Oculina patagonica: a non-lessepsian scleractinian coral invading the Mediterranean Sea

Abstract.

The scleractinian coral Oculina patagonica De Angelis is a new immigrant from the Southwest Atlantic to the Mediterranean Sea, having established itself only recently along the Israeli coast. This species is the only scleractinian coral reported to have invaded a new region. In order to understand the swift establishment of this species along the Israeli coast, from 1994 to 1999 we studied its distribution, abundance, reproduction, recruitment, survival, and the effect of bleaching events on its population abundance. In addition, population studies of O. patagonica were performed at several localities along the eastern and western Mediterranean coasts. Highest abundance was recorded along the Spanish coast, reaching 30±7 colonies per 10 m line transect in shallow water. Second in abundance was the Israeli coast, with a maximum of 10±2 colonies per transect. O. patagonica was rare along the coast of Italy, and absent along the Mediterranean coast of France. During the study, both mortality and recruitment along the Israeli coast were very low. In contrast, recruitment along the Spanish coast was very high. Reproduction of the species was studied using gonadal histology. O. patagonica is gonochoric. Female gonads were first observed in May and male gonads in July, both reaching maturity in late August and early September. Naturally occurring azooxanthellate colonies of O. patagonica inhabiting small dark caves developed gonads and spawned in parallel to zooxanthellate colonies exposed to light. No gonads were found in zooxanthellate colonies that underwent bleaching during the reproduction season. The high incidence of bleaching events along the Israeli coast observed throughout the years of this study may explain the low recruitment of new colonies during the same period. In view of its current recruitment patterns, we expect further expansion of O. patagonica in range and abundance in the western Mediterranean, but very small expansion of the population in the eastern Mediterranean, due to repetitive annual bleaching events.