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Stable Isotope Ecology Laboratory

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Impact of Shifting Subpolar Front on Phytoplankton Dynamics in the Western Margin of East/Japan Sea 이미지
Impact of Shifting Subpolar Front on Phytoplankton Dynamics in the Western Margin of East/Japan Sea
  • 작성자SIEL
  • 조회수310
  • Impact of Shifting Subpolar Front on Phytoplankton Dynamics in the Western Margin of East/Japan SeaFrontiers in Marine Science (2021) 8:790703. doi: 10.3389/fmars.2021.790703Dongyoung Kim, Rubao Ji, Hyun Je Park, Zhixuan Feng, Jaebin Jang, Chung Il Lee, Yun-Ho Kang, Chang-Keun KangA 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 biomassand 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 SPFon 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 ecosystemchanges in this region.
  • 등록일2021-12-07 11:29:34
Biochemical Composition of Seston Reflecting the Physiological Status and Community Composition of Phytoplankton in a Temperate Coastal Embayment of Korea 이미지
Biochemical Composition of Seston Reflecting the Physiological Status and Community Composition of Phytoplankton in a Temperate Coastal Embayment of Korea
  • 작성자SIEL
  • 조회수359
  • Biochemical Composition of Seston Reflecting the Physiological Status and Community Composition of Phytoplankton in a Temperate Coastal Embayment of KoreaWater 2021, 13(22), 3221. https://doi.org/10.3390/w13223221Riaz Bibi, Hee Yoon Kang,Dongyoung Kim, Jaebin Jang, Changseong Kim, Goutam K. Kundu, Chang-Keun KangThe 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 (>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 (>2.5) in the saline deep-bay area during the warmer months (>2.0) emphasized the importance of temperature and photoperiod over nutritional conditions. The low POC:Chla (<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.
  • 등록일2021-11-16 17:29:14
Phytoplankton Fuel Fish Food Webs in a Low-Turbidity Temperate Coastal Embayment: A Stable Isotope Approach 이미지
Phytoplankton Fuel Fish Food Webs in a Low-Turbidity Temperate Coastal Embayment: A Stable Isotope Approach
  • 작성자SIEL
  • 조회수315
  • Phytoplankton Fuel Fish Food Webs in a Low-Turbidity Temperate Coastal Embayment: A Stable Isotope ApproachFront. Mar. Sci. 8:751551. doi: 10.3389/fmars.2021.751551Goutam Kumar Kundu, Changseong Kim, Dongyoung Kim, Riaz Bibi, Heeyong Kim, Chang-Keun KangTrophic 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 d13C and d15N values of whole nekton communities along with dominant benthic macro-invertebrates, zooplankton, and their putative primary food sources. The d13C and d15N 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 ourunderstanding of marine ecosystems.
  • 등록일2021-10-29 18:06:59
Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analyses 이미지
Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analyses
  • 작성자SIEL
  • 조회수802
  • Food web trophic structure at marine ranch sites off the east coast of KoreaHee Yoon Kang, Young-Jae Lee, Changseong Kim, Dongyoung Kim, Doo-Ho Kim, Jun-Ho Kim, Dong-Lim Choi, Chang-Keun KangFront. Mar. Sci. 8:653281. doi: 10.3389/fmars.2021.653281Understanding 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 d13C and d15N, 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 d13C and d15N values of consumers were distinct and separate among functional groups at both ranches. The consumer d13C values spanned a broad range between pelagic and benthic sources of organic matter, and their d15N 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 d13C values of predators, including E. dofleini, were arrayed between the two primary consumer groups. Neither d13C nor d15N 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.
  • 등록일2021-05-20 14:44:26
Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analyses 이미지
Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analyses
  • 작성자SIEL
  • 조회수200
  • Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analysesHee Yoon Kang, Byeong-Gweon Lee, Hyun Je Park, Sung-Gyu Yun, Chang-Keun KangMarine Pollution Bulletin 169 (2021) 112474, https://doi.org/10.1016/j.marpolbul.2021.112474The 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.
  • 등록일2021-05-19 14:43:22
Assessment of restoration success in a transplanted seagrass bed based on isotopic niche metrics 이미지
Assessment of restoration success in a transplanted seagrass bed based on isotopic niche metrics
  • 작성자SIEL
  • 조회수178
  • Assessment of restoration success in a transplanted seagrass bed based on isotopic niche metricsHyun Je Park, Tae Hee Park, Hee Yoon Kang, Kun-Seop Lee, Young Kyun Kim, Chang-Keun KangEcological Engineering 166 (2021) 106239. https://doi.org/10.1016/j.ecoleng.2021.106239A 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.
  • 등록일2021-04-06 14:40:41
Identifying patterns in the multitrophic community and food-web structure of a low-turbidity temperate estuarine bay 이미지
Identifying patterns in the multitrophic community and food-web structure of a low-turbidity temperate estuarine bay
  • 작성자SIEL
  • 조회수384
  • Identifying patterns in the multitrophic community and food‑web structure of a low‑turbidity temperate estuarine bayHeeYoon Kang, Changseong Kim, Dongyoung Kim, Young‑Jae Lee, Hyun Je Park, Goutam K. Kundu, Young Kyun Kim, Riaz Bibi, Jaebin Jang, Kwang‑Hun Lee, Hyun‑Woo Kim, Sung‑GyuYun, Heeyong Kim & Chang‑Keun KangScientific Reports (2020) 10:16637.https://doi.org/10.1038/s41598-020-73628-6Food 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 anddeep-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.
  • 등록일2020-10-14 10:24:46
Dominance of autochthonous phytoplankton-derived particulate organic matter in a low-turbidity temperate estuarine embayment, Gwangyang Bay, Korea 이미지
Dominance of autochthonous phytoplankton-derived particulate organic matter in a low-turbidity temperate estuarine embayment, Gwangyang Bay, Korea
  • 작성자SIEL
  • 조회수287
  • Dominance of autochthonous phytoplankton-derived particulate organic matter in a low-turbidity temperate estuarine embayment, Gwangyang Bay, KoreaRiaz Bibi, Hee Yoon Kang,Dongyoung Kim,Jaebin Jang,Kumar Kundu, Young Kyun Kim,Chang-Keun KangFrontiers in Marine Science,doi: 10.3389/fmars.2020.580260In 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 (<20 mg L−1). The channel carries river discharge, with a large quantity of nutrients (NO3 and SiO2), into the bay. The especially low SPM concentrations in the estuary (range: 2.0–29.1 mg L−1), and generous nutrient source, create an exceptionally low-turbidity condition in the water column and high primary productivity with no conspicuous spatial or seasonal trends. Gradually increasing 13C values, low POC:Chla (<200), and low molar C:N (4–8) in the SPM, together with higher Chla concentrations at low SPM locations along the longitudinal transect, suggest that local production of phytoplankton has a strong influence on the distributional patterns of particulate organic matter. Short water-residence times, within the bay system, impede the accumulation of diverse-origin organic matter. The community composition of phytoplankton, distinguished by their size group, also plays a role in characterizing SPM quantity and composition. The results indicate that autochthonous pelagic production governs biogeochemical features in the low-turbidity estuarine embayment, contrasting with a prevalence of allochthonous organic matter, and its active processing, in highly turbid and/or longer residence-time systems.
  • 등록일2020-09-10 17:16:48
Incorporation of Cochlodinium bloom-derived organic matter into a temperate subtidal macrobenthic food web as traced by stable isotopes 이미지
Incorporation of Cochlodinium bloom-derived organic matter into a temperate subtidal macrobenthic food web as traced by stable isotopes
  • 작성자SIEL
  • 조회수682
  • Incorporation of Cochlodinium bloom-derived organic matter into a temperate subtidal macrobenthic food web as traced by stable isotopesHyun Je Park, Jung Hyun Kwak, Hee Yoon Kang, Kee-Young Kwon, Weolae Lim, Chang-Keun KangMarine Pollution Bulletin 154, 111053https://doi.org/10.1016/j.marpolbul.2020.111053Harmful algal blooms involving the dinoflagellate Cochlodinium polykrikoides occur every summer off the Korean peninsula's central southern coast. To determine whether Cochlodinium bloom-derived organic carbon is incorporated into the subtidal macrobenthic food web, we compared the δ13C and δ15N values of suspended particulate organic matter (SPOM) and sedimentary organic matter, and macrobenthic consumers between bloom and non-bloom seasons. Chemotaxonomic analysis revealed the presence of Cochlodinium blooms in summer and a predominance of diatoms in autumn. Both the δ13C and δ15N values of SPOM were higher in the bloom than in the non-bloom seasons. Such temporal shifts in the δ13C and δ15N values were also observed for most macrobenthic consumers collected in both seasons. Consistent temporal isotopic shifts in SPOM and macrobenthos revealed that the Cochlodinium bloom-derived carbon was incorporated into the coastal benthic food web, resulting from its increasing availability during blooms.
  • 등록일2020-04-23 11:54:23
Growth of the longline-cultured sea squirt Halocynthia roretzi in a temperate bay of Korea: Biochemical composition and physiological energetics 이미지
Growth of the longline-cultured sea squirt Halocynthia roretzi in a temperate bay of Korea: Biochemical composition and physiological energetics
  • 작성자SIEL
  • 조회수469
  • Growth of the longline-cultured sea squirt Halocynthia roretzi in a temperate bay of Korea: Biochemical composition and physiological energeticsYoung-Jae Lee, Michael J. Wilberg, Eunah Han, Kwang-Sik Choi, Won Chan Lee, Chang-Keun KangAquaculture 516, 734526https://doi.org/10.1016/j.aquaculture.2019.734526The broad temperature range on the temperate coast of Korea has led fishermen to develop a unique and specialized procedure for the longline culture of ascidians. In Korea, warming of the coastal sea in winter has accelerated over the past few decades. After warmer winters, the rising temperatures of earlier springs have precluded the rearing of the ascidian spat in the culturing area and have imposed spring spat cultivation in colder-water nursery grounds. To examine the seasonal dynamics of energy reserves and the physiological strategies to optimize energy balance for the growth in the cultured sea squirt Halocynthia roretzi, its gross biochemical composition and physiological energetics were investigated monthly over two culturing periods from July 2005 to January 2006 and July 2013 to January 2014 in Geoje-Hansan Bay on the south coast of Korea. No indicators of the growth performance of sea squirts showed differences between the two culture practices (2005–2006 and 2013–2014) carried out using spat reared in different localities, i.e., the grow-out area and the colder nursery grounds. The seasonal patterns in accumulation and utilization of biochemical constituents in the sea squirt tissues were similar between the two periods. During the culturing period in the grow-out area, sea squirts retained physiological functions across the temperature range. Food energy acquisition and metabolic cost were positively related to water temperatures in the field conditions, probably due to the low and narrow range of suspended particulate matter (SPM) concentrations. A less-clear seasonal variability in food consumption rates yielded a seasonal discrepancy in scope for growth (SFG; i.e., negative during summer vs positive during autumn–winter). Consequently, the tissue weight and protein reserves of sea squirts varied concomitantly with the seasonal changes in SFG, supporting a fast growth during autumn–winter. Our results suggest that the spat reared in colder nursery grounds are suitable for cultivating sea squirts in the traditional grow-out area and support their sustainable culturing performance as an adaptation strategy to the winter–spring warming conditions that are unique to coastal seas.
  • 등록일2020-02-23 11:53:57
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