Caulacanthus ustulatus (Gigartinales, Rhodophyta) from Brittany (France) is an introduction from the Pacific Ocean

Abstract

Caulacanthus ustulatus (Turner) Kützing was originally described from Cádiz (SW Spain) and is the only species of the genus found in Europe. For many years, the known northern limit was in the Bay of Biscay (Biarritz, south-west France), but the alga was recently recorded in Brittany, France. DNA sequences of the plastid encoded Rubisco spacer and sequences of the nuclear ribosomal DNA internal transcribed spacer (rDNA ITS2) were used to determine the relationships between samples of Caulacanthus from Brittany (Roscoff), southern Europe (Gibraltar and Albufeira in Portugal) and East Asia (China, Japan). The sequence data obtained revealed two distinct groupings: a Pacific group containing the samples from China, Japan and Roscoff and a group containing the samples from southern Europe. This finding is consistent with the hypothesis that Caulacanthus in Brittany has been introduced from the Pacific Ocean. Minor morphological differences were observed between isolates from the two groups grown under identical culture conditions.