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In this study, using Illumina sequencing, we sequenced first the complete mitochondrial genome (mitogenome) of two deep-sea eels, Histiobranchus bathybius and Simenchelys parasitica, collected from the East Mariana Basin in the Western Pacific Ocean. The complete length of the H. bathybius and S. parasitica mitogenomes were 16,696 and 16,687 bp, respectively, each containing 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 ribosomal RNA genes). To enhance the accuracy of the identification of H. bathybius and S. parasitica, we performed a phylogenetic analysis of multiple deep-sea eels based on the mitochondrial DNA gene (cytochrome c oxidase subunit I [COI]) using the maximum likelihood method. Our phylogenetic tree analysis confirmed that the specimens collected in this study are congeneric species of H. bathybius and S. parasitica reported in previous studies. Based on these results, we report the first complete mitogenomes of H. bathybius and S. parasitica and a new record for the two species in the East Mariana Basin. [ABSTRACT FROM AUTHOR]

The geoduck clam is a high-value species in South Korea. However, the molecular and morphological characteristics of geoduck clams from the southern coast of South Korea remain unexamined. The accurate identification of native geoduck clams is crucial for their conservation and management. Therefore, this study used a combination of molecular and morphological analyses to characterize native geoduck clams from the southern coast of South Korea. Based on complete mitochondrial genome and morphological analyses, the native species of geoduck clam from this study area was identified as Panopea sp. 1. The complete mitochondrial genome sequencing of Panopea sp. 1 revealed a total of 16,225 bp in length with 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes). It was also shown that Panopea sp. 1 belongs to the family Hiatellidae based on a phylogenetic analysis tree with 11 bivalve species. In particular, Panopea sp. 1 is closely related to three other Panopea species (Panopea sp., Panopea abrupta, and Panopea japonica). The phylogenetic analysis correlated with the morphological analysis. Overall, this is the first reliable record of Panopea sp. 1 in South Korea. These findings provide a basis for accurate species identification based on morphological characteristics and complete mitochondrial genome sequencing. [ABSTRACT FROM AUTHOR]

Owing to the constant wind generated by the vast ocean, energy production from offshore wind farms (OWFs) plays an important role in the expansion of renewable energy. However, areas close to large wind farms are often left unutilized, and aquaculture farmers find it difficult to efficiently utilize these unoccupied spaces due to limited information showing the feasibility of utilization of OWFs as potential scallop culture sites. To analyze whether the two scallop species Zhikong scallop (Chlamys farreri) and bay scallop (Argopecten irradians) can be grown at OWFs of Gochang and Buan, Jeollabuk-do, Republic of Korea, the growth characteristics of the two scallop species were analyzed and compared with those grown at the Tongyeong Megacosm Test Station. The results clearly showed that the growth of scallops at the OWF was significantly lower with respect to the shell lengths, height, width, and weight, compared to those grown at the megacosm station. However, scallops grown at the OWF still showed consistent growth in parallel with those grown at the megacosm test station. Yet, there was a species-specific mortality rate between the two sites. In addition, our results suggest that temperature may be a key determinant of the growth of C. farreri and A. irradians. Overall, this study contributes to establishing a foundation for the stable and continuous farming of marine bivalves (e.g., clams, oysters, mussels, and scallops) in OWF areas. [ABSTRACT FROM AUTHOR]

In this study, we document the first recorded range extension of the genus Synaphobranchus from the East Mariana Basin in the Western Pacific Ocean. We sequenced the complete mitochondrial (mt) genome of two deep-sea eels (Synaphobranchus brevidorsalis and S. affinis) collected in the East Mariana Basin in the Western Pacific Ocean. The complete mt genomes of S. brevidorsalis and S. affinis were 16,686 bp and 16,677 bp in length, respectively, and consisted of 13 protein-coding genes, 22 tRNA genes, and two rRNA genes. Molecular phylogenetic analysis of the two deep-sea eel species was performed, based on the mt cytochrome c oxidase subunit I (COI) gene using the maximum likelihood method. The molecular phylogenetic tree demonstrated that S. brevidorsalis and S. affinis were congeneric species of S. brevidorsalis and S. affinis reported in previous studies with bootstrap values of 100% and 100%, respectively. This is the first report on the complete mt genomes of S. brevidorsalis and S. affinis collected in the East Mariana Basin in the Western Pacific Ocean. Overall, our study highlights the potential of molecular approaches in identifying species diversity and distribution in the Western Pacific Ocean. [ABSTRACT FROM AUTHOR]

Geoduck clams are important commercial marine resources in Southeast Asia. However, the complete mitochondrial genome of the native geoduck clam in South Korea has not been reported yet. This study reports a geoduck clam collected from the east coast of South Korea. Based on its morphological characteristics and molecular data, the geoduck clam was identified as Panopea sp. belonging to the bivalve family Hiatellidae. We determined the complete mitochondrial genome of this species and investigated the seasonal reproductive pattern for monthly changes in sex ratio, gametogenesis, and reproductive cycle from September 2019 to August 2020. The total length of the complete mitochondrial genome sequence is 16,006 bp, containing 13 protein-coding, 22 transfer RNA, 2 ribosomal RNA, and a control region (D-loop). A molecular phylogenetic comparison with 10 bivalve species showed that the geoduck clam specimen belongs to the family Hiatellidae, clustering with Panopea abrupta Chinese strain, P. generosa, and P. globosa. The gametogenesis of the geoduck clam was identified in six stages by histological analysis. The sex ratio was biased towards males from May 2019 to July 2019, the main spawning activity from the frequency of the gonads with ripe and spent stages occurred from October 2018 to April 2019, and there was no clear pattern of spawning peaks from May to August 2019 with gonads developed asynchronously between both sexes. This is the first study to report new records of the genus Panopea based on the complete mitochondrial genome and to examine the seasonal reproductive pattern of the native geoduck clam Panopea sp. in South Korea, providing valuable information for its sustainable management in South Korea. [ABSTRACT FROM AUTHOR]

Benthic habitat zonation is described from in situ observations and seabed photographs taken from the coastal area of Weno Island, Chuuk, Micronesia. Habitat groups, types, and boundaries are defined by visible substratum characteristics (i.e., in situ and by digital imaging of photo-quadrats along transect lines), and by cluster and ordination analyses using relative coverage percentage of identified classification categories. The statistical similarity between habitat groups is determined by Analysis of similarity (ANOSIM). Benthic habitat groups with significant influence on the determination of habitat type are isolated by the similarity percentage (SIMPER) test. In addition to the standard practices of using transect lines and collecting data in accordance with the already well-implemented and thoroughly-tested benthic habitat classification scheme for tropical reef monitoring, we applied simple statistics that enable comparative data interpretation. Our simple, repeatable methods provide a framework for benthic habitat-related monitoring research that allows the comparison of results across regions. [ABSTRACT FROM AUTHOR]

Two deep-sea eels collected from the East Mariana Basin in the western Pacific Ocean are described in this study. Based on their morphological features, two eel specimens were assumed to belong to the Gray cutthroat eel family, Synaphobranchidae. Mitochondrial DNA (mtDNA) genes have been widely used as genetic markers to identify fish species. To accurately identify the species of the two eel specimens, we sequenced the mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA (16S rRNA) genes from the two eel specimens. The sequences from the specimens were 100% identical. The molecular phylogenetic tree confirmed that the two eel specimens were closely related to Synaphobranchus affinis with a bootstrap value of 100%. This is the first study to report new records of S. affinis from the East Mariana Basin in the western Pacific Ocean. [ABSTRACT FROM AUTHOR]

In this study, we investigated the reproductive pattern of the commercially and ecologically important species, Ostrea denelamellosa, to inform stock management strategies in South Korea. Prior to the reproduction experiment, the complete mitochondrial (mt) genome of the flat oyster, Ostrea denselamellosa, was analyzed using next-generation sequencing technology. Then, to determine the reproductive pattern of Ostrea denselamellosa, we investigated monthly changes in the gametogenesis, reproductive cycle, and sex ratio from January to October 2021 in females. The total length of the mt genome sequence of O. denselamellosa was 16,225 bp and contained 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes). Molecular phylogenetic comparison with 20 known species of Pteriomorphia showed that O. denselamellosa belongs to the family Ostreidae. In addition, O. denselamellosa clustered together with the O. denselamellosa Chinese strain, with a bootstrap value of 100%. Histological analysis indicated a discrepancy in gamete development of O. denselamellosa with synchronous maturation of oocytes and asynchronous development of spermatozoa in gonads. The spawning activity occurred between May and September with a temperature range gap of 6.5 °C. The spawning activity occurred from May when the temperature reached 16.7 °C until September when the temperature dropped below 23.2 °C. Furthermore, sex ratio bias was observed. This is the first study to report the complete mt genome sequence and examine the reproductive pattern in native O. denselamellosa in South Korea. Overall, these findings will help enhance the knowledge for the management and sustainable fishery of endangered oyster species including O. denselamellosa in the South Sea of Korea. [ABSTRACT FROM AUTHOR]

The seasonal variations in the species composition of set net fisheries were investigated on the Eastern coast of Korea, from 2007 to 2008. In total, 51 species were found that were classified into 15 orders and 33 families. The water temperature of the study area was 0.1–1.8 °C in 2007 and 0.6–2.1 °C in 2008, which was higher than the average water temperature in the previous decade. The monthly variation in the number of species peaked twice, in May (spring) and November (autumn) when the water temperature increased and decreased, respectively, and the monthly variation in the number of individuals showed a remarkably high trend in winter and autumn and was mainly caused by large migratory species. Based on the cluster analysis of the 18 most dominant species with more than 0.4% of the total number of individuals, we divided the species composition and community structures into three groups: fishes with a temporary appearance (Group A), fishes with a long-term appearance (Group B), and dominant pelagic fishes appearing with a long-term appearance (Group C). We could conclude that the seasonal variation in the structure of the fish community was mainly caused by the pelagic migration of species under high water temperature conditions during the study period. [ABSTRACT FROM AUTHOR]