Identification and quantification of phytoplankton groups in lakes using new pigment ratios – a comparison between pigment analysis by HPLC and microscopy

1. Pigment analysis by high‐performance liquid chromatography (HPLC) combined with data analysis using the CHEMTAX program has proven to be a fast and precise method for determining the abundance of phytoplankton groups in marine environments. To determine whether CHEMTAX is applicable also to freshwater phytoplankton, 20 different species of freshwater algae were cultured and their pigment/chlorophyll a (Chl a) ratios determined for exponential growth at three different light intensities and for stationary growth at one light intensity. 2. The different treatments had a relatively insignificant impact on the absolute values of the diagnostic pigment/Chl a ratios, with the exception of cyanobacteria and cryptophytes for which the zeaxanthin/Chl a and alloxanthin/Chl a ratios varied considerably. 3. The pigment ratios were tested on samples collected in six different eutrophic Danish lakes during two summer periods using the CHEMTAX program to calculate the biomass of the phytoplankton groups as Chl a. The CHEMTAX‐derived seasonal changes in Chl a biomass corresponded well with the volume of the microscopically determined phytoplankton groups. More phytoplankton groups were detected by the pigment method than by the microscopic method. 4. Applying the pigment ratios developed in this study, the pigment method can be used to determine the abundance of the individual phytoplankton groups, which are useful as biological water quality indicators when determining the ecological status of freshwater lakes.     

Refined carotenoid analysis of the major light-harvesting complex of Mantoniella squamata

The major light-harvesting complex (LHC) of the prasinophycean alga Mantoniella squamata is unique compared to other chlorophyll (Chl) a/b-binding LHC with respect to the primary protein structure and the pigmentation. Although the presence of Chl a, Chl b, a Chl c-type pigment and the xanthophylls neoxanthin, violaxanthin and prasinoxanthin was clearly determined, several carotenoids remained unidentified or were described controversially. We re-analysed the carotenoid composition and identified a new set of xanthophylls present in the LHC: uriolide, micromonol, micromonal and dihydrolutein. Additionally, one hydrophobic component was detected, presumably a xanthophyll. The pigment analysis in combination with quantitative protein determinations revealed a pigment-protein stoichiometry of 6 Chl a, 6 Chl b, 2 Chl c* and about 2 prasinoxanthin molecules per polypeptide. The other xanthophylls were present in sub-stoichiometric amounts. A comparison of results from LHC isolated either by sucrose density centrifugation or SDS-polyacryl gel electrophoresis revealed a decline in the amount of prasinoxanthin and a loss of violaxanthin using the latter preparation procedure, while the stoichiometric ratios of the other 6 xanthophylls remained constant. The fact that 8 different xanthophylls were found in the LHC of M. squamata can be explained best in terms of an oligomeric, presumably trimeric LHC organisation with subunits of heterogeneous pigmentation. Especially, the very stable assembly of most of the minor xanthophylls led to the assumption that these components play an important role in stabilisation and probably also in trunerisation of the LHC in vivo. This revised version was published online in August 2006 with corrections to the Cover Date.     

Benthic infaunal community variability on the northern Svalbard shelf

Marine benthic communities are effective indicators of environmental change. Yet in the Arctic, there are few empirical tests of how sustained climatic change may influence community structure. Northern Svalbard is influenced by both warm Atlantic and cold Arctic water masses, providing an opportunity to assess potential effects of long-term environmental changes by examining spatial variation in community structure. We examined benthic macroinfaunal communities and sediment pigments under Atlantic and Arctic water masses on the northern shelf and fjords of Svalbard. We report on infaunal biomass, abundance, species composition, and diversity at 10 stations spanning 79°–81°N and ranging in depth from 200 to 500?m. Benthic biomass averaged 128?g?WW?m^?2 (48–253?g?WW?m^?2), mean density was 3,635?ind.?m^?2 (780–7,660?ind.?m^?2), and species richness varied from 45 to 136?taxa?stn.^?1. Abundance-based community structure clustered stations in groups related to water mass characteristics, with Atlantic and Arctic shelf stations being well distinguished from each other. Dominant taxa were different in Atlantic- and Arctic-influenced locations. Faunal biomass was highest in the Atlantic-influenced fjords, followed by Arctic fjords and Arctic shelf stations, with Atlantic shelf stations having the lowest biomass. Species richness and diversity were inversely related to biomass. Patterns in faunal biomass were strongly correlated with sedimentary pigments (R ²?=?0.74 for chl a and R ²?=?0.77 for phaeopigments), with large differences in sedimentary pigment concentration among stations. These relationships suggest that benthic fauna on the northern Svalbard shelf are food limited and dependent on predictable, albeit episodic, delivery of organic matter from the water column.     

Spatial distribution and life-cycle timing of zooplankton in the marginal ice zone of the Barents Sea during the summer melt season in 1995

The marginal ice zone (MIZ) in the northern Barents Sea is ecologically important because it represents a highly productive area in Arctic water masses north of the Polar Front. During a multi-disciplinary cruise in 1995, ecological and oceanographic processes were investigated at four stations located in a north-south transect in the MIZ. This study was carried out in Arctic water masses north of the Polar Front where ice conditions varied from dense first-year pack ice to open water. Also, the phytoplankton development varied along the transect from a pre-bloom situation at the northern-most station to a post-bloom situation in the open water. This paper includes a study of the zooplankton community and population structure of some of the dominant copepod species. Numerically, the most important mesozooplankton components were the copepods Calanus glacialis, Pseudocalanus minutus and Oithona similis. Copepods of Atlantic origin, such as Calanus finmarchicus and Oithona atlantica, gave evidence of an advection of Atlantic water masses into the area. It is concluded that the occurrence of new cohorts of Arctic copepods coincides with the onset of the phytoplankton bloom in the MIZ, and, that therefore, the spawning relies on stored energy.      

Increased intrusion of warming Atlantic water leads to rapid expansion of temperate phytoplankton in the Arctic

The Arctic Ocean and its surrounding shelf seas are warming much faster than the global average, which potentially opens up new distribution areas for temperate‐origin marine phytoplankton. Using over three decades of continuous satellite observations, we show that increased inflow and temperature of Atlantic waters in the Barents Sea resulted in a striking poleward shift in the distribution of blooms of Emiliania huxleyi, a marine calcifying phytoplankton species. This species' blooms are typically associated with temperate waters and have expanded north to 76°N, five degrees further north of its first bloom occurrence in 1989. E. huxleyi's blooms keep pace with the changing climate of the Barents Sea, namely ocean warming and shifts in the position of the Polar Front, resulting in an exceptionally rapid range shift compared to what is generally detected in the marine realm. We propose that as the Eurasian Basin of the Arctic Ocean further atlantifies and ocean temperatures continue to rise, E. huxleyi and other temperate‐origin phytoplankton could well become resident bloom formers in the Arctic Ocean.     

An HPLC analysis of the summer phytoplankton assemblage in Lake Baikal

1. The enormous size and spatial heterogeneity of Lake Baikal require rapid methods for large sample sets. We therefore tested the applicability of a novel, high‐performance liquid chromatography (HPLC)‐based, combination of methods for analysing phytoplankton. In July 2001, samples were collected in a transect across the lake at various depths down to 30 m. Phytoplankton (>3 μm) and autotrophic picoplankton (APP) were counted under light and epifluorescence microscopes, respectively. Pigments were analysed with HPLC. 2. The pigment data allowed the contributions of the dominant phytoplankton groups to the total chlorophyll a (Chl a) in the lake to be estimated by multiple linear regression and by the CHEMTAX matrix factorisation program. Three marker pigments, fucoxanthin, lutein and zeaxanthin, were shown to be useful indicators of the abundance and spatial distribution of certain phytoplankton groups. The relative contributions of the various phytoplankton groups to the total Chl a in the lake determined using these marker pigments were similar, but not identical, to those determined by cell counts. 3. Pigment analyses of isolated strains from Lake Baikal and some European lakes confirmed that phycoerythrin‐containing Cyanobacteria with very high amounts of zeaxanthin were responsible for the low Chl a/zeaxanthin ratios of the water samples. A picoplanktonic species of Eustigmatophyceae was isolated from the lake. Its high violaxanthin content, responsible for very low Chl a/violaxanthin ratios of some water samples, can be used to estimate the contribution of this group to total Chl a.     

Ice algal assemblages and vertical export of organic matter from sea ice in the Barents Sea and Nansen Basin (Arctic Ocean)

Algal communities and export of organic matter from sea ice were studied in the offshore marginal ice zone (MIZ) of the northern Barents Sea and Nansen Basin of the Arctic Ocean north of Svalbard by means of ice cores and short-term deployed sediment traps. The observations cover a total of ten stations within the drifting pack ice, visited over a period of 3 years during the period of ice melt in May and July. Maximum flux of particulate organic carbon and chlorophyll a from the ice at 1 m depth (1,537 mg C m⁻² per day and 20 mg Chl a m⁻² per day) exceeded the flux at 30 m by a factor of 2 during spring, a pattern that was reversed later in the season. Although diatoms dominated the ice-associated algal biomass, flagellates at times revealed similarly high biomass and typically dominated the exported algal carbon. Importance of flagellates to the vertical flux increased as melting progressed, whereas diatoms made the highest contribution during the early melting stage. High export of ice-derived organic matter and phytoplankton took place simultaneously in the offshore MIZ, likely as a consequence of ice drift dynamics and the mosaic structure of ice-covered and open water characteristic of this region.     

Chlorophyll <Emphasis Type="Italic">a</Emphasis> as a measure of seasonal coupling between phytoplankton and the monsoon periods in the Gulf of Oman

We present data from a long time-series study to describe the factors that control phytoplankton population densities and biomass in the coastal waters of Oman. Surface temperature, salinity, nutrients, dissolved oxygen, chlorophyll a (Chl a), and phytoplankton and zooplankton abundance of sea water were measured as far as possible from February 2004 through February 2006, at two stations along the southern coast of the Gulf of Oman. The highest concentrations of Chl a (3 mg m⁻³) were recorded during the southwest monsoon (SWM) when upwelling is active along the coast of Oman. However, results from our study reveal that the timing and the amplitude of the seasonal peak of Chl a exhibited interannual variability, which might be attributed to interannual differences in the seasonal cycles of nutrients caused either by coastal upwelling or by cyclonic eddy activity. Monthly variability of SST and concentrations of dissolved nitrate, nitrite, phosphate, and silicate together explained about 90% of the seasonal changes of Chl a in the coastal ecosystem of the Gulf of Oman. Phytoplankton communities of the coastal waters of Oman were dominated by diatoms for most part of the year, but for a short period in summer, dinoflagellates were dominant.     

Impacts of seabird-derived nutrients on water quality and diatom assemblages from Cape Vera,Devon Island,Canadian High Arctic

Relationships between key phytoplankton attributes including Chl a-specific light absorption, pigment composition and concentration, photosynthesis, primary production and community structure were studied in two open shallow nutrient-poor coastal systems receiving similar amounts of sewage water. Both systems were significantly nitrogen limited. However, differences in wastewater treatment (primary vs secondary) and sewage dilution (50%) between the two systems caused a greater difference between systems than locally around the outflows. For both systems, water at the outlet had significantly lower water transparency caused by a 20% higher absorption by coloured dissolved organic matter. Nutrient concentrations were also elevated, gradually decreasing with distance north (governing current) of the outflows, causing higher abundance of nano-sized phytoplankton, higher content of carotenoid pigments, 20–50% higher Chl a-specific absorption coefficients and higher photosynthetic capacity. Although maximum rates of Chl a-normalised photosynthesis were strongly related to nitrate availability, no effects were found on the derived areal primary production or algal biomass suggesting that photosynthetic and optical parameters are more sensitive indicators of nutrient enrichment than biomass or productivity. Handling editor: Tasman Peter Crowe     

Determining algal assemblages in oligotrophic lakes and streams: comparing information from newly developed pigment/chlorophyll a ratios with direct microscopy

1. Pigment analyses by high performance liquid chromatography (HPLC) are commonly used for determining algal groups in marine and estuarine areas but are underdeveloped in freshwaters. In this study, 15 characteristic pelagic algal species (representing five algal groups) of oligo‐ / mesotrophic lakes were cultured and pigment / Chl a ratios determined at three light intensities. 2. With the exception of cyanophytes, light treatment had little effect on pigment / Chl a ratios. This justifies the use of the same pigment / Chl a ratios during seasonal studies where light conditions may change. 3. The determined pigment / Chl a ratios were tested on seasonal samples from five oligo‐ / mesotrophic lakes and three streams using CHEMTAX software. Pigment ratios of both pelagic and benthic algal communities from the lakes and streams were analysed to determine whether the pelagic algae‐based ratios can be used for benthic algal communities. 4. HPLC combined with CHEMTAX was useful for identifying freshwater phytoplankton classes and for quantifying the abundance of phytoplankton groups. However, although correlations were significant for six of seven phytoplankton classes studied, they were weak and varied with season. 5. HPLC was valid for quantifying benthic diatom groups in stream samples, whereas for lakes more benthic algal groups were recorded with HPLC than with microscopy and correlations between the two methods were not significant. 6. The use of both HPLC and microscopy is recommended as a cost‐efficient method for analysing many samples. It is crucial, however, that the CHEMTAX software is calibrated with the correct information, and the user is aware of the limitations.     

Spatial and temporal photosynthetic compartments during summer in Antarctic Lake Kitiesh

Summary Four autotrophic compartments were recognised in Lake Kitiesh, King George Island (Southern Shetland) at the beginning of the summer in 1987: snow microalgae, ice bubble communities, phytoplankton in the water column and benthic communities of moss with epiphytes. Chlorophyll a concentration and pigment absorption spectra were obtained in these four compartments before and/or after the thawing of the ice cover. During the ice free period, carbon fixation and biomass was measured in the phytoplankton and in the benthic moss Campyliadelphus polygamus. From these measurements we conclude that the benthic moss is the most significant autotrophic component in this lake in terms of biomass, chlorophyll a content and primary productivity. The integral assimilation number (The ratio of carbon fixation per unit area to biomass per unit area) values were similar for both phytoplankton and the moss, ranging from 3.6 to 5.4 mg C (mg Chl a)^–1h^–1in phytoplankton and from 4.0 to 6.4 mgC (mg Chl a)^–1h^–1 in the benthic moss. This approach allows comparisons of carbon fixation efficiency of the chlorophyll a under a unit area between compartments in their different light environments.     

Metabarcoding reveals high diversity of benthic foraminifera linked to water masses circulation at coastal Svalbard

Arctic marine biodiversity is undergoing rapid changes due to global warming and modifications of oceanic water masses circulation. These changes have been demonstrated in the case of mega- and macrofauna, but much less is known about their impact on the biodiversity of smaller size organisms, such as foraminifera that represent a main component of meiofauna in the Arctic. Several studies analyzed the distribution and diversity of Arctic foraminifera. However, all these studies are based exclusively on the morphological identification of specimens sorted from sediment samples. Here, we present the first assessment of Arctic foraminifera diversity based on metabarcoding of sediment DNA samples collected in fjords and open sea areas in the Svalbard Archipelago. We obtained a total of 5,968,786 reads that represented 1384 amplicon sequence variants (ASVs). More than half of the ASVs (51.7%) could not be assigned to any group in the reference database suggesting a high genetic novelty of Svalbard foraminifera. The sieved and unsieved samples resolved comparable communities, sharing 1023 ASVs, comprising over 97% of reads. Our analyses show that the foraminiferal assemblage differs between the localities, with communities distinctly separated between fjord and open sea stations. Each locality was characterized by a specific assemblage, with only a small overlap in the case of open sea areas. Our study demonstrates a clear pattern of the influence of water masses on the structure of foraminiferal communities. The stations situated on the western coast of Svalbard that are strongly influenced by warm and salty Atlantic water (AW) are characterized by much higher diversity than stations in the northern and eastern part, where the impact of AW is less pronounced. This high diversity and specificity of Svalbard foraminifera associated with water mass distribution indicate that the foraminiferal metabarcoding data can be very useful for inferring present and past environmental conditions in the Arctic.     

Is the poleward expansion by Atlantic cod and haddock threatening native polar cod, <Emphasis Type="Italic">Boreogadus saida</Emphasis>?

During a recent period of increased influx of warm Atlantic water to the western coast of Svalbard, we have observed a northward expansion of boreal Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) into areas dominated by the native polar cod (Boreogadus saida). To determine the potential impact of new ecological interactions, we studied the diet of co-occurring juvenile gadoids in fjords, open water, and sea ice around Svalbard. We also reviewed the available literature on polar cod feeding in different habitats across the Arctic to determine whether region, habitat, or fish size may influence diet. Feeding by polar cod in the pelagic zone was size dependent, with small fish primarily consuming Calanus spp. and smaller copepods, with an increasing ration of Themisto spp. at larger sizes. In benthic habitats, diets were more varied and included considerably more unidentified material and sediment. Less than 40% dietary overlap was detected among the three species when they were found together. Stable isotope analyses indicated these patterns were representative of longer-term assimilation. The low interspecific dietary overlap suggests little direct competition. Future increases in abundance and the high predation potential of the boreal taxa, however, may impact the persistence of polar cod on some Arctic shelves.     

COCCOID EUKARYOTIC MARINE ULTRAPLANKTERS WITH FOUR DIFFERENT HPLC PIGMENT SIGNATURES1

Pigment compositions of 16 coccoid eukaryotic ultraplanktonic clones isolated from coastal and oceanic waters were investigated by high-performance liquid chromatography (HPLC). Four distinct pigment signatures were observed, and clones were classified into subgroups based on the presence or absence and relative abundances of selected chlorphylls and carotenoids. The first subgroup (5 clones) was pigmented like chlorophyll b-containing higher plants and resembled true chlorophycean algae. The second subgroup (3 clones) contained chlorophyll b and relatively high levels of prasinoxanthin, a carotenoid characteristic of certain members of the Prasinophyceae (sometimes grouped as the Micromonadophyceae). The third subgroup (5 clones) was pigmented in a similar fashion but had a twofold lower prasinoxanthin-to-chlorophyll a ratio and an unidentified carotenoid. The fourth subgroup (3 clones) lacked chlorophyll b and was pigmented like certain members of the Chrysophyceae (e. g. 19′-butanoyloxyfucoxanthin-containing Pelagococcus subviridis Norris) Online diode array spectral analysis of selected clonal extracts revealed the presence of Mg 2,4-divinylphaeoporphyrin a₅ monomethyl ester-like and chlorophyll c-like pigments in representatives of the prasinophyte-like and chrysophyte like clones, respectively. These findings plus the occurrence of chlorophyll b, prasinoxanthin and 19′-butanoyloxyfucoxanthin in the North Atlantic Ocean suggest that chrysophyte- and prasinophyte-like organisms can be important biomass components of marine phytoplankton.     

Biogeography and Photosynthetic Biomass of Arctic Marine Pico-Eukaroytes during Summer of the Record Sea Ice Minimum 2012

Information on recent photosynthetic biomass distribution and biogeography of Arctic marine pico-eukaryotes (0.2–3 μm) is needed to better understand consequences of environmental change for Arctic marine ecosystems. We analysed pico-eukaryote biomass and community composition in Fram Strait and large parts of the Central Arctic Ocean (Nansen Basin, Amundsen Basin) using chlorophyll a (Chl a) measurements, automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing. Samples were collected during summer 2012, the year with the most recent record sea ice minimum. Chl a concentrations were highest in eastern Fram Strait and pico-plankton accounted for 60–90% of Chl a biomass during the observation period. ARISA-patterns and 454-pyrosequencing revealed that pico-eukaryote distribution is closely related to water mass distribution in the euphotic zone of the Arctic Ocean. Phaeocystaceae, Micromonas sp., Dinophyceae and Syndiniales constitute a high proportion of sequence reads, while sequence abundance of autotrophic Phaeocystaceae and mixotrophic Micromonas sp. was inversely correlated. Highest sequence abundances of Phaeocystaceae were observed in the warm Atlantic Waters in Fram Strait, while Micromonas sp. dominated the abundant biosphere in the arctic halocline. Our results are of particular interest considering existing hypotheses that environmental conditions in Nansen Basin might become more similar to the current conditions in Fram Strait. We propose that in response, biodiversity and biomass of pico-eukaryotes in Nansen Basin could resemble those currently observed in Fram Strait in the future. This would significantly alter biogeochemical cycles in a large part of the Central Arctic Ocean.     

Phytoplankton Assemblages and Their Dominant Pigments in the Nervion River Estuary

In the Nervion River estuary surface samples were taken from March to September 2003 at six sites covering most of the salinity range with the aim to know the biomass and taxonomic composition of phytoplankton assemblages in the different segments. Nine groups of algae including cyanobacteria, diatoms, dinoflagellates, chlorophytes, prasinophytes, euglenophytes, chrysophytes, haptophytes, raphidophytes and cryptophytes were identified by means of a combination of pigment analysis by high-performance liquid chromatography (HPLC) and microscopic observations of live and preserved cells. Diatoms, chlorophytes and cryptophytes were the most abundant algae in terms of cells number, whereas fucoxanthin, peridinin, chlorophyll b (Chl b) and alloxanthin were the most abundant auxiliary pigments. Based on multiple regression analysis, in the outer estuary (stations 0, 1, 2 and 3) about 93% of the chlorophyll a (Chl a) could be explained by algae containing fucoxanthin and by algae containing Chl b, whereas in the rest of the estuary most of the Chl a (about 98%) was accounted for by fucoxanthin, Chl b and alloxanthin containing algae. The study period coincided with that of most active phytoplankton growth in the estuary and fucoxanthin was by far the dominant among those signature pigments. Several diatoms, chrysophytes, haptophytes and raphydophytes were responsible for fucoxanthin among identified species. Besides, dinoflagellates with a pigment pattern corresponding to chrysophytes and type 4 haptophytes were identified among fucoxanthin-bearing algae. Cryptophytes were the most abundant species among those containing alloxanthin. The maximum of Chl b registered at the seaward end in April coincided with a bloom of the prasinophytes Cymbomonas tetramitiformis, whereas the Chl b maxima in late spring and summer were accounted for by prasinophytes in the middle and outer estuary and by several species of chlorophytes in the middle and inner estuary. Other Chl b containing algae were euglenophytes and the dinoflagellate Peridinium chlorophorum. Dinoflagellates constituted generally a minor component of the phytoplankton.     

Increased sea ice melt as a driver of enhanced Arctic phytoplankton blooming

Phytoplankton primary production in the Arctic Ocean has been increasing over the last two decades. In 2019, a record spring bloom occurred in Fram Strait, characterized by a peak in chlorophyll that was reached weeks earlier than in other years and was larger than any previously recorded May bloom. Here, we consider the conditions that led to this event and examine drivers of spring phytoplankton blooms in Fram Strait using in situ, remote sensing, and data assimilation methods. From samples collected during the May 2019 bloom, we observe a direct relationship between sea ice meltwater in the upper water column and chlorophyll a pigment concentrations. We place the 2019 spring dynamics in context of the past 20 years, a period marked by rapid change in climatic conditions. Our findings suggest that increased advection of sea ice into the region and warmer surface temperatures led to a rise in meltwater input and stronger near-surface stratification. Over this time period, we identify large-scale spatial correlations in Fram Strait between increased chlorophyll a concentrations and increased freshwater flux from sea ice melt.     

Analysis of the deep chlorophyll maximum across the Azores Front

Physical, chemical and biological observations made in late July and August 1997 across the Azores Front (37° N, 32°W to 32° N, 29°W) are presented. The objectives of the study were: (1) to analyse horizontal and vertical profiles of temperature, salinity, density, nutrients and chlorophyll-a (Chl a) of the top 350 m; (2) to identify the main differences in the deep Chl a Maximum (DCM) and hydrographic structure between the water masses that pass north and south of the Azores Front; and (3) to estimate phytoplankton primary production in these water masses. Horizontal and vertical profiles of salinity, temperature, density, nutrients and phytoplankton pigments in the top 350 m were analysed. The Front separates two distinct water types: the 18°C Mode Water (18 MW) of sub-tropical origin, and the 15°C Mode Water (15 MW) of sub-polar origin. Differences in the DCM and hydrographic structure between 18 MW and 15 MW were observed in the contour plots of each section. The average Chl a concentration between 5 and 200 m depth decreased significantly from 15 MW to 18 MW. The same pattern was observed for the Chl a concentration at the DCM depth. A vertical one-dimensional model was used to estimate the phytoplankton primary production in the 15 MW and 18 MW and led to an estimated water column average gross primary productivity (GPP) between 1.08 and 2.71 mg C m^–3 d^–1 for the 15 MW and about half of these values for the 18 MW. These results indicate that the typical south–north positive slope on DCM depth parallels a latitudinal increase on GPP, suggesting that the location of the Azores Front may have a significant regional impact on GPP.     

PIGMENT SUITES AND TAXONOMIC GROUPS IN PRASINOPHYCEAE1

Pigment analysis performed on 30 Prasinophyceae strains revealed two main groups: the prasinoxanthin‐containing and prasinoxanthin‐less Prasinophyceae. Prasinoxanthin‐containing Prasinophyceae comprised the orders Mamiellales, Pseudoscourfieldiales (Pycnococcaceae), and Prasinococcales. For this group, classification with pigment composition showed a good agreement with molecular phylogeny. Mamiellales, except Crustomastix stigmatica, accumulated uriolide, micromonal, dihydrolutein, and the pigment Unidentified M1 as characteristic pigments. Prasinococcales and Pseudoscourfieldiales (Pycnococcaceae) lacked micromonal and Unidentified M1. In addition, Pseudoscourfieldiales (Pycnococcaceae) lacked uriolide. A chl c₃‐like pigment was present in prasinoxanthin‐containing strains isolated from the deep sea. Common green algae pigments, a loroxanthin derivative, and siphonaxanthin plus derivatives were found in the prasinoxanthin‐less Prasinophyceae, which included strains from Pyramimonadales, Pseudoscourfieldiales (Nephroselmidiaceae), Chlorodendrales, and a new order. Although some associations could be observed, the correspondence between pigments and molecular taxonomy was less clear for this group.     

The Status and Characteristics of Eutrophication in the Yangtze River (Changjiang) Estuary and the Adjacent East China Sea, China

Eutrophication has become increasingly serious and noxious algal blooms have been of more frequent occurrence in the Yangtze River Estuary and in the adjacent East China Sea. In 2003 and 2004, four cruises were undertaken in three zones in the estuary and in the adjacent sea to investigate nitrate (NO₃–N), ammonium (NH₄–N), nitrite (NO₂–N), soluble reactive phosphorus (SRP), dissolved reactive silica (DRSi), dissolved oxygen (DO), phytoplankton chlorophyll a (Chl a) and suspended particulate matter (SPM). The highest concentrations of DIN (NO₃–N+NH₄–N+NO₂–N), SRP and DRSi were 131.6, 1.2 and 155.6 μM, respectively. The maximum Chl a concentration was 19.5 mg m⁻³ in spring. An analysis of historical and recent data revealed that in the last 40 years, nitrate and SRP concentrations increased from 11 to 97 μM and from 0.4 to 0.95 μM, respectively. From 1963 to 2004, N:P ratios also increased from 30–40 up to 150. In parallel with the N and P enrichment, a significant increase of Chl a was detected, Chl a maximum being 20 mg m⁻³, nearly four times higher than in the 1980s. In 2004, the mean DO concentration in bottom waters was 4.35 mg l⁻¹, much lower than in the 1980s. In comparison with other estuaries, the Yangtze River Estuary was characterized by high DIN and DRSi concentrations, with low SRP concentrations. Despite the higher nutrient concentrations, Chl a concentrations were lower in the inner estuary (Zones 1 and 2) than in the adjacent sea (Zone 3). Based on nutrient availability, SPM and hydrodynamics, we assumed that in Zones 1 and 2 phytoplankton growth was suppressed by high turbidity, large tidal amplitude and short residence time. Furthermore, in Zone 3 water stratification was also an important factor that resulted in a greater phytoplankton biomass and lower DO concentrations. Due to hydrodynamics and turbidity, the open sea was unexpectedly more sensitive to nutrient enrichment and related eutrophication processes.