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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.

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.

The spatio-temporal variability of the chlorophyll-a (chl-a) concentration in the East Sea (Japan Sea) (EJS) was investigated using Moderate Resolution Imaging Spectroradiometer (MODIS) data over 13 years from 2003 to 2015 to understand the impact of physical environmental changes on low-trophic level marine ecosystems. The chl-a images were composited to produce gridded monthly chl-a images using a weighted average method after applying a speckle removal algorithm to each path image. Missing pixels without any satellite observations because of cloud coverage were objectively filled using three-dimensional optimal interpolation. The first empirical orthogonal function (EOF) mode of the monthly chl-a images, accounting for 14% of the total variance, showed higher eigenvectors values in the eastern part of the EJS and distinct annual peaks each spring. The amplitudes of the first EOF mode, despite the dominant year-to-year variations in chl-a, tended to increase during spring over time. The recent 13-year trend of chl-a showed differences between the southwestern part and the northeastern part of the EJS, and this difference clearly appeared in the monthly trend maps for March and April. The eastern coast of Korea showed a highly positive trend during summer, particularly during August. The changes in chl-a over the decade were related to the physical environmental changes in sea surface wind, mixed layer depth, and stratification of upper sea water in the EJS.

The bioaccumulation potential (“B”) of compounds is one of the major considerations in assessing chemical hazards. A variety of metrics, including hydrophobicity (KOW), bioconcentration factor (BCF), bioaccumulation factor (BAF), and to an increasing degree biomagnification factor (BMF) and trophic magnification factor (TMF), are widely used to characterize “B”. In the present study, the variation and hydrophobicity-dependence of each of these metrics for recalcitrant hydrophobic organochlorine compounds (HOCs) was determined from four food webs collected in two different seasons at two different sites of the Han River, Korea. Measured environmental parameters and stable isotopic ratios exhibited distinct seasonal and spatial shifts in the ecological condition of the river. The observed values of individual metrics were positively and linearly related with their log KOW values, but linearized slopes differed significantly among the four food webs, with the largest variation being exhibited by TMF and log fugacity ratio (log F) followed by log BMF > log BAF. When based on field-derived mean linear equations, different log KOW values were obtained for a critical point for the identification of biomagnification of HOCs. Consequently, the biomagnification potential of HOCs and its relationship with KOW can vary, being seriously affected by not only on the metrics used for its assessment but also on spatial and temporal variations in ecological conditions. Our results indicate that TMF for “B” might be more robust than the other metrics but the development of new methodologies to reduce uncertainty and to enhance the accuracy of TMFs by correcting for ecological variation, together with addition efforts to harmonize individual metrics for “B”.

Short-term biological responses to sea surface wind field over mesoscale eddies were investigated using hourly ocean color chlorophyll-a (chl-a) concentration data from the Geostationary Ocean Color Imager (GOCI), scatterometer wind data, and satellite sea surface temperature (SST) data. Four warm eddies were identified from SST fronts, by subjectively fitting ellipses to selected points, and anticyclonically rotating current vectors were estimated from sequential chl-a images. Scatterometer data confirmed wind speed strengthening by approximately 30% over anticyclonic eddies, regardless of wind direction, caused by stability changes in the marine atmospheric boundary layer. The modified wind speed field produced a characteristic pattern of wind stress curl and Ekman pumping (EKP) over the eddies, showing positive and negative values on the left and right sides of the upwind direction, respectively. The EKP field was divided into three components: eddy current-induced, relative vorticity gradient-induced, and crosswind SST-induced terms. Short-term changes in the chl-a concentration showed a positive relation with EKP variations over most eddies. SST-induced EKP played a significant role in the eddies for 76% of the total variations, which is much higher than that in other oceans. This study emphasizes the significant effect of SST distribution and the biological responses to changes in an EKP field in relation to air–sea interactions and feedback processes in the East Sea (Sea of Japan).

Coastal water around the archipelago off southwestern Korea has been bathed in an unprecedented pool of warm water in summer in recent years. Here, we examined phytoplankton community responses to amplified seasonal temperature fluctuation around the archipelago based on chemotaxonomic analysis in association with physicochemical properties in the shallow coastal water from June 2016 to March 2018. Concentrations of dissolved inorganic nutrients were significantly higher during the warm season than during the cold season. Canonical correspondence analysis revealed that water temperature was a main driver controlling the phytoplankton community. Generalized additive models denoted that small phytoplankton groups (cryptophytes, cyanobacteria, and prasinophytes) were more resistant to high temperatures (> 25°C) compared with diatoms. Indeed, dominance of diatoms was significant (80%) during the cold season and sharply declined (to 49%) during the warm season. Small phytoplankton were dominant (62%) as the water temperature exceeded 22°C. Our results highlight the effects of temperature-dependent bifurcated seasonality on phytoplankton communities in coastal waters. Furthermore, unprecedentedly high summer temperatures in August 2016 coincided with a remarkable increase in the importance (∼70%) of small phytoplankton. Accumulating evidence provides indications regarding future scenarios: while small phytoplankton will probably account for summer blooms, diatom blooms will shift to winter.

The coastal zone has distinguishable but tightly connected ecosystems from rivers to the ocean and globally contributes to nutrient cycling including phytoplankton-derived organic matter. Particularly, bacterial contributions to phytoplankton-derived dimethylsulfoniopropionate (DMSP) degradation have been recently evaluated by using advanced sequencing technologies to understand their role in the marine microbial food web. Here, we surveyed the bacterial diversity and community composition under seasonal water mixing in the bay of Gwangyang (GW), a semi-enclosed estuary at the southern tip of the Korea Peninsula. We detected phylogenetic dissimilarities among season-specific habitats in GW and their specific bacterial taxa. Additionally, bacterial contribution to degradation of phytoplankton-derived DMSP from estuarine to coastal waters at euphotic depths in GW was investigated as the presence or absence of DMSP demethylation gene, encoded by dmdA. Among the operational taxonomic units (OTUs) in GW bacterial communities, the most dominant and ubiquitous OTU1 was affiliated with the SAR11 clade (SAR11-OTU). The population dynamics of SAR11-OTU in dmdA-detected GW waters suggest that water mass mixing plays a major role in shaping bacterial communities involved in phytoplankton-derived DMSP demethylation.

Organisms inhabiting tidal mixing-front zones in shallow temperate seas are subjected to large semidiurnal temperature fluctuations in summer. The ability to optimize energy acquisition to this episodic thermal oscillation may determine the survival, growth and development of these ectotherms. We compared the physiological and molecular responses of Haliotis discus hannai cultivated in suspended cages to fluctuating or stable temperature conditions. Several physiological indicators (respiration, excretion rates and O:N) were measured in both conditions, and alterations in the proteome during thermal fluctuations were assessed. No summer mortality was observed in abalone cultivated in fluctuating temperatures compared with that at stable high temperatures. Metabolic rates increased sharply during stable warm summer conditions and fluctuated in accordance with short-term temperature fluctuations (20–26 °C). Ammonia excretion rates during acute responses were comparable in both conditions. When abalone were exposed to fluctuating temperatures, enzyme activities were downregulated and structure-related protein expression was upregulated compared with that at an acclimation temperature (26 °C), highlighting that exposure to low temperatures during fluctuations alters molecular processes. Our results reveal that modulation of physiological traits and protein expression during semidiurnal thermal fluctuations may buffer abalone from the lethal consequences of extreme temperatures in summer.

Sexual reproduction in corals is pivotal for the survival of populations in the face of climate change. Off Jeju Island, which lies off the south coast of Korea, a high-latitude scleractinian coral, Alveopora japonica, has experienced a population explosion over the past couple of decades (at 5–15 m depths). A second species, Oulastrea crispata, which is generally present at high latitudes and extreme environments, has a stable population and dominates in the shallow subtidal waters of southern Jeju. This study examined the annual gametogenesis patterns of A. japonica off the north (33°24′N, 126°13′E) and south (33°14′N, 126°36′E) coasts of Jeju Island, and of O. crispata in the south. Histological analysis revealed that the oogonia and spermatogonia in A. japonica developed in separate mesenterial filaments, while the gonads in O. crispata developed in the same filament. Alveopora japonica had the same brooding period during late summer and early fall (Aug–Sep 2015) at both sites. The spawning period of O. crispata was also during late summer and early fall. Brooding in A. japonica was concordant with previous observations of its planula during the brooding period. This study provides the first data on the timing of reproduction of these two high-latitude corals from Jeju Island, which may help our understanding of the population dynamics of corals in other high-latitude environments.

Spatiotemporal patterns in the basal resources fueling the macrobenthic food web of a temperate coastal embayment subject to a low-turbidity riverine discharge (Gwangyang Bay, Korea) were evaluated using carbon and nitrogen stable isotopes. This study examined trophic links of macrobenthic food web with primary production in diverse wetland habitats along the riverine–estuarine–coastal marine continuum. δ13C and δ15N values of macrobenthic assemblages collected along the salinity gradient of the main channel and their putative sources of organic matter (i.e., riverine particulate organic matter (RPOM), Phragmites australis, microphytobenthos (MPB), phytoplankton, and Zostera marina) were determined. A permutational analysis of variance test showed seasonal uniformity in the isotopic niches of the macrobenthic community within different channel locations. In contrast, isotopic nestedness calculated for the microbenthic community emphasized clearly different trends in its isotopic niches among locations. The δ13C values of phytoplankton, suspended and sedimentary organic matter, and macrobenthic community displayed a consistently positive relationship with salinity, characterizing an important contribution of local phytoplankton to the nutrition of macrobenthic community. The isotope mixing model revealed that Phragmites-derived organic matter contributed considerably to the nutrition in the estuarine channel, whereas MPB and Zostera provided trophic subsidies to the deep bay and offshore communities. The nutritional importance of RPOM was minimal at all sites. Overall results suggest that phytoplankton production is a major nutritional contributor to the macrobenthic community in the main channel and that trapping POM originated from neighboring wetlands leads to a longitudinal isotopic niche shift in the macrobenthic community.

The bay scallop Argopecten irradians, a warm-water and hermaphroditic bivalve species, is native of the Atlantic coast of North America and was introduced for aquaculture to the Chinese coast in 1982 and, in turn, to the Korean coast in 1996. The present study analyzed the gross biochemical composition and stable isotope ratios of separated organs (i.e., the adductor muscle, digestive gland, gonad, mantle, and gill tissues) of the scallop over a culturing cycle (September 2015 to May 2016), to understand its energy-storage allocation strategy in association with reproductive success for survival in the new habitat. The condition index (CI) of the bay scallop increased slowly but steadily from the beginning of deployment in the grow-out area in September and peaked in the following month of March. The gonadosomatic index (GSI) increased rapidly in April and peaked in May, when the CI decreased drastically. The seasonal somatic growth, as defined by dry tissue weight, of whole tissues and individual organ tissues differed from each other. Most of the energy reserves were stored in the adductor muscle in the summer–fall period. The subsequent sudden decreases in proteins and carbohydrates in the adductor muscle suggested that these reserves were used as catabolic substrates during winter maintenance in the December–January period, and during spring spawning in the April–May period. The δ13C values of all the lipid-free organ tissues displayed seasonal fluctuations in parallel with those of phytoplankton. Seasonal fluctuations in gross weights of biochemical constituents as well as δ13C and δ15N values of individual organ tissues confirmed a mobilization of proteins from the digestive gland to the gonad, suggesting that gonadal growth is catabolized by recently assimilated food (i.e., phytoplankton). Overall, our results clearly indicate that, although the bay scallop in a newly introduced coast of Korea possessed slightly different energy-gain-allocation processes vs the native US populations, they might adapt to new environments and keep an intrinsic trait of fast growth and reproductive success through a slight modification of adaptive strategy for survival.

Seasonal variations in the condition, biochemical composition, and reproduction of Ruditapes philippinarum were investigated from August 2009 to October 2010, 18 months after the Hebei Spirit oil spill off Malipo Beach on the west coast of Korea. No significant differences in physical and nutritional conditions were found between the oil-damaged and the undamaged control beaches. At the undamaged Mongsanpo Beach, all the biometric components (dry tissue weights and biochemical components) remained at low levels during autumn–winter but increased rapidly through spring, followed by a dramatic drop in August. In contrast, at the oil-damaged beach, no clear seasonal fluctuations were detected in the biometric components during the study period. Absolute values of all the components were much higher at the control than at the damaged site. This lack of energy reserves in the clams in the damaged area likely resulted in a failure of gametogenic development. Gonadal maturity index peaked in summer at both beaches. However, the gross egg weight was much higher at the control than at the damaged site during June–July. In addition, its different peak timing between sites indicated a month’s lag in the major spawning pulse at the oil-damaged beach. The spatial variations in all the biometric components of the clams observed in this study clearly implied that the Hebei Spirit oil spill may interfere with the clam phenology at Malipo Beach within 2 to 3 years after the incident.

The aim of this study was to assess the temporal variability in the trophic structure of a fish community and the trophic levels of dominant fish species off the eastern coast of Korea. We analyzed the community composition and the stable carbon and nitrogen isotope ratios (δ13C and δ15N) for fish species in Hupo coastal waters over four seasons. Fish assemblages were mainly dominated by resident benthic and benthopelagic fish. In contrast, there were low numbers of pelagic fish, including migrating and occasional species, which varied significantly by season. The fish assemblages generally had relatively wide ranges of δ13C and δ15N (− 21.1 to − 16.3‰ and 10.0 to 14.2‰, respectively), reflecting a clear distinction between resident (mostly benthic or benthopelagic) vs migratory (mostly pelagic) fish. Resident species showed no seasonal differences in their isotopic signatures, whereas pelagic species showed temporal variability in δ13C and δ15N values. The isotopic niche of fish assemblages showed distinctly different patterns between spring–summer and winter–fall with the seasonal changes in the fish community. These patterns might be associated with seasonal variation in the fish community caused by seasonal changes in environmental conditions (e.g., hydrographic parameters and food availability). Our results can offer baseline information/trophic data for ecosystem models that can be used to evaluate the effects of climate on marine ecosystems.

To evaluate the modification of carbon flow in estuarine systems by a dike construction, we compared the trophic structures of the macrobenthic food webs in two contrasting estuaries, one with and one without a dike, on the western and southern coasts of Korea, by measuring the δ13C and δ15N values of subtidal macrobenthic consumers. The isotopic values of most organic matter sources were similar between the two estuaries, but there was a different pattern in the isotopic spatial variability between them. For the consumer δ13C values in the diked estuary, there were no significant spatial differences among sites and the isotopic niche widths were much narrower than those in the dike-free estuary. Moreover, the indices of community-wide metrics were smaller in the diked estuary than in the dike-free estuary. These results suggest a lower trophic diversity of macrobenthic consumers with their increased trophic redundancy in the diked estuary. These differences between the dike and dike-free estuaries might be explained by the decrease of benthic producers and then their lower food availabilities for consumers resulting from the presence of the dike. Our findings provide evidence that dike construction and subsequent alteration of hydrologic and circulation processes may lead to modification of the trophic structure of estuarine macrobenthic communities.

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 deployment of artificial reefs (ARs) has become a popular technique for creating new hard-bottom habitats, and for enhancing biodiversity and resource abundance for fisheries. We compared colonizing faunal assemblages and reef-associated food-web structures between ARs and nearby natural reefs (NRs) off the Korean coast using stable isotope techniques. Reef communities showed high compositional disparities in colonizing assemblages. Distinct δ13C and δ15N ranges of functional groups could be used to distinguish pelagic from benthic trophic pathways in the reef food web. The isotopic niches of entire faunal assemblages, as well as individual functional groups, overlapped between NRs and ARs, resulting in equivalency for the isotopic functional indices. Mixing model estimates for carnivorous invertebrates and fish suggested strong trophic links to reef-associated faunal prey at both reef types. Finally, these results highlight a convergence in trophic structure between ARs and NRs in accordance with functional diversity in the colonized faunal assemblages.

Here, we explore the potential role of formyl peptide receptor 2 (FPR2) during Brucella abortus infection. FPR2 manipulation affected B. abortus internalization but not its growth within macrophages. During the activation of FPR2 induced by its agonist AGP-8694, a high level of Brucella uptake was accompanied by an increase in ERK phosphorylation, while intracellular survival at 24 h postincubation was observed to be associated with slightly reduced nitrite accumulation but augmented superoxide anion production. Attenuated secretion of IL-6 and IL-10 were observed 48 h postincubation in the bone marrow-derived macrophages (BMDMs) treated with the FPR2 antagonist WRW4. An opposite pattern of bacterial uptake was observed upon treatment with the FPR2 antagonist, but no significant changes in the activation of MAPKs or the production of nitrite or superoxide anion were observed. Interestingly, AGP-8694 treatment of mice did not lead to differences in spleen or liver weight but slightly enhanced bacterial proliferation was observed in the spleen. Although the weights of the spleen or liver did not differ, WRW4 treatment led to reduced bacterial proliferation in the spleen. Furthermore, FPR2 antagonist treatment was associated with high serum levels of the proinflammatory cytokines IL-12, TNF-α, IFN-γ and MCP-1, while the production of TNF-α was inhibited in AGP-8694-treated mice. IL-6 and IL-10 levels were slightly increased in AGP-8694-treated mice at 24 h postinfection. Our findings demonstrated the contribution of FPR2 via manipulating this receptor using its reported agonist AGP-8694 and antagonist WRW4 in both in vitro and in vivo systems. Although activation of the receptor did not consistently induced Brucella infection, FPR2 inhibition may be a promising strategy to treat brucellosis in animals which encourages further investigation.

Food web dynamics outline the ecosystem processes that regulate community structure. Challenges in the approaches used to capture topological descriptions of food webs arise due to the difficulties in collecting extensive empirical data with temporal and spatial variations in community structure and predator–prey interactions. Here, we use a Kohonen self-organizing map algorithm (as a measure of community pattern) and stable isotope-mixing models (as a measure of trophic interaction) to identify food web patterns across a low-turbidity water channel of a temperate estuarine-coastal continuum. We find a spatial difference in the patterns of community compositions between the estuarine and deep-bay channels and a seasonal difference in the plankton pattern but less in the macrobenthos and nekton communities. Dietary mixing models of co-occurring dominant taxa reveal site-specific but unchanging food web topologies and the prominent role of phytoplankton in the trophic base of pelagic and prevalent-detrital benthic pathways. Our approach provides realistic frameworks for linking key nodes from producers to predators in trophic networks.

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 (

We examined the effects of nutrient availability and turbidity on phytoplankton biomass over 9 years in Gwanyang Bay, Korea, which is an anthropogenically polluted and complex estuary. While dredging and reclamation shaped geochemical features, river discharge with low-turbidity water and sewage treatment plants contributed to nutrient loading. The replete levels of nutrients and short water-residence time suggest the inapplicability of the washout theory, whereas the presence of NH4+ suppressed the growth of phytoplankton. A reduction in the river discharge caused a concomitant decline in the loading and dilution of suspended particles. All these features led to an increase in SPM, light limitation, and NH4+ concentration. GLM estimates revealed negative effects of NH4+ and SPM on chlorophyll a over 9 years while SEM verified synergistic effects of NH4+ and SPM compared with positive effects of NO2 + NO3−. Our findings provide new insights into phytoplankton bloom dynamics in Gwangyang Bay.

Coastal vegetated habitats such as mangroves, salt marshes, and seagrasses, referred to as blue carbon ecosystems, play an important role in climate change mitigation by an effective CO

We examined microbial food webs in Seomjin River and Gwangyang Bay in South Korea, using 18S rRNA amplicon sequencing of environmental DNA (eDNA) with a weighted gene correlation network analysis (WGCNA) – Cytoscape analysis, considering various environmental variables. WGCNA with weight >0.5 revealed two taxon-specific trophic interactions. One was composed of Chlorophyceae and Cryptophyceae-based primary producers and ciliates-based primary consumers. In another one, Bacillariophyceae was a main primary producer while rotifer and ciliates were primary consumers. The Bray-Curtis dissimilarity and correlation matrix of gene abundance with gene significance related to environmental variables showed that the Chlorophyceae and Cryptophyceae-based microbial food web was a function of dissolved inorganic nitrogen in the Seomjin River, whereas the Bacillariophyceae-based microbial food web was a function of dissolved inorganic phosphate in the Gwangyang Bay. Our study provides new insight into microbial food webs while considering the nutrient status of estuarine ecosystems.

Biochemical composition of phytoplankton is a key indicator of the physiological and nutritional status of phytoplankton. A balanced biochemical pattern represents a healthy and productive metabolism in the autotrophic levels which can facilitate proper functioning of higher level organisms. The estimation of biochemical compositions was initiated in the early 1970’s. However, there has been a significant set of modifications in the extraction method and improvements in the sampling and analysis techniques since then. Similarly, the extent of biochemical measurements from various aquatic ecosystems around the globe has also increased. Recently, biochemical patterns are being used as a tool to track the changes in the physiological status of phytoplankton as a response to climate change. Such investigations are also forming part of research works on marine food webs and the nutritional status of ecosystems. This article is a brief review of research works carried out so far in an attempt to understand the biochemical compositions of phytoplankton in the global oceans and the implications with regard to changing environmental conditions.

A metabolically-engineered Deinococcus radiodurans R1 strain capable of producing phytoene, a colorless C40 carotenoid and a promising antioxidant, has been developed. To make this base strain, first, the crtI gene encoding phytoene desaturase was deleted to block the conversion of phytoene to other carotenoids such as lycopene and γ-carotene. This engineered strain produced 0.413 ± 0.023 mg/l of phytoene from 10 g/l of fructose. Further enhanced production of phytoene up to 4.46 ± 0.19 mg/l was achieved by overexpressing the crtB gene encoding phytoene synthase and the dxs genes encoding 1-deoxy-D-xylulose-5-phosphate synthase gene, and by deleting the crtD gene. High cell-density culture of our final engineered strain allowed production of 10.3 ± 0.85 mg/l of phytoene with the yield and productivity of 1.04 ± 0.05 mg/g and 0.143 ± 0.012 mg/l/h, respectively, from 10 g/l of fructose. Furthermore, the antioxidant potential of phytoene produced by the final engineered strain was confirmed by in vitro DPPH radical-scavenging assay.

We determined the dietary composition and trophic position (TP) of walleye pollock in the western East Sea (Japan Sea), based on the δ13C and δ15N values of this species, sympatric dominant fish and invertebrates, and their putative food sources in winter. A broad range of the consumer δ13C′ (lipid-corrected) values reflected clear distinctions between benthic and pelagic feeders, differentiating benthic vs. pelagic trophic pathways. The intermediate δ13C′ and δ15N values of pollock fell between those of benthic and pelagic feeders, indicating their trophic links through both pathways. Increases of their isotopic values with increasing body length suggest an ontogenetic change in dominant diets from pelagic to benthic prey as confirmed by stomach content analysis. Their ontogenetic pattern in resource utilization might be associated with deeper migration range with size, increasing TP during ontogeny.

An undescribed species of Tanaidacea was collected from Yokji Harbor in the southern coast of Korea. Hexapleomera yokjidona n. sp. can be distinguished from other species of the genus by the distinguishing features of a uropod with five articles, a pleopod basal article lacking inner seta, a mandible setal row with two setae, maxilliped coxa with two proximal setae, pereonites 1–3 together longer than wide, and pereopods 2–3 propodus with three ventral setae. To prove that H. yokjidona is a new species, detailed morphological characteristics of both genders are described and a comprehensive comparison among the species of the genus is tabulated. Additionally, diagnostic characteristics previously used to identify the species of Hexapleomera are reassessed and upgraded.

Oh, Y.; Sohn, H.; Lee, D.; An, Y.-R.; Kang, C.-K.; Kang, M.G., and Lee, S.H., 2018. Feeding patterns of ‘Finless porpoise (Neophocaena asiaeorientalis)’ in the yellow sea as indicated by stable carbon and nitrogen ratios. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 386–390. Coconut Creek (Florida), ISSN 0749-0208.Finless porpoise (Neophocaena asiaeorientalis) is a representative marine mammal that has the largest habitat near the Korean coastal area. However, little information on their trophic ecology has been reported in Korea to date. The stable carbon and nitrogen isotope ratios from muscle samples (n = 60) were analyzed for their trophic ecology. The muscle tissues from the stranded or by caught porpoises in the Yellow Sea were obtained in 2015 (n = 37) and 2016 (n = 23) by Cetacean Research Institute in Korea. The averages of δ13C and δ15N for all the samples were −17.74 ‰ (S.D. = ±0.74 ‰) and 12.96 ‰ (S.D. = ±0.95 ‰), respectively. The mean isotopic values of the porpoise groups obtained from different seasons were −18.13 ‰ (±0.56 ‰) and 12.43 ‰ (±0.73 ‰) and −17.06 ‰ (±0.46 ‰) and 13.87 ‰ (±0.46 ‰) for summer (n = 38) and spring (n = 22), respectively, which were significantly different among the two seasons (t-test; p < 0.01, n = 60, respectively). These increasing isotope values from summer to spring reflected a shift in major prey sources. The small increasing in δ15N values could be caused partly by different body lengths of the porpoises. However, the most plausible reason for the large shift in δ13C value relative to δ15N could be a change from pelagic to benthic prey in the different seasons since benthic diets are reported for enriched δ13C over the pelagic diets. For better understanding, further validation should be conducted.

Jo, N.; Kang, J.J.; Park, W.G.; Lee, B.R.; Lee, J.H.; Kim, Y.; Ahn, S.H.; Lee, D.; Min, J.-O.; Kang, C.-K., and Lee, S.H., 2018. Carbohydrate-dominant phytoplankton and protein-high zooplankton in the northern part of the southwestern East/Japan Sea in 2015. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 371–375. Coconut Creek (Florida), ISSN 0749-0208. The biochemical compositions of phytoplankton and zooplankton were monthly investigated in the northern part of the southwestern East/Japan Sea from May to October in 2015 except August. Among the biochemical compositions of phytoplankton, carbohydrate composition (55.5 ± 7.3%) was most dominant during the study period. A significant negative relationship (r = −0.855, p < 0.01, n = 39) was found between the carbohydrate and lipid compositions of phytoplankton in this study, which can be due to a switc...

The biochemical composition of seston along a salinity gradient were examined in the low-turbidity, temperate, estuarine embayment, Gwangyang Bay in Korea. Seasonal variations in sestonic protein (PRT), carbohydrate (CHO), and lipid (LIP) concentrations were analyzed to assess the effects of physiological status and taxonomic composition of phytoplankton. The concentrations of biochemical compounds displayed a close relationship with chlorophyll a (Chla). PRT:CHO ratios were high (&gt, 1.0) in the estuarine channel in warmer months and in whole bay in February, indicating a N-replete condition for phytoplankton growth. High CHO:LIP ratios (&gt, 2.5) in the saline deep-bay area during the warmer months (&gt, 2.0) emphasized the importance of temperature and photoperiod over nutritional conditions. The low POC:Chla (&lt, 200), molar C:N (~7) ratios, and biopolymeric carbon concentrations coupled with high primary productivity indicated a low detrital contribution to the particulate organic matter pool. Diatom dominance throughout the year contributed to consistently high carbohydrate concentrations. Furthermore, generalized additive models highlighted that phytoplankton community (i.e., size) structure may serve as an important descriptor of sestonic biochemical composition. Collectively, our results suggest that physiological and taxonomic features of phytoplankton play prominent roles in determining the biochemical composition of seston, supporting the fact that the ecosystem processes in Gwangyang Bay are largely based on phytoplankton dynamics.

Brucella abortus, one of the most important members of the genus Brucella responsible for human disease, is an intracellular pathogen capable of avoiding or interfering components of the host immune responses that are critical for its virulence. GPR84, on the other hand, is a seven-transmembrane GPCR involved in the inflammatory response and its induced expression was associated with B. abortus infection of RAW264.7 cells. Here we examined the effects of the reported GPR84 surrogate and endogenous agonists, namely 6-n-octylaminouracil (6-OAU) and lauric acid (LU), respectively in the progression of B. abortus infection in a cell and mouse models. The in vitro studies revealed the LU had bactericidal effect against Brucella starting at 24 h post-incubation. Adhesion of Brucella to RAW264.7 cells was attenuated in both 6-OAU and LU treatments. Brucella uptake was observed to be inhibited in a dose and time-dependent manner in 6-OAU but only at the highest non-cytotoxic concentration in LU-treated cells. However, survival of Brucella within the cells was reduced only in LU-treated cells. We also investigated the possible inhibitory effects of the agonist in other Gram-negative bacterium, Salmonella Typhimurium and we found that both adhesion and uptake were inhibited in 6-OAU treatment and only the intracellular survival for LU treatment. Furthermore, 6-OAU treatment reduced ERK phosphorylation and MCP-1 secretion during Brucella infection as well as reduced MALT1 protein expression and ROS production in cells without infection. LU treatment attenuated ERK and JNK phosphorylation, MCP-1 secretion and NO accumulation but increased ROS production during infection, and similar pattern with MALT1 protein expression. The in vivo studies showed that both treatments via oral route augmented resistance to Brucella infection but more pronounced with 6-AOU as observed with reduced bacterial proliferation in spleens and livers. At 7 d post-treatment and 14 d post-infection, 6-OAU-treated mice displayed reduced IFN-γ serum level. At 7 d post-infection, high serum level of MCP-1 was observed in both treatments with the addition of TNF-α in LU group. IL-6 was increased in both treatments at 14 d post-infection with higher TNF-α, MCP-1 and IL-10 in LU group. Taken together, 6-OAU and LU are potential candidates representing pharmaceutical strategy against brucellosis and possibly other intracellular pathogens or inflammatory diseases.

A major highlight of restoration efforts is to improve the ecological structure and function of the natural ecosystem in the restored habitat. Assessment of restoration success is a crucial component of an optimal ecological management strategy. In studies to determine the restoration success of a transplanted seagrass habitat by assessing trophic recovery, we examined carbon and nitrogen stable isotope ratios of organic matter sources and macrobenthic assemblages in a transplanted eelgrass Zostera marina bed. The eelgrass bed was restored about 2 years after transplantation in a southern coastal bay of Korea, and consequently, the food web structure in the bed was compared with that in a natural reference site. Our results revealed no significant differences in isotopic values of both macrobenthic consumers and their putative food sources between the transplanted and natural seagrass beds. These isotopic similarities in florae and faunae in the two beds suggest a uniformity in food web structure formed by the diversity and availability of resources, and thereby suggest similarities in the resource–consumer relationship. Isotopic niche indices and high dietary overlaps of feeding guilds in the transplanted and natural beds further suggest the transplanted habitat provides similar ecological functions and ecosystem services to its natural counterpart. Collectively, our results suggest the eelgrass transplantation led to successful restoration of a common seagrass bed, with recovery of the functional properties of the food web structure. Finally, our findings support the idea that stable isotope measures can provide a better understanding of the functioning of restored ecosystems, and improve post-transplantation monitoring efforts for the future planning and managing of successful habitat restoration.

The East/Japan Sea (EJS) is well ventilated to deep water via brine rejection from ice formations and thermohaline convection, resulting in a short overturning period in several decades. Due to these characteristics, the dissolved oxygen concentration in the EJS deep water is much higher (190–200 μg L −1 at 3000 m water depth) than that found at the same depths of the Northwestern Pacific (30 μg L −1 ) or anywhere in the Pacific Ocean. The total mercury (THg) and methylmercury (MeHg) distributions, and MeHg mass budgets were investigated to identify how the EJS's distinct circulation pattern affects Hg speciation. Whereas the THg concentration in the surface seawater (ranging from 0.20 to 1.2 pM, mean 0.59 ± 0.24 pM) showed no site variation between the Japan Basin and the Ulleung Basin, the MeHg concentration in the surface seawater was significantly higher (p −2 yr −1 ) than in the Ulleung Basin (1.9 nmol m −2 yr −1 ) due to the shallow thermocline depths in the Japan Basin. In contrast, the MeHg concentration in deep seawater (1000–3000 m) was similar between the Japan Basin (530 ± 87 fM) and the Ulleung Basin (610 ± 99 fM) and significantly (p

The Ulleung Basin in the southwestern East/Japan Sea (hereafter East Sea) is known as a biologically productive “hot spot” but climate-associated changes in the physicochemical oceanographic conditions and some biological changes have been reported. In this study, our main objective was to determine the contribution of small phytoplankton to the total primary production, which is valuable information for detecting marine ecosystem changes in the Ulleung Basin. The small phytoplankton productivity contributions determined by Moderate-Resolution Imaging Spectroradiometer (MODIS)-derived monthly productivities using a phytoplankton community-based productivity algorithm was significantly consistent with the field-measured productivity contributions of small phytoplankton in this study. The daily primary productivity of small phytoplankton ranged from 42.7 to 418.7 mg C m −2 d −1 with an average of 172.9 mg C m −2 d −1 (S.D. = ±61.4 mg C m −2 d −1 , n = 120), and the annual contribution of small phytoplankton ranged from 19.6% to 28.4% with an average of 23.6% (S.D. = ±8.1%) in the Ulleung Basin from 2003 to 2012. Overall, large phytoplankton were a major contributor to the total primary production in the Ulleung Basin (76.4 ± 8.2%) from 2003 to 2012, which indicates that the Ulleung Basin is a highly productive region. A significantly negative relationship (p

Korea-Russia joint expeditions have been conducted mainly in the less studied Russian sector of the East/Japan Sea to understand the physical and ecological structures. In this study, the carbon uptake rates of phytoplankton measured in 2012 (middle-late October) and 2015 (middle April-early May) were analyzed to understand seasonal and spatial distributions of phytoplankton production, using a 13C-15N dual isotope tracer technique. The water columns in the euphotic layers were well mixed during our cruise periods in both years. The water column-integrated chl-a concentrations (mean ± S.D. = 2.28 ± 1.47 mg m−3) in 2015 was significantly higher (t-test, p 20 μm) was observed near the Russian coast. The daily carbon uptake rates in this study were 180.5 and 441.6 mg C m−2 d−1 in 2012 and 2015, respectively which are significantly (t-test, p < 0.01) lower than the averaged values previously reported in the East/Japan Sea (863 ± 679.6 mg C m−2 d−1). The potential reasons for the lower rate in this study are discussed. The small phytoplankton contribution (47.4%) averaged from the two different cruises in this study is consistent with the result (47%) reported in temperate regions. Moreover, a significantly (t-test, p < 0.01) lower contribution of small phytoplankton in total primary production than total phytoplankton biomass in this study is consistent with the results from other regions. Lower total primary production might be expected due to increasing contribution of small phytoplankton under warmer conditions.

Step changes to seawater temperature (SWT) in the East Asian marginal seas (EAMS) are associated with three recent climate regime shifts (CRS) occurring in the mid-1970s, late 1980s, and late 1990s, but the responses of the ocean conditions and marine ecosystems had regional differences. A step change in SWT in the East China Sea (ECS) was detected after the CRS of the 1970s as were step changes in the North Pacific Index (NPI), Pacific Decadal Oscillation Index (PDOI), and East Asian Winter Monsoon Index (EAWMI). SWT in the ECS decreased with decreasing warm water volume transport into the EAMS and a strong monsoon, but step changes in SWT in other regions were not detected as clearly. After the CRS of the 1980s, SWT in all EAMS increased rapidly with step changes detected in all five climate indices examined. These changes were associated with a weak winter monsoon, increasing surface air temperature (SAT), and increasing warm water volume transport into the EAMS. However, after the CRS of the 1990s, a decrease in SWT around the EAMS was detected in the northern part of East China Sea (NECS), and the ECS with step changes also in the EAWMI and the Arctic Oscillation Index (AOI). In contrast, SWT in the East Sea/Sea of Japan (EJS) and the Yellow Sea (YS) continuously increased during this time. Long-term changes in zooplankton biomass were affected by regional differences in the responses of atmospheric and oceanic variability to CRSs. Specifically, long-term changes in the timing of peaks in zooplankton abundances exhibited differences. During warm periods (e.g. after the 1980s CRS) in the EJS, the amount of zooplankton biomass in October increased, while in February it decreased. On the contrary, in the YS and the NECS, the peaks of October and June in zooplankton biomass occurred during cold periods (after the 1970s and 1990s CRS). Major fisheries resources also responded to the three CRSs, although warm and cold water species responded differently to changes in oceanographic conditions in regional spawning grounds.

Three cruises were undertaken along a meridional transect in the East/Japan Sea (EJS) in spring (May 2007), summer (July 2009), and fall (October 2012) to determine the geographic variations in phytoplankton biomass and community composition. This study revealed a gradient of surface temperature and a fluctuation of hydrographic conditions along the transect. Although a subpolar front (SPF) formed between the warm- and cold-water masses (37–40°N), no significant differences in phytoplankton biomass and community composition were detected between the southern and northern parts of the EJS. These results disprove our initial hypothesis that different water masses may contain differently structured phytoplankton communities. In the present study, isothermal layers (≤ 12 °C) fluctuated over a depth of 50 m in both warm- and cold-water masses, depending on the SPF. In contrast, the nitracline (i.e. 2.5 μM nitrate isopleth) depth was recorded within a limited range of 20–40 m in spring, 30–50 m in summer, and 40–60 m in fall. The chlorophyll a concentrations at the subsurface chlorophyll maxima (SCM) were significantly higher in spring and summer (356 ± 233 and 270 ± 182 ng L –1 , respectively) than in fall (117 ± 89 ng L –1 ). The relative contributions of individual phytoplankton groups to the depth-integrated chlorophyll a concentration conformed to the composition of the phytoplankton community in the SCM layer, showing a dominance of diatoms (58 ± 19% in spring, 48 ± 11% in summer, and 30 ± 20% in fall). Canonical correspondence analysis revealed that the geographic structures of phytoplankton communities were strongly associated with the vertical structures of water temperature and nutrient concentration in the water column rather than with horizontal gradients of hydrographic conditions. Finally, our findings suggest that water column stability and light–nutrient availability in the euphotic zone play a key role in determining geographical consistency of the biomass and the community structure of phytoplankton in the EJS.

The minke whale ( Balaenoptera acutorostrata ) is the most common baleen whale among several marine mammal species observed in Korea. Since a high concentrated condition of prey to whales can be obtained by physical structures, the foraging whale distribution can be an indicator of biological hotspot. Our main objective is verifying the coastal upwelling-southwestern East Sea as a productive biological hotspot based on the geographical distribution of minke whales. Among the cetacean research surveys of the National Institute of Fisheries Science since 1999, 9 years data for the minke whales available in the East Sea were used for this study. The regional primary productivity derived from Moderate-Resolution Imaging Spectroradiometer (MODIS) was used for a proxy of biological productivity. Minke whales observed during the sighting surveys were mostly concentrated in May and found mostly (approximately 70%) in the southwestern coastal areas ( −2 y −1 ) estimated in the southwestern coastal region of the East Sea belongs to the highly productive coastal upwelling regions in the world. A change in the main spatial distribution of minke whales was found in recent years, which indicate that the major habitats of mink whales have been shifted into the north of the common coastal upwelling regions. This is consistent with the recently reported unprecedented coastal upwelling in the mid-eastern coast of Korea. Based on high phytoplankton productivity and high distribution of minke whales, the southwestern coastal regions can be considered as one of biological hotspots in the East Sea. These regions are important for ecosystem dynamics and the population biology of top marine predators, especially migratory whales and needed to be carefully managed from a resource management perspective.

We investigated bacterial production (BP) and respiration (BR), as well as the physico-chemical properties of the water column, to elucidate the effect of upwelling on heterotrophic bacterial metabolic activities and growth efficiency (BGE) in July 2012 and May 2013 in the Ulleung Basin (UB), East/Japan Sea. The upwelled conditions were characterized by higher chlorophyll-a (Chl-a) concentrations resulting from the upward shift of the nitracline compared to that of the non-upwelled condition. Analyses of the size fractions of Chl-a and pigment composition revealed that large size phytoplankton (> 20 µm), mainly consisting of diatoms, appeared to be the major phytoplankton component. BP and BR were significantly correlated with Chl-a (P 0.05). These results suggest that bacterial metabolic activities are stimulated by the availability of organic resources enhanced by upwelling in the UB. Further statistical analysis showed that the difference in BP and BGE with variations in upwelling intensity were significant (P = 0.018 for BP, P = 0.035 for BGE), but the difference in BR was not significant (P = 0.321). These results suggest that metabolic energy is partitioned more for BP under a strong upwelling condition, i.e. high nutrient and Chl-a conditions. In contrast, the energy generated via respiration was partitioned more for maintaining metabolism rather than for biomass production under weakly or non-upwelled conditions, i.e. stratified and low Chl-a conditions. Overall, our results suggest that any changes in upwelling intensity would significantly affect the carbon cycle associated with the fate of primary production, and the role of the microbial loop in the UB where changes in the intensity and frequency of upwelling associated with climatic changes are in progress.

Seasonal variability of sinking fluxes of total mass (TMF), particulate organic carbon and nitrogen (POC and PON) was examined using sinking particles collected from sediment traps during July 2011 to December 2011, and December 2012 to June 2013 at an offshore channel site; and from November 2013 to August 2014 at a nearshore slope site of the Ulleung Basin in the East/Japan Sea. δ13C and δ15N values of sinking particles were measured to elucidate the major export processes of POC and PON. Annual TMF (112–638 g m−2 yr−1) and fluxes of POC and PON (9.6–32.1 g C m–2 yr–1 and 1.2–4.5 g N m−2 yr−1, respectively) in the Ulleung Basin corresponded to the upper limit of values reported for other open seas and oceans in the world. No great seasonal variability in both quantitative (TMF, and fluxes and contents of POC and PON) and qualitative (C/N ratios, and δ13C and δ15N values) estimates of vertical fluxes was observed, reflecting a steady standing stock of chlorophyll a in the upper part of water column. Furthermore, high contents of POC and PON and nearly constant δ13C and δ15N values in sinking particles collected in the sediment traps, indicate that primary production in the euphotic zone may be a good predictor of TMF and export flux of organic matter. In this regard, our pilot study points out the importance of high annual primary production and low water temperature (

The East/Japan Sea (EJS) where is surrounded by the Korean peninsula, the Japanese islands, and the Russian coast has been experiencing a large change in physicochemical properties. Based on biochemical composition analysis (carbohydrates, proteins, and lipids), the current qualitative status of phytoplankton was identified in the northern EJS from two different sampling seasons (fall and spring in 2012 and 2015, respectively). The average chlorophyll-a (chl-a) concentration integrated from the euphotic depths was significantly higher in 2015 (99.3 ± 69.2 mg m−2) than 2012 (21.5 ± 6.7 mg m−2). Large phytoplankton (> 2 µm) were predominant in 2015 accounting for 64.5 ± 19.7% whereas small-size phytoplankton (0.7–2 µm) were dominant (49.1 ± 17.5%) in 2012. The biochemical compositions of phytoplankton were predominated by lipids (42.6 ± 7.8%) in 2012 whereas carbohydrate composition largely contributed (53.2 ± 11.7%) to the total biochemical composition in 2015, which is mainly due to different nutrient availabilities and growth stages. Interestingly, the averaged FM concentrations and calorific values for phytoplankton based on the biochemical compositions had similar values between the two years, although the integrated chl-a concentrations were substantially different between 2012 and 2015. In terms of different cell sizes of phytoplankton, we found that small phytoplankton assimilate more FM and calorific energy per unit of chl-a concentration than total phytoplankton. Our results are meaningful for the understanding of future marine ecosystems where small phytoplankton will become dominant at a scenario of ongoing warmer oceans.

The pattern of somatic growth of the Pacific oyster Crassostrea gigas cultured in suspension in Geoje–Hansan Bay, Korea was evaluated between July 2013 and March 2014 comparing culturing sites and depths. Gross biochemical composition of oyster tissues provided a measure of physiological status, and clearance rates of oysters provided a measure of feeding physiology at different water flow speeds. A growth curve model indicated greater tissue growth in the surface than in the bottom layers, and advanced summer growth by more than 4 months in the stagnant inner bay compared with winter growth in the more rapidly flowing outer bay. Our results suggest that rapid tissue growth of oysters in the surface layer in summer is supported by high primary productivity in the inner bay. In contrast, oyster growth performance at the outer bay in late fall and winter may be related to seasonal food availability that is regulated by short residence time and thereby rapid renewal of water compared to the inner bay. Furthermore, a combination of the water flow regime of the bay and the flow rate-dependent feeding physiology of oysters proved to be an important determinant of seasonal growth dynamics. Finally, oyster growth was better explained by water flow rates than by hydrographic conditions.

The biochemical composition of particulate organic matter (POM) produced through phytoplankton photosynthesis is important in determining food quality for planktonic consumers as well as the physiological conditions of phytoplankton. Major environmental factors controlling the biochemical composition were seasonally investigated in Gwangyang Bay, South Korea, which has only natural conditions (e.g., no artificial dams). Water samples for the biochemical compositions were obtained from three different light depths (100, 30, and 1 %) mainly at three sites in Gwangyang Bay from April 2012 to April 2013. Different biochemical classes (carbohydrates, CHO; proteins, PRT; and lipids, LIP) were extracted, and then the concentrations were determined by the optical density measured with a spectrophotometer. The highest and lowest PRT compositions among the three biochemical classes were found in April 2012 (58.0 %) and August 2012 (21.2 %), whereas the highest and lowest LIP compositions were found in August 2012 (49.0 %) and April 2012 (24.8 %), respectively. The CHO composition was recorded as high in January 2013 and remained above 25 % during the study period. The calorific contents of the food material (FM) ranged from 1.0 to 6.1 Kcal m−3 (annual average ± SD = 2.8 ± 1.1 Kcal m−3). Based on a Pearson's correlation coefficient analysis, a major governing factor in the biochemical composition of POM was dissolved inorganic nitrogen loading from the river input in Gwangyang Bay. In conclusion, a relatively larger amount of FM and the higher calorific contents of POM found in this study compared to other regions reflected good nutritive conditions for sustaining productive shellfish and fish populations in Gwangyang Bay. Continuous observations are needed to monitor the marine ecosystem response to potential environmental perturbations in Gwangyang Bay.

This study investigates the biological pump system in the East Sea (Japan Sea) by conducting an analysis of the total particle flux, biogenic material composition, and carbon isotope ratios of sinking particles. The samples were collected for one year starting from March 2011 using time-series sediment traps deployed at depths of 1040 m and 2280 m on bottom-tethered mooring at Station EC1 (37.33°N, 131.45°E; 2300 m water depth) in the Ulleung Basin (UB), southwestern part of the East Sea. The temporal variation in the particulate organic carbon (POC) flux at 1000 m shows a good relationship with the primary production in the corresponding surface water. The ratio of POC flux at 1000 m to satellite-based primary production in the corresponding region in the UB was ~ 3%, which is comparable to the values of 2 to 5% estimated from previous studies of other part of the East Sea. The lithogenic material accounted for > 17% of the sinking particles at 1000 m and for a larger fraction of 40 to 60% at 2280 m. The radiocarbon contents of the sinking POC at both trap depths imply the additional supply of aged POC, with a much greater contribution at 2280 m. Overall, the particle flux in the deep interior of the East Sea appears to be controlled by the supply of complex sources, including aeolian input, the lateral supply of resuspended sediments, and biological production in the surface water.

To date, the implications of interleukin 6 (IL-6) for immune responses in the context of Brucella infection are still unknown. In the present study, we found that Brucella abortus infection induced marked production of IL-6 in mice that was important for sufficient differentiation of CD8+ T cells, a key factor in Brucella clearance. Blocking IL-6 signaling also significantly induced serum IL-4 and IL-10, together with a decreased gamma interferon (IFN-γ) level, suggesting that IL-6 is essential for priming the T-helper (Th) 1 cell immune response during Brucella infection. The IL-6 pathway also activated the bactericidal activity of primary and cultured macrophages. Bacterial killing was markedly abrogated when IL-6 signaling was suppressed, and this phenomenon was mainly associated with decreased activity of lysosome-mediated killing. Interestingly, suppressor of cytokine signaling 3 (SOCS3) was important for regulating the IL-6-dependent anti-Brucella activity through the JAK/STAT pathway. During early infection, in the absence of SOCS3, IL-6 exhibited anti-inflammatory effects and lysosome-mediated killing inhibition; however, the increase in SOCS3 successfully shifted functional IL-6 toward proinflammatory brucellacidal activity in the late stage. Our data clearly indicate that IL-6 contributes to host resistance against B. abortus infection by controlling brucellacidal activity in macrophages and priming cellular immune responses.

To date, the implications of interleukin 6 (IL-6) for immune responses in the context of Brucella infection are still unknown. In the present study, we found that Brucella abortus infection induced marked production of IL-6 in mice that was important for sufficient differentiation of CD8(+) T cells, a key factor in Brucella clearance. Blocking IL-6 signaling also significantly induced serum IL-4 and IL-10, together with a decreased gamma interferon (IFN-γ) level, suggesting that IL-6 is essential for priming the T-helper (Th) 1 cell immune response during Brucella infection. The IL-6 pathway also activated the bactericidal activity of primary and cultured macrophages. Bacterial killing was markedly abrogated when IL-6 signaling was suppressed, and this phenomenon was mainly associated with decreased activity of lysosome-mediated killing. Interestingly, suppressor of cytokine signaling 3 (SOCS3) was important for regulating the IL-6-dependent anti-Brucella activity through the JAK/STAT pathway. During early infection, in the absence of SOCS3, IL-6 exhibited anti-inflammatory effects and lysosome-mediated killing inhibition; however, the increase in SOCS3 successfully shifted functional IL-6 toward proinflammatory brucellacidal activity in the late stage. Our data clearly indicate that IL-6 contributes to host resistance against B. abortus infection by controlling brucellacidal activity in macrophages and priming cellular immune responses.

The interleukin-1 (IL-1) family of cytokines, particularly IL-1α and IL-1β, are potent regulators of innate immunity that play key roles in host defense against infection, hence we evaluated the role of these cytokines in the control of brucellosis within RAW 264.7 cells. Marked expression and secretion of IL-1α and IL-1β were observed during Brucella infection in macrophages. Blocking of IL-1α and IL-1β reduced induction of IL-10, IL-1β and TNF, and IL-6 and TNF, respectively. However, interference of IL-1α and not IL-1β signaling notably augmented susceptibility of macrophages to Brucella infection which indicates that IL-1α is required for a downstream signaling cascade of innate immunity for efficient clearance of Brucella. This protection requires binding to interleukin-1 receptor (IL-1R) mediated by myeloid differentiation factor 88 (MyD88) signaling and associated with increased lysosomal-mediated killing and nitric oxide (NO) production. Expression of pro-inflammatory cytokines was observed to be mediated via NF-κB-p50, HIF-1α and CEBPA, but negatively controlled by CEBPB while transcription of some important phagolysosomal genes was regulated via CEBPA and c-Jun which indicates the important role of these transcription factors in the control of Brucella infection in macrophages via IL-1α signaling pathway.