, which is why it is currently under study and evaluation (EcoInvadiz project) for helping the local Administration to establish, if needed, an appropriate management program.