Two sea cucumber species, Holothuria impatiens and Oestergrenia digitata, were reported officially on Mar Menor coastal lagoon (SE Spain). Seven specimens of the first species were identified, using traditional taxonomy and genetic barcoding, in Los Narejos (Mar Menor). However, only one belonging to O. digitata species was found in Los Urrutias (Mar Menor). These findings could support the mediterranisation' process of the lagoon favoured by the enlargement of the El Estacio inlet in 1972. In the last several years, there has been a decrease in salinity, a smoothing of the most extreme temperatures and many anthropogenic actions which have produced modifications in Mar Menor, affecting the seagrass and seaweed coverage and causing an increase of organic matter in sediments. These modifications, together with the current patterns, are favouring the colonisation of Mar Menor by Mediterranean species.