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Diatoms are important phytoplankton and contribute greatly to the primary productivity of marine ecosystems. Despite the ecological significance of diatoms and the importance of programmed cell death (PCD) in the fluctuation of diatom populations, little is known about the molecular mechanisms of PCD triggered by different nutrient stresses. Here we describe the physiological, morphological, biochemical, and molecular changes in response to low levels of nutrients in the ubiquitous diatom Skeletonema marinoi The levels of gene expression involved in oxidation resistance and PCD strongly increased upon nitrogen (N) or phosphorus (P) starvation. The enzymatic activity of caspase 3-like protein also increased. Differences in mRNA levels and protein activities were observed between the low-N and low-P treatments, suggesting that PCD could have a differential response to different nutrient stresses. When cultures were replete with N or P, the growth inhibition stopped. Meanwhile, the enzymatic activity of caspase 3-like protein and the number of cells with damaged membranes decreased. These results suggest that PCD is an important cell fate decision mechanism in the marine diatom S. marinoi Our results provide important insight into how diatoms adjust phenotypic and genotypic features of their cell-regulated death programs when stressed by nutrient limitations. Overall, this study could allow us to better understand the molecular mechanism behind the formation and termination of diatom blooms in the marine environment. IMPORTANCE Our study showed how the ubiquitous diatom S. marinoi responded to different nutrient limitations with PCD in terms of physiological, morphological, biochemical, and molecular characteristics. Some PCD-related genes (PDCD4, GOX, and HSP90) induced by N deficiency were relatively upregulated compared to those induced by P deficiency. In contrast, the expression of the TSG101 gene in S. marinoi showed a clear and constant increase during P limitation compared to N limitation. These findings suggest that PCD is a complex mechanism involving several different proteins. The systematic mRNA level investigations provide new insight into understanding the oxidative stress- and cell death-related functional genes of diatoms involved in the response to nutrient fluctuations (N or P stress) in the marine environment., (Copyright © 2020 American Society for Microbiology.)

Urea has been shown to contribute more than half of total nitrogen (N) required by phytoplankton in some estuaries and coastal waters and to provide a substantial portion of the N demand for many harmful algal blooms (HABs) of dinoflagellates. In this study, we investigated the physiological and transcriptional responses in Prorocentrum donghaiense to changes in nitrate and urea availability. We found that this species could efficiently utilize urea as sole N source and achieve comparable growth rate and photosynthesis capability as it did under nitrate. These physiological parameters were markedly lower in cultures grown under nitrate- or urea-limited conditions. P. donghaiense N content was similarly low under nitrate- or urea-limited culture condition, but was markedly higher under urea-replete condition than under nitrate-replete condition. Carbon (C) content was consistently elevated under N-limited condition. Consequently, the C:N ratio was as high as 21:1 under nitrate- or urea-limitation, but 7:1 under urea-replete condition and 9:1 to 10:1 under nitrate-replete condition. Using quantitative reverse transcription PCR, we investigated the expression pattern for four genes involved in N transport and assimilation. The results indicated that genes encoding nitrate transport, urea hydrolysis, and nickel transporter gene were sensitive to changes in general N nutrient availability whereas the urea transporter gene responded much more strongly to changes in urea concentration. Taken together, our study shows the high bioavailability of urea, its impact on C:N stoichiometry, and the sensitivity of urea transporter gene expression to urea availability.

After damming of the Yangtze River, in order to explore the impacts of the Three-Gorge Dam (TGD) on the aquatic ecosystem, phytoplankton composition, abundance and biomass spatial distribution were studied in the Three-Gorge Reservoir (TGR), and the closest upstream anabranch Xiangxi River, which is 38 km away from the Three-Gorge Dam (TGD) during August (rainy season) 2004 and April (dry season) 2005. In surveys, 6 transects (2 downstream and 4 cross-stream) and 25 stations have been investigated and 314 samples were collected from the surface to the river bed with water samplers. In TGR, 63 taxa and 60 taxa were identified in the rainy and dry seasons, respectively. In the Xiangxi River, 39 taxa were observed in the rainy and dry seasons. Algal blooms occurred in the Xiangxi River and at the influx region of the Yangtze and Xiangxi in both seasons, but had not occurred prior to damming. In the rainy season, the dominant species was Chroomonas acuta with 1.84x10(7) cells l-1, and in the dry season the dominant species were Asterionella formosa and Cryptomonas ovata with 1.34x10(7) cells l-1 and 1.79x10(6) cells.l-1, respectively. In the main channel of TGR, there were no significant correlations between phytoplankton abundance and the concentrations of the main soluble nutrients. In the Xiangxi River, significant negative correlations were observed between phytoplankton abundance and nitrate (Spearman, p<0.01, n=21), phosphate (Spearman, p<0.05, n=21) and silicate (Spearman, p<0.01, n=21) in the rainy season, and similar correlations were also observed with nitrate (Spearman, p<0.05, n=28) and silicate (Spearman, p<0.01, n=28), but not with phosphate in the dry season. Since the damming of the Yangtze River, eutrophication in the anabranch within the backwater has occurred and become severe, and the frequency of algal bloom within TGR and anabranches is expected to increase.

Over the past decades, jellyfish occurred increasingly and abundantly in coastal areas worldwide. Usually, biomass of jellyfish, especially when they bloom, can be determined by visual counting. However, tiny individuals of jellyfish (e.g., planulae, polyps, and ephyrae) are difficult to detect in the field. In this study, species-specific quantitative real-time PCR assays (qPCR) (SYBR Green I) targeting the mitochondrial 16S rDNA (mt-16S rDNA) of jellyfish were developed and were used to estimate the distribution and seasonal fluctuations of four jellyfish species (Nemopilema nomurai, Cyanea nozakii, Rhopilema esculentum, and Aurelia coerulea) in Jiaozhou Bay (JZB), China in 2013. The mt-16S rDNA of A. coerulea and N. nomurai was detected in most of the survey months and it peaked in July (1.03×104 copies/L) and September (1.08×106 copies/L), respectively. The mt-16S rDNA of C. nozakii occurred from August to October only with monthly mean values of 7.18–46.17 copies/L and was mainly located from the middle part to the outer part of the bay. The mt-16S rDNA of R. esculentum was the least abundant among the four species and was detected in only one sample (B2 station in March), with a value of 88.49 copies/L. The Spearman correlation test revealed that phytoplankton biomass was significantly and positively correlated with the mt-16S rDNA abundance of A. coerulea (R=0.37, P<0.01) and negatively with the mt-16S rDNA of N nomurai (R=-0.36, P<0.01). The qPCR assay will enable the identification and quantification of jellyfish species in their whole life history and can be used as an approach in combination of the traditional jellyfish survey. [ABSTRACT FROM AUTHOR]

Diatoms are widely distributed in many temperate areas and some species frequently form extensive blooms in spring. Hence, monitoring the variations of specific genera or species of diatoms is necessary for studying phytoplankton population dynamics in marine ecosystems. To test whether pigment ratios can be used to identify diatoms at a below-class taxonomic level, we analyzed 14 species/strains of diatoms isolated from Chinese seas using high performance liquid chromatography (HPLC). We normalized all pigment concentrations to total chlorophyll a to calculate the ratios of pigment to chlorophyll a, and calculated the ratios between accessory pigments (or pigment sums). Cluster analysis indicated that these diatoms could be classified into four clusters in terms of three accessory pigment ratios: chlorophyll c: chlorophyll c, fucoxanthin:total chlorophyll c and diadinoxanthin:diatoxanthin. The classification results matched well with those of biological taxonomy. To test the stability of the classification, pigment data from one species, cultured under different light intensities, and five new species/strains were calculated and used for discriminant analysis. The results show that the classification of diatom species using pigment ratio suites was stable for the variations of pigment ratios of species cultured in different light intensities. The introduction of new species, however, may confuse the classification within the current scheme. Classification of marine diatoms using pigment ratio suites is potentially valuable for the fine chemotaxonomy of phytoplankton at taxonomic levels below class and would advance studies on phytoplankton population dynamics and marine ecology. [ABSTRACT FROM AUTHOR]

Abstract: We conducted studies of phytoplankton and hydrological variables in a semi-enclosed bay in northern China to understand the spatial–temporal variability and relationship between these variables. Samples were collected during seven cruises in Jiaozhou Bay from November 2003 to October 2004, and were analyzed for temperature, nutrients and phytoplankton pigments. Pigments from eight possible phytoplankton classes (Diatoms, Dinoflagellates, Chlorophyceae, Prasinophyceae, Chrysophyceae, Haptophyceae, Cryptophyceae and Caynophyceae) were detected in surface water by high performance liquid chromatography (HPLC). Phytoplankton pigment and nutrient concentrations in Jiaozhou Bay were spatially and temporally variable, and most of them were highest in the northern and eastern parts of the sampling regions in spring (May) and summer (August), close to areas of shellfish culturing, river estuaries, dense population and high industrialization, reflecting human activities. Chlorophyll a was recorded in all samples, with an annual mean concentration of 1.892μgL−1, and fucoxanthin was the most abundant accessory pigment, with a mean concentration of 0.791μgL−1. The highest concentrations of chlorophyll a (15.299μgL−1) and fucoxanthin (9.417μgL−1) were observed in May 2004 at the station close to the Qingdao Xiaogang Ferry, indicating a spring bloom of Diatoms in this area. Although chlorophyll a and other biomarker pigments showed significant correlations, none of them showed strong correlations with temperature and nutrients, suggesting an apparent de-coupling between the pigments and these hydrological variables. The nutrient composition and phytoplankton community composition of Jiaozhou Bay have changed significantly in the past several decades, reflecting the increasing nutrient concentrations and decline of phytoplankton cell abundance. The unchanged total chlorophyll a levels indicated that smaller species have filled the niche vacated by the larger species in Jiaozhou Bay, as revealed by our biomarker pigment analysis. [Copyright &y& Elsevier]

Nuclease protection assay (NPA) probes were designed to target the rRNA of Chaetoceros curvisetus and Skeletonema costatum, and quantitative sandwich hybridization integrated with nuclease protection assay (NPA-SH) was developed to detect C. curvisetus and S. costatum in culture and field samples in Jiaozhou Bay, China. The specificity and validity of the NPA-SH technique were tested with cultured pure strains, mixed strains and field samples, and by comparison with that of microscopy observation. The linear detection range for C. curvisetus was 4.2 × 104 to 1.2 × 106 cells with a detection limit of 42 cells ml−1. The linear range for S. costatum was 6.0 × 104 to 1.0 × 106 cells with a detection limit of 60 cells ml−1. The NPA-SH in this study provides a convenient tool for rapid assessment of HAB species in marine environments. [ABSTRACT FROM AUTHOR]

Abstract: Surface sediments were collected from the inner shelf of the highly dynamic East China Sea (ECS) in December 2009 and November 2010. In between the two cruises, a big flood event occurred in July, 2010. Elemental, stable C, N isotope, radiocarbon isotope (∆14C), black carbon (BC) analysis, and chemical biomarkers were utilized to study the effect of the sources, short-term events and physical processes on the composition, abundance, and age of the surface sedimentary OC in this dynamic system. Bulk N/C ratio of 0.10 to 0.14 and δ13C of −23.1‰ to −20.9‰ in these samples indicated a mixture source of terrestrial, deltaic and marine derived OC during both cruises. The TOC was 1,980 to 5,040yr old based on ∆14C, and BC extracted from two 2009 sediment samples was older: 5,480 and 5,920yr old. While the Changjiang River was a main source of the terrestrial derived OC, refractory BC and reworked marine organic matter seemed to comprise the older, less reactive carbon pool in the surface sediments of the ECS. Monte Carlo simulations indicated that more than 50% of the TOC was derived from the marine end-member, followed by the deltaic OC. The chlorophyll a of the 2010 sediment samples (11.06±10.15nmolg−1 OC, n=7) was significantly lower than that of the 2009 samples (34.58±20.29nmolg−1 OC, n=7). However, zeaxanthin, a biomarker for cyanobacteria, had significantly higher concentration in the 2010 sediment samples (9.26±3.48nmolg−1 OC, n=7) than that of the 2009 samples (5.50±4.62nmolg−1 OC, n=7). The lack of benthic–pelagic coupling of pigment concentrations in surface sediments after the flood of 2010 was likely due to lateral transport of surface sediments to and from this region. While there were no significant linkages between in situ shelf-derived phytoplankton sources of OC and surface sediment pigment concentrations in 2010, other algal inputs from local deltaic lakes may have contributed to the compositional changes in concentration of sediment carotenoids. The flood of summer 2010 likely played a critical role in the observed shift of the locations for the highest terrestrial biomarker concentrations in sediments. Little evidence remained from the 2010 flood event, which suggested that winter wind/wave energy and hydrodynamic sorting had a substantial effect on sediment OC redistribution. [Copyright &y& Elsevier]

Summary: The impacts of anthropogenic activities on nutrient transport in the Huanghe/estuary were investigated using biogeochemical observations carried out during 2008–2009 to examine how nutrient change during a water–sediment regulation event. Nutrient concentrations in the Huanghe are characterized by relative high concentrations of nitrate and dissolved silicate but low phosphate and DOP levels and shows seasonal variations with very high DIN/PO43- ratios. The water–sediment regulation event resulted in high monthly average water discharge and sediment load occurring at least 2months prior to before the event. The nutrient transport fluxes increased 8–30 times during that period. The regulation event has shifted the seasonal patterns of water and nutrient transport, which cannot only increase nutrient inputs to the coastal ecosystem but can also result in nutrient imbalance, affecting phytoplankton production and composition. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports on the spatial distribution patterns and investigates the controlling mechanisms of phytoplankton biomarkers (brassicasterol for diatoms, alkenones for haptophytes, dinosterol for dinoflagellates) and terrestrial biomarkers (odd C number long-chain (C27 +C29 +C31) n-alkanes) in surface sediments from the southern Yellow Sea (SYS). The contents of the phytoplankton biomarkers in the SYS surface sediments reveals a clear spatial pattern, with low values near the coasts and increased values seaward, caused by higher phytoplankton primary productivity and low sedimentation rates in the basin. The contents of terrestrial biomarkers show high values in the northern part of the study areas off the Shandong Peninsula and Jiangsu coast, caused by inputs of materials from the modern Huanghe River and the old Huanghe delta, respectively. The results also indicate that biomarker ratios offer the best approach for reconstructing marginal sea C cycles, as these proxies can be used to estimate the contributions of both terrestrial and marine organic matter and to reconstruct paleoproductivity and paleoecological changes in the SYS. [Copyright &y& Elsevier]