ORIGINAL PAPER The solitary ascidian Herdmania momus: native (Red Sea) versus non-indigenous (Mediterranean) populations N. Shenkar Æ Y. Loya Received: 8 April 2007 / Accepted: 17 January 2008 / Published online: 30 January 2008 Ó Springer Science+Business Media B.V. 2008 Abstract During 2005 monthly samples of the solitary ascidian Herdmania momus were collected along the Mediterranean and Red Sea coasts of Israel, in order to investigate possible differences in life history strategies of the two populations. The samples were preserved, dissected, and measurements were made of length, total weight, gonad weight, oocyte diameter and the occurrence of symbionts was recorded. Additionally, field surveys showed that in the Mediterranean H. momus exclusively inhabit artificial substrates, and are common at greater depths than in Eilat (Red Sea). Individuals of H. momus in Eilat reproduced year round. Although individuals from the Mediterranean were significantly larger than individuals collected in Eilat their gonad indices and oocyte diameter measurements indicate that they have a short reproductive season. Copepods were found in 50% of the samples from both sites, while a ponton- iine shrimp was found in 14% of the samples from Eilat only. The marked differences between the native vs. non-indigenous populations of H. momus are attributed to differential food availability, water temperature, currents and wave exposure. The increas- ing evidence of negative effects of non-indigenous ascidians on natural fauna from other regions in the world emphasizes the need for additional research regarding the ecology of ascidians along the coasts of Israel. Keywords Lessepsian migration Á Marine bioinvasion Á Ascidians Á Anthropogenic transport Introduction One of the most extensively documented marine bioinvasion phenomena is the invasion of Red Sea species to the Mediterranean Sea through the Suez Canal (Lessepsian migration, Por 1978 also referred to as Erythrean invasion, Galil 2000). Since the opening of the Suez Canal in 1869, more than 300 Red Sea species of algae, invertebrates and fish have entered the Mediterranean through the canal (Safriel and Ritte 1986; Spanier and Galil 1991; Barash and Denin 1992; Lotan et al. 1994; Golani 1998; Galil 2000). For example, the invasive jellyfish Rhopilema nomadica appears in mass swarms along the Medi- terranean coasts of Israel every summer, causing severe damage to coastal fishing, tourism and coastal installations (Spanier and Galil 1991). The Red Sea mussel Brachidontes pharaonis forms massive beds and is believed to have displaced the local species Mytilaster minimus (Rilov et al. 2004). Other Les- sepsian migrants, mostly fish, may be of economic N. Shenkar (&) Á Y. Loya Department of Zoology, The George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv 69978, Israel e-mail: levinn@post.tau.ac.il 123 Biol Invasions (2008) 10:1431–1439 DOI 10.1007/s10530-008-9217-2