Interaction between phytoplankton and heterotrophic bacteria in Arctic fjords during the glacial melting season as revealed by eDNA metabarcoding.

The hydrographic variability in the fjords of Svalbard significantly influences water mass properties, causing distinct patterns of microbial diversity and community composition between surface and subsurface layers. However, surveys on the phytoplankton-associated bacterial communities, pivotal to ecosystem functioning in Arctic fjords, are limited. This study investigated the interactions between phytoplankton and heterotrophic bacterial communities in Svalbard fjord waters through comprehensive eDNA metabarcoding with 16S and 18S rRNA genes. The 16S rRNA sequencing results revealed a homogenous community composition including a few dominant heterotrophic bacteria across fjord waters, whereas 18S rRNA results suggested a spatially diverse eukaryotic plankton distribution. The relative abundances of heterotrophic bacteria showed a depth-wise distribution. By contrast, the dominant phytoplankton populations exhibited variable distributions in surface waters. In the network model, the linkage of phytoplankton (Prasinophytae and Dinophyceae) to heterotrophic bacteria, particularly Actinobacteria, suggested the direct or indirect influence of bacterial contributions on the fate of phytoplankton-derived organic matter. Our prediction of the metabolic pathways for bacterial activity related to phytoplankton-derived organic matter suggested competitive advantages and symbiotic relationships between phytoplankton and heterotrophic bacteria. Our findings provide valuable insights into the response of phytoplankton-bacterial interactions to environmental changes in Arctic fjords.

Evaluation of Post-Surgical Recovery in Olive Flounder (Paralichthys olivaceus) by Assessing Behavior, Heart Rate, and Wound Healing.

This study examined the post-surgery recovery of olive flounder (Paralichthys olivaceus) following tag insertion by analyzing behavior, heart rate, and wound healing. The experiments used 30 individuals (length: 38.67 ± 2.12 cm; weight: 742.48 ± 116.41 g). Heart rate was measured using a DST milli-HRT (Star-Oddi) bio-logger. To assess the influence of water temperature on the recovery process after surgical tag insertion, behavioral analyses, heart rate, and wound healing were conducted in two experimental groups: Experiment 1 (22 °C, optimal water temperature); Experiment 2 (28 °C, high water temperature); and control group (22 °C, non-operated fish). The experiment was repeated twice over a 7-day period for each experimental group. Compared to the non-operated fish, the operated fish exhibited stable levels after the 3rd to 4th day in Experiment 1. Statistical analyses based on heart rate in Experiment 1 indicated that the appropriate post-surgery recovery time point was approximately 3 days, representing the point at which behavioral fluctuations stabilized. In the case of Experiment 2, abnormal behavioral patterns (e.g., tilted swimming) and changes in average swimming time and daily heart rate were found to stabilize after 4 days post-surgery.

Taxonomic reassessment of chaetognaths (Chaetognatha, Sagittoidea, Aphragmophora) from Korean waters.

Since the first record of chaetognaths (arrow worms) reported from Korean waters by Molchanov in 1907, three families, 12 genera and 21 species have been additionally described. Eighteen of the 21 recorded species have been reported under scientific names different from the latest taxonomic system. This study aimed to address this issue by conducting a taxonomic re-evaluation of chaetognaths collected from Korean waters. Furthermore, the taxonomic usefulness of morphological differences in corona ciliata and distribution of ciliary sense receptors were re-examined using specimens stained with 1% Chlorazol black E (CBE) solution. This study includes taxonomically-validated voucher specimens of 18 species from Korean waters. Based on the specimens, re-description including image data and CBE staining pattern, distribution, ecological information and improved key were provided for each species. However, Decipisagittadecipiens, Serratosagittaserratodentata and Sagittapseudoserratodentata from Korean waters is still questioned because of the paucity of the voucher specimen and scientific literature.

Three new species of Heteromastus (Annelida, Capitellidae) from Korean waters, with genetic evidence based on two gene markers.

Three undescribed species of Heteromastus Eisig, 1887 were collected from intertidal to sublittoral habitats in western and southern waters of Korea. Heteromastus namhaensis sp. nov. is distinguishable from other congeners by the presence of hemispheric notopodial lobes in the posterior abdomen. Heteromastus gusipoensis sp. nov. closely resembles H. tohbaiensis Yabe & Mawatari, 1998 in the absence of posteriorly extended abdominal notopodial lobes, but differs in the absence of eyespots on the prostomium and distinct node on the shaft of thoracic hooks in H. gusipoensis. Heteromastus koreanus sp. nov. is similar to H. filiformis sensu Hutchings & Rainer, 1982 in the shape of abdominal notopodia, but clearly differs in dentition of the abdominal hooks and methylene green staining pattern (MGSP). DNA sequences (mtCOI and histone H3) of these new Korean species were compared with all sequences of Heteromastus species available in the public database. Molecular results showed distinct genetic differences among these three new Korean species at species level. Comparison of mtCOI gene revealed significant genetic difference between H. filiformis and these Korean species. A comprehensive comparison between three Heteromastus species of present study and their closely related congeners is conducted based on morphological and genetic results.

A new Notomastus (Annelida, Capitellidae) species from Korean waters, with genetic comparison based on three gene markers.

Notomastus koreanussp. n., collected from the sublittoral muddy bottom of Korean waters, is described as a new species. The Korean new species closely resembles N. torquatus Hutchings & Rainer, 1979 in the chaetal arrangement and the details of abdominal segments, but differs in the position of genital pores and the absence of eyes. DNA sequences (mtCOI, 16S rRNA, and histone H3) of the new species were compared with all the available sequences of Notomastus species in the GenBank database. Three genes showed significant genetic differences between the new species and its congeners (COI: 51.2%, 16S: 38.1-47.3%, H3: 3.7-9.3%). This study also includes a comprehensive comparison of the new Korean Notomastus species with its most closely similar species, based on the morphological and genetic results.

A new species of the genus Hexapleomera Dudich, 1931 from the South Korea, with molecular evidence (Crustacea, Tanaidacea, Tanaididae).

Two populations of new species are described for Hexapleomera Dudich, 1931 from the southeastern coast and Jeju island of South Korea (north west Pacific). The specimens were collected using a light trap set overnight at the entrance near a pier or harbour. Hexapleomera ulsanasp. n. is clearly differentiated from other species in the genus by the uropod with five articles, a maxillule palp with four distal setae, the maxilliped coxa with three proximal setae, the epignath with short and blunt spiniform seta, the propodus of pereopods 2-3 with three ventral setae, and the maxilla with a rugged shape of the distal margin. Differences of mitochondrial cytochrome c oxidase subunit I (mtCOI) gene observed between two populations of H. ulsana from different regions (Ulsan and Jeju Island) and between H. ulsana and H. urashima (Japan) were 1.1 % and 32.4 %, respectively. Two genetically-close populations differed in the setae on pleopod 3, the proximal setae on the maxilliped coxa, and the ventral setae on pereopods 2-3, which showed that geographical distance affected the morphological divergence. In addition, a comprehensive comparison with previous records of Hexapleomera was conducted and close examinations on the appendages, known to have morphological variations between the individuals of one species and/or between different genders, were carried out based on new species and discussed herein.

A new species of Leiochrides from the Korean subtidal waters with notes on the taxonomic status of the genus Pseudomastus (Annelida, Capitellidae).

Leiochrides yokjidoensissp. n., collected from the sublittoral muddy bottom in southern Korea, is described as a new species. The taxonomic status of the monospecific genus Pseudomastus has been a subject of controversy for many years, as its characteristics overlap those given in recent generic definitions of Leiochrides. The results of a comprehensive review and comparison regarding the two genera, based on previous records showed minor differences. In this study, a detailed description of L. yokjidoensissp. n. is given and a comparison with closely related species is tabulated and discussed.The taxonomic status of Pseudomastus is discussed and the genus placed in synonymy with Leiochrides.