Trophic structures of artificial reef communities off the southern coast of the Korean peninsula as determined using stable isotope analyses
- 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
- 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
- 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
- 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
- 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
Growth of the longline-cultured sea squirt Halocynthia roretzi in a temperate bay of Korea: Biochemical composition and physiological energetics
- 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
Temperature-Dependent Bifurcated Seasonal Shift of Phytoplankton Community Composition in the Coastal Water off Southwestern Korea
- Temperature-Dependent Bifurcated Seasonal Shift of Phytoplankton Community Composition in the Coastal Water off Southwestern KoreaYoonja Kang, Hee-Yoon Kang, Dongyoung Kim, Young-Jae Lee, Tae-Ik Kim & Chang-Keun KangOcean Science Journal (2019) 54, 467–486,https://doi.org/10.1007/s12601-019-0025-7Coastal 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.
- 등록일2019-08-07 11:51:46
Physiological responses of the abalone Haliotis discus hannai to daily and seasonal temperature variations
- Physiological responses of the abalone Haliotis discus hannai to daily and seasonal temperature variationsHee Yoon Kang, Young-Jae Lee, Woo-Young Song, Tae-Ik Kim, Won-Chan Lee, Tae Young Kim & Chang-Keun KangScientific Reports 9: 8019 (2019)https://doi.org/10.1038/s41598-019-44526-3Organisms 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.
- 등록일2019-06-01 11:13:30
Isotopic variation of macroinvertebrates and their sources of organic matter along an estuarine gradient
- Isotopic Variation of Macroinvertebrates and Their Sources of Organic Matter Along an Estuarine GradientChangseong Kim, Hee Yoon Kang, Young-Jae Lee, Sung-Gyu Yun, Chang-Keun KangEstuaries and Coasts (2019). https://doi.org/10.1007/s12237-019-00543-zSpatiotemporal 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.
- 등록일2019-03-16 20:25:24