Paracartia grani originates from high latitudes and has progressively been recorded in the Mediterranean Sea since the 1980s. In Thau lagoon, while Acartia clausi and Acartia discaudata present maximum peaks of abundance from January to April and in November and December, both species being perennial over the year, P. grani and Paracartia latisetosa appear in May, develop during summer, in July and August, and slowly decrease in autumn before disappearing from the water column in December. The Acartiidae populations have changed over the years at our monitoring station. Indeed, P. latisetosa was last recorded in August 1983 while P. grani appeared in the lagoon in 1998.