Early stages of establishment of the non-indigenous ascidian herdmania momus (Savigny, 1816) in shallow and deep water environments on natural substrates in the mediterranean sea

The solitary ascidian Herdmania momus (Savigny, 1816) was first recorded in the Eastern basin of the Mediterranean, off the coast of Israel, in 1958. Since then, H. momus established along the shores of Israel, albeit restricted to artificial substrates (e.g., pier pillars, artificial reefs, and shipwrecks) and deeper waters (20–30 m) in comparison to its native range. It has recently spread to natural substrates (i.e. the rocky reef) and shallow water environments (< 1 m). Field surveys, augmented by observations by recreational divers, were conducted along the Israeli Mediterranean coast on natural substrates to assess the present distribution. H. momus was detected on natural substrates at eleven sites, some of them at very shallow depths. This change in the distribution of H. momus that now includes natural substrates in shallow waters along with deep water environments may have negative impacts on the native fauna in the Eastern Mediterranean.