HPLC Pigment Analysis Research Articles

Picophytoplankton diversity and photoacclimation in the Strait of Sicily (Mediterranean Sea) in summer. I. Mesoscale variations

Phytoplankton dynamics were investigated at the mesoscale in the northern part of the Strait of Sicily in July-August 1997 on fractionated samples ( 3 μm) using HPLC pigment analysis and flow cytometry. Distribution, diversity and photoacclimation varied within the different water masses and features present at the time of sampling, including a surface filament of deep, cold water. Picophytoplankton ( 3 μm) appeared to respond to different cues. Chlorophyll pigment content per cell of Synechococcus spp., Prochlorococcus spp. or picoeukaryotes was estimated by coupling pigment data with flow cytometric counts. In Prochlorococcus spp., we found an average of 0.44 and 1.56 fg divinyl-chlorophyll a (dvchl a) cell -1 in surface and DCM layers, respectively. In contrast, chl a content in the picoeukaryote group ranged between 17 and 168 fg chl a cell -1 , depending upon depth and water mass, which suggested strong photoacclimation and photoadaptation with depth. The relative contribution of each eukaryote pigment to one size class or the other changed through the water column, and reflected size segregation within single taxonomic groups.

CHARACTERIZATION OF NW MEDITERRANEAN KARLODINIUM SPP. (DINOPHYCEAE) STRAINS USING MORPHOLOGICAL, MOLECULAR, CHEMICAL, AND PHYSIOLOGICAL METHODOLOGIES1

Recurrent fish kills in the Spanish Alfacs Bay (NW Mediterranean) have been detected during winter seasons since 1994, and were attributed to an unarmored, ichthyotoxic, dinoflagellate, initially identified as Gyrodinium corsicum Paulmier, Berland, Billard, & Nezan. Several strains were isolated from the bay and their clonal cultures were compared by combined techniques, including light and electron microscopy, internal transcribed spacer and 5.8S rDNA nucleotide sequencing, and HPLC pigment analyses, together with studies of their photochemical performance, growth rates, and toxicity. Using phylogenetic analyses, all strains were identified as members of the genus Karlodinium, but they were separated into two genetically distinct groups. These groups, identified as Karlodinium veneficum (Ballantine) J. Larsen and K. armiger Bergholtz, Daugbjerg et. Moestrup, were also supported by the other techniques used. Detailed analyses of fine structural characteristics (including plug‐like structures in amphiesma and a possible layer of semi‐opaque material beneath the outer membrane) allowed discrimination of the mentioned two species. Specific differences in pigment patterns coincided with that expected for low‐ (K. veneficum) and high‐light (K. armiger) adapted relatives. The higher photosynthetic efficiency of K. veneficum and the longer reactivation times of the PSII reaction centers observed for K. armiger were in agreement with this hypothesis. The two species differed in toxicity, but the strains used always induced mortality when incubated with bivalves, rotifers, and finfish. Compared with K. armiger, strains of K. veneficum yielded higher cell densities, but had lower growth rates.

Lipid biomarkers and trophic linkages between phytoplankton, zooplankton and anchovy (Engraulis encrasicolus) larvae in the NW Mediterranean

Identification and quantification of the main fatty acids in phytoplankton, zooplankton and Engraulis encrasicolus larvae were used to study the relationship among the different trophic levels. Three northwestern Mediterranean sea areas were studied as representative of potentially heterogeneous environments. HPLC pigment analysis was performed to assess the contribution of different phytoplankton groups to total chlorophyll biomass. In spite of the physical variability, a homogeneous pattern in phytoplankton composition among areas was found, with the Prymnesiophyceae representing more than half of the phytoplankton chlorophyll biomass. This homogeneous spatial pattern was also reflected in the phytoplankton fatty acid proportions. Thus, significant amount of 14:0, 18:1(n-9) and 18:4(n-3) could be related to the dominance of the prymnesiophytes; the low proportion of fatty acid markers of diatoms and dinoflagellates agreed with the low abundances of those phytoplankton groups. Zooplankton fatty acids also showed homogeneous proportions in the studied areas, with a preferential accumulation of 16:1(n-7) and 20:5(n-3), and 22:6(n-3). This observation may indicate a preferential grazing on diatoms and dinoflagellates. Anchovy larvae displayed differing fatty acids contributions related to size. Large larvae contained a higher proportion of polyunsaturated fatty acid (PUFA). Small larvae showed a high percentage of 18:1(n-9) and 18:4(n-3) fatty acids, considered Prymnesiophyceae biomarkers. These results suggest an additional food resource for the anchovy that is complementary to a zooplankton diet, but probably of protozoan origin (i.e. microzooplankton). Significant logarithmic relationships were found between dry mass and 20:5(n-3) and 22:6(n-3) fatty acid proportions in E. encrasicolus larvae. These PUFA are considered essential for the fish-larvae development.

Spatial variation in phytoplankton dynamics in the Belgian coastal zone of the North Sea studied by microscopy, HPLC-CHEMTAX and underway fluorescence recordings

Spatial variation in the succession of phytoplankton in the Belgian Coastal Zone (BCZ) was investigated by monitoring phytoplankton biomass and community composition using microscopical cell counts, HPLC pigment analyses and in vivo fluorescence recordings. Monthly monitoring of phytoplankton community composition at five stations revealed a succession of three distinct diatom communities. The succession of these three communities was the same at each site, but the succession from the winter-spring to the summer community occurred one month earlier and the succession from the summer to the autumn community one month later at the SW than at the NE stations of the BCZ. Monthly monitoring of chlorophyll a at ten fixed sites and inspection of in vivo fluorescence recordings during various cruises of RV ‘Zeeleeuw’ indicated that the spring bloom started about one month earlier in the SW part of the BCZ than in the NE part. The spatial difference in the onset of the spring bloom was ascribed to the higher water column turbidity at the NE coast compared to the SW coast. Although a Phaeocystis bloom occurred at all monitoring stations, a clear spatial variation in the magnitude of such blooms was observed, with more intense blooms at the NE coast than at the SW coast. A close relation was observed between the intensity of the Phaeocystis bloom and the availability of inorganic nutrients (N and P) before the onset of the bloom. Comparison of microscopical cell counts and CHEMTAX analysis of accessory pigment data indicated that HPLC analysis may be a useful tool for monitoring Phaeocystis in the North Sea. The presence of chlorophyll c 3 containing diatoms, however, probably resulted in the detection of small quantities of Phaeocystis by HPLC-CHEMTAX analysis when microscopical analyses showed that the species was absent.

Study of selective feeding in the marine cladoceran Penilia avirostris by HPLC pigment analysis

Food selection by the marine cladoceran Penilia avirostris was studied in the field by HPLC analysis of phytoplankton marker pigments and in the laboratory by microscopic measurement of cell removal. Comparison between pigment composition in natural phytoplankton and in P. avirostris showed that P. avirostris preferred diatoms, cryptophytes and chlorophytes, and ignored prymnesiophytes and dinoflagellates. Peridinin, the marker pigment for dinoflagellates was found in P. avirostris only when the dinoflagellate populations were dominated by Prorocentrum. Pigment degradation rates ranged from 13.73% for alloxanthin to 36.62% for chlorophyll a. Clearance rates measured in the laboratory provided further evidence of strong preference for diatoms and cryptophytes, and avoidance of dinoflagellates. Microscopic counts suggested that P. avirostris was feeding on prymnesiophytes, although ingestion of prymnesiophytes could not be confirmed by pigment analysis.

Phytoplankton community dynamics assessed by ships-of-opportunity sampling in the northern Baltic Sea: A comparison of HPLC pigment analysis and cell counts

The dynamics of phytoplankton diversity constitute crucial data in environmental monitoring, food-web studies and ecosystem modeling. Proper assessment of phytoplankton community composition requires large investments in offshore sampling and taxonomic competence because these communities can change fundamentally on a weekly scale. Cheap and high-frequent offshore phytoplankton sampling can be achieved by using ships-of-opportunity, and in the present study we used the Alg@line facilities onboard a passenger ferry during its regular route between Finland and Sweden in the northern Baltic Sea. The first aim was to test if pigment analysis, as a cheaper alternative to cell counts, can be used to detect environment-correlated variation in phytoplankton communities. It has been shown that spatial variation (salinity differences) and variation throughout one annual cycle (changes in temperature and nutrients) were strongly reflected by pigment composition. The second aim was to test if pigment analyses and cell counts detect environment-correlated variation in phytoplankton communities equally well. It has been shown that spatial and seasonal variations were reflected by pigment composition while cell counts reflected seasonal variation only. This suggests that the pigment analyses detected aspects of the phytoplankton that were neglected or misinterpreted by cell counts. It is advocated that available resources of long-term studies, such as environmental monitoring, can be used more efficiently by utilizing the high ecological resolution of pigment composition in combination with high-frequent ships-of-opportunity sampling. To assess heterotrophic and/or toxic species, such programs could also include sampling for cell counts in a complementary manner, with actually performing counts only for crucial samples (e.g. between large community changes) as indicated by multivariate statistical analysis of pigment composition. Some aspects of analyzing phytoplankton data with multivariate statistics are also discussed.

TOXIN PROFILE, PIGMENT COMPOSITION, AND LARGE SUBUNIT RDNA PHYLOGENETIC ANALYSIS OF AN ALEXANDRIUM MINUTUM (DINOPHYCEAE) STRAIN ISOLATED FROM THE FLEET LAGOON, UNITED KINGDOM1

Paralytic shellfish toxins, pigment composition, and large subunit (LSU) rDNA sequence were analyzed for a clonal culture of Alexandrium minutum Halim isolated in 2000 from the coastal Fleet Lagoon, Dorset, United Kingdom. The HPLC pigment analysis revealed the presence of chl a, peridinin, and diadinoxanthin as major pigments and chl c1+c2 and c3, diatoxanthin, and β‐carotene as minor components. The toxins responsible for paralytic shellfish poisoning were analyzed by HPLC with postcolumn derivatization and fluorescence detection. The paralytic shellfish poisoning toxin profile of the Fleet Lagoon strain of A. minutum in exponential growth phase was dominated by gonyautoxin‐3 up to 54%, whereas gonyautoxin‐2 made up 10% and saxitoxin (STX) 36%. The average toxicity of the culture was 3.8 pg STX Eq·cell−1, and total toxin content varied from 5.6 fmol·cell−1 on day 1 to a maximum of 16.8 fmol·cell−1 during the early stationary phase. Sequence analysis of the LSU rDNA revealed the strain to be closely related to several European strains of A. minutum and one isolated from Australian waters, although most of these do not produce STX. The shallow Fleet Lagoon may provide a favorable environment for A. minutum to bloom, and the presence of highly potent saxitoxins in this strain indicates potential for future shellfish contamination.

A comparison of HPLC pigment analyses and biovolume estimates of phytoplankton groups in an oligotrophic lake

Assessment of the contribution of distinct algal groups to phytoplankton biomass in oligotrophic lakes by marker pigments is compared with assessment by cell-counting biovolume estimates. Seasonal samples from an oligotrophic alpine lake (Redon, Pyrenees) mostly included species of chrysophytes, dinoflagellates, cryptophytes and chlorophytes. The chlorophyl a (Chl a) corresponding to each algal group was estimated using HPLC pigment analyses and the CHEMTAX program. Chl a estimates and biovolume showed a significant correlation for all the groups during the ice-free season except for chlorophytes. However, some of the samples from the initial phase of the ice cover presented a clear departure from the relationship during the ice-free period in most groups. On the other hand, the ratios between a specific marker pigment and the biovolume of the marked algal group were significantly constant within the photic zone (>1% surface irradiance) for most of the pigments and groups, including chlorophytes. Nevertheless, the ratios increased and showed a large variability for samples below the photic depth or below the ice cover. The violaxanthin-chrysophyte biovolume ratio presented an opposed tendency to other pigment-biovolume ratios, which increased in inverse proportion to the depth of the sample. The results are discussed in terms of methodological limitations, acclimation responses and species composition.

A comparison of HPLC pigment analyses and biovolume estimates of phytoplankton groups in an oligotrophic lake

A comparison of HPLC pigment analyses and biovolume estimates of phytoplankton groups in an oligotrophic lake

Using HPLC pigment analysis to investigate phytoplankton taxonomy: the importance of knowing your species

Phytoplankton microscopic enumerations and HPLC analyses of their pigments were performed weekly for a complete year at a coastal station in the English Channel. The taxonomic composition of the phytoplankton community was assessed using the HPLC results combined with the mathematical tool CHEMTAX in two different ways. Firstly, without using the species level taxonomic information obtained at the microscopic level (blind analyses), and secondly by including the information from the microscopic taxonomic analysis (directed analyses). The results indicate that, due to the particular pigment composition of some species (for example, the dinoflagellate, Karenia mikimotoi and the haptophyte, Phaeocystis pouchetii), a blind analysis would result in very significant errors in the taxonomic determination of the bloom events at this station. Major blooms of Karenia mikimotoi and P. pouchetii were mistaken for blooms of diatoms on the basis of a blind HPLC-CHEMTAX analysis. Only with the information from the microscopic observations was it possible to obtain an accurate representation of the phytoplankton community.

Routine quantification of phytoplankton groups—microscopy or pigment analyses?

Phytoplankton pigments in samples taken from nutrient-enriched and non-enriched 3m 3 seawater enclosures were separated and quantified using high-performance liquid chromato- graphy (HPLC). The enclosures were with and without inorganic (N, P, Si) and organic (glucose, C) nutrient enrichments, resulting in a variation of phytoplankton groups in time and space. The relative contribution of the major phytoplankton groups to the total chlorophyll a (i.e. chlorophyll a plus chlorophyllide a) was estimated by the CHEMTAX program. The results were compared to phyto- plankton groups identified and quantified by light and epifluorescence microscopy. For the pig- mented flagellate groups the results obtained by microscopy and pigment analyses using the CHEMTAX program showed similar trends. The picocyanobacteria were readily quantified by microscopy and the results were similar to those obtained by flow-cytometry, while the CHEMTAX program for the cyanobacteria revealed different trends. Microscopy and pigment analyses provided similar trends in diatom population development. Estimated diatom contributions to total phyto- plankton biomass, however, were considerably higher when based on microscopy than when based on the CHEMTAX program, especially in Si-amended enclosures. Total chlorophyll a:carbon ratios for diatoms were at the lower end of a previously reported range between 1:27 and 1:67. For the pigmented flagellate groups the total chlorophyll a:carbon ratios were above that range. In routine monitoring of phytoplankton we recommend the use of the CHEMTAX program based on HPLC pigment analyses accompanied by a screening for the dominating species by microscopy, and by flow-cytometry for quantification of picocyanobacteria.

Phytoplankton community structure in Singapore's coastal waters using HPLC pigment analysis and flow cytometry

To investigate phytoplankton distributions in the coastal waters of Singapore, seawater samples from the Singapore Strait and the Johor Strait were analysed by high performance liquid chromatography and flow cytometry. Chlorophyll a (Chl a) concentrations were generally high, accompanied by significant amounts of fucoxanthin. Chlorophyll b and other major carotenoids, including zeaxanthin and alloxanthin, were also dominant in the Singapore Strait but were undetectable at most stations in the Johor Strait. Using ratios of Chl a to pigment that were characteristic of the different algal classes, it was shown that diatoms comprised ∼72% of the total Chl a in the Singapore Strait, whereas in the Johor Strait they comprised 88%. Synechococcus contributed another 18% of total Chl a in the Singapore Strait but was insignificant in the Johor Strait. Besides providing rapid enumeration of total phytoplankton, flow cytometric analysis was able to discriminate successfully two different types of Synechococcus (‘bright’ and ‘dim’) in the Singapore Strait based on their different orange fluorescence characteristics under blue light excitation. However, no ‘bright’ Synechococcus was found in the Johor Strait. Overall, the higher biodiversity of the phytoplankton community as well as the lower cell concentration and biomass in the Singapore Strait reflect a more oligotrophic/mesotrophic condition than the Johor Strait.

TAKAYAMA GEN. NOV. (GYMNODINIALES, DINOPHYCEAE), A NEW GENUS OF UNARMORED DINOFLAGELLATES WITH SIGMOID APICAL GROOVES, INCLUDING THE DESCRIPTION OF TWO NEW SPECIES1

A new potentially ichthyotoxic dinoflagellate genus, Takayama de Salas, Bolch, Botes et Hallegraeff gen. nov., is described with two new species isolated from Tasmanian (Australia) and South African coastal waters: T. tasmanica de Salas, Bolch et Hallegraeff, sp. nov. and T. helix, de Salas, Bolch, Botes et Hallegraeff, sp. nov. The genus and two species are characterized by LM and EM of field samples and laboratory cultures as well as large subunit rDNA sequences and HPLC pigment analyses of several cultured strains. The new Takayama species have sigmoid apical grooves and contain fucoxanthin and its derivatives as the main accessory pigments. Takayama tasmanica is similar to the previously described species Gymnodinium pulchellum Larsen, Gyrodinium acrotrochum Larsen, and G. cladochroma Larsen in its external morphology but differs from these in having two ventral pores, a large horseshoe‐shaped nucleus, and a central pyrenoid with radiating chloroplasts that pass through the nucleus. It contains gyroxanthin‐diester and a gyroxanthin‐like accessory pigment, both of which are missing in T. helix. Takayama helix has an apical groove that is nearly straight while still being clearly inflected. A ventral pore or slit is present. It has numerous peripheral, strap shaped, and spiraling chloroplasts with individual pyrenoids and a solid ellipsoidal nucleus. The genus Takayama has close affinities to the genera Karenia and Karlodinium.

Temporal variation in phytoplankton assemblages and pigment composition at a fixed station of the Rı́a of Pontevedra (NW Spain)

Phytoplankton composition and abundance were studied at a fixed station (P2, Rı́a of Pontevedra, NW Spain) weekly during a 2-year period (1999–2000). In addition to microscopic cell counts, a chemotaxonomic approach based on HPLC pigment analysis and CHEMTAX data processing was studied on two size classes. The contribution of the picoplankton fraction to the total chlorophyll (chl) a averaged 13±10%. Pigment suites of the picoplankton fraction were mainly provided by picoeukaryotes. Chl b dominated in the picoplankton whereas chls c ( c 2, c 1 and c 3) were the major accessory chlorophylls in the micro-nanoplankton. Despite this, fucoxanthin was by far the most abundant carotenoid in both size classes (often >70% of total carotenoids). Major ‘pigment groups’ in the picoplankton were ‘prasinophytes’ (with prasinoxanthin and carotenoids of the uriolide series) and ‘chlorophytes’, which contributed up to 60% total chl a during winter. ‘Diatoms’ and ‘haptophytes’ were other relevant picoplanktonic groups along the seasonal cycle. Micro-nanoplankton was dominated by ‘diatoms I’ (chl c 1 and chl c 2) and ‘diatoms II’ (chl c 3 and chl c 2), which contributed up to 70% of total chl a in spring. Chl c composition during diatom blooms exhibited higher chl c 1:chl c 2 ratios in winter–spring and higher chl c 3:chl c 2 ratios in summer–autumn.

Seasonal changes in the sensitivity of river microalgae to atrazine and isoproturon along a contamination gradient

A study was undertaken to investigate the environmental impact of herbicides on natural communities of freshwater periphyton and phytoplankton in the river Ozanne and in related nearby water reservoirs, including both pristine and pesticide- (atrazine and isoproturon) contaminated stations. The microalgal toxicity of both herbicides was investigated by short-term studies, using the in vivo fluorescence pattern to perform dose-effect experiments. The taxonomic composition of the communities sampled was assessed by microscopy and by HPLC pigment analysis. The EC50 (periphyton) or EC125 (phytoplankton) values, calculated using in vivo fluorescence endpoints, increased with the herbicide concentration found in the water. In contrast, the structure of the algal communities (periphyton) inhabiting the contaminated stations seemed to be permanently affected when compared to the reference community. A ‘memory effect’ could be detected, both in herbicide sensitivity and in the structure of periphytic communities that persisted even when peak contaminations had disappeared. This study shows that the response of algal communities is likely to reflect past selection pressures, and suggests that the function and structure of a community could both be modified by the persistent or repeated presence of microcontaminants in natural environments. We could use short-term ecotoxicological tests on freshwater microalgae to assess the effects of past temporary contaminations by agricultural pesticides, and combining this with diversity indices could make it possible to assess the ecotoxicological risk of herbicide contamination even when a complete chemical analysis of the contamination is not feasible.

Phytoplankton and pigment distributions in an anticyclonic slope water oceanic eddy (SWODDY) in the southern Bay of Biscay

An anticyclonic slope water oceanic eddy (SWODDY), named AE6, was sampled in the southern Bay of Biscay from 12 to 31 August 1998 to assess changes in the abundance and composition of phytoplankton assemblages related to the mesoscale feature. SWODDY AE6 showed characteristic biological signatures. A twofold increase in chlorophyll a concentration was found at the eddy centre relative to surrounding waters. Picoplankton cells accounted for a lower fraction of total chlorophyll a values at the eddy centre (44−50%) than outside the eddy (54−61%). Microscopic cell counts and HPLC pigment analysis showed that diatoms were almost entirely confined to the eddy centre, but both techniques yielded different results when studying other phytoplankton groups. Microscopic cell counts indicated that the spatial distribution of diatoms, dinoflagellates and unidentified flagellates was significantly influenced by SWODDY AE6, showing maximum abundance inside the mesoscale feature. HPLC pigment analysis provided more detailed information about the composition of pico–nanoplanktonic organisms. Pigment data processed by means of the CHEMTAX program showed "chlorophytes", "haptophytes" and "dinoflagellates II" (having haptophyte-like pigments and gyroxanthin-diester) as the more abundant "pigment classes" at the eddy centre, whereas dominance of "chlorophytes" and higher contribution of "cyanobacteria" (type Synechococcus) were estimated in the surrounding waters.

The use of HPLC pigment analysis to study microphytobenthos communities

The use of HPLC pigment analysis has become a widespread tool for investigating the taxonomic composition of phytoplankton. However, for micropytobenthos, due to the complexity of these communities and the accumulation of vegetal senescent material, the application of this technique presents further problems. Samples of unialgal cultures from representative taxa of microphytobenthos and samples of surface sediment from intertidal mudflats were collected, extracted in methanol and analyzed for photosynthetic pigments in a HPLC system, with a fluorimeter and a photodiode array detector. A total of 11 chlorophylline pigments and 19 carotenoids were identified. Absorbance chromatograms from cultures and natural populations are displayed. Pigment ratios from five species belonging to different taxonomic classes are compared. Pigment composition and diversity of intertidal muddy sites are discussed; the increase of degraded compounds of chlorophyll a and carotenoids along a vertical profile of 5 cm is shown on different sediment types.

High irradiance-induced changes in carotenoid composition and increase in non-photochemical quenching of Chl a fluorescence in primary wheat leaves

The effect of acclimation to high irradiance stress (HIS, 250 Wm-2) in wheat leaves grown under three different irradiances was investigated by HPLC analyses of pigments, chlorophyll a fluorescence parameters and photochemical activities of chloroplasts. Significant loss of beta-carotene was observed compared to the xanthophylls in all three types of seedlings exposed to HIS. However, the effect of HIS on neoxanthin and lutein contents was not significant. The loss of partial electron transport (Asc-DCPIP to MV, PSI activity) was less than the whole chain (H2O to MV) and PS II activity (H2O to DCPIP) suggesting that PS I is less susceptible to HIS compared to PS II. The percent of reductions in Fv/Fm and phi PS II were less in plants grown under high irradiance (HI-1, 30 Wm-2 and HI-2, 45 Wm-2) compared to those grown under moderate irradiance (MI, 15 Wm-2). On the other hand, the percent of NPQ increased more in the leaves of HI plants compared to the leaves of MI when exposed to HIS which suggests a more efficient non-radiative dissipation of excess excitation energy in HI plants compared to MI. These observations suggest that plants grown under relatively high irradiance are better adapted to HIS condition.

Estuarine phytoplankton group-specific responses to sublethal concentrations of the agricultural herbicide, atrazine

Atrazine is a common agricultural herbicide that is readily transported into estuaries through surface water runoff. In this study, we determined the short-term (24–48 h) sublethal effects of atrazine on estuarine phytoplankton biomass and community composition. Phytoplankton group-specific responses to atrazine exposure (25 μg l −1) were measured using natural water samples collected from two locations in Galveston Bay, Texas. Addition bioassays, coupled with HPLC pigment analysis, were used to quantify changes in the relative abundances of algal groups. For all algal groups except prasinophytes, the addition of atrazine in combination with nitrate was not significantly different from nitrate additions alone. These results suggest no significant negative effect of atrazine on phytoplankton under the specified environmental conditions for the bioassays. Although low concentrations of atrazine may have minimal impacts on phytoplankton, herbicide loadings need to be further characterized before generalizations can be applied to estuarine and coastal ecosystems.

Phytoplankton assemblages in the Gerlache and Bransfield Straits (Antarctic Peninsula) determined by light microscopy and CHEMTAX analysis of HPLC pigment data

Abstract The distribution and composition of phytoplankton assemblages were studied in the Gerlache and Bransfield Straits (Antarctic Peninsula) during the FRUELA 95 (December 1995) and FRUELA 96 (January 1996) cruises, using light microscopy and HPLC pigment analysis. Based on phytoplankton size and composition, two regions could be distinguished. The first region embraced the southwestern part of the Gerlache Strait, including a frontal system in the northeastern area. Chlorophyll (Chl) a values were generally high in surface waters (from 3.5 to 26.2 μg l−1). Phytoplankton assemblages in the stratified waters of the southwestern Gerlache Strait were dominated by large diatoms and the flagellate Pyramimonas sp. (mixed with Phaeocystis in FRUELA 95). Pigment patterns included Chl a, Chl b, different Chls c, and fucoxanthin as the major carotenoid. The frontal zone was characterized by a bloom of Pyramimonas. Following a transect from southwestern Gerlache Strait towards the Bransfield Strait an increased contribution of Chl b, violaxanthin, and two unknown carotenoids (tentatively identified as loroxanthin and loroxanthin-ester) was observed which paralleled the Pyramimonas distribution. The marker pigment lutein, usually associated with chlorophytes and prasinoxanthin-lacking prasinophyceans, was only detected at very low concentrations. The second region, embracing the Bransfield Strait and one station in the Drake Passage, was characterized by stratified waters and low Chl a concentration (from 0.18 to 3.88 μg l−1). Phytoplankton assemblages were dominated by the nanoplankter Cryptomonas sp. (FRUELA 95), the colonial haptophyte Phaeocystis cf. antarctica, and small flagellates (FRUELA 96). Pigment composition was mainly constituted by Chl a, Chl c2, Chl c3, alloxanthin, fucoxanthin, 19′-butanoyloxyfucoxanthin, and 19′-hexanoyloxyfucoxanthin. HPLC pigment data were processed using a factorization matrix program (CHEMTAX) to estimate the contribution of different algal classes to total Chl a. Four ‘algal groups’ were included in the chemotaxonomic approach: ‘diatoms’, ‘Phaeocystis’, ‘cryptophytes’, and ‘Pyramimonas’. A fifth ‘chemotaxonomic group’ was defined to reconstruct the distribution of an assemblage consisting of autotrophic peridinin-lacking dinoflagellates, some haptophytes, and chrysophytes, which were probably included by cell counting into the single group of ‘small flagellates’. The distribution patterns of the CHEMTAX groups were in agreement with cell counts of diatoms, cryptophytes, and Pyramimonas. Discrepancies were observed for P. cf. antarctica as well as for small flagellates and dinoflagellates. Significant positive correlations were found between phytoplankton cell counts and different Chls c, suggesting the chemotaxonomic usefulness of Chls c as marker pigments for phytoplankton groups in addition to carotenoids.