## 2020 Vol. 39, No. 10

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2020, (10): 1-2.
Abstract:
2020, 39(10): 1-10. doi: 10.1007/s13131-020-1655-4
Abstract:
The data of field surveys during 2009 to 2018 was analyzed to understand the seasonality and inter-annual variability of the floating Ulva and Sargassum in the Subei Shoal, the southwestern Yellow Sea of China on decadal scale. The floating Ulva biomass was consistently originated from the central region of the Subei Shoal in middle to late April, increased rapidly, drifted and extended into the offshore water in May and June. The average floating Ulva biomass in the shoal generally increased over the years with evident inter-annual fluctuations. In contrast, pelagic Sargassum was accumulated in the Subei Shoal and formed the spring bloom only in 2013, 2017 and 2018, and the biomass was higher than the co-occurring Ulva during the survey in these three years. Compared to the raft-origin floating Ulva, genesis and development of the pelagic Sargassum was distinct. Based on the current research, the Sargassum biomass was exotic and often initiated in the offshore water in March, and intruded into the shoal in April and May. The analysis on the environmental parameters was inconclusive since multiple anthropogenic and non-indigenous factors could influence the green tides in this region. Further research covering both the East China Sea and the Yellow Sea is needed to trace the origin of the floating Sargassum and to understand the interactions between these two co-occurring seaweeds.
2020, 39(10): 11-26. doi: 10.1007/s13131-020-1656-3
Abstract:
Investigating the spatiotemporal variability of biogeochemical processes and ecological responses under multiple physical controls in shelf seas is of great importance for obtaining an in-depth understanding of marine ecosystem. Based on a compiled data set of historical observations and remote sensing data, the spatiotemporal variability and heterogeneity of physical-biogeochemical processes in the semi-enclosed South Yellow Sea (SYS) are investigated, and the intrinsic connectivity among different subregions and the associated mechanisms are examined. The results show that the seasonal alternation between southward transport in cold seasons and upwelling-induced vertical delivery in warm seasons is the primary physical control of the biogeochemical processes and primary production off Shidao and in the area adjacent to the Haizhou Bay. The northeastward expansion of coastal waters in the Subei Shoal constitutes an important physical driver for the offshore transport of Ulva prolifera in summer. Stratification significantly affects the biogeochemical processes in the Yellow Sea Cold Water Mass (YSCWM)-dominated area during warm seasons, and nutrients can accumulate in bottom waters from spring to autumn, making the Yellow Sea Cold Water Mass (YSCWM) be an important nutrient pool. Upwelling around the YSCWM boundary in the stratified season leads to consistency among the high chlorophyll a (Chl a) area, high primary productivity region and low-temperature upwelling zone. During cold seasons, the interactions of the southward cold waters in the western nearshore area and the northward warm waters in the central region lead to an “S”-shaped front in the SYS. In summer, upwelling can extract nutrients from the YSCWM; thus, the biogeochemical-ecological processes inside the cold-water mass and in the frontal zone are well connected via upwelling, and three typical physical-biogeochemical coupling regions are generated, namely, the Shidao coast, the area beyond the Haizhou Bay and the area off the Subei Shoal. This work refines and integrates studies on regional oceanography in the SYS and provides a comprehensive and systematic framework of physical-biogeochemical-ecological processes.
2020, 39(10): 27-34. doi: 10.1007/s13131-020-1657-2
Abstract:
microRNAs (miRNA) families play a critical role in plant growth, development, and responses to abiotic stress. In this study, we characterized Up-miR-843 and its targets genes in Ulva prolifera responses to nitrogen depravation and heat stress. The data demonstrated that 184 target genes of Up-miR-843 could be successfully validated. N deficiency not heat stress stimulus induced increase in abundance of the Up-miR-843 while exhibited reverse expression of target genes, including cyclin A3 and cyclin L, which were strictly required for cell cycle progression. In addition, U. prolifera with highly expression of Up-miR-843 showed improved biomass, and photosynthesis compared with that under normal growth conditions. Thus, the N deprivation and heat responsive miRNAs might be a possible member mediating the expression of these target genes, which further regulated the growth of U. prolifera.
2020, 39(10): 35-41. doi: 10.1007/s13131-020-1658-1
Abstract:
Ulvophytes are attractive model systems for understanding the evolution of growth, development, and environmental stress responses. They are untapped resources for food, fuel, and high-value compounds. The rapid and abundant growth of Ulva species makes them key contributors to coastal biogeochemical cycles, which can cause significant environmental problems in the form of green tides and biofouling. Until now, the Ulva mutabilis genome is the only Ulva genome to have been sequenced. To obtain further insights into the evolutionary forces driving divergence in Ulva species, we analyzed 3 905 single copy ortholog family from U. mutabilis, Chlamydomonas reinhardtii and Volvox carteri to identify genes under positive selection (GUPS) in U. mutabilis. We detected 63 orthologs in U. mutabilis that were considered to be under positive selection. Functional analyses revealed that several adaptive modifications in photosynthesis, amino acid and protein synthesis, signal transduction and stress-related processes might explain why this alga has evolved the ability to grow very rapidly and cope with the variable coastal ecosystem environments.
2020, 39(10): 42-49. doi: 10.1007/s13131-020-1659-0
Abstract:
Triacylglycerols (triglycerides, TAGs) are the major carbon and energy storage forms in various organisms, and important components of cellular membranes and signaling molecules; they have essential functions in multiple physiological processes and stress regulation. Acyl-CoA: diacylglycerol acyltransferase (DGAT) catalyzes the final and only committed acylation step in the synthesis of TAGs in eukaryotes. The present work identified and isolated a novel gene, UpDGAT1, from the green tide alga Ulva prolifera. The activity of UpDGAT1 was confirmed by heterologous expression in a Saccharomyces cerevisiae TAG-deficient quadruple mutant. Results of thin-layer chromatography and BODIPY staining indicated that UpDGAT1 was able to restore TAG synthesis and lipid body formation in the yeast. Lipid analysis of yeast cells revealed that UpDGAT1 showed broad substrate specificity, accepting saturated as well as mono- and polyunsaturated acyl-CoAs as substrates. High salinity and high temperature stresses increased UpDGAT1 expression and TAG accumulation in U. prolifera. The present study provides clues to the functions of UpDGAT1 in TAG accumulation in, and stress adaptation of, U. prolifera.
2020, 39(10): 50-57. doi: 10.1007/s13131-020-1577-1
Abstract:
Ulva prolifera is a green alga that plays an important role in green tides. Carotenoid biosynthesis is a basic terpenoid metabolism that is very important for maintaining normal life activities in algae. In this study, we first reported the complete sequences of all genes in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, which is the only carotenoid synthesis pathway in U. prolifera. Then, we compared these genes with those of other species. Additionally, by detecting the carotenoid contents and expression levels of key genes participating in carotenoid biosynthesis in U. prolifera under three different light (1 000 lx, 5 000 lx and 12 000 lx) and salinity (12, 24 and 40) regimes, we found that carotenoid synthesis could be influenced by light and salinity, such that low light and high salinity could promote the synthesis of carotenoids. The results showed that the expression levels of genes involved in the MEP and the downstream pathway could affect the biosynthesis of carotenoids at the molecular level. This study contributes to a better understanding of the roles of genes participating in carotenoid biosynthesis in U. prolifera and the environmental regulation of these genes.
2020, 39(10): 58-69. doi: 10.1007/s13131-020-1660-7
Abstract:
Transparent exopolymer particles (TEPs) are ubiquitous throughout the oceans, and their sedimentation is considered an efficient biological carbon sink pathway. To investigate the role of coastal TEPs in sinking carbon from the upper layer, samples were collected in the spring and summer of 2011 in the Changjiang River (Yangtze River) Estuary, a typical coastal water. The concentrations and sinking rates of TEPs were measured, and potential sedimentation flux of TEPs was estimated. TEPs concentrations ranged from 40.00 μg/L to 1 040.00 μg/L (mean=(209.70±240.93) μg/L) in spring and 56.67 μg/L to 1 423.33 μg/L (mean=(433.33±393.02) μg/L) in summer, and they were higher at bloom stations than at non-bloom stations during both cruises. A significant positive correlation between TEPs concentration and chlorophyll a (Chl a) concentration was detected, suggesting that phytoplankton was the primary source of TEPs in this area. TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of (0.28±0.14) m/d in spring and 0.10 m/d to 1.08 m/d with a mean of (0.34±0.31) m/d in summer. The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d) to 29.40 mg/(m2·d) with a mean of (14.66±8.83) mg/(m2·d) in spring and 6.80 mg/(m2·d) to 30.45 mg/(m2·d) with a mean of (15.71±8.73) mg/(m2·d) in summer, which was ~17.81% to 138.27% (mean=65.15%±31.75%) of sedimentation flux of phytoplankton cells in the study area. Due to the increase of TEPs concentrations and their sinking rates, sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises. This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary, especially during bloom events, and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.
2020, 39(10): 70-80. doi: 10.1007/s13131-020-1661-6
Abstract:
Rapid changes on nutrient supply and CO2 concentration that occurred in the northern South China Sea (SCS) during the Early Oligocene, provides an ideal natural laboratory, allowing us to peer into the coccolithophores’ physiology in the geological records. In this study, we established a new nannofossil assemblage index, termed as E* ratio, which is calculated by the relative abundance of eutrophic taxa and meso-oligotrophic taxa (\begin{document}${E^*}=\frac{e}{{e + c}}\times100$\end{document}, where e is eutrophic taxa, and c is meso-oligotrophic taxa). Eutrophic taxa include small Reticulofenestra, Reticulofenestra lockeri group, Reticulofenestra bisecta group and Coccolithus pelagicus group, while meso-oligotrophic taxa include Cyclicargolithus spp. The E* ratio is well correlated with nutrient proxy during the Early Oligocene, while with different covarying patterns under the higher and lower CO2 condition. By comparing the assemblage changes to the published data, we suggest that coccolithophores may change the way they use carbon source and nutrient with the decline of CO2. Furthermore, this implies a possible initiation of the carbon concentrating mechanism.
2020, 39(10): 81-95. doi: 10.1007/s13131-020-1663-4
Abstract:
The Nankai Trough subduction zone is a typical subduction system characterized by subduction of multiple geological units of the Philippine Sea Plate (the Kyushu-Palau Ridge, the Shikoku Basin, the Kinan Seamount Chain, and the Izu-Bonin Arc) beneath the Eurasian Plate in the southwest of Japan. This study presents a geophysical and geochemical analysis of the Nankai Trough subduction zone in order to determine the features and subduction effects of each geological unit. The results show that the Nankai Trough is characterized by low-gravity anomalies (–20 mGal to –40 mGal) and high heat flow (60–200 mW/m2) in the middle part and low heat flow (20–80 mW/m2) in the western and eastern parts. The crust of the subducting plate is 5–20 km thick. The mantle composition of the subducting plate is progressively depleted from west to east. Subduction of aseismic ridges (e.g., the Kyushu-Palau Ridge, the Kinan Seamount Chain, and the Zenisu Ridge) is a common process that leads to a series of subduction effects at the Nankai Trough. Firstly, aseismic ridge or seamount chain subduction may deform the overriding plate, resulting in irregular concave topography along the front edge of the accretionary wedge. Secondly, it may have served as a seismic barrier inhibiting rupture propagation in the 1944 Mw 8.1 and 1946 Mw 8.3 earthquakes. In addition, subduction of the Kyushu-Palau Ridge and hot and young Shikoku Basin lithosphere may induce slab melting, resulting in adakitic magmatism and the provision of ore-forming metals for the formation of porphyry copper and gold deposits in the overriding Japan Arc. Based on comparisons of their geophysical and geochemical characteristics, we suggest that, although the Izu-Bonin Arc has already collided with the Japan Arc, the Kyushu-Palau Ridge, which represents a remnant arc of the Izu-Bonin Arc, is still at the subduction stage characterized by a single-vergence system and a topographic boundary with the Japan Arc.
2020, 39(10): 96-106. doi: 10.1007/s13131-020-1679-9
Abstract:
The Huanghe River (Yellow River) is known by its high suspended sediment concentration (SSC) in its river mouth tidal flat. However, the factors controlling the high SSC over there are not well understood. Therefore, we conducted 7-d hydrodynamic observations (water depth, wave height, and current velocity) and SSC measurements on the tidal flat off the Huanghe River Mouth. The data shows that in most of time, under the calm sea condition, the SSC ranges 0.1–3.5 g/L, and sediment discharge from the river is the main source. However, when hydrodynamics are enhanced in a tidal cycle and large-scale erosion occurs on the seafloor, resuspended sediment becomes the main source, and the SSC in the water column reaches 17.3 g/L. We find the suspended sediment flux is mainly controlled by the tidal current and Stokes drift, while the wave-induced shear stress could also affect the variation of suspended sediment flux. During the observation period, when sea under calm-rippled conditions, the current-induced resuspended sediment concentration (RSC) was greater than the wave-induced RSC. In contrast, in smooth-wavelet sea conditions, the wave-induced RSC was greater than the current-induced RSC, for instance, a single wave event was found to cause 11.8 cm seabed erosion within 6 h. This study reveals different controlling factors for the high SSC near a river-influenced tidal flat, and helps us get a better understanding of a delta's depositional and erosional mechanisms.
2020, 39(10): 107-119. doi: 10.1007/s13131-020-1602-4
Abstract:
As one of the top four commercially important species in China, yellow croaker (Larimichthys polyactis) with two geographic subpopulations, has undergone profound changes during the last several decades. It is widely comprehended that understanding its population dynamics is critically important for sustainable management of this valuable fishery in China. The only two existing population dynamics models assessed the population of yellow croaker using short time-series data, without considering geographical variations. In this study, Bayesian models with and without hierarchical subpopulation structure were developed to explore the spatial heterogeneity of the population dynamics of yellow croaker from 1968 to 2015. Alternative hypotheses were constructed to test potential temporal patterns in yellow croaker’s population dynamics. Substantial variations in population dynamics characteristics among space and time were found through this study. The population growth rate was revealed to increase since the late 1980s, and the catchability increased more than twice from 1981 to 2015. The East China Sea’s subpopulation witnesses faster growth, but suffers from higher fishing pressure than that in the Bohai Sea and Yellow Sea. The global population and two subpopulations all have high risks of overfishing and being overfished according to the MSY-based reference points in recent years. More conservative management strategies with subpopulation considerations are imperative for the fishery management of yellow croaker in China. The methodology developed in this study could also be applied to the stock assessment and fishery management of other species, especially for those species with large spatial heterogeneity data.
2020, 39(10): 120-128. doi: 10.1007/s13131-020-1664-3
Abstract:
To determine if water-sediment regulation has affected macrobenthic community structure in the Huanghe River Estuary, China, macrobenthic samples were collected following regulation events from 2012 to 2016. We identify seven phyla and 138 macrobenthic species from within samples throughout the survey area, over time. Species richness and abundance in 2012 were significantly higher than in 2016. Biomass did not differ significantly during 2012–2016. Dominant species were mostly small polychaetes, with mollusks, arthropods, and echinoderms all being relatively rare. In 2016, dominant species were small polychaetes. MDS reveals macrobenthic communities at all surveyed distances from the estuary to have become the same community structure over time. Shannon-Wiener diversity and Margalef richness indexes trended down over time. CCA reveals the most dominant sediment-dwelling species to prefer lower dissolved oxygen, sulfides, and pH, and sediments with high D50 and low clay content. We speculate that water-sediment regulation has affected seabed communities, particularly Region A in our survey area.
2020, 39(10): 129-139. doi: 10.1007/s13131-020-1580-6
Abstract:
As an economically important marine fish, the large yellow croaker Larimichthys crocea suffered from marine white spot disease caused by the ectoparasite Cryptocaryon irritans in recent years. This disease not only could result in physiological damage, but also lead to secondary bacterial invasion. Reports indicated some AMPs (antimicrobial peptides) were of antiparasitic activity to C. irritans. Hepcidin-like (Lc-HepL) was one of the significant differential expression genes excavated from the transcriptome following a challenge with C. irritans. In this study, we characterized this AMP’s bioactivity based on the levels of mRNA and protein. After challenged by C. irritans, qRT-PCR showed Lc-HepL was significantly upregulated in six tissues, including gill, muscle, liver, head kidney and spleen during theront infection, trophont falling off, and secondary bacterial invasion stages, which implicated a role Lc-HepL played in the immune defense against C. irritans and secondary bacterial infection. Recombinant Lc-HepL (rLc-HepL) was induced and purified successfully. rLc-HepL exhibited antibacterial activity to certain bacteria in a dose- and time-dependent manners. Anti-C. irritans activity was explored for the first time and found it could cause the theronts membrane rupture and contents leakage. These results provided the first evidence that Lc-HepL had strong antiparasitic activity against marine fish ectoparasites C. irritans theronts. Together, data indicated that Lc-HepL might be an important component in the innate immune system against C. irritans and has the potential to be employed in future drug development.
2020, 39(10): 140-146. doi: 10.1007/s13131-020-1635-8
Abstract:
Rapid and accurate identification of Vibrio species has been problematic because phenotypic characteristics are variable within species and biochemical identification requires two or more days to complete. Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) has become a powerful tool for rapidly distinguishing between related bacterial species. However, its accuracy depends on the number of strains in a database. In the current study, we extend and apply the Vibrio database based on MALDI-TOF MS. A total of 74 strains of Vibrio representing 28 species were identified and included in new database. A phylogenetic tree based on rpoB sequence and dendrograms were constructed. We analyzed 30 clinical Vibrio of three species to evaluate the new database and carried out PCA dendrogram analyses for differences of strains. We created a new database that offered fast and accurate Vibrio identification. MSP and PCA dendrogram analyses provided technical support to track sources and incidences of Vibrio infection. In addition, the discovery of characteristic and differential peaks is useful for the future identification of Vibrio. This represents a powerful tool for the rapid and accurate classification and identification of Vibrio and closely related species.
2020, 39(10): 147-154. doi: 10.1007/s13131-020-1630-0
Abstract:
Cadmium (Cd) is a common heavy metal pollutant in the aquatic environment, generally toxic to plant growth and leading to growth inhibition and biomass reduction. To study the oxidation resistance in Sargassum fusiforme seedlings in response to inorganic Cd stress, we cultured the seedlings under two different Cd levels: natural seawater and high Cd stress. High Cd stress significantly inhibited the seedlings growth, and darkened the thalli color. Additionally, the pigment contents, growth rate, peroxidase (POD) activity, dehydroascorbic acid (DHA) content, and glutathione reductase (GR) activity in S. fusiforme were significantly reduced by high Cd treatment. Contrarily, the Cd accumulation, Cd2+ absorption rate, dark respiration/net photosynthetic rate (Rd/Pn), ascorbic acid (Vc) content, soluble protein (SP) content, glutathione (GSH), and the activities of superoxide dismutase (SOD) and catalase (CAT) of S. fusiforme under Cd treatment significantly increased compared to the control group. The decrease of malondialdehyde (MDA) was not significant. Although S. fusiforme seedlings increased the antioxidant activities of POD, SOD, Vc, and the AsA-GSH cycle to disseminate H2O2 and maintain healthy metabolism, high Cd stress caused Cd accumulation in the stem and leaves of S. fusiforme seedlings. The excessive Cd significantly restricted photosynthesis and reduced photosynthetic pigments in the seedlings, resulting in growth inhibition and deep morphological color, especially of the stems. High levels of Cd in seawater had toxic effects on commercial S. fusiforme seedlings, and risked this edible seaweed for human food.
2020, 39(10): 155-161. doi: 10.1007/s13131-020-1662-5
Abstract:
As the largest genus of Halymeniaceae, Grateloupia has been widely reported. Here, we observed the life history and early development of Grateloupia constricata Li et Ding and investigated the effects of temperature, irradiance, and photoperiod on the discoid crust and sporeling development of G. constricata under laboratory conditions. We observed that the type of carpospore development was “mediate discal type”. The life history included homotypic gametophyte (haploid), carposporophyte (diploid), and tetrasporophyte (diploid), with typical isomorphic alternation of generations. The results of double factorial analysis showed that both single factorial effects and interaction among temperature, photoperiod, and irradiance were obviously significant on the discoid crust and sporeling development. Furthermore, we found that the optimum combination of condition for the early growth and development of G. constricata was temperature 20°C, irradiance 80 μmol photons/(m2·s) and photoperiod 16L:8D. This study provides the theoretical basis and technical support for the conservation of the Grateloupia germplasm, artificial breeding, large-scale cultivation and sustainable development.
2020, 39(10): 162-170. doi: 10.1007/s13131-020-1586-0
Abstract:
Due to extensive morphological plasticity, the taxonomy of Cladophora species remains unclear. As one of the widely distributed species, C. gracilis was reported to hold many varieties, which make it difficult to identify the species. This study explored the morphology diversity of nine C. gracilis samples collected along the coast of western Yellow Sea. Some samples showed extremely varied characteristics, by which one cannot classify them correctly. Hence, 18S rDNA and nuclear ribosomal DNA internal transcribed spacer regions (ITS) sequences were employed to delimit species. For 18S rDNA, sequence similarity ranged from 99.6% to 100%. For ITS region, the similarity ranged from 98.7% to 100%. Molecular data strongly suggested that the morphologically heterogeneous samples were actually the same species. Characteristics comparison of the samples revealed that the taxonomy criteria including branching pattern and density, thallus color, height and texture varied widely, influenced by environmental conditions and age of alga. Besides, cell dimensions, as the relatively stable criterion, also exhibited intraspecific variance. Successful application of 18S rDNA and ITS sequences indicated that molecular method can be a powerful assistant as DNA barcodes to traditional morphology taxonomy.