Polyopes lancifolius (Harvey) Kawaguchi et Wang 2002

Burel, Thomas, Helias, Mathieu & Duff, Michel Le, 2023, Range expansion of some non-indigenous seaweeds along the coasts of Brittany - English Channel, Botanica Marina (Warsaw, Poland) 66 (3), pp. 151-164 : 156

3.4 Polyopes lancifolius (Harvey) Kawaguchi et Wang 2002

Polyopes lancifolius is a red seaweed belonging to the order Halymeniales and the family Halymeniaceae ( Kawaguchi et al. 2002) . This species was first described as Gigartina lancifolia Harvey and is native to Japan, China ( Liu 2008) and Korea (NW Pacific Ocean). The species was found during summer 2008 on the shore of Toulindac (Baden, Gulf of Morbihan) ( Mineur et al. 2010). This finding, the first outside the native distribution range of the species, is the result of a recent introduction because the species does not appear in the list of marine species introduced in Morbihan published in 2008 ( Le Roux 2008). For many years the species was circumscribed to this single location. It has since spread in the Gulf of Morbihan and is found now at Locmiquel and in the port of Arradon. The second European record of the species, outside the Gulf of Morbihan, was in May 2011 on the island of Jersey, English Channel ( Chambers 2011) but it has not been observed there since 2013. In North Brittany, it was found in August 2021 on the island of Bréhat and more recently on October 8, 2021, on the island of Carantec (île Callot). Specimens collected in North Brittany are smaller and narrower than those observed by Mineur et al. (2010) in the Gulf of Morbihan. They reach a total length of 15–20 cm and a width of 1–1.5 cm ( Figure 7c ). Their shape and texture are similar to that already reported: main axes are elongated and lanceolate, they have little to no branching, the texture is cartilaginous and the thickness of blade is 350–500 µm ( Figure 7d ). They are covered with lanceolate proliferations found on both blade and margins of the thallus, whose size is around 1 cm. These proliferations are very characteristic of the species and give the thallus a spiky appearance ( Figure 7a ). Even if young thalli are reddish-brown in color, they discolor by late summer and become yellowish or greenish ( Figure 7b ).

Figures

Figure 7: Polyopes lancifolius from Brittany: (a) general habit showing characteristic proliferations; (b) in situ material from Bréhat (picture by T. Burel); (c) dried specimen from the Gulf of Morbihan (Herbarium A. Le Roux), winter form lacking proliferations; (d) vertical section through old axis showing a thick cortex. Scale bars: (a–c) 2 cm; (d) 50 µm.