First records of the non-indigenous green algal species Siphonocladus tropicus (Cladophorales, Chlorophyta) and Caulerpa integerrima (Bryopsidales, Chlorophyta) in the Mediterranean Sea

ABSTRACT We provide an account of two newly recorded non-indigenous tropical seaweed species, Siphonocladus tropicus (Cladophorales, Chlorophyta) and Caulerpa integerrima (Caulerpaceae, Chlorophyta), from the northern and central Levantine Mediterranean shores of Israel. Reports are supported by morphological and molecular evidence. The new record of C. integerrima, thought to be endemic to the Red Sea, increases the number of non-indigenous Caulerpa species in the Mediterranean Sea to eight. Siphonocladus tropicus, a widespread tropical species, is also being reported from the northern Red Sea. Furthermore, morphological comparison of populations from the northern Red Sea and the Levantine Mediterranean shore of Israel revealed that there might be a regional variant or form of this species in the northern Red Sea and might indicate that this new invader does not necessarily originate from the Red Sea. The increasingly tropical conditions in the eastern Levantine Sea as a result of global warming probably paved the way for the establishment of both species in the region. Aspects of the new invaders’ ecology in the Israeli Levantine Sea, the possible vectors of introduction and origins, as well as the status of other Caulerpa species from both Levantine and Red Sea shores, are discussed. HIGHLIGHTS Siphonocladus tropicus and Caulerpa integerrima are new non-native species found lately in the Mediterranean Sea. Caulerpa integerrima originated from the Red Sea whereas the origin of Siphonocladus tropicus is uncertain. The introduction of these two alien species, especially Caulerpa integerrima, might pose a threat to the local marine flora and fauna.