Suncheonman Bay, Korea’s most representative estuary, is an invasive coastal wetland composed of 22.6 km² of tidal flats surrounded by the Yeosu and Goheung Peninsulas. In January 2006, this region was registered in the Ramsar Convention list in Korea, representing the first registered wetland. Estuaries are generally known to have high species diversity. In particular, several studies have been conducted on planktonic and epipelic diatoms as primary producers. Suncheonman Bay has already been involved in many biological and geochemical studies, but fossil diatoms have not been evaluated. Therefore, we investigated fossil diatoms in Suncheonman Bay and introduced sub-fossil diatoms recorded in Korea. One sedimentary core has been extracted in 2018. We identified 87 diatom taxa from 52 genera in the SCW03 core sample. Of these, six species represent new records in Korea: Cymatonitzschia marina, Fallacia hodgeana, Navicula mannii, Metascolioneis tumida, Surirella recedens, and Thalassionema synedriforme. These six newly recorded diatom species were examined by light microscopy and scanning electron microscopy. The ecological habitats for all the investigated taxa are presented.

Late Holocene diatoms were identified from four sediment cores from the Gonggeomji Wetland in Korea. In total, 52 diatom species belonging to three classes, 21 families, and 29 genera were investigated. Of these, 14 species were new records for Korea: Caloneis wardii, Cocconeis klamathensis, Encyonema vulgare, Eunotia myrmica, Fallacia californica, Gomphonema asiaticum, Gomphonema insigniturris, Gomphonema neoapiculatum, Gomphonema tumens, Pinnularia fusana, Pinnularia parvulissima, Punctastriata lancettula, Sellaphora capitata, and Staurosira dimorpha. Eleven taxa could not be identified to the species level. All identified diatoms are illustrated by high-quality scanning electron microphotographs, reference taxonomic data, dimensions of the observed cells, and information on ecology and distribution are included.

Lagoons are natural bodies of water that are isolated from the sea due to the development of a sand bar or spit. Each lagoon has distinct ecological characteristics, and these sites also serve as popular tourist attractions because they are common habitats for migratory birds and are characterized by beautiful natural scenery. Lagoons also have distinct ecological characteristics from those of their associated estuaries, and there are active research efforts to classify, qualify, and quantify the high biodiversity of lagoons. The lagoons in Korea are primarily distributed in the East Sea, and are represented by Hwajinpo, Yeongrangho, and Gyeongpoho. Here, we report the discovery of 11 unrecorded diatom species (Diploneis didyma, Mastogloia elliptica, Cosmioneis citriformis, Haslea crucigera, Pinnularia bertrandii, Pinnularia nodosa var. percapitata, Gyrosigma sinense, Gomphonema guaraniarum, Gomphonema italicum, Navicula freesei, Trybionella littoralis var. tergestina) among samples collected from the Hwajinpo, Hyangho, Maeho, Gapyeongri wetland, Cheonjinho, and Gyeongpoho lagoons in Korea during a survey from 2018–2020. We present the taxonomic characteristics, ecological information, habitat environmental conditions, and references for these 11 species.

An unknown Giffenia taxon was sampled from the tidal flat sediment of Suncheonman Bay in the Republic of Korea on June 11, 2018. To identify the species, a detailed analysis using light and electron microscopy and a literature review were conducted. The important morphological characteristics—thin lip-shaped sternum, elongated alveoli, and eccentric raphe slit—were found in the species. These features are not present in previously described Giffenia taxa (Giffenia cocconeiformis). The new diatom species is characterized by (1) a slightly undulated valve face, (2) a lip-shaped sternum with a slightly rough surface, (3) numerous elongated alveoli on the valve face, and (4) an eccentric raphe slit. We propose Giffenia koreana sp. nov. as a new epipelic diatom taxon.