Temperature and salinity sensitivity of the invasive ascidian Microcosmus exasperatus Heller, 1878

Environmental factors, such as temperature and salinity, are known to influence distribution patterns and invasion success in ascidians. The solitary ascidian Microcosmus exasperatus Heller, 1878 has a wide global distribution and can be found in both tropical and sub-tropical waters. In the Mediterranean Sea, it is considered to be an invasive species introduced through the Suez Canal, with a restricted distribution in the eastern Mediterranean. Despite its global distribution, the environmental tolerances of this species are poorly known. We examined the effect of varying temperature and salinity on the survival of adult individuals of M. exasperatus in a laboratory setting to partially determine its environmental tolerance range. In addition, it’s global and local distribution as well as the seasonal abundance in ‘Akko Bay (northern Mediterranean coast of Israel) were examined. Field observations and laboratory experiments show that M. exasperatus is able to tolerate a temperature range of 12- 30 ºC, and salinity of 37- 45, but it survived poorly in salinity of 33-35 and temperatures > 32 ºC. Considering this relatively wide tolerance range of M. exasperatus to temperature and salinity together with the anticipated rise in anthropogenic disturbances, we expect this species to further spread into new locations along the Mediterranean coast.