As one of efforts to conserve a genetic resource of the endemic cobitid species in the Korean peninsula, the complete mitogenome of Cobitis hankugensis (Kim, Park, Son & Nalbant, 2003) was determined using Illumina MiSeq system. The circular mitogenome was 16,557 bp length and encoded 13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 tRNA genes, and a control region. Only the COX1 gene was identified with an aberrant initiation codon GTG, and an incomplete termination codon (T—/TA–) was identified in six PCGs including COX2, COX3, ND2, ND3, ND4, and Cytb genes. Phylogenetic analysis using 30 mitochondrial genomes belonging to Cobitidae, Botiidae, and Gyrinocheilidae showed that the highest identity (92.38%) with Kichulchoia brevifasciata (NC_027166). The complete mitogenome of C. hankugensis, an endemic species in Korea, will provide fundamental data on the evolutionary relationship of Cobitidae species.

The global exploration of evolutionary trends in groupers, based on mitogenomes, is currently underway. This research extensively investigates the structure of and variations in Cephalopholis species mitogenomes, along with their phylogenetic relationships, focusing specifically on Cephalopholis taeniops from the Eastern Atlantic Ocean. The generated mitogenome spans 16,572 base pairs and exhibits a gene order analogous to that of the ancestral teleost’s, featuring 13 protein-coding genes (PCGs), two ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs), and an AT-rich control region. The mitogenome of C. taeniops displays an AT bias (54.99%), aligning with related species. The majority of PCGs in the mitogenome initiate with the start codon ATG, with the exceptions being COI (GTG) and atp6 (TTG). The relative synonymous codon usage analysis revealed the maximum abundance of leucine, proline, serine, and threonine. The nonsynonymous/synonymous ratios were <1, which indicates a strong negative selection among all PCGs of the Cephalopholis species. In C. taeniops, the prevalent transfer RNAs display conventional cloverleaf secondary structures, except for tRNA-serine (GCT), which lacks a dihydrouracil (DHU) stem. A comparative examination of conserved domains and sequence blocks across various Cephalopholis species indicates noteworthy variations in length and nucleotide diversity. Maximum likelihood, neighbor-joining, and Bayesian phylogenetic analyses, employing the concatenated PCGs and a combination of PCGs + rRNAs, distinctly separate all Cephalopholis species, including C. taeniops. Overall, these findings deepen our understanding of evolutionary relationships among serranid groupers, emphasizing the significance of structural considerations in mitogenomic analyses.

The Japanese sea lion, Zalophus japonicus, is an extinct pinniped species, which had inhabited along the coast of the Japanese archipelago and Korean peninsula. Its mitochondrial genome was determined by the assembly of PCR amplicons from the skeletal remains excavated from the Ulleungdo, South Korea. The whole mitogenome was 16,698 bp in length, which encoded 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNA), 2 ribosomal RNAs (rRNA), an origin of light-strand replication (OL), and a control region (D-loop). Unusual start codons were identified in ND2 (ATA), ND3 (ATA), and ND5 (ATC), while COIII, ND3, and ND4 were terminated with an incomplete stop codon (T–/TA-). Phylogenetic analysis showed that Z. japonicus was a sister species to Z. californianus with 98.61% nucleotide sequence identity among 11 pinniped species in the infraorder Pinnipedia, which supported the previous results. The complete mitochondrial genome sequence of Z. japonicus would be valuable information for its restoration and the evolutional understandings of pinniped species in the Pacific Ocean.

To estimate the impact of aggregate mining on a marine ecosystem, fish assemblages and phytoplankton communities were analyzed using environmental DNA metabarcoding. Metabarcoding analysis revealed 152 fish amplicon sequence variants (ASVs) (88 in September and 118 in February), which were assigned to 29 orders, 62 families, 104 genera, and 114 species (73 in September and 89 in February). Heatmap analysis showed that the fish assemblages in the mining area clearly differed from those in the surrounding area and that Pagrus major, Lateolabrax japonicus, Zeus faber, and Eopsetta grigorjewi were significantly more abundant there than in the surrounding area. In the phytoplankton community in September, the phyla Cyanobacteria and Haptophyta differed significantly between the mining area and its surroundings. By contrast, no such significant differences were identified in February, presumably due to the low temperature impeding phytoplankton growth. Taking these findings together, mining activities clearly affect fish and phytoplankton communities, but further long-term study is required to assess their impacts on marine ecosystems.

Ophiuroids are a diversified benthic taxon in the deep sea. Given their various dispersal strategies, they are considered an adequate group to assess genetic connectivity, especially in the seamounts that function as islands. Ophioleila elegans A.H. Clark, 1949, in the family Ophiothamnidae, was previously reported from the Caiwei Guyot, a seamount in the northwest Pacific Ocean. Here, we described the mitochondrial genome of O. elegans collected from another seamount in the northwest Pacific. The whole mitogenome is 16,376 bp in length and encodes 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes. Phylogenetic analysis based on the mitogenome sequences showed that O. elegans was clustered with Histampica sp., the only species for which mitogenome sequence has been reported within the family Ophiothamnidae. The complete mitogenome of O. elegans first reported in the present study provides useful information for population genetics and evolutionary relationship of this taxon, especially in the northwest Pacific seamounts.