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 Journal54, 467–486 (2019)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
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