From Fresh to Salt Waters: First Reports of the Red Swamp Crayfish Procambarus clarkii (Girard, 1852) in Mediterranean Marine Waters

The red swamp crayfish Procambarus clarkii (Girard, 1852), native to the southern/southeastern United States and northern Mexico, has been introduced in many countries worldwide. The species has a remarkable invasiveness due to its high reproductive rate and ability to tolerate broad ranges of water parameters like salinity. Nevertheless, no consistent observations of P. clarkii have been reported in the marine environment until now. Data demonstrating the presence of the crayfish within marine ecosystems were collected by a personal acquaintance and two volunteers who published photos of the species on Facebook marine biology and fishing groups. The species was identified based on photos taken by these people in the described areas. P. clarkii has been spotted in three different localities, in two of which observations are recurrent. The species can survive miles from the nearest freshwater stream and could potentially colonise marine waters at depths up to 20 m. The multiple observations of P. clarkii collected in our study uncover a persistent presence of the species within some marine areas, rather than its mere sporadic occurrence. Our results highlight the need for further investigation to obtain a comprehensive understanding of the crayfish’s ability to withstand salinity and colonise the marine environment.