The thermophilic Asteroidea Ophidiaster ophidianus on the NW Mediterranean coasts : evidence of frequency increase

The purple starfish Ophidiaster ophidianus (Lamarck, 1816) is a thermophilic Atlanto-Mediterranean species whose Mediterranean distribution range (reviewed here) was restricted to the warmer sectors of the basin. Its occurrence on the northern, colder, continental coasts, which was formerly very occasional, is now more and more frequent as attested by the number of sightings recorded by divers along the coasts of Provence and the French Riviera. These scattered individuals may come from a single pulse recruitment. However, as this starfish may be considered as a reliable indicator of climate warming, its monitoring should be undertaken in order to record patterns of change in its abundance and the possible establishment of a viable population in the northern Mediterranean.