Sargassum horneri (Turner) C. Agardh, 1820

Belleza, Dominic Franco C., Tateishi, Hiroto, Tanimae, Shin-Ichiro, Kobayashi, Taishun, Aota, Tomoyuki, Urasawa, Toshiki & Nishihara, Gregory N., 2025, An annotated list of brown seaweeds (Phaeophyceae) from Nakadori Island (northern Goto Islands, Nagasaki, Japan), Phytotaxa 694 (1), pp. 1-24 : 14

Sargassum horneri (Turner) C. Agardh, 1820

Japanese name: アカモク (akamoku)

Basionym: Fucus horneri Turner

Type locality: —In the Straits of Corea

Description and remarks: —Specimens are densely branched with a thicker main axis at the bottom (2.5–3 mm) and thinner at the top (1 mm). The main axis and the primary branches in the lower portions have small spines while the upper parts are smooth. Branching is alternately bipinnate with the leaves having a prominent midrib with deeply incised and alternating margins. The vesicles are 1–1.5 cm long, cylindrical and are found in the apical regions. The apex of each vesicle is terminated by a leaflet with thin, alternating, deeply pinnatisect margins. In Naname, this species forms dense forests grows to heights reaching over 3–5 m in early to late spring.

This species is known for producing large floating rafts in the East China Sea region during macroalgal blooms, known as “golden tide”, and is considered as a nuisance when they drift ashore ( Zhuang et al. 2021, Qi et al. 2022). In 2015, massive rafts of drifting S. horneri from China were recorded to have drifted ashore in many parts of the Goto Islands (Naru, Fukue, Kamigoto), mainland Nagasaki and to the islands in Iki and Tsushima ( Kiriyama et al. 2016). Despite this problem, these floating rafts provide refuge for juvenile pelagic species such as yellowtail ( Seriola quinqueradiata ), an important fishery species ( Mizuno et al. 2014).

Materials examined: —18ECS1-125 (1 to 7)