First record of invasive green algae Caulerpa racemosa var. cylindracea in Oran Bay (Western Algeria)

Abstract

Caulerpa racemosa var. cylindracea (hereafter Caulerpa cylindracea) was first reported in the Mediterranean Sea in1926 1 in Tunisian waters and then in Tripoli harbor in Libya, in 1990. In late 90s it invaded the southern shore of Europe. InAlgeria, this invasive species was reported for the first time in 20072, five years after it appeared about 450 km from the firstsite in the eastern part of the Oranian littoral. This situation required widespread monitoring of this invasive species all along124 km of the coastline. More than 10 stations were patrolled and monitored since then, studied by scuba diving between thesurface and 30 m depth.The observations devoted to the distribution of Caulerpa cylindracea in Oran showed that specimens presented the sameappearance with irregularly entangled branched stolons attached to the substrate by colorless rhizoids from which the nameof the variety cylindracea was derived. Chronologically, the invasion direction seems to move from the bottom to the surfacewith an orientation from east to west, in the Oranian coastline. In situ observations confirmed high propagation speed ofCaulerpe in the Oranian coastline where invasions were signaled in several stations. The seaweed was observed for the firsttime in late 2011 and early 2012 (pers.obs) in Arzew Gulf (Cap Carbon) at the extreme east of the littoral, where the firstfronds were noticed. Then it extended geographically to the center of the coastline, in Kristel, early 2013. In 2014, it wasobserved in Ain Turc and Cap Falcon. In 2015, it was observed in the western shoreline near Bousfer beach and in 2016 itreached the “Plane” island (Paloma).This alien species was encountered at depths ranging from a few centimeters in microcuvettes up to 37 m, on varioussubstrates (hard, sandy, muddy) between marine phanerogams rhizomes and, also between the lower mid-littoral and infralittoralssuperior algae, with Posidonia oceanica herbarium. The study suggested a strong need for scientific monitoring andmanagement program, using optimized methodslike biological control or manual eradication for controlling the invasion.