The solitary ascidian Herdmania momus: native (Red Sea) versus non-indigenous (Mediterranean) populations

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 pontoniine 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 increasing 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.