Benthic polychaete community structure in the Yellow Sea Bottom Cold Water zone (YSBCW): Species diversity, temporal-spatial distribution, and feeding guilds.

The Yellow Sea Bottom Cold Water zone (YSBCW) is a unique seasonal phenomenon in the Yellow Sea, where sea-floor cold water formed in winter is maintained until summer. This survey was conducted at 36 sites from 2018 to 2020. We identified 130 species of polychaetes, with an average density of 275 individuals/m2. The number of species and density were different outside and inside of the YSBCW, and the outside was generally high. The remaining dominant species were all deposit feeders, although differences were observed in the surface or subsurface (burrowers). Correlations between polychaete community and environmental variables strongly correlated with depth, temperature, gravel, and sand. This study investigated polychaete community distribution, environmental characteristics, and feeding guilds in the YSBCW and can be used as a basic database for comprehensive research related to the Yellow Sea in the future.

A New Branchipolynoe (Aphroditiformia: Polynoidae) Scale Worm from the Onnuri Deep-sea Hydrothermal Vent Field, Northern Central Indian Ridge.

Deep-sea hydrothermal vents are dynamic environments with exotic fauna, including bathymodiolin mussels and scale worm annelids that are often in close association. In this study, we found a new species of Branchipolynoe (Aphroditiformia: Polynoidae) living in the recently discovered mussel Gigantidas vrijenhoeki in deep-sea hydrothermal vents and methane seeps at 2,014-2,023 m depth. Based on the morphology and full mitochondrial genome sequences of specimens of Branchipolynoe from the Onnuri vent field (OVF) on the northern Central Indian Ridge, we describe them as a new species: Branchipolynoe onnuriensis sp. nov. This species resembles B. longqiensis and B. tjiasmantoi, but can be distinguished from these species by the shape of the notopodial acicular lobe and the tips of the subacicular neurochaetae. This identity is well-supported by genetic distance and phylogenetic analyses based on the mitochondrial c oxidase subunit I (COI) gene, with the new species being closest to the Western Pacific species B. tjiasmantoi. Phylogenetic analyses support close relationships between the Indian Ocean and Western Pacific hydrothermal polychaetes. Our data provide a foundation for exploring the evolutionary relationship between scale worms and bathymodiolin mussels.

First transcriptome assembly of a newly discovered vent mussel, Gigantidas vrijenhoeki, at Onnuri Vent Field on the northern Central Indian Ridge.

This is the first report of a transcriptome assembly of a newly discovered hydrothermal vent mussel, Gigantidas vrijenhoeki (Bivalvia: Mytilidae), on the Central Indian Ridge. Gigantidas vrijenhoeki was identified from material collected at the newly discovered Onnuri Vent Field (OVF) on the Central Indian Ridge in 2018, and was reported as a new species, distinct from another dominant hydrothermal vent mussel, Bathymodiolus marisindicus, in 2020. We sequenced the transcriptome of G. vrijenhoeki using the Illumina HiSeq X System. De novo assembly and analysis of the coding regions predicted 25,405 genes, 84.76% of which was annotated by public databases. The transcriptome of G. vrijenhoeki will be a valuable resource in studying the ecological and biological characteristics of this new species, which is distinct from other deep-sea mussels. These data should also support the investigation of the relationship between the environmental conditions of hydrothermal vents and the unique distribution of G. vrijenhoeki in the OVF of the Central Indian Ridge.

Rapid recovery of coastal environment and ecosystem to the Hebei Spirit oil spill's impact.

The 2007 Hebei Spirit oil spill (HSOS), the largest in the national history, has negatively impacted the entire environment and ecosystem along the west coast of South Korea. Although many studies have reported the damages and impacts from the HSOS, quantitative assessment evaluating the recovery time and status have not been documented. Here, we first address the recovery timeline of the HSOS, by comprehensive analyses of 10-years accumulated data in quantitative manner. Concentrations of residual oils in seawater, sediments, and oysters rapidly dropped to backgrounds in 16, 75, and 33 months, respectively. Also, damaged benthic communities of intertidal and subtidal areas were fully recovered only after ~6 years. The present results collectively indicated unexpectedly fast recovery of the damaged environment and ecosystem from such a huge oil spill. The high tidal mixing (~9 m tidal height) and intensive human cleanup (~1.2 million volunteers) at the initial cleanup period might have contributed to rapid recovery; cf. 4-5 times faster than the Exxon Valdez oil spill. However, potential risk to human health remains unclear. Thus, it is warranted to conduct more in depth epidemiological studies to address chronic health effects associated with the cleanup volunteers as well as the local residents who have been living nearby the oil spill impacted sites.

Description of two deep-water copepods of the genus Leptotachidia Becker from the northwestern Pacific (Harpacticoida, Pseudotachidiidae).

The monospecific genus Leptotachidia Becker, 1974 (Pseudotachidiidae Lang, 1936) was previously known only from the deep Atlantic. Female specimens of two unknown species of this genus were collected from abyssal sediments during an expedition to the northwestern Pacific on board research vessel ISABU (Korea Institute of Ocean Science and Technology) in November 2017. In this paper we describe the females of two new species, L. senaria sp. nov. and L. apousia sp. nov. The new species were attributed to the genus Leptotachidia by the combination of the five-segmented female antennule, presence of the Brodskaya organ on the distal antennulary segment, and the second exopodal segments of second to fourth legs without inner setae. An outstanding character of both Pacific species is the reduced armature of thoracic legs in contrast to the type species, L. iberica Becker, 1974. In addition, the setal armature of L. senaria sp. nov. and L. apousia sp. nov. is unique within the genus in that the female leg 5 of L. senaria sp. nov. has six elements instead of five; and the antennary exopod of L. apousia sp. nov. bears a single seta on the proximal segment instead of two. This is the first record of Leptotachidia from the Pacific. A key to all three species of Leptotachidia is provided.

Diverse responses of sporophytic photochemical efficiency and gametophytic growth for two edible kelps, Saccharina japonica and Undaria pinnatifida, to ocean acidification and warming.

Ocean acidification and warming represent major environmental threats to kelp mariculture. In this study, sporophytic photochemical efficiency and gametophytic growth of Saccharina japonica and Undaria pinnatifida were evaluated under different pCO2 levels (360, 720, and 980 ppmv) and temperatures (5, 10, 15, and 20 °C for sporophytes; 15 and 20 °C for gametophytes). Sporophytic photochemical efficiencies of both kelps were significantly greater at 720 ppmv than at 360 and 980 ppmv. Female gametophytes of both kelps grew significantly better at 360 ppmv than at higher pCO2 levels. The growth of U. pinnatifida gametophytes was significantly greater at 20 °C than at 15 °C, while no significant difference was observed for the growth of S. japonica. These results indicate that increased pCO2 stimulated sporophytic photochemical efficiency while inhibited gametophytic growth of these kelps, which might negatively affect their seedling cultivation. U. pinnatifida exhibited higher productivity in warmer ocean than S. japonica.

Effect of increased pCO2 in seawater on survival rate of different developmental stages of the harpacticoid copepod Tigriopus japonicus.

The rapid increase in carbon dioxide levels in seawater is causing ocean acidification and is expected to have significant effects on marine life. To explore the ability of the harpacticoid copepod Tigriopus japonicus to adapt to an increased concentration of dissolved carbon dioxide (CO2) in seawater, we compared the survival rates of adult and nauplius stages at 400, 1000, and 1550 ppm pCO2 over a 14-day period. The survival rate of T. japonicus dramatically decreased over time with increase in pCO2 concentration. At 1550 ppm, the survival rate showed a decrease of more than 20% at the end of the experimental period over that at 400 ppm. Furthermore, the survival rate decreased by a greater amount at all concentrations in nauplii than in adults, with a greater effect in wild-collected specimens than in culture-derived individuals. The results suggest that future ocean acidification may negatively influence the sustainability of T. japonicus and thus may eventually influence benthic ecosystems.

Description of two new species of Neotanais Beddard, 1886 (Crustacea, Tanaidacea) from KODOS area.

Two new species of Neotanais Beddard, 1886 are described from the Korea Deep Ocean Study (KODOS) area in the Clarion-Clipperton Fracture Zone, based on the collections performed on board R/V Onnuri from a depth of 5180 m. Neotanais triqueturus n. sp. is similar to the 'pfaffi group' characterized by pereonites with a swollen distolateral margin, pleonites with mid-ventral spurs and tapered lateral margins but can be differentiated by a longer cephalothorax (length: width 1.6: 1), a cheliped with a large protrusion on the mid-dorsal margin of the fixed finger, and the presence of a ventral process on the cheliped carpus. Neotanais brevis n. sp. has the characteristics of the 'micromopher' group, with pleonites narrower than pereon, a cheliped carpus without a ventral process, and a uropod endopod with nine articles but can be differentiated by a combination of the pleonites without mid-ventral spurs, a relatively longer pleotelson (length: width 1: 1.5 vs. 1: 2), a uropod basis with one seta on each of the ventral and dorsal margins, and the cheliped fixed finger with proximal denticles. In this study, in order to prove N. triqueturus and N. brevis were new species, full descriptions and a comparison with the closely related species are given. In addition, comprehensive comparisons with the species of Neotanais from the east-central Pacific are tabulated and discussed.

Stable isotope analysis of a newly established macrofaunal food web 1.5 years after the Hebei Spirit oil spill.

We examined trophic relationships in a newly established community 1.5 years after the Hebei Spirit oil spill on the west coast of Korea. Carbon and nitrogen stable isotope ratios in consumers and their potential food sources were compared between the oil-spill site and reference site, located 13.5 km from the oil-spill spot. The isotopic mixing model and a novel circular statistics rejected the influx of petrogenic carbon into the community and identified spatial consistencies such as the high contributions of microphytobenthos, food-chain length, and the isotopic niche of each feeding guild between sites. We suggested that high level of trophic plasticity and the prevalence of omnivory of consumers may promote the robustness of food web against the oil contamination. Furthermore, we highlighted the need of holistic approaches including different functional groups to quantify changes in the food web structure and assess the influence of different perturbations including oil spill.

Initial impacts of the Hebei Spirit oil spill on the sandy beach macrobenthic community west coast of Korea.

Petroleum hydrocarbon contamination and macrobenthos in the sandy tidal flats of Taean were monitored for 1 year to assess the impacts of Hebei Spirit oil on the macrobenthic community. A total of 207 macrobenthic fauna was collected, and the mean density and biomass of macrobenthic fauna continued to decrease until 12 months after the oil spill, but macrobenthic density at the most heavily affected sites increased by about twofold. In January 2008, the dominant species occurred at very low densities in strongly affected sites. The macrobenthic communities differed between oil-affected and unaffected sites. In particular, differences in community structure at Mallipo beach were larger than those at Shinduri. We suggest that long-term monitoring is needed to assess the specific effects of oil pollution on the sandy intertidal macrobenthic community.