Diatom assemblages on Nanaura mudflat, Ariake Sea, Japan: with reference to the biogeography of marine benthic diatoms in Northeast Asia

Abstract

A study was conducted to understand the floral characteristics and diversity of benthic diatoms (Bacillariophyceae) at Nanaura mudflat (E 130 degrees 10', N 33 degrees 04') on the coast of the Ariake Sea, Japan. A literature review was also performed to better understand the biogeography of the marine benthic diatoms of Northeast Asia. Light microscopic and scanning electron microscopic observations revealed a total of 90 Nanaura taxa. All species were listed along with their dimensions, microstructural densities, and if necessary, their ultrastructures. Dominant species found were Navicula sp. 1 (12.6%), Paralia sulcata (10.3%), Tryblionella gratudata (8.8%), Navicula flantanica (6.8%), Gyrosigma wansbeckii (5.8%) and Cyclotella striata (5.6%). The abundance of the six species collectively accounted for ca. 50% of the total. As for salinity requirements, marine and brackish-marine forms were dominant, while brackish and freshwater species were also observed. Species composition of diatom flora at the study site showed relatively close similarity with those of mudflat (e.g., Isahaya Bay) and brackish lagoon (Matsukawaura Lagoon) in Japan, but were also similar to those of other localities, e.g. at Songdo mudflat in Korea and Fujian coast in China. Thirteen reports of the benthic diatoms from Northeast Asia were selected for comparison based on diatom habitats and data quality. Twenty-one species of Nanaura diatoms, including Cymatotheca weissflogii and Tryblioptychus cocconeiformis, whose reports are rare in the Western Hemisphere and Europe, occurred across Japan, Korea, and China, and represent common benthic diatoms in Northeast Asia.