HPLC Pigment Analysis Research Articles

Effect of Mytilus coruscus selective filtration on phytoplankton assemblages

The feeding selectivity of bivalves can play an important role in shaping the structure of phytoplankton communities of natural waters. This could be particularly true in waters with intensive bivalves farming, like Sungo Bay, Northern China. Understanding the role of bivalve feeding behavior is important for assessing how the dense cultivation of bivalves may affect phytoplankton community composition and food web structure in farm areas. In this study, we investigated the feeding selectivity of blue mussel Mytilus coruscus on natural phytoplankton assemblages in Sungo Bay using both optical microscopy and HPLC-pigment analysis. Results showed that cryptophytes dominated the phytoplankton community and made up 66.1% of the total phytoplankton abundance. A comparison of phytoplankton composition between natural and filtered seawater showed that M. coruscus preferred cryptophytes and dinoflagellates than Chaetoceros spp. and Skeletonema spp. Cryptophytes were not detected in gut contents by microscopic observation, while their marker pigment alloxanthin was present, suggesting they were also consumed by M. coruscus and can be readily digested. This highlights the shortcomings of microscopic methods and the significance of HPLC-pigment analysis in obtaining a comprehensive understanding of feeding selectivity of bivalves. The proportions of Chaetoceros spp. and Skeletonema spp. in gut contents were significantly lower than their proportions in the seawater, and contrastingly, the proportions of Cocconeis spp. and Pinnularia spp. showed opposite patterns. The marker pigments prasinoxanthin and zeaxanthin were detected in the gut of M. coruscus indicating that picophytoplankton (e.g., prasinophytes and Synechococcus) are also food sources for this bivalve. This information furthers our understanding of bivalve aquaculture and environment interactions.

Extreme harmful algal blooms, climate change, and potential risk of eutrophication in Patagonian fjords: Insights from an exceptional Heterosigma akashiwo fish-killing event

The Patagonian fjords have experienced intense harmful algal blooms (HABs) in the last decade, affecting important aquaculture areas in southern Chile. Climatic anomalies have recently triggered ‘super blooms’ of opportunistic toxic microalgal genera, especially due to persistent thermal stratification which likely provides an optimal niche for HABs development in fjord systems. In March-April 2021, an intense and widespread bloom of the raphidophyte Heterosigma akashiwo caused high salmon mortalities (>6,000 t) in the Comau fjord, Los Lagos Region. A climate variability analysis showed the effects of the positive phase of the Southern Annular Mode (SAM > 1.2 hPa) overcame those of La Niña (Niño3.4 = -0.9 °C) leading to an intense drought on the northern part of Patagonia with record low rainfall (the 2nd driest summer in the last 70 years) and increased water temperature. A regional satellite analysis revealed an extreme and persistent shallow Mixed Layer Depth (MLD) during summer periods since 2019 within the inland seas. In situ vertical fine-resolution measurements during the bloom event showed high cell abundances in the first 3 m of the water column (max. ∼ 70,000 cells mL−1), associated with warmer water temperature (∼15.5 – 17.5 °C), low salinity (∼25–30 psu), moderate to high dissolved oxygen (5 – 8.5 mg/L) and extremely high fluorescence signals in dense superficial cell aggregations (max. 74.9 µg/L). A 18S rRNA metabarcoding analysis formally confirmed the presence of H. akashiwo and its almost monospecific bloom development at the water surface. HPLC pigment analysis showed the carotenoid fucoxanthin in high proportion (48.8 %) compared to other photosynthetic pigments, becoming a potential pigment biomarker for early satellite H. akashiwo detection. Cell growth and cytotoxic in vitro experiments revealed high phenotypic plasticity of Chilean H. akashiwo against sudden changes in salinity. An RTgill-W1 gill cell assay revealed high cytotoxic activity (viability down to ∼ 50 – 30 % of controls) only at high cell abundances (>40,000H. akashiwo cells mL−1), which was in accordance with histological examination of moribund salmon that showed gill damage and circulatory disorders mainly due to long-term exposure to hypoxic conditions and not to potent cytotoxic effects. The Party-MOSA particles dispersion model revealed a high retention of water masses within the Comau fjord during the H. akashiwo outbreak, a scenario that may have boosted fish kills due to enhanced cells patchiness, ichthyotoxins persistence and hypoxic conditions. A historical dissolved inorganic nutrient data analysis showed that inner Patagonian fjords maintain low N and P concentrations including those environments considered of high eutrophication risk. Low N:P (<16:1) ratios measured at Comau fjord during the 2021 suggests that toxic flagellates growth could be favored over diatoms; however, low N:Si (<1:1 – N deficiency) evidences a clear need for better understanding of the role of mixotrophy in the persistence of the 2021H. akashiwo bloom for several weeks. These results highlight the fact that HABs responses against climate drivers and potential eutrophication are not universal and need to be assessed yearly and locally, particularly because extreme droughts and intensive aquaculture in northern Patagonia are expected to continue throughout the 21st century.

Characterization of Seasonal Phytoplankton Pigments and Functional Types around Offshore Island in the East/Japan Sea, Based on HPLC Pigment Analysis

In this study, we investigated the seasonal phytoplankton community and phytoplankton functional types (PFTs) in the vicinity of Dokdo Island, located in the East/Japan Sea, in 2019. With strong seasonal winds, the water column was well mixed in winter. In spring and autumn, the upper mixed layer depth (MLD) was relatively deep, and the Subsurface Chlorophyll Maximum (SCM) formed in the middle layer. Small phytoplankton were dominant in the summer, which is a time of high water temperatures and strong stratification associated with a shallower MLD. Based on CHEMTAX analysis, in spring, the high phytoplankton biomass was mainly derived from cyanobacteria, diatoms, and dinoflagellates. In summer, &gt;73.2% of the surface biomass was comprised of cyanobacteria. In autumn, pelagophytes accounted for the highest proportion of the biomass. The fraction of microphytoplankton (fmicro) was highest in winter and spring, whereas the fraction of nanophytoplankton (fnano) was highest in autumn and summer. A high fraction of picophytoplankton (fpico) was evident in the surface layers in summer. Values for both the photoprotection index (PI) and the ratio of photoprotective carotenoids (PPC) to photosynthetic carotenoids (PSC) indicate that this study area had high primary productivity in 2019. In order to predict long-term changes in marine food webs due to climate change, it is important to evaluate the size and composition of phytoplankton.

Size-Fractionated Microbiome Structure in Subarctic Rivers and a Coastal Plume Across DOC and Salinity Gradients.

Little is known about the microbial diversity of rivers that flow across the changing subarctic landscape. Using amplicon sequencing (rRNA and rRNA genes) combined with HPLC pigment analysis and physicochemical measurements, we investigated the diversity of two size fractions of planktonic Bacteria, Archaea and microbial eukaryotes along environmental gradients in the Great Whale River (GWR), Canada. This large subarctic river drains an extensive watershed that includes areas of thawing permafrost, and discharges into southeastern Hudson Bay as an extensive plume that gradually mixes with the coastal marine waters. The microbial communities differed by size-fraction (separated with a 3-μm filter), and clustered into three distinct environmental groups: (1) the GWR sites throughout a 150-km sampling transect; (2) the GWR plume in Hudson Bay; and (3) small rivers that flow through degraded permafrost landscapes. There was a downstream increase in taxonomic richness along the GWR, suggesting that sub-catchment inputs influence microbial community structure in the absence of sharp environmental gradients. Microbial community structure shifted across the salinity gradient within the plume, with changes in taxonomic composition and diversity. Rivers flowing through degraded permafrost had distinct physicochemical and microbiome characteristics, with allochthonous dissolved organic carbon explaining part of the variation in community structure. Finally, our analyses of the core microbiome indicated that while a substantial part of all communities consisted of generalists, most taxa had a more limited environmental range and may therefore be sensitive to ongoing change.

Kleptoplast distribution, photosynthetic efficiency and sequestration mechanisms in intertidal benthic foraminifera

Foraminifera are ubiquitously distributed in marine habitats, playing a major role in marine sediment carbon sequestration and the nitrogen cycle. They exhibit a wide diversity of feeding and behavioural strategies (heterotrophy, autotrophy and mixotrophy), including species with the ability of sequestering intact functional chloroplasts from their microalgal food source (kleptoplastidy), resulting in a mixotrophic lifestyle. The mechanisms by which kleptoplasts are integrated and kept functional inside foraminiferal cytosol are poorly known. In our study, we investigated relationships between feeding strategies, kleptoplast spatial distribution and photosynthetic functionality in two shallow-water benthic foraminifera (Haynesina germanica and Elphidium williamsoni), both species feeding on benthic diatoms. We used a combination of observations of foraminiferal feeding behaviour, test morphology, cytological TEM-based observations and HPLC pigment analysis, with non-destructive, single-cell level imaging of kleptoplast spatial distribution and PSII quantum efficiency. The two species showed different feeding strategies, with H. germanica removing diatom content at the foraminifer’s apertural region and E. williamsoni on the dorsal site. All E. williamsoni parameters showed that this species has higher autotrophic capacity albeit both feeding on benthic diatoms. This might represent two different stages in the evolutionary process of establishing a permanent symbiotic relationship, or may reflect different trophic strategies.

Monitoring of saxitoxin production in lakes in Denmark by molecular, chromatographic and microscopic approaches

Diversity of phytoplankton in three eutrophic and two mesotrophic lakes in Denmark was determined by microscopic and HPLC pigment analyses to identify and quantify potential saxitoxin (STX) producing cyanobacteria. Potential dominant STX-producers were identified to the filamentous genera Dolichospermum, Cuspidothrix, Phormidium and Planktolyngbya. Presence of STX production was documented by extraction of five intracellular STXs that included (in declining concentration in the cyanobacteria) dc-neo-STX, neo-STX, dc-STX, STX and GTX. Total concentrations of the five STXs varied from 9 to 142 fg per potential STX producer, corresponding to 87 to 985 ng L−1 in the lakes. For molecular detection of the STX-producers, a quantitative PCR method was developed by design of a new robust primer set with broad coverage to target the sxtA gene that is common to all STX-producing cyanobacteria. After validation, copy numbers of the sxtA gene were determined to vary from about 104 (mesotrophic lakes) to 108 per mL (the most eutrophic lake). A moderate but significant correlation was observed between abundance of the sxtA copies and concentrations of the five intracellular STXs. The qPCR assay was found to be a rapid and robust procedure for quantification of STX producers. Saxitoxin and its analogs appeared not to cause health concerns in the lakes, but commercial fishing for pike perch in the most eutrophic lake should be monitored to test for food web accumulation of STXs.

Mesozooplankton Selective Feeding on Phytoplankton in a Semi-Enclosed Bay as Revealed by HPLC Pigment Analysis

Mesozooplankton have been known to be important consumers of phytoplankton, and the community plays an important role in removing the primary production in the marine ecosystem. In the present study, mesozooplankton grazing on phytoplankton were studied in situ at two sampling stations (TM4 and TM8) in Tolo Harbour. HPLC analysis showed that diatoms were the dominant phytoplankton in the two stations throughout the year, and contributed on average to over 40% of total phytoplankton biomass. Dinoflagellates were the second most abundant group of phytoplankton in the two monitoring stations, while the contribution of haptophytes, green algae, cyanobacteria, and cryptophytes was negligible. Feeding experiments, combined with HPLC pigment analysis, were conducted to measure mesozooplankton selective feeding on phytoplankton. The results demonstrated that mesozooplankton displayed a clear feeding selectivity for phytoplankton in Tolo Harbour. Firstly, mesozooplankton showed strong preference for the phytoplankton with the size of 20–200 μm, which suggested that the grazing selectivity and grazing rates of mesozooplankton were affected by the size of the food particles. On the other hand, mesozooplankton assemblages in Tolo Harbour displayed significant feeding selectivity for diatoms, dinoflagellates, and cryptophytes over other types of phytoplankton. The three algae groups are all the major phototrophic components in marine planktonic communities, and they often cause red tides in the marine environment. These results, taken together, suggested that mesozooplankton should play an important role in the regulation of red tides.

Effects of iron and humic acid on competition between Microcystis aeruginosa and Scenedesmus obliquus revealed by HPLC analysis of pigments

Iron is a vital micronutrient for growth of bloom-forming Microcystis aeruginosa and competition with other algae, and its availability is affected by humic acid. The effect of iron and humic acid on growth and competition between M. aeruginosa and Scenedesmus obliquus was assessed. The results showed the growth of M. aeruginosa and S. obliquus in mono-cultures was inhibited by humic acid at low iron concentrations (0.01 mg/L); the maximum inhibition ratios were 67.84% and 38.31%, respectively. The inhibition of humic acid on the two species was significantly alleviated when iron concentrations were 1.00 mg/L, with the maximum inhibition rate reduced to 5.82% for M. aeruginosa and to 23.06% for S. obliquus. S. obliquus was the dominant species in mixed cultures, and the mutual inhibition between M. aeruginosa and S. obliquus at low iron concentration was greater than that at high iron concentration. The inhibition of S. obliquus on M. aeruginosa was reduced at low iron concentrations; it increased at high iron concentrations, as concentrations of humic acid rose.

Synthesis, Regulation and Degradation of Carotenoids Under Low Level UV-B Radiation in the Filamentous Cyanobacterium Chlorogloeopsis fritschii PCC 6912.

Carotenoids in cyanobacteria play an important role in protecting against and in repairing damage against low level UV-B radiation. Here we use transcriptomics and metabolomic HPLC pigment analysis to compare carotenoid pathway regulation in the filamentous cyanobacterium Chlorogloeopsis fritschii PCC 6912 exposed to white light and to white light supplemented with low level UV-B. Under UV-B changes in carotenoid transcription regulation were found associated with carotenogenesis (carotenoid synthesis), photoprotection and carotenoid cleavage. Transcriptional regulation was reflected in corresponding pigment signatures. All carotenogenesis pathway genes from geranylgeranyl-diphosphate to lycopene were upregulated. There were significant increases in expression of gene homologs (crtW, crtR, cruF, and cruG) associated with routes to ketolation to produce significant increases in echinenone and canthaxanthin concentrations. There were gene homologs for four β-carotene-ketolases (crtO and crtW) present but only one crtW was upregulated. Putative genes encoding enzymes (CruF, CrtR, and CruG) for the conversion of γ-carotene to myxol 2′-methylpentoside were upregulated. The hydroxylation pathway to nostaxanthin via zeaxanthin and caloxanthin (gene homologs for CrtR and CrtG) were not upregulated, reflected in the unchanged corresponding pigment concentrations in zeaxanthin, caloxanthin and nostaxanthin, Transcripts for the non-photochemical quenching related Orange-Carotenoid-Protein (OCP) and associated Fluoresence-Recovery-Protein (FRP) associated with photoprotection were upregulated, and one carotenoid binding Helical-Carotenoid-Protein (HCP) gene homolog was downregulated. Multiple copies of genes encoding putative apocarotenoid related carotenoid oxygenases responsible for carotenoid cleavage were identified, including an upregulated apo-β-carotenal-oxygenase gene homologous to a retinal producing enzyme. Our study provides holistic insight into the photoregulatory processes that modulate the synthesis, photoprotection and cleavage of carotenoids in cyanobacterial cells exposed to low level UV-B. This is important to understanding how regulation of metabolism responds to a changing environment and how metabolism can be modulated for biotechnological purposes.

HPLC separation of cyanobacterial and algal photosynthetic pigments

Photosynthetic pigments analysis has become a standard tool in ecological and physiological studies of photosynthetic organisms. With numerous methods previously published, there is no one ideal protocol that could satisfy all the research needs. Therefore, regarding the purpose of HPLC pigment analyses, a suitable method should be chosen. In this study, two C18 columns (i.e., LiChrospher 100 RP18e and Spherisorb ODS2) and three sets of eluents (based on acetone, acetonitrile, methanol, and water) were used to develop three separation protocols. They were then examined with respect to their resolution and sensitivity, by analyzing pigment extracts obtained from 10 cyanobacterial and algal cultures and two types of environmental samples, i.e. phytoplankton and microphytobenthos. All the protocols provided highly repeatable results and allowed for the separation of all taxonomically most relevant chlorophylls and carotenoids. They had similar resolution and sensitivity. The Syst1 method was the shortest, while Syst2 had better resolution of pigments in the middle part of the protocol when most of the diagnostic pigments are separated (i.e., alloxanthin, diatoxanthin, lutein, chlorophyll b). Syst3, on the other hand, enabled distinguishing the highest number of pigments, including their derivatives and degradation products. The results showed that all protocols may be used for routine analysis of cyanobacterial and algal pigments in various sample types.

Distribution of epipelic algae and related environmental nutrients in Taihu Lake, revealed by HPLC analysis

Epipelic algal biomass and composition (determined by HPLC pigment analysis) and related environmental nutrients were investigated in a phytoplankton-dominated area (Meiliang Bay), a macrophyte-dominated area (East Taihu Lake) and a transition zones (Gonghu Bay) in a shallow eutrophic freshwater lake (Taihu Lake, eastern China). Surface sediment samples were collected at 11 sampling sites in April and August 2016. Average epipelic algal biomass for Meiliang Bay, Gonghu Bay and East Taihu Lake was 6.5, 4.9 and 4.6μg chlorophyll (Chl)-ag–1 sediment respectively in April, and 3.8, 7.4 and 2.7μg Chl-ag–1 sediment respectively in August. The maximum biomass of epipelic algae appeared at the G1 sampling site (9.6μg Chl-ag–1 sediment) in August, whereas the minimum biomass of epipelic algae appeared at the E4 sampling site (1.7μg Chl-ag–1 sediment). Pigment (fucoxanthin, zeaxanthin and Chl-b) to Chl-a ratios indicated that epipelic algae were primarily diatoms, secondarily cyanobacteria and lastly green algae in Taihu Lake. Epipelic algae were significantly correlated with total nitrogen in the water and total phosphorus in the sediment (P&amp;lt;0.05), except for green algae. In general, using pigment as an indicator revealed that the epiphytic algal community varied over time and space. The distribution of variations in epipelic algae was related to the heterogeneity of environmental factors.

Monthly Variations of Phytoplankton Community in Geoje-Hansan Bay of the Southern Part of Korea Based on HPLC Pigment Analysis

Kang, J.J.; Lee, J.H.; Kim, H.C.; Lee, W.C.; Lee, D.; Jo, N.; Min, J.-O., and Lee, S.H., 2018. Monthly variations of phytoplankton community in Geoje-Hansan bay of the southern part of Korea based on HPLC pigment analysis. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 356–360. Coconut Creek (Florida), ISSN 0749-0208.Seasonal variations in environmental parameters such as temperature, salinity, and nutrients can significantly affect the community structure of phytoplankton, the primary food source of a marine ecosystem. To understand the influences of environmental factors on phytoplankton community structure, phytoplankton pigments analysis were conducted in the Geoje-Hansan bay situated at the southern part of Korea during January to December, 2016 on monthly basis. Salinity in the water was observed to be fairly stable throughout the study period except for the rainy periods during the summer season (August: 30.3 ± 0.3 and September: 31.1 ± 0.2 psu). Water temperature showed typical seasonal patterns similar to the temperate oceans with maximum values during summer seasons (24.9 ± 0.9 °C). Major nutrients (nitrogen, phosphate, and silicate; hereafter N, P, Si) showed similar patterns of seasonal variation with averages of 3.677 ± 2.707μM, 0.338 ± 0.270μM, and 17.614 ± 9.287μM, respectively, with peak values during December. Phytoplankton community composition estimated using the CHEMTAX program showed distinctive seasonal variations during the study period. The results showed a dominance of dinoflagellates during November – March (>64%) with an exception in December whereas diatoms appeared to be dominant during May – October (60.1%). Dinoflagellates exhibited a negative correlation with temperature, whereas diatoms showed a positive correlation with temperature based on principal components analysis (PCA). Given these findings, a diatom-dominant ecosystem would be expected throughout the year under ongoing ocean warming conditions, which could provide different food qualities to upper trophic levels in the Geoje-Hansan bay.

Optical Detection of Diatom Bloom in the Coastal Waters of Bay of Bengal Using Oceansat-2 OCM

Phytoplankton blooms are the indicators of marine ecosystem health status and their monitoring is a key component in the effective management of coastal and oceanic resources. It remained as a challenge in the coastal waters due to the presence of suspended sediments and dissolved organic matter which interferes with the phytoplankton signal. Several methods and techniques were developed to detect, map and monitor the phytoplankton blooms in the coastal waters using in situ and satellite data. To address this issue ISRO took an initiative to monitor and identify the phytoplankton blooms in the North Indian Ocean to be specific in the coastal waters. As part of this program, the blooms are monitored using Oceansat-2 Ocean Colour Monitor (OCM-2) data all along the East coast of India. This paper presents a case study in the bloom dominated coastal waters along Off Godavari delta covering Kakinada and Yanam in the East coast of India. In-situ measurements collected onboard during a bloom event are optical parameters like Remote Sensing reflectance, Rrs(λ), Water leaving radiance Lw(λ) from the Hyperpro-II under water radiometer, absorption due to phytoplankton, aph(λ), from the spectrophotometer, biological parameters of phytoplankton cell counts and HPLC pigments. From the in situ biological measurements, it is confirmed that the bloom was dominated by with diatom species of Skeletonema costatum with a high concentration of Fucoxanthin as the biomarker for diatoms from the HPLC pigment analysis. Based on these results obtained, optical detection of the bloom species using spectral discrimination of Rrs for different cell enumerations was considered and further spectral derivative analysis (first to fifth order) has been carried out to identify the peaks to detect the bloom forming species. The criteria considered as the minima in the second order derivative (dλ2Rrs) for identifying the peak to discriminate the spectra of the bloom forming species. From the analysis, a unique peak at 483 nm which is identified in particular to S. costatum species in the coastal waters which are identified from the chlorophyll product derived from OCM-2. From the results observed, it can ensure that diatom blooms can be detected from OCM-2 using 490 nm spectral band.

Kleptoplast photosynthesis is nutritionally relevant in the sea slug Elysia viridis

Several sacoglossan sea slug species feed on macroalgae and incorporate chloroplasts into tubular cells of their digestive diverticula. We investigated the role of the “stolen” chloroplasts (kleptoplasts) in the nutrition of the sea slug Elysia viridis and assessed how their abundance, distribution and photosynthetic activity were affected by light and starvation. Elysia viridis individuals feeding on the macroalga Codium tomentosum were compared with starved specimens kept in dark and low light conditions. A combination of variable Chl a fluorescence and hyperspectral imaging, and HPLC pigment analysis was used to evaluate the spatial and temporal variability of photopigments and of the photosynthetic capacity of kleptoplasts. We show increased loss of weight and body length in dark-starved E. viridis as compared to low light-starved sea slugs. A more pronounced decrease in kleptoplast abundance and lower photosynthetic electron transport rates were observed in dark-starved sea slugs than in low light-starved animals. This study presents strong evidence of the importance of kleptoplast photosynthesis for the nutrition of E. viridis in periods of food scarcity. Deprived of photosynthates, E. viridis could accelerate the breakdown of kleptoplasts in the dark to satisfy its’ energy requirements.

Sea-ice eukaryotes of the Gulf of Finland, Baltic Sea, and evidence for herbivory on weakly shade-adapted ice algae

To determine community composition and physiological status of early spring sea-ice organisms, we collected sea-ice, slush and under-ice water samples from the Baltic Sea. We combined light microscopy, HPLC pigment analysis and pyrosequencing, and related the biomass and physiological status of sea-ice algae with the protistan community composition in a new way in the area. In terms of biomass, centric diatoms including a distinct Melosira arctica bloom in the upper intermediate section of the fast ice, dinoflagellates, euglenoids and the cyanobacterium Aphanizomenon sp. predominated in the sea-ice sections and unidentified flagellates in the slush. Based on pigment analyses, the ice-algal communities showed no adjusted photosynthetic pigment pools throughout the sea ice, and the bottom-ice communities were not shade-adapted. The sea ice included more characteristic phototrophic taxa (49%) than did slush (18%) and under-ice water (37%). Cercozoans and ciliates were the richest taxon groups, and the differences among the communities arose mainly from the various phagotrophic protistan taxa inhabiting the communities. The presence of pheophytin a coincided with an elevated ciliate biomass and read abundance in the drift ice and with a high Eurytemora affinis read abundance in the pack ice, indicating that ciliates and Eurytemora affinis were grazing on algae.

Size-dependent depletion and community disturbance of phytoplankton under intensive oyster mariculture based on HPLC pigment analysis in Daya Bay, South China Sea

In this study, we conducted a 14-month investigation in Daya Bay, southern China to understand the effects of oyster farming on phytoplankton community and biomass by using size-fractionated phytopigments. Results proved the filtering effects of oysters on phytoplankton biomass. During the oyster culture period, the average concentration of total chlorophyll a (sum of size-fractionated Chl a) within the farming area was approximately 60% lower than that at the reference site. Phytoplankton depletion in the aquaculture zone mainly occurred in micro-sized fractions (>20 μm) of Chl a, fucoxanthin, and peridinin. The influence of oyster filtration on nano-sized (2.7–20 μm) pigments seemed less than that on micro-sized ones. The depletion of peridinin and 19′-hex-fucoxanthin in aquaculture zone was higher than those of the other pigments, which indicated that flagellated cells might be selectively filtered by oysters and could be more easily influenced by oyster aquaculture. The pico-sized Chl a (<2.7 μm) comprised 24% of total Chl a on the average in the aquaculture zone during the cultural period compared to 6% in the reference site. Picoeukaryote abundance, which was determined via flow cytometry, was significantly higher in the aquaculture zone than in the non-aquaculture areas. The abundance of picoeukaryote is significantly and positively correlated with the concentrations of pico-sized prasinoxanthin, violaxanthin, and neoxanthin, indicating that picoeukaryote is dominated by those in prasinophyte. The results suggest that oyster aquaculture might stimulate the growth of prasinophyte, although the seasonal variations are mainly controlled by the water temperature in the study area. This research highlights the successful use of size-fractionated phytopigments to estimate size-specific phytoplankton biomass and community, which can be applied as a routine method to monitor the environmental effect and food resources of bivalve aquaculture.

Response of a natural phytoplankton community from the Qingdao coast (Yellow Sea, China) to variable CO 2 levels over a short-term incubation experiment

Since marine phytoplankton play a vital role in stabilizing earth's climate by removing significant amount of atmospheric CO 2 , their responses to increasing CO 2 levels are indeed vital to address. The responses of a natural phytoplankton community from the Qingdao coast (NW Yellow Sea, China) was studied under different CO 2 levels in microcosms. HPLC pigment analysis revealed the presence of diatoms as a dominant microalgal group; however, members of chlorophytes, prasinophytes, cryptophytes and cyanophytes were also present. δ 13 C POM values indicated that the phytoplankton community probably utilized bicarbonate ions as dissolved inorganic carbon source through a carbon concentration mechanism (CCM) under low CO 2 levels, and diffusive CO 2 uptake increased upon the increase of external CO 2 levels. Although, considerable increase in phytoplankton biomass was noticed in all CO 2 treatments, CO 2 -induced effects were absent. Higher net nitrogen uptake under low CO 2 levels could be related to the synthesis of CCM components. Flow cytometry analysis showed slight reduction in the abundance of Synechococcus and pico-eukaryotes under the high CO 2 treatments. Diatoms did not show any negative impact in response to increasing CO 2 levels; however, chlorophytes revealed a reverse tend. Heterotrophic bacterial count enhanced with increasing CO 2 levels and indicated higher abundance of labile organic carbon. Thus, the present study indicates that any change in dissolved CO2 concentrations in this area may affect phytoplankton physiology and community structure and needs further long-term study.

Study of photosynthetic productivity in the Northern Gulf of Mexico: Importance of diel cycles and light penetration

Based on 14C uptake assays, in vivo chlorophyll (chl) a fluorescence and HPLC pigment analysis, phytoplankton photosynthetic physiology and productivity in 24-h diel cycles were characterized at three stations in April and August 2012 in the Northern Gulf of Mexico. The results indicated the sub-pycnocline primary production accounted for 5–48% of the total integrated primary production, emphasizing the important influence of euphotic zone in shallow coastal areas. During the diel cycles, chl a-specific light-saturated photosynthesis (PmaxB) as measured with photosynthesis versus irradiance curves (P–I) and the photoprotective pigment pool (diadinoxanthin, diatoxanthin, chl a) showed phytoplankton acclimation to be strongly influenced by water column structure (mixing versus stratification). Changes in chl a fluorescence and transformations between photoprotective pigments were most recognizable in surface samples. The dominate phytoplankton groups (diatoms and cyanobacteria in April and August respectively) also influenced the measured photosynthetic parameters. The Northern Gulf of Mexico is a typical coastal ecosystem with high variability of nutrients, light (intensity and attenuation) and mixing. Our study provided evidence that phytoplankton in this area are adapted to changing environmental conditions by means of fast responses as well as long-term photoacclimation strategies. Understanding the major drivers could help us to improve models involving the calculation of primary productivity, such as those focused towards understanding mechanisms controlling hypoxia.

Dominance of picophytoplankton in the newly open surface water of the central Arctic Ocean

Picophytoplankton are the main primary producers in oligotrophic oceans. They account for more than 90 % of the phototrophic biomass. Investigations of picophytoplankton in the central Arctic Ocean region are rare because these waters used to be completely covered with sea ice. Large, newly exposed water areas, however, appeared in the sea ice zone during the summer of 2010. This provided the first opportunity to study the Arctic picophytoplankton community in these newly open surface waters. This study focuses on the picophytoplankton in the areas near the Alpha-Mendeleev Ridge and Makarov Basin. Here, HPLC pigment analysis with CHEMTAX was used to study community populations, and 454 pyrosequencing with bioinformatics analysis was used to identify the dominant genera (species). Both Pearson correlation analysis and canonical correlation analysis were used to study the relationships between the community and environmental factors. We found chlorophyll a concentrations were low (0.05–0.39 μg l−1), and picophytoplankton dominated these areas. The abundances of picophytoplankton were 1.58 × 106–9.47 × 106 cells l−1 and made up 44–80 % of the total chlorophyll a. Prasinophytes made up 0–88 % of the picoplanktonic chlorophyll a with the following distributions: diatoms (2–80 %), cyanobacteria (0–20 %), haptophytes (4–14 %), and dinoflagellates (2–11 %). The dominant genera (species) in the picoeukaryotes were Pyramimonas (Pyramimonas gelidicola), Micromonas (Micromonas pusilla), and Phaeocystis. Salinity and latitude were the primary factors controlling the community structure of the picophytoplankton.

First record of the green microalgae Coccomyxa sp. in blue mussel Mytilus edulis (L.) from the Lower St. Lawrence Estuary (Québec, Canada)

During autumn 2012 and spring 2013, blue mussels Mytilus edulis (L.) with strongly deformed (L-shaped) posterior shell margins and green spots in soft tissue (microalgae) were collected from intertidal zone along the south shore of the Lower St. Lawrence Estuary near Rimouski (Québec, Canada). Identification of algal cells infesting mussels as Coccomyxa sp. was confirmed by rRNA sequencing and HPLC pigment analysis. Flow cytometric analysis revealed the presence of algal cells in the hemolymph and extrapallial fluid in mussels with deformed and non-deformed shells; concentrations of algal cells were ranged from about 200mL−1 in mussels with actually non-deformed shells to concentrations reaching up to 3.8×107mL−1 in mussels with heavily deformed ones. Chemical analyses of soft tissues led us to conclude that butyltin compounds and trace metals cannot be considered among factors responsible for the shell deformity observed. Using scanning electron microscopy, the biogenic nature of the erosion on the external shell surface and aragonitic lenses of prisms in the curvature zone of deformed shells (in sections) were recorded. The sequence of the green algae from M. edulis of the Lower St. Lawrence Estuary was closely related to Coccomyxa sp. infecting M. edulis from the Flensburg Fjord (North Sea) and Modiolus modiolus (L.) from the Vityaz Bay (Sea of Japan).