In 2015, an unknown snapping shrimp of the genus Alpheus was collected in the San Pedro River inlet (Bay of Cadiz, SW Spain). Initially, its identification was not possible only based on DNA barcoding or morphology, considering the difficulties in the Alpheus taxonomy and the low percentage of DNA sequences of Alpheus spp. available in public databases. However, recent studies from Kuwait, Qatar and Iraq describing the morphology of Alpheus cf. lobidens allowed us to place the exotic Alpheus in this species complex. There are also recent sequences of 16S mtRNA and COI deposited in GenBank and BOLD that match >99% of similarity with the sequences of the specimens from the Bay of Cadiz. These sequences have the same origin in the Persian Gulf, but they have been attributed to different Alpheus species. Here we discuss these mismatches, and data about the distribution in the Gulf of Cadiz as well as the habitat of Alpheus cf. lobidens. Additionally, DNA barcodes, and a detailed morphological description and illustrations are provided. Some hypotheses about possible ways of introduction are discussed, and the most plausible route seems to be a natural expansion to the west after entering the Mediterranean Sea by the Suez Canal.

Weakfish (Cynoscion regalis) has been present in Iberian waters since at least 2011, when it was first recorded in the Guadalquivir estuary. Little is known about the preferences and feeding strategies of weakfish outside of its native range; therefore, in this work, we carried out a comprehensive study between March 2021 and September 2021 to elucidate these matters. In total, the stomach contents of 300 fish were examined. The fish were collected in spring and summer in the Gulf of Cadiz (Spain), with individuals caught ranging from 185 to 590 mm in total length. Due to the sampling period and size range of individuals, ontogenic and seasonal (spring–summer) variations in the diet were also explored. Overall, fish and crustaceans were the dominant groups consumed by weakfish. The European anchovy (Engraulis encrasicolus) and caramote prawn (Penaeus kerathurus) were the most abundant prey in each group. While no differences were found in the percentage of occurrence of fish in the non-empty stomachs analyzed in spring and summer (83%), a small increase was found in the percentage of occurrence of crustaceans from spring (20%) to summer (29%). In addition, the analysis of the results also suggested that weakfish of smaller sizes feed more on crustaceans, while bigger individuals feed mainly on fish. Our findings indicate that weakfish is a fully carnivorous species with a preference for fish. All this is in line with the diet and strategy that weakfish exhibits in its native area and with the first assessment made with the existing population in the Sado Estuary (Portugal). In recent years, due to the appearance of non-native species, there is increasing concern among local fishermen and the local authorities about the reduction in captures of certain species such as Penaeus kerathurus; therefore, this study could help researchers to understand the role of weakfish concerning this matter. The present study contributes to the ecological knowledge about this species in the Iberian Peninsula and the Gulf of Cadiz, helping the local authorities to establish, if needed, an appropriate management program to cope with this recently introduced species.

The ready availability of abundant food sources can be a key factor in the success of biological invasions. This study provides information about feeding habits, dietary niche, and seasonal and ontogenetic diet changes of the American invasive weakfish Cynoscion regalis in the Gulf of Cádiz, where its population is increasing exponentially since 2011 when its presence was reported in the area. By content analysis of 340 stomachs, we assessed the diet composition, prey diversity and abundance of juveniles and adults present in the Guadalquivir River Estuary. Fish and crustaceans accounted for more than 90% of their diet. Mysids are the main food intake for juveniles and piscivory becomes more important as C. regalis grows in size. Stomachs were significantly fuller during the summer and autumn months, coinciding with the higher abundance of small pelagic fish during that time in the estuary, especially the anchovy Engraulis encrasicolus, the main prey consumed through all months of the year, that showed a consumption peak in September and October. Adults also show significant monthly variations in the diet composition (P < 0.01) respect to Total Length. Juveniles show a specialist behaviour feeding almost exclusively on Mesopodopsis slabberi, while adults show a mixed feeding strategy. This research constitutes a comprehensive study of weakfish diet along the year in the non-native area, including for the first time, juvenile’s stages.