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
Seasonal variations in primary productivity and biomass of phytoplankton in Geoje-Hansan Bay on the southern coast of Korea
- Seasonal Variations in Primary Productivity and Biomass of Phytoplankton in Geoje-Hansan Bay on the Southern Coast of KoreaDongyoung Kim, Young-Jae Lee, Hee Yoon Kang, Kee-Young Kwon, Won-Chan Lee, Jung Hyun KwakOcean Sci. J. (2019). https://doi.org/10.1007/s12601-019-0005-yPhytoplankton constitutes an important dietary item of oysters in suspended longline aquaculture systems. Primary productivity and the community structure of phytoplankton, as well as hydrographic and nutritional conditions of the water column, were monitored monthly in Geoje-Hansan Bay on the southern coast of Korea between July 2013 and July 2014 to determine the seasonal variation patterns of productivity and structures of phytoplankton assemblages. All measured physicochemical and biological components exhibited temporal variabilities common to all four sampling sites within the bay system. The hydrographic features were characterized by a summer stratified and fall–winter wellmixed structure of the water column. Daily primary productivity in the bay (0.16–2.88 g C m–2 d–1) peaked in summer; it displayed a unimodal cycle, and the most dominant phytoplankton group shifted from diatoms to dinoflagellates. Canonical correspondence analysis, based on environmental factors and the phytoplankton community, enabled the identification of seasonal patterns of phytoplankton assemblage in relation to temporal variations of hydrographic and nutritional conditions. Results indicated that increase of the watercolumn stability and enhanced nutrient input by freshwater discharge during the summer monsoon and possible upward flux from bottom sediment led to the peaking primary productivity and diatomdominated community during that time, supporting high annual productivity (371 g C m–2 yr–1). Our findings suggest that seasonal properties of hydrodynamics and nutritional conditions play a key role in determining the primary productivity and structuring of the phytoplankton community. Summer peaks in productivity and diatom dominance most likely ultimately determine oyster growth and the final success of aquaculture.
- 등록일2019-03-14 19:56:12
Trophic structures of two contrasting estuarine ecosystems with and without a dike on the temperate coast of Korea as determined by stable isotopes
- Trophic Structures of Two Contrasting Estuarine Ecosystems With and without a Dike on the Temperate Coast of Korea as Determined by Stable IsotopesHyun Je Park, Jung Hyun Kwak, Young-Jae Lee, Hee Yoon Kang, Eun Jung Choy, Chang-Keun KangEstuaries and Coasts (2019). https://doi.org/10.1007/s12237-019-00522-4To 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.
- 등록일2019-02-01 17:02:38
Gross biochemical and isotopic analyses of nutrition-allocation strategies for somatic growth and reproduction in the bay scallop Argopecten irradians newly introduced in
- Gross biochemical and isotopic analyses of nutrition-allocation strategies for somatic growth and reproduction in the bay scallop Argopecten irradians newly introduced into Korean watersHee Yoon Kang, Young-Jae Lee, Won-Chan Lee, Hyung Chul Kim, Chang-Keun KangAquaculture 503, 2019, 156-166. https://doi.org/10.1371/journal.pone.0152427The 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.
- 등록일2019-01-01 17:00:47
Variability in copepod trophic levels and feeding selectivity based on stable isotope analysis in Gwangyang Bay of the southern coast of the Korean Peninsula
- Variability in copepod trophic levels and feeding selectivity based on stable isotope analysis in Gwangyang Bay of the southern coast of the Korean PeninsulaMianrun Chen, Dongyoung Kim, Hongbin Liu, and Chang-Keun KangBiogeosciences, 15, 2055-2073, 2018Trophic preference (i.e., food resources and trophic levels) of different copepod groups was assessed along a salinity gradient in the temperate estuarine Gwangyang Bay of Korea, based on seasonal investigation of taxonomic results in 2015 and stable isotope analysis incorporating multiple linear regression models. The δ13C and δ15N values of copepods in the bay displayed significant spatial heterogeneity as well as seasonal variations, which were indicated by their significant relationships with salinity and temperature, respectively. Both spatial and temporal variations reflected those in isotopic values of food sources. The major calanoid groups (marine calanoids and brackish water calanoids) had a mean trophic level of 2.2 relative to nanoplankton as the basal food source, similar to the bulk copepod assemblage; however, they had dissimilar food sources based on the different δ13C values. Calanoid isotopic values indicated a mixture of different genera including species with high δ15N values (e.g., Labidocera, Sinocalanus, and Tortanus), moderate values (Calanus sinicus, Centropages, Paracalanus, and Acartia), and relatively low δ15N values (Eurytemora pacifica and Pseudodiaptomus). Feeding preferences of different copepods probably explain these seasonal and spatial patterns of the community trophic niche. Bayesian mixing model calculations based on source materials of two size fractions of particulate organic matter (nanoplankton at < 20 µm vs. microplankton at 20–200 µm) indicated that Acartia and Centropages preferred large particles; Paracalanus, Calanus, Eurytemora, and Pseudodiaptomus apparently preferred small particles. Tortanus was typically carnivorous with low selectivity on different copepods. Labidocera preferred marine calanoids Acartia, Centropages, and harpacticoids; on the other hand, Sinocalanus and Corycaeus preferred brackish calanoids Paracalanus and Pseudodiaptomus. Overall, our results depict a simple energy flow of the planktonic food web of Gwangyang Bay: from primary producers (nanoplankton) and a mixture of primary producers and herbivores (microplankton) through omnivores (Acartia, Calanus, Centropages, and Paracalanus) and detritivores (Pseudodiaptomus, Eurytemora, and harpacticoids) to carnivores (Corycaeus, Tortanus, Labidocera, and Sinocalanus).
- 등록일2018-04-09 16:52:55
Physiological processes and gross energy budget of the submerged longline-cultured Pacific oyster Crassostrea gigas in a temperate bay of Korea
- Physiological processes and gross energy budget of the submerged longline-cultured Pacific oyster Crassostrea gigas in a temperate bay of KoreaYoung-Jae Lee, Eunah Han, Michael J. Wilberg, Won Chan Lee, Kwang-Sik Choi, Chang-Keun KangPLoS ONE 13(7): e0199752. https://doi.org/10.1371/journal.pone.0199752Physiological processes and gross energy budget of the longline-cultured Pacific oyster Crassostrea gigas were investigated in Geoje–Hansan Bay, Korea during two entire culturing periods. Based on physiological measurements of food consumption, feces production, ammonium excretion, and respiration from July 2008 to February 2009 and from July 2013 to February 2014, scope for growth appeared to be positive during most of the culturing period, except for one period with extremely high temperatures (up to 25°C). Estimates of physiological energy production matched well with tissue energy increment measured by gross biochemical composition during the culturing period, suggesting that the oysters might adjust their physiological performance to relatively low concentrations of suspended particulate matter in the bay to optimize energy acquisition. Such an adaptive adjustment includes an increased absorption of energy and a reduced loss of metabolic and excretory energy, resulting in positive production under high culturing density. Using physiological measurements, we further assessed the feedback effects of the longline aquaculture of oysters on the bay system. Ecological efficiency, estimated by a series of energetic efficiencies at the whole bay level, was low compared with Lindeman’s law of trophic efficiency. Biodeposition and ammonia excretion rates in this study were relatively low compared with other intertidal plastic bag cultures. These results indicate that the cultured oysters might have only minor effects on benthic and pelagic environments of the bay. Overall, our results suggest that the adaptive physiological performance of oysters and consequently weak feedback effects on ambient habitats should facilitate sustainable longline aquaculture in the bay for a prolonged period without severe habitat deterioration.
- 등록일2018-07-05 16:41:19