Marine algal flora of the southern islands of Japan

In 1995–2019, marine algae were sampled in the intertidal and upper subtidal zones of the Amakusa Archipelago (Shimoshima islands) and the southern islands of the Ryukyu Archipelago (Okinawa, Sesoko, Ieshima, Akajima, Miyako, Ishigaki, Iriomote, and Yonaguni). A total of 569 species and taxonomic forms of benthic macroalgae were identified. Out of them, 57% belonged to red algae; 15%, to brown algae; and 28%, to green algae. On these islands, 153 taxa were found for the first time. During the specified period, the benthic marine flora of individual islands was analyzed with varying degrees of care. The most thoroughly studied island of the Amakusa group was Shimoshima (14 localities during all seasons), and of the Ryukyu Archipelago, Sesoko (8 localities during all seasons). The comparison of taxonomic and biogeographic characteristics of marine floras of these two archipelagos – biodiversity of species and forms, taxonomic composition of algal communities, and potential capabilities of geographic (latitudinal) distribution of taxa – give us the grounds to classify the Shimoshima Island as a warm-temperate region of the Northern Hemisphere in East Asia, and the southern islands of the Ryukyu Archipelago, as a tropical biogeographic region.