| Species |
Recipient region |
Date of the first record |
|
| Siphonaria crenata | Israel | 1965 |  |
| Siphonaria pectinata | Greece / Eastern Mediterranean | 1973 | |
| Sirpus monodi | Greece / Central Mediterranean | 2006 | |
| Sirpus monodi | Greece / Eastern Mediterranean | 2002 | |
| Sirpus zariquieyi | Turkey / Black Sea | 1982 | |
| Skeletonema subsalsum | Ukraine / Black Sea | From 1993 | |
| Skistodiaptomus pallidus | Germany / North Sea | To 2010 | |
| Smaragdia souverbiana | Greece / Central Mediterranean | 2012 | |
| Smaragdia souverbiana | Greece / Eastern Mediterranean | 1993 | |
| Smaragdia souverbiana | Israel | 1987 | |
| Smittina nitidissima | Israel | 1986 | |
| Smittina nitidissima | Italy / Central Mediterranean | 2014 | |
| Smittoidea prolifica | Germany / North Sea | 2011 | |
| Smittoidea prolifica | Netherlands | 1995 | |
| Solieria chordalis | United Kingdom (Britain) / Celtic seas | 1976 | |
| Solieria chordalis | United Kingdom (Britain) / English Channel | 1976 | |
| Solieria dura | Israel | 1954 | |
| Solieria filiformis | Australia / Bass strait | 1957 | |
| Solieria filiformis | France / Western Mediterranean | 1999 | |
| Solieria filiformis | Italy / Adriatic Sea | 2003 | |
| Solieria filiformis | Italy / Central Mediterranean | 1922 | |
| Solieria filiformis | United Kingdom (Britain) / English Channel | 1978 | |
| Solmundella bitentaculata | Turkey / Black Sea | 2010 | |
| Sorites orbiculus | Italy / Central Mediterranean | 2005 | |
| Sorites orbiculus | Turkey / Black Sea | 2010 | |
| Sorsogona prionota | Israel | 1946 | |
| Sousa plumbea | Greece / Eastern Mediterranean | 2017 | |
| Spartina alterniflora | France / Biscay Gulf | 1806 | |
| Spartina alterniflora | France / Celtic seas | 1960 | |
| Spartina alterniflora | France / English Channel | 1960 | |
| Spartina densiflora | Spain / Iberian Coastal | 1950 - 1959 | |
| Spartina patens | France / Biscay Gulf | 1901 | |
| Spartina patens | France / Celtic seas | 1901 | |
| Spartina patens | France / Western Mediterranean | 1849 | |
| Spartina patens | Portugal / Iberian Coastal | 1999 | |
| Spartina patens | Spain / Iberian Coastal | To 1997 | |
| Spartina townsendii var. anglica | Belgium | 1920 - 1929 | |
| Spartina townsendii var. anglica | Denmark / Baltic Sea | 1948 - 1953 | |
| Spartina townsendii var. anglica | Denmark / North Sea | 1930 - 1940 | |
| Spartina townsendii var. anglica | France / Biscay Gulf | 1924 | |
| Spartina townsendii var. anglica | France / Celtic seas | 1894 | |
| Spartina townsendii var. anglica | France / English Channel | 1894 | |
| Spartina townsendii var. anglica | France / North Sea | To 1990 | |
| Spartina townsendii var. anglica | Germany / North Sea | 1927 | |
| Spartina townsendii var. anglica | Ireland | 1925 | |
| Spartina townsendii var. anglica | Netherlands | 1924 | |
| Spartina townsendii var. anglica | Sweden / North Sea | From 2007 | |
| Spartina townsendii var. anglica | United Kingdom (Britain) / Celtic seas | 1850 - 1859 | |
| Spartina townsendii var. anglica | United Kingdom (Britain) / English Channel | 1850 - 1859 | |
| Spartina x neyrauti | France / Biscay Gulf | 1897 | |
