Ship Hull-Fouling Diatoms on Korean Research Vessels Revealed by Morphological and Molecular Methods, and Their Environmental Implications.

Ship biofouling is one of the main vectors for the introduction and global spread of non-indigenous organisms. Diatoms were the early colonizers of ship hulls; however, their community composition on ships is poorly understood. Herein, we investigated the diatom community on the hull samples collected from two Korean research vessels Isabu (IRV) and Onnuri (ORV) on September 2 and November 10, 2021, respectively. IRV showed low cell density (345 cells/cm2) compared to ORV (778 cells/cm2). We morphologically identified more than 15 species of diatoms from the two research vessels (RVs). The microalgae in both RVs were identified as Amphora, Cymbella, Caloneis, Halamphora, Navicula, Nitzschia, and Plagiogramma. Of them, the genus Halamphora was found to be predominant. However, both RVs had a varied dominant species with a significant difference in body size; Halamphora oceanica dominated at IRV, and Halamphora sp. at ORV, respectively. Molecular cloning showed similar results to morphological analysis, in which Halamphora species dominated in both RVs. The hull-attached species were distinct from species found in the water column. These results revealed diatoms communities that are associated with ship hull-fouling at an early stage of biofilm formation. Moreover, ships arriving from different regions could show some variation in species composition on their hull surfaces, with the potential for non-indigenous species introduction.

Population Genetic Structures and Demographic Expansion of the Exotic Jellyfish Carybdea brevipedalia in Korean Coasts Inferred from Mitochondrial COI Analysis.

Carybdea brevipedalia Kishinouye, 1891 is a poisonous jellyfish that usually occurs only in Japanese coastal regions. However, it was recently found on the Korean coast, thus expanding its known geographical range. In this study, we analyzed the population genetics and demographic histories of 113 C. brevipedalia specimens from the southern and eastern coastal regions of Korea by sequencing mitochondrial DNA cytochrome c oxidase subunit I (COI). We identified 42 C. brevipedalia COI haplotypes with high genetic diversity and a significant genetic structure. Populations were highly differentiated based on geographic location and distinctly divided into A and B clades. The results of Mantel tests indicated that geographic distance influenced the genetic distance between the two clades. Moreover, demographic analyses (neutrality tests) and the star-like profile of the Templeton, Crandall, and Sing (TCS) haplotype network indicated that C. brevipedalia had recently expanded into the southern and eastern coastal regions of Korea. These findings suggest that C. brevipedalia populations along the Korean coast have significant genetic differentiation that could be influenced by geographic isolation and subsequent adaptation to regional ecological conditions.

Population Genetic Structures of the Jellyfish Aurelia coerulea Polyps along Korean Coasts and Implications as Revealed by Mitochondrial COI.

The moon jellyfish, Aurelia coerulea, is is globally distributed, and its blooms have been responsible for severe environmental impacts. Benthic polyp populations are important for forming and maintaining medusa populations; however, their genetic structures are mostly unknown. Here, we analysed the genetic structure and phylogeographic pattern of A. coerulea polyps using the mitochondrial COI of 229 specimens collected from four different coastal regions of Korea. Molecular discrimination by COI assigned all polyps to A. coruelea. Population genetics revealed 53 haplotypes with high diversity and significant genetic structure, distinguishing two haplogroups (A and B) that coexist in all regions. Haplogroup A exhibited a star-like haplotype network pattern, while haplogroup B demonstrated a branched haplotype network pattern. Our results suggest that, the two haplogroups detected have existed in sympatry along Korean coasts. However, haplogroup A may have been established by a recent population expansion, while haplogroup B may have been established a long time ago. The strong genetic structure found within the polyp population of A. coerulea may have an effect on the moon jellyfish blooms on Korean coasts.

Evaluation of the complete nuclear rDNA unit sequence of the jellyfish Cyanea nozakii Kishinouye (Scyphozoa: Semaeostomeae) for molecular discrimination.

The harmful jellyfish Cyanea nozakii Kishinouye has frequently occurred on Korean coasts, and its blooms have caused serious ecological and economic damages. DNA sequences of the C. nozakii for molecular detection and discrimination are relatively scarce. In this study, we determined the complete sequence of a single unit of tandemly repeated ribosomal DNA (rDNA) of the Korean C. nozakii and characterized the molecular features of the rDNA. The complete rDNA contained 8,003 bp (48.4% GC) with the same gene arrangement (18S, ITS1, 5.8S, ITS2, 28S, and IGS) to the typical eukaryotes. Dot plot analysis showed that the coding regions (18S, 5.8S, and 28S) were highly conserved, while the non-coding regions (ITS1, ITS2, and IGS) were more variable and parsimony-informative. The IGS contained a putative transcription termination signal (poly(T) tract) and four repeats of block minisatellites. Phylogenetic analyses using 18S and 28S rDNA revealed well-resolved relationships of C. nozakii within the order Semaeostomeae, separating it from other Cyanea species. The complete rDNA sequence provides various options for the selection of jellyfish taxonomic markers and may be useful for discriminating between species of C. nozakii and phylogeny reconstruction with close relatives.