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.