Search

Abstract Pulsed flows following heavy monsoon rain events alter riverine food webs, but their impact on headwater stream food webs across the continuum from forested canopy to open agricultural land use remains unclear. We investigated carbon and nitrogen stable isotopes in macroinvertebrates and fish in two tributaries of the Suyeung River, Korea, before and after heavy monsoon rains to assess changes in community trophic niches. Basal resources (leaf litter and biofilms) exhibited consistent δ13C and δ15N values across seasons, with biofilms showing higher δ13C values. δ15N values increased from forested to agricultural reaches, indicating varied nutrient inputs. Consumer isotope values remained stable over time but varied longitudinally, reflecting reliance on local resources. Trophic niches differed between watershed locations but overlapped seasonally. Despite a decrease in consumer δ13C ranges after heavy rainfalls, variations in their δ15N ranges and the ellipse centroid (SEAc) of isotopic niches between sites resulted in broadly consistent SEAc across locations and seasons. This indicates limited evidence for directional reshaping of food-web properties across channel reaches following monsoon rains. Downstream isotopic shifts suggest substantial agricultural influences on food webs. Overall, our findings highlight that monsoon rains may have minimal effects on the community trophic niches of stream food webs.

The walleye pollock, Gadus chalcogrammus (Pallas, 1814), is one of the most commercially and ecologically valuable species in the Northwestern Pacific. However, combined pressures of overfishing and environmental changes have led to a substantial decline in its production in Japan and Russia since the 1990s, and a collapse in Korea since the 2000s. The objective of this study was to comprehensively examine its genetic diversity and population structure with an extensive sampling effort of 16 populations across the Northwestern Pacific including South Korea, Japan, and Russia. A multiplex PCR assay composed of seven microsatellite markers revealed a moderate level of observed heterozygosity (Ho = 0.369–0.599), which is lower than that reported in previous studies of this species. All loci were highly polymorphic, with the mean PIC ranging from 0.608 to 0.793. The structure of the 16 populations was characterized by heterozygote deficiency, a modest effective allele number (Ne = 4.551–7.969), low genetic differentiation (FST = 0.000–0.054), a weak population structure, a genetic admixture, and no significant correlation between the genetic and geographic distance. These characteristics are typical of pelagic marine species with large population sizes due to a consistent gene flow among populations when there are no physical boundaries in the open ocean. The seasonal and country-specific genetic structure indicated that G. chalcogrammus populations in the Northwestern Pacific region should be managed as a single management unit. The findings from this study provide critical information for future genetic monitoring, conservation management, and the development of strategies aimed at restoring the populations of this species.

We investigated the trophic dynamics between neustonic copepod communities and particulate organic matter (POM) sourced from contrasting water masses, i.e., high- and low-salinity areas, within the northeastern East China Sea. The sampling of neustonic copepod communities occurred three times in the summer (June, August, and September) of 2021, and considered the influx of the Yangtze River Diluted Water (YRDW) and the extension of the Tsushima Warm Current (TWC). To examine the relationship between the neustonic copepods and surface POM, we employed stable isotope techniques. Surprisingly, the neustonic copepod community exhibited a reluctance to feed on surface POM. The neustonic copepod community in the YRDW-dominated area in August showed higher δ13C values than those in the TWC-dominated area. The trophic groups within the neustonic copepod population appeared to consume selectively depending on the individual preferred prey sizes and composition. Using the POM from the water masses that affected the food sources consumed by neustonic copepods, we found a strong dependence on prey items originating from the TWC. This result suggests that the marine neustonic copepod community does not rely significantly on food sources derived from riverine freshwater.

Abstract Nutrient dynamics function globally, flowing from rivers to the ocean (estuarine–coastal zone), and are vulnerable to climate change. Microbial habitats can be affected by marine nutrient dynamics and may provide a clue to predict microbial responses to environmental heterogeneity in estuarine–coastal zones. We surveyed surface seawater in Gwangyang Bay, a semi-enclosed estuary in Korea, from 2016 to 2018 using a metabarcoding approach with prokaryotic 16S and eukaryotic 18S rRNA genes. Bacterial and microeukaryotic communities in these waters showed distinct local communities in response to environmental heterogeneity and community transition at spatiotemporal scales in the estuarine–coastal zone. The relative abundance of prokaryotic and eukaryotic operational taxonomic units suggested a microbial trophic interaction in the Gwangyang Bay waters. We found that the community assembly process in prokaryotic communities was primarily influenced by biological interaction (immigration–emigration), whereas that in eukaryotic communities was more affected by environmental stress (habitat specificity) rather than by biotic factors. Our findings in the Gwangyang Bay waters may provide information on underlying (biotic or abiotic) factors of the assembly process in microbial communities in the estuarine–coastal zone.

Spatial and temporal variability in the trophic base of food webs is an inevitable ecological attribute in aquatic ecosystems with the role of aquatic and terrestrial sources varying from system to system. Despite high algal biomass, an apparent increase in terrestrial detritus during the East Asian summer monsoon would be expected to alter the dominant food web base from the pre- to post-monsoon period. The δ13C and δ15N values of common aquatic invertebrates and fish were compared with those of their potential sources of organic matter across the upstream channel and lacustrine habitats during the pre- and post-monsoon periods in the Se-oak Stream system of Korea. The purpose was to identify the variability in trophic structure (niche and diversity) at the community level and to quantify the contribution of terrestrial and aquatic carbon sources to the food web base. The δ13C and δ15N values of the major potential organic matter sources differentiated allochthonous leaf litter and riparian vegetation from autochthonous biofilm and seston, but with no significant spatial and temporal changes. The δ13C values of consumers fell within a narrower range than that of organic matter sources, consistent with the instream biofilm and seston values. However, the consumer δ15N values spanned a broad range, increasing from invertebrates to fish. The resultant niche overlaps of consumers in the isotopic niche space between seasons and locations, their narrower horizontal niche breadths compared to organic matter sources, and the isotope mixing-model estimates indicated that aquatic production was the primary source of organic matter supporting the aquatic food webs. Overall, the results revealed a consistent dominance of autochthonous trophic bases in both lotic and lentic food webs before and after the summer monsoon. Our findings, which highlight the trophic importance of aquatic algal production facilitated by anthropogenic nutrients in this shallow, low-turbidity, and well-illuminated stream food web, may provide insight into ecosystem processes that counteract potential terrestrial-aquatic links to influence food web dynamics based on natural nutrient sources in deep, highly turbid, or shaded stream counterparts.

Knowledge of physiological responses of important shellfish species to rising temperatures is crucial in assessing the impacts of climate change on marine aquaculture production. The physiological components of energy balance that support growth performance were measured seasonally at different exposure temperatures in the ark clams (Anadara kagoshimensis) cultured in the shallow muddy bottom sediment in Yeoja Bay, Korea. We tested the effects of winter minimum (3–8°C) and summer maximum (23–28°C) temperature elevations on individual physiological processes (ingestion, respiration, egestion, and excretion) and the combined energetic physiology (scope for growth [SFG] and net growth efficiency [K2] measures). The seasonal cycle of dry flesh tissue weight (DW) was also investigated from January 2016 to November 2018, to compare its variation at contrasting cold vs. warm regimes. The rates of physiological components were related to DW, generating significant allometric equations. The weight exponents of the equations for ingestion rate and respiration rate were low at the winter minimum compared with the remaining season temperatures, indicating a higher thermal sensitivity in larger individuals. The physiological rates that were re-calculated for individual components based on estimates of the slope and intercept of the equations increased with increasing temperature, revealing an incapability of thermal acclimation and a temperature effect at seasonally different endogenous conditions. The thermal sensitivity (Q10) of the ingestion rate and respiration rate was reversed between the winter minimum and the summer maximum temperature elevations, yielding negative SFG and K2 values at 3 and 28°C. Furthermore, the interannual difference in the seasonal cycle of clam DW displayed variations in the period of increment prior to spawning and the post-spawning loss/recovery in association with its energy balance status in the winter and summer temperature conditions. Overall, these results indicate that warming is projected to affect physiological performance and the seasonal DW cycle of clams in different manners between winter and summer: physiological benefits and advanced weight gain vs. heat stress and progressive weight loss, respectively. The mechanistic adjustment of the clam energy balance across thermal conditions seems to explain the recent advancement in its seasonal biological cycle, as well as the failure in spat collection and the mass summer mortality observed at this culturing site.

The diet of the Antarctic toothfish (Dissostichus mawsoni) was analyzed using metabarcoding to determine whether spatiotemporal factors are related to its feeding ecology. A diet metabarcoding analysis was conducted for five years from 2016 to 2020 using 1,777 samples collected from two distantly located subareas, 88.3 and 58.4.1. Metabarcoding results revealed 105 prey haplotypes (29 families, 45 genera) in the stomach contents of D. mawsoni, which can serve as valuable genetic information for the accurate identification of piscine species inhabiting the Southern Ocean. Most of the stomach contents of D. mawsoni consisted of fish taxa, comprising 99.61% of read count, which is consistent with other studies indicating that D. mawsoni is piscivorous. The prey compositions were highly different between the two subareas (88.3 and 58.4.1) regardless of the year, indicating that the diet of D. mawsoni strongly reflects the fish assemblages in geographically different habitats. These results strongly suggest that the stomach contents are good ecological indicators for monitoring any changes in the marine ecosystem caused by either the fishery of D. mawsoni, the most voracious piscine predator in its habitat, or environmental changes. In addition, quantitative polymerase chain reaction results of the two most abundant Macrourus prey species of Antarctic toothfish, M. caml and M. whitsoni, showed that the distribution of these two species may be related to the dynamics of gyres, which flow along the Antarctic continent.

In this study, to determine the spatiotemporal variability of satellite-observed chlorophyll-a (Chl-a) concentrations in the East Sea (Japan Sea, EJS), monthly composite images were generated via noise processing using Level-2 MODIS Chl-a data from 2003 to 2020. Harmonic analysis was performed on time-series Chl-a data to present the spatial distribution of seasonal and intraseasonal variability with 1–4 cycles per year. In the EJS, seasonal cycles contributed less than approximately 30% to the total variance in Chl-a variability, indicating the existence of dominant interannual variability. Analysis of the temporal trend in Chl-a concentrations showed that they increased (< 0.06 mg m–3 yr–1) in most of the EJS over almost two decades (2003–2020). In recent years, in the areas showing positive trends in Chl-a, it tended to increase with time, especially in the northern part of the EJS. As a result of examining the trend associated with the physical environment that affects the long-term trend in Chl-a concentrations, sea surface temperature (SST) trends were mostly increased. The wind speeds showed a characteristic strengthening trend in the northeastern part of the EJS and the North Korean coast. Long-term changes in wind direction indicated strengthening of the northerly wind components on the Russian coast and the westerly components on the eastern coast of the Korean Peninsula. These wind changes were closely related to the Arctic Oscillation (AO) index variability in relation to the recent warming of the Arctic Ocean. When the AO index was greater than 1, the wind speed tended to be weakened and the SSTs showed a tendency to increase. This led to general increasing responses in Chl-a concentrations during positive AO. The summer SST anomaly revealed an inverse relationship between higher positive values during the La Niña period and lower ones during the El Niño period. When the amplitude of MEI (Multi-variate ENSO Index) was high (| MEI| > 1), the SST anomaly indicated an inverse correlation with the Chl-a concentration anomaly in the EJS. This study demonstrated the regional effects of climate change on Chl-a variability in the EJS in response to tropical–subtropical and arctic–subarctic interactions between ocean and atmospheric variations.

Coastal benthic communities in temperate regions have been influenced by climate change, including increasing sea-surface temperature. Nevertheless, scleractinian coral Alveopora japonica Eguchi, 1968, is thriving in shallow subtidal hard bottoms around Jeju Island, off the southern coast of Korea. The presence of this corals has negatively impacted subtidal kelp populations in Jeju Island. However, there is no study to document how the presence or absence of this coral relates to other benthic communities. This study investigated the benthos in three shallow subtidal sites (Shinheung (SH), Bukchon (BC), and Seongsan (SS)) in northern Jeju using underwater photography. Macro-benthic organisms appearing on a 1 × 20 m line transect installed at depths of 5, 10, and 15 m at each site were analyzed. Results showed that of the three sites investigated, A. japonica colonies were most abundant at BC, accounting for 45.9% and 72.8% of the total transect area at 10 m and 15 m, respectively. At SS, A. japonica occupied 15.3% of the total area at 15 m and less than 1% at 5 m and 10 m. The same at SH accounted for 10% of the total area at 5 m, and less than 1% at 10 m and 15 m. Dead and bleached colonies accounted for 1.2-11.5% and 1.8-5.7%, respectively, at 5, 10, and 15 m at three sites. At SS, canopy-forming brown algae Ecklonia cava and Sargassum spp. accounted for 20.2 and 24.3% of the total transect area, respectively, at 5 m depth. In contrast, the percent cover of E. cava and Sargassum spp. at SH and BC ranged from 0.1 to 1.8%, respectively. Moreover, non-geniculate coralline algae dominated the subtidal substrate at SH, ranging between 60.2 and 69% at 15 and 10 m. The low cover of A. japonica in SS (at 5 m) coincided with a high percent cover of canopy-forming brown algae. However, canopy-forming brown algae were rare at all depths at SH and BC and were dominated instead by coralline algae and the scleractinian corals. This study, by utilizing a non-destructive method, provides a baseline qualitative and quantitative information for understanding the site and depth-dependent distribution of A. japonica and algal populations, which is important to understand climate change related changes in benthic communities in Jeju and elsewhere.

Aquatic animals, which are ecologically important consumers in aquatic ecosystems and widely distributed in rivers, lakes, and seas, which occupy 70% of the earth’s surface, respond in unique ways to environmental changes at various temporal and spatial scales, and have optimized strategies for survival [...]

A subpolar front (SPF) generated between the East Korea Warm Current (EKWC) and the North Korea Cold Current (NKCC) in the western margin of the East/Japan Sea has shifted northward in recent decades. This study investigated the biomass and composition of the phytoplankton assemblage in relation to hydrological and biogeochemical features in the shallow shelf and slope off the Korean coast from January to June in 2016 and 2017, to determine the mechanistic effects of SPF on spring–summer phytoplankton bloom dynamics. Monthly average depth-integrated chlorophyll a (Chl a) levels and the contribution of phytoplankton classes revealed bimodal diatom blooms in early spring and summer in the frontal zone. Canonical correspondence analysis showed that the distribution of high Chl a was associated with cold, low-salinity NKCC water in March 2016. No Chl a peak was observed in March 2017 when the warm saline EKWC water mass invaded. These results suggest that the NKCC intrusion acts as a forcing mechanism leading to enhanced phytoplankton biomass in the frontal zone. In contrast, positive correlations of Chl a concentration with water density and nutrient concentrations suggest that summer blooms were fed by the subsurface chlorophyll maximum (SCM) driven by shoaling of the pycnocline and nitracline. Varying water-column stratification determined the thickness of the SCM layer, driving year-to-year variability in the magnitude of diatom blooms. These findings further suggest that seasonal/interannual variability in the timing of algal blooms affects regional trophodynamics and hence could be an important factor in explaining ecosystem changes in this region.

Trophic contributions of diverse OM sources to estuarine and coastal food webs differ substantially across systems around the world, particularly for nekton (fish, cephalopods, and crustaceans), which utilize basal resources from multiple sources over space and time because of their mobility and feeding behaviors at multiple trophic levels. We investigated the contributions of putative OM sources to fish food webs and assessed the spatiotemporal patterns, structures, and trophic connectivity in fish food webs across four seasons from three closely spaced (10–15 km) sites: an estuarine channel (EC), a deep bay (DB), and an offshore (OS) region in Gwangyang Bay, a high-productivity, low-turbidity estuarine embayment off the Republic of Korea. While nearly all previous studies have focused on few representative species, we examined δ13C and δ15N values of whole nekton communities along with dominant benthic macro-invertebrates, zooplankton, and their putative primary food sources. The δ13C and δ15N values coupled with MixSIAR, a Bayesian mixing model, revealed that these communities utilized multiple primary producers, but phytoplankton comprised the primary trophic contributor (46.6–69.1%). Microphytobenthos (15.8–20.4%) and the seagrass Zostera marina (8.6–19.8%) made substantial contributions, but the role of river-borne terrestrial organic matter was negligible. Spatially different species composition and stable isotope values, but higher utilization of coastal phytoplankton by estuarine fish, indicated disparate food webs structures between the EC and DB/OS coastal areas, with considerable trophic connectivity. Greater overlaps in fish and cephalopod isotopic niches than among other consumers and a higher estimated carbon trophic enrichment factor for EC nekton confirmed feeding migration-mediated biological transport of coastal OM sources to the estuary. Further, the seasonally consistent structures and resource utilization patterns indicate that fish food webs are resilient to changes at lower trophic levels. Our results contrast with those for other highly turbid coastal systems depending highly on diversified basal sources, including exported terrestrial and wetland detritus alongside autochthonous phytoplankton. Finally, this study provides a novel perspective on the role of OM sources in such low turbidity and highly productive coastal embayments and enhances our understanding of marine ecosystems.

Understanding the magnitude and causes of isotopic fractionation between organisms and their dietary resources is crucial for gaining knowledge on stable isotope ecology. However, little is known regarding the diet-tissue fractionation values of marine ciliates, which play a critical role in the reconstruction of microbial food webs. In the present study, we conducted experiments on two benthic (Pseudokeronopsis pararubra and Protocruzia labiata) and two pelagic (Strombidium sulcatum and Uronemella filificum) marine ciliates, where they were fed with isotopically constant foods (Chaetoceros calcitrans and Isochrysis galbana) under laboratory culture conditions to determine their carbon and nitrogen isotopic fractionation values (Δ13C and Δ15N). The stable isotope values (δ13C and δ15N) of ciliates for all experiments rapidly increased after the initial feeding, with half-lives ranging from 6.1 to 23.0h for δ13C and from 3.1 to 24.9h for δ15N. The Δ13C and Δ15N for all ciliates represented significantly positive enrichments, with overall mean fractionations of 0.6±0.2 and 1.2±0.4, respectively. Irrespective of the dietary type, both Δ13C and Δ15N were very similar for the same ciliate species. These results suggest that Δ13C and Δ15N for marine ciliates are similar to those found in common marine organisms with very little food-dependent variation. Overall, quantifying the specific isotopic fractionation of marine ciliates is expected to provide fundamental information on the trophic transfer of carbon, nitrogen, and energy flow through the microbial pathway in marine ecosystems.

We investigated long-term variations in the dominant phytoplankton groups with improvements in water quality over 11 years in the Yeongil Bay on the southeastern coast of Korea. River discharge declined during the study period but TN from river discharge remained stable, indicating the input of enriched nutrients to the bay was fairly consistent. NH4+ levels decreased with a decrease in TN from the POSCO industrial complex. While the study region was characterized by the P-limited and deficient environment, cryptophytes dominated with the intensified P-limitations. The relative abundance of cryptophytes declined from 70% in 2010 to 10% in 2016, but that of diatoms increased from 70% in 2009 to 90% in 2016. Correlation analysis showed a positive correlation of cryptophytes with NH4+ and a negative correlation with photic depth. Generalized additive models also exhibited an increase in diatom dominance and a decrease in cryptophyte dominance with an increase in water quality, indicating that a decrease in NH4+ and increase in light favored the diatom growth but suppressed the cryptophyte growth. Thus, water quality improvements shift the dominant group in the coastal ecological niche from cryptophytes to diatoms.

Understanding the trophic ecology of the giant Pacific octopus Enteroctopus dofleini is challenging in developing marine ranches and in reestablishing its regional stocks against the severe stress of fishing. We adopted carbon and nitrogen stable isotope techniques (termed δ13C and δ15N, respectively) to identify the trophic niche (i.e., pathways and positions) of this species systematically in the entire food webs of two marine ranches off the east coast of the Korean peninsula. While a slight spatial shift in the isotopic nestedness of faunal communities was observed, the δ13C and δ15N values of consumers were distinct and separate among functional groups at both ranches. The consumer δ13C values spanned a broad range between pelagic and benthic sources of organic matter, and their δ15N values recorded a stepwise trophic-level enrichment, indicating that suspension feeders and herbivore-deposit feeders served as baselines of pelagic- and benthic-based trophic pathways, respectively. The δ13C values of predators, including E. dofleini, were arrayed between the two primary consumer groups. Neither δ13C nor δ15N values showed any remarkable variations with increasing octopus weight. Dietary mixing-model calculations indicated that E. dofleini is a generalist predator relying on both benthic- and pelagic-affinity prey, similar to some teleost species that consume a diverse spectrum of prey. In contrast, other teleost groups showed prevalent trophic links with either pelagic- or benthic-based pathways. The trophic-level estimations revealed that E. dofleini occupies an intermediate position slightly below the teleosts. A lack of discrete trophic positions between E. dofleini and teleosts seemed to be indicative of the released teleost predation but instead reflects the imposed food competition. Overall, the results demonstrated that despite compositional changes in the taxa constituting individual trophic groups, E. dofleini occupied a very similar trophic niche in both ranching systems. Finally, as extracted from information based on octopus marine ranches launched on natural rocky bottoms, our isotopic evidence provides a greater understanding of the trophic ecology of this octopus species in nearshore natural habitats along the southwestern margin of its distribution range.

The spatiotemporal distribution of fish larvae and eggs is fundamental for their reproduction and recruitment in aquatic ecosystems. Here, a metabarcoding strategy was employed as an alternative to a conventional ichthyoplankton survey, which requires a considerable amount of time, labor, and cost. First, a piscine-specific universal primer set (FishU) was designed to amplify the region, flanking the highly conserved mitochondrial 12S and 16S ribosomal genes, and it was optimized for the MiSeq platform. Based on both in silico and in vitro analyses, the newly designed FishU primers outperformed the two previously reported fish-specific universal primer sets (ecoPrimer and MiFish) in taxon coverage, specificity, and accuracy in species identification. The metabarcoding results by FishU primers successfully presented the diversity of ichthyoplankton directly from the zooplankton net samples in the East/Japan Sea, presenting more accurate and plentiful species numbers than those by MiFish primers. Thus, the metabarcoding analysis of ichtyoplankton using the newly designed FishU primers is a promising tool for obtaining useful data to understand the reproduction of fish, such as spawning sites, reproductive periods, population structures, feeding ecology, and diet.

The current phytoplankton community structure is expected to change, with small phytoplankton becoming dominant under ongoing warming conditions. To understand and evaluate the ecological roles of small phytoplankton in terms of food quantity and quality, the carbon uptake rates and intracellular biochemical compositions (i.e., carbohydrates, CHO; proteins, PRT; and lipids, LIP) of phytoplankton of different sizes were analyzed and compared in two different regions of the western East/Japan Sea (EJS): the Ulleung Basin (UB) and northwestern East/Japan Sea (NES). The average carbon uptake rate by the whole phytoplankton community in the UB (79.0 ± 12.2 mg C m–2 h–1) was approximately two times higher than that in the NES (40.7 ± 2.2 mg C m–2 h–1), although the average chlorophyll a (chl a) concentration was similar between the UB (31.0 ± 8.4 mg chl a m–2) and NES (28.4 ± 7.9 mg chl a m–2). The main reasons for the large difference in the carbon uptake rates are believed to be water temperature, which affects metabolic activity and growth rate, and the difference in euphotic depths. The contributions of small phytoplankton to the total carbon uptake rate were not significantly different between the regions studied. However, the rate of decrease in the total carbon uptake with increasing contributions from small phytoplankton was substantially higher in the UB than in the NES. This result suggests that compared to other regions in the EJS, the primary production in the UB could decrease rapidly under ongoing climate change. The calorific contents calculated based on biochemical compositions were similar between the small (1.01 ± 0.33 Kcal m–3) and large (1.14 ± 0.36 Kcal m–3) phytoplankton in the UB, whereas the biochemical contents were higher in the large phytoplankton (1.88 ± 0.54 Kcal m–3) than in the small phytoplankton (1.06 ± 0.18 Kcal m–3) in the NES. The calorific values per unit of chl a were higher for the large phytoplankton than for the small phytoplankton in both regions, which suggests that large phytoplankton could provide a more energy efficient food source to organisms in higher trophic levels in the western EJS.

In estuaries, the sources of organic matter, its composition, and its functional role in the coastal ecosystem food web are all influenced by dominant estuarine processes. We investigated seasonal variations in the quantity and composition of dissolved inorganic nutrients, suspended particulate matter (SPM), and phytoplankton across a low-turbidity estuarine–coastal continuum in Gwangyang Bay, South Korea. The narrow estuarine channel has a sharp salinity gradient (from 0 to around 30) and low SPM concentrations (

Wandogarida canalicula gen. n et sp. n. (Tanaidacea, Sphyrapodidae) is described from the southern coast of Korea (NW Pacific). The genus is included in the subfamily Sphyrapodinae Guţu, 1980 by having a mandible lacking a palp. It has a close affinity with the genus Poligarida Bamber & Marshall, 2013 in the third pereonite having lateral pointed apophyses, the antennule of males with fringes of aesthetascs on articles 1 and 2 of the outer flagellum and the antenna with an elongate article 2. However, it is distinguished from Poligarida by having a maxillular palp. Wandogarida gen. n. can be differentiated from other genera within the subfamily Sphyrapodinae by the unique shape characterised by the male’s antennule article 1 with its rough denticles and a deep groove, pleonites each with a ventral hyposphenium, the maxillule with uniarticulate palp and the presence of prominent sexual dimorphism in the mouthparts. An identification key to the five genera of the subfamily Sphyrapodinae is presented.

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 ulsana sp. 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.

In recent years, the change of marine environment due to climate change and declining primary productivity have been big concerns in the East/Japan Sea, Korea. However, the main causes for the recent changes are still not revealed clearly. The particulate organic carbon (POC) to chlorophyll-a (chl-a) ratio (POC:chl-a) could be a useful indicator for ecological and physiological conditions of phytoplankton communities and thus help us to understand the recent reduction of primary productivity in the East/Japan Sea. To derive the POC in the East/Japan Sea from a satellite dataset, the new regional POC algorithm was empirically derived with in-situ measured POC concentrations. A strong positive linear relationship (R2 = 0.6579) was observed between the estimated and in-situ measured POC concentrations. Our new POC algorithm proved a better performance in the East/Japan Sea compared to the previous one for the global ocean. Based on the new algorithm, long-term POC:chl-a ratios were obtained in the entire East/Japan Sea from 2003 to 2018. The POC:chl-a showed a strong seasonal variability in the East/Japan Sea. The spring and fall blooms of phytoplankton mainly driven by the growth of large diatoms seem to be a major factor for the seasonal variability in the POC:chl-a. Our new regional POC algorithm modified for the East/Japan Sea could potentially contribute to long-term monitoring for the climate-associated ecosystem changes in the East/Japan Sea. Although the new regional POC algorithm shows a good correspondence with in-situ observed POC concentrations, the algorithm should be further improved with continuous field surveys.

Microbial community structures of harmful algal bloom (HAB) caused by Heterosigma akashiwo in Geoje were analyzed using the MiSeq platform. To analyze phytoplankton communities without cross-reactivity with predominant bacteria, a new phytoplankton-specific 23S universal primer set was designed by modifying two previously used ones. The new universal primer set turned out to be a useful tool for the analysis of the phytoplankton community; it showed a high specificity for phytoplankton without cross-reactivity to bacterial sequences as well as the wide taxon coverage presenting from prokaryotic cyanobacteria to eukaryotic algae. Next Generation Sequencing (NGS) data generated by two universal primer sets (16S and 23S) provided useful information about the H. akashiwo bloom. According to the 23S universal primer set, proportions of H. akashiwo increased by more than 200-fold as the bloom occurred and its numbers were high enough to detect in control sites. Its operational taxonomic units (OTUs) were detected in the bloom sites at low proportions suggesting that the 16S universal primer set may not be as effective for monitoring harmful algal blooming (HAB) as the 23S universal primer set. In addition, several abundant OTUs in Chlorophyta were not presented by the 16S universal primer set in this study. However, the 16S primer set was useful for detecting decreases in Foraminifera as HAB occurred suggesting that genomic analyses using two universal primer sets would provide more reliable data for understanding microbial community changes by various environmental or ecological events, including HAB. Genomic analyses using two universal primer sets was also useful for determining a correlation between microbial components as HAB occurred. Heterosigma akashiwo was positively correlated with other bloom species, including Karenia mikimotoi, Teleaulax amphioxeia, and bacteria in Verrucomicrobia.

Physiological processes and gross energy budget of the longline-cultured Pacific oyster Crassostrea gigas were investigated in Geoje-Hansan Bay, Korea during two entire culturing periods. Based on physiological measurements of food consumption, feces production, ammonium excretion, and respiration from July 2008 to February 2009 and from July 2013 to February 2014, scope for growth appeared to be positive during most of the culturing period, except for one period with extremely high temperatures (up to 25°C). Estimates of physiological energy production matched well with tissue energy increment measured by gross biochemical composition during the culturing period, suggesting that the oysters might adjust their physiological performance to relatively low concentrations of suspended particulate matter in the bay to optimize energy acquisition. Such an adaptive adjustment includes an increased absorption of energy and a reduced loss of metabolic and excretory energy, resulting in positive production under high culturing density. Using physiological measurements, we further assessed the feedback effects of the longline aquaculture of oysters on the bay system. Ecological efficiency, estimated by a series of energetic efficiencies at the whole bay level, was low compared with Lindeman's law of trophic efficiency. Biodeposition and ammonia excretion rates in this study were relatively low compared with other intertidal plastic bag cultures. These results indicate that the cultured oysters might have only minor effects on benthic and pelagic environments of the bay. Overall, our results suggest that the adaptive physiological performance of oysters and consequently weak feedback effects on ambient habitats should facilitate sustainable longline aquaculture in the bay for a prolonged period without severe habitat deterioration.

Although seagrass species in the genus Halophila are generally distributed in tropical or subtropical regions, H. nipponica has been reported to occur in temperate coastal waters of the northwestern Pacific. Because H. nipponica occurs only in the warm temperate areas influenced by the Kuroshio Current and shows a tropical seasonal growth pattern, such as severely restricted growth in low water temperatures, it was hypothesized that this temperate Halophila species diverged from tropical species in the relatively recent evolutionary past. We used a phylogenetic analysis of internal transcribed spacer (ITS) regions to examine the genetic variability and evolutionary trend of H. nipponica. ITS sequences of H. nipponica from various locations in Korea and Japan were identical or showed very low sequence divergence (less than 3-base pair, bp, difference), confirming that H. nipponica from Japan and Korea are the same species. Halophila species in the section Halophila, which have simple phyllotaxy (a pair of petiolate leaves at the rhizome node), were separated into five well-supported clades by maximum parsimony analysis. H. nipponica grouped with H. okinawensis and H. gaudichaudii from the subtropical regions in the same clade, the latter two species having quite low ITS sequence divergence from H. nipponica (7-15-bp). H. nipponica in Clade I diverged 2.95 ± 1.08 million years ago from species in Clade II, which includes H. ovalis. According to geographical distribution and genetic similarity, H. nipponica appears to have diverged from a tropical species like H. ovalis and adapted to warm temperate environments. The results of divergence time estimates suggest that the temperate H. nipponica is an older species than the subtropical H. okinawensis and H. gaudichaudii and they may have different evolutionary histories.

The climate-induced changes in marine fishery resources in South Korea have been a big concern over the last decades. The climate regime shift has led to not only a change in the dominant fishery resources, but also a decline in fishery landings in several species. The habitat suitability index (HSI) has been widely used to detect and forecast fishing ground formation. In this study, the catch data of the Todarodes pacificus (Japanese Common Squid) and satellite-derived environmental parameters were used to estimate the HSI for the T. pacificus around South Korea. More than 80% of the total catch was found in regions with a sea surface temperature (SST) of 14.91−27.26 °C, sea surface height anomaly (SSHA) of 0.05−0.20 m, chlorophyll-a of 0.32−1.35 mg m−3, and primary production of 480.41−850.18 mg C m−2 d−1. Based on these results, the HSI model for T. pacificus was derived. A strong positive relationship (R2 = 0.9260) was found between the HSI and the fishery landings. The climatological monthly mean HSI from 2002 to 2016 showed several hotspots, coinciding with the spawning and feeding grounds of T. pacificus. This outcome implies that our estimated HSI can yield a reliable prediction of the fishing ground for T. pacificus around South Korea. Furthermore, the approach with the simple HSI model used in this study can be applied elsewhere, and will help us to understand the spatial and temporal distribution of fishery resources.

We developed a cost-effective metabarcoding strategy to analyze phytoplankton community structure using the Illumina MiSeq system. The amplicons (404–411 bp) obtained by end-pairing of two reads were sufficiently long to distinguish algal species and provided barcode data equivalent to those generated with the Roche 454 system, but at less than 1/20th of the cost. The original universal primer sequences targeting the 23S rDNA region and the PCR strategy were both modified, and this resulted in higher numbers of eukaryotic algal sequences by excluding non-photosynthetic proteobacterial sequences supporting effectiveness of this strategy. The novel strategy was used to analyze the phytoplankton community structure of six water samples from the East/Japan Sea: surface and 50 m depths at coastal and open-sea sites, with collections in May and July 2014. In total, 345 operational taxonomic units (OTUs) were identified, which covered most of the prokaryotic and eukaryotic algal phyla, including Dinophyta, Rhodophyta, Ochrophyta, Chlorophyta, Streptophyta, Cryptophyta, Haptophyta, and Cyanophyta. This highlights the importance of plastid 23S primers, which perform better than the currently used 16S primers for phytoplankton community surveys. The findings also revealed that more efforts should be made to update 23S rDNA sequences as well as those of 16S in the databases. Analysis of algal proportions in the six samples showed that community structure differed depending on location, depth and season. Across the six samples evaluated, the numbers of OTUs in each phylum were similar but their relative proportions varied. This novel strategy would allow laboratories to analyze large numbers of samples at reasonable expense, whereas this has not been possible to date due to cost and time. In addition, we expect that this strategy will generate a large amount of novel data that could potentially change established methods and tools that are currently used in the realms of oceanography and marine ecology.

The suspension-feeding Manila clam Ruditapes philippinarum is a native species of the western Pacific that is now widely distributed around the globe because of its commercial importance. To determine the adaptive physiological responses to changing thermal and nutritional conditions, clearance, filtration, feces production, ammonium excretion, respiration rates, and scope for growth (SFG) were measured in adult clams. The clams were exposed to 24 treatments involving the combination of four water temperatures (8, 13, 18, and 23°C) and six concentrations of suspended particulate matter (SPM: 9.5 to 350.5 mg L(-1)). Physiological rates were standardized by using the mean (480 mg) of tissue dry weights of experimental clams using allometric equations between physiological variables and tissue dry weight. Higher clearance rates were recorded at higher temperatures and lower SPM concentrations, and these rates decreased with increasing SPM concentration at individual temperatures. Consumed energy increased with increasing temperature and SPM concentration, peaking at around 100-200 mg L(-1) at 18-23°C. Whereas fecal energy was largely determined by SPM concentration, ammonia excretion was mainly governed by temperature. Respiration rate studies revealed a predominant quadratic effect of temperature on the metabolism, indicating a lack of acclimatory adjustment of metabolic rate to rising temperature. SFG values were positive under almost all the treatment conditions and were much higher at higher SPM concentrations (> 45 mg L(-1)), with the highest level being recorded at 18°C and 100-200 mg L(-1) SPM. Increased filtration rate offset the increased metabolic cost at warm temperatures. Our holistic findings suggest that a high degree of physiological plasticity allows R. philippinarum to tolerate the wide range of temperatures and SPM concentrations that are found in tidal flats, accounting in part for the successful distribution of this species over a wide variety of geographical areas.

Photoacclimatory responses of the seagrass Zostera marina in the intertidal and subtidal zones were investigated by measuring chlorophyll a fluorescence parameters, photosynthetic pigments, leaf δ13C values, and shoot morphology in two bay systems. Intertidal plants had higher carotenoid concentrations than subtidal plants to avoid photodamage under excess light conditions during the day. The maximum relative electron transport rate (rETRmax) and minimum saturation irradiance (Ek) of the intertidal plants were higher than those of the subtidal plants, whereas photosynthetic efficiency (α) and maximum quantum yield (Fv/Fm) were higher in subtidal plants. The intertidal plants also had significantly greater Stern-Volmer non-photochemical quenching (NPQ) than that of the subtidal plants. These results suggest that the subtidal plants photoacclimated to use limited light more efficiently, and the intertidal plants exhibited photosynthetic responses to minimize photodamage at excess irradiance. The δ13C values of leaf tissues were more negative in the intertidal plants than those in the subtidal plants, suggesting that the intertidal plants used atmospheric or dissolved CO2 for photosynthesis during emersion. Effective quantum yield (ΔF/Fm´) in the intertidal plants decreased more slowly after emersion than that in the subtidal plants, indicating higher desiccation tolerance of the intertidal plants. The intertidal plants also recovered more rapidly from desiccation damage than the subtidal plants, suggesting photosynthetic adaptation to desiccation stress. The photosynthetic plasticity of Z. marina in response to variable environmental conditions most likely allows this species to occur in the intertidal and subtidal zones.

The retreat and thinning of Arctic sea ice associated with climate warming is resulting in ever-changing ecological processes and patterns. One example is our discovery of myriad new "marine aquaria" formed by melt holes in the perennial sea ice. In previous years, these features were closed, freshwater melt ponds on the surface of sea ice. Decreased ice thickness now allows these ponds to melt through to the underlying ocean, thus creating a new marine habitat and concentrating a food source for the ecosystem through accumulation of algae attached to refreezing ice in late summer. This article describes the formation of these late-season algal masses and comments on their overall contribution to Arctic ecosystems and the consequences of a continued decline in sea ice.

We examined stable carbon and nitrogen isotope ratios for a large variety of consumers in intertidal and subtidal habitats, and their potential primary food sources [i.e., microphytobenthos (MPB), phytoplankton, and Phragmites australis] in a coastal bay system, Yeoja Bay of Korea, to test the hypothesis that the transfer of intertidal MPB-derived organic carbon to the subtidal food web can be mediated by motile consumers. Compared to a narrow δ13C range (-18 to -16‰) of offshore consumers, a broad δ13C range (-18 to -12‰) of both intertidal and subtidal consumers indicated that 13C-enriched sources of organic matter are an important trophic source to coastal consumers. In the intertidal areas, δ13C of most consumers overlapped with or was 13C-enriched relative to MPB. Despite the scarcity of MPB in the subtidal, highly motile consumers in subtidal habitat had nearly identical δ13C range with many intertidal foragers (including crustaceans and fish), overlapping with the range of MPB. In contrast, δ13C values of many sedentary benthic invertebrates in the subtidal areas were similar to those of offshore consumers and more 13C-depleted than motile foragers, indicating high dependence on phytoplankton-derived carbon. The isotopic mixing model calculation confirms that the majority of motile consumers and also some of subtidal sedentary ones depend on intertidal MPB for more than a half of their tissue carbon. Finally, although further quantitative estimates are needed, these results suggest that direct foraging by motile consumers on intertidal areas, and thereby biological transport of MPB-derived organic carbon to the subtidal areas, may provide important trophic connection between intertidal production and the nearshore shallow subtidal food webs.

The East/Japan Sea (hereafter, the East Sea) is highly dynamic in its physical phenomena and biological characteristics, but it has changed substantially over the last several decades. In this study, a recent decadal trend of primary productivity in the East Sea was analyzed based on Moderate-Resolution Imaging Spectroradiometer (MODIS)-derived monthly values to detect any long-term change. The daily primary productivities averaged using monthly values from 2003 to 2012 were 719.7 mg·C·m−2·d−1 (S.D. ± 197.5 mg·C·m−2·d−1, n = 120) and 632.3 mg·C·m−2·d−1 (S.D. ± 235.1 mg·C·m−2·d−1, n = 120) for the southern and northern regions of the East Sea, respectively. Based on the daily productivities, the average annual primary production in the East Sea was 246.8 g·C·m−2·y−1, which was substantially higher than that previously reported in deep oceans. However, a decreasing trend (13% per 10 years) in the annual primary production was observed in the East Sea within the study period from 2003 to 2012. The shallower mixed layers caused by increased temperature could be a potential cause for the decline in annual production. However, this decline could also be part of an oscillation pattern that is strongly governed by the Pacific Decadal Oscillation (PDO). A better understanding of primary productivity patterns and their subsequent effects on the marine ecosystem is required for further interdisciplinary studies in the East Sea.

Leopard cat (Prionailurus bengalensis euptilurus) is a small wild cat assessed as an endangered wildlife in Korea. There have been very few reports of their diseases. Herein, we describe fibrinous pleuritis caused by Streptococcus canis infection with excessive pleural effusion, hydropericardium, mild ascites, and liver fibrosis in a leopard cat. S. canis is a commensal microflora in domestic cats and often affects the upper respiratory tract inducing chronic and severe respiratory diseases. However, there is no literature regarding the S. canis in leopard cats. Therefore, we first report fibrinous pleuritis associated with an S. canis infection in a leopard cat. [ABSTRACT FROM AUTHOR]