New evidence of Melithaea erythraea colonization in the Mediterranean

Abstract The Indo-Pacific gorgonian coral Melithaea erythraea (Melithaeidae, previously Acabaria) was first recorded in the Mediterranean in 1999 in the harbor of the Hadera power station, Israel. This species is the only octocoral known to have invaded the Mediterranean Sea. In the past two decades, it has demonstrated a stable population in this harbor, and never found outside this location, not even on the adjacent natural rocky reefs. Then, during 2015, several specimens of M. erythraea were found on a natural substrate at Nahsholim, Israel, about 23 km north of the power station. This is the first evidence of this coral's existence beyond the power plant harbor. The number of colonies there suggests that the population is sustainable, but further study is needed. Although no genetic differences were found among specimens from Nahsholim, Hadera, and the Red Sea, their bacterial epibiota has undergone change following migration. The carbon source and trophic position are similar between the Red Sea and the Mediterranean, suggesting that there is no nutritional barrier to migration for the coral. The larval connectivity model supports the hypothesis that the planulae that have settled in Nahsholim originated from the Port of Hadera, although other arrival scenarios are also possible. The spread of this species suggests that the eastern Mediterranean is becoming increasingly suitable for migrating corals, joining the many other Indo-Pacific migrants that have already established populations there.