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A comparison of phytoplankton size-fractions in Mondsee, an alpine lake in Austria: Distribution, pigment composition and primary production rates

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Abstract

Production rates, abundance, chlorophyll a (Chl a) concentrations and pigment composition were measured for three size classes (<2μm, 2–11μm and >11μm) of phytoplankton from May to December 2000 in deep, mesotrophic, alpine lake Mondsee in Austria. The study focuses on differences among phytoplankton size fractions characterised by their surface area to volume ratio ([mm2l−1: mm3l−1]), pigment distribution patterns and photosynthetic rates. Particular attention was paid to autotrophic picophytoplankton (APP, fraction <2μm) since this size fraction differed significantly from the two larger size fractions. Among the three fractions, APP showed the highest surface area to volume ratios and a high persistence in the pattern of lipophilic pigments between temporarily and spatially successive samples (about 80% similarity of pigment composition between samples over seasons and depths). The epilimnetic abundance of APP varied seasonally with an annual maximum of 180×103cellsml−1 in June (at 4–9m). The minimum (October at 12m) was more than an order of magnitude lower (4.9×103ml−1). APP peaked during autumn and contributed between 24% and 42% to the total area-integrated Chl a (10–23mgm−2) and between 16% and 58% to total area-integrated production (5–64mgm−2h−1) throughout seasons.

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... Higher contribution values were described in a small meromictic lake (Little Round Lake, USA), where APP composed 22-97% of the planktonic primary production. In a mesotrophic deep lake in Austria (Lake Mondsee), APP constituted 16-58% of the total, area-integrated primary production (Greisberger et al., 2008). In eutrophic, humic shallow lakes from the floodplain of the Lower Parana River (Argentina) picoplankton production represented 36-93% of the total carbon fixation (Izaguirre et al., 2010;Rodriguez et al., 2012). ...
... Similar results were found in the case of Lake Simcoe (Canada), where winter APP contribution was 40% on average at nearshore sites and 30% at offshore sites (Kim et al., 2015), and showed a higher share (up to 90%) from spring to autumn. In contrast, in Lake Mondsee, APP contribution to total primary production was highest (as much as 58%) in the autumn-winter period (Greisberger et al., 2008). However, it should be noted that in the case of Lake Kinneret, the minimum temperature in winter does not drop below 10°C (Malinsky-Rushansky et al., 1997), as opposed to the abovementioned lakes, which usually possess ice cover. ...
... In general, the winter contribution of APP to phytoplankton biomass and primary production in the studied lakes was similar to values observed in other meso-eutrophic freshwater lakes (e.g. Greisberger et al., 2008;Kim et al., 2015;Ochs and Rhew, 1997;Peltomaa and Ojala, 2010). According to the earlier study on Lake Balaton, their contribution showed no seasonal trend at Station 1, ranging between 43 and 56% from May to October (Vörös et al., 1991). ...
Article
Studies on autotrophic picoplankton (APP; < 3 μm) in shallow lakes are mainly confined to the spring through fall seasons, when sampling efforts are not complicated by adverse and unsafe conditions that occur during winter. The aim of the present work was to study the role and diversity of winter APP communities in temperate shallow lakes by means of analysis of measures of size-fractionated photosynthesis and culture-based molecular taxonomic identification. Our results show that APP comprised a substantial part of planktonic primary production in shallow Central European great lakes (13–46% in Lake Balaton and 11–42% in Lake Fertő). Better acclimation of APP than that of the larger phytoplankton (> 3 μm) to low-temperature and low-light winter environment was confirmed by their higher maximum photosynthetic rate and light utilization parameter. Maximum photosynthetic rate and light saturation parameter increased significantly with both temperature and available light, but with different impact on the two size groups. Twenty-two picoeukaryotic strains were isolated and identified based on 18S rRNA gene sequence analysis. Taxonomic composition of the picoeukaryotic community in the studied shallow lakes was similar to other freshwater lakes in the temperate zone: members of genera Choricystis and Mychonastes were dominant, however, in Lake Balaton, common freshwater taxa such as Stichococcus bacillaris and Nannochloris bacillaris were also found.
... Vörös et al. (1991) found that autotrophic picoplankton contributed up to 50% of primary production in mesotrophic and hypereutrophic lakes of Hungary. On the other hand, Greisberger et al. (2008) analysed the contribution of three phytoplankton size fractions (\2, 2–11 and [11 lm) to the total chlorophyll-a (Chl-a) concentration and primary productivity in a mesotrophic alpine lake of Austria and found that the contribution of smaller phytoplankton to productivity depended upon seasonality, being up to 58% of primary productivity in autumn. In a shallow oligotrophic lake of Austria, Steitz & Velimirov (1999) found that picophytoplankton contributed with up to 74% of carbon fixation in the growing season. ...
... In this sense, the efficient use of low irradiances by picoplankton has been previously described (Fogg, 1986; Stockner & Antia, 1986; Raven, 1998; Callieri et al., 2007). Thus, our more elevated values recorded for P max and a values were even higher than those reported in other studies (Stockner, 1988; Schweizer & Heusel, 1992; Malinsky-Rushansky et al., 1997; Callieri et al., 2005; Greisberger et al., 2008, among others), all of them referred to systems less restricted in regard to irradiance conditions. The analysis on mean values and percentiles for P max , a and E k values obtained in this study indicates that the higher values obtained here for these parameters were generally an exception, and mean values were in the range as those reported in the literature. ...
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We conducted a 1-year survey in two humic shallow lakes from the floodplain of the Lower Paraná River, Laguna Grande Lake (LGL) and a relictual oxbow lake (ROL). We aimed to test two hypotheses: (1) the efficiency in light use of picoplankton (0.2–3 μm) is greater as light restriction increases and (2) the contribution of picoplankton to the total productivity is higher when the total photosynthetic biomass is lower. We performed P–E curves for picoplankton and nano- and microplankton (>3 μm) using the 14C assimilation technique. The light environments of the water bodies differed mainly owing to the development of free floating plants on the surface of the ROL and the dominance of phytoplankton in LGL. Primary productivity patterns in LGL were seasonality driven whilst in the ROL they were related to the coverage of floating macrophytes, which promoted light limitation and a lower productivity. In LGL, nano- and microplankton were in general more productive and the relative contribution of picoplankton to the total phytoplankton production decreased with the increase in total photosynthetic biomass. Hence, our study extends previously observed patterns to subtropical shallow lakes, where seasonality and free floating plants may influence the dynamics of phytoplankton production.
... This result is in agreement with Greisberger, Dokulil, and Teubner (2007) that found the maximum picophytoplankton cell numbers in deeper water layers (4-9 m). Also, these smallsized cyanobacteria were directly correlated with turbidity (p < 0.05), indicating their ability to survive in the low underwater light. ...
... In this context, the GLM analysis for the genera Microcystis and Aphanocapsa indicates that the total P at the reservoir surface may have contributed to the transition of genera dominance since it was the second most strong variable in the Aphanocapsa model and the weakest variable in the Microcystis model. The result is corroborated by Greisberger et al. (2007) who found that nutrients had a great effect on the growth of cyanobacteria, especially the picocyanobacteria. ...
... This result is in agreement with Greisberger, Dokulil, and Teubner (2007) that found the maximum picophytoplankton cell numbers in deeper water layers (4-9 m). Also, these smallsized cyanobacteria were directly correlated with turbidity (p < 0.05), indicating their ability to survive in the low underwater light. ...
... In this context, the GLM analysis for the genera Microcystis and Aphanocapsa indicates that the total P at the reservoir surface may have contributed to the transition of genera dominance since it was the second most strong variable in the Aphanocapsa model and the weakest variable in the Microcystis model. The result is corroborated by Greisberger et al. (2007) who found that nutrients had a great effect on the growth of cyanobacteria, especially the picocyanobacteria. ...
... Their great importance in the pelagic food webs has been largely documented (Stockner & Porter 1988, Weisse 1993, Vörös et al. 1998, Callieri & Stockner 2002, Drakare 2002, and now it is widely recognized that this fraction is the major contributor to the carbon fl ow in many aquatic systems, particularly in oligotrophic waters (Agawin et al. 2000, Bell & Kalff 2001, Richardson & Jackson 2007. Their contribution to total carbon production has been estimated ranging from 16 to 80% for different freshwater systems (Nagata et al. 1994, Steitz & Velimirov 1999, Greisberger et al. 2007). ...
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This article provides an overview of the studies on photosynthetic picoplankton (PPP) carried out in water bodies from different latitudes of Argentina, including Patagonian lakes and shallow lakes from the Chaco-Pampean Plain Region. The PPP of the different aquatic systems: shallow and deep lakes, turbid and transparent water bodies, and lakes with contrasting trophic state are characterized. We focus our attention on light intensity as the major axes of niche differentiation in Pcy. We present examples regarding the distribution of distinct Pcy ecotypes adapted to high-and low-light intensities at different depths in the water column of deep and shallow transparent lakes. In ultraoligotrophic Patagonian lakes phycoerythrin (PE)-rich picocyanobacteria (Pcy) are dominant, whereas eutrophic and hypertrophic shallow lakes from the Pampa Plain present a wide range of PPP abundances dominated by phycocyanin (PC)-rich Pcy. The relevance of the depth of the euphotic layer and nutrient concentration as the main abiotic features explaining the variability encountered are discussed. The PPP from eutrophic shallow lakes and relict oxbow lakes from wetlands from the Lower Paraná Basin are mainly represented by PC-rich Pcy, and Peuk in a lesser extent. Changes in the free-fl oating plants coverage were found to play a crucial role in structuring the PPP, and on the other hand, there is evidence of a negative relation between the PPP abundance and the hydrometric level. For different aquatic systems the PPP populations are compared by means of the patterns resulting from the fl ow cytometry analyses.
... The size classifications of planktonic organisms, in relation to phytoplankton, have important physical and physiological implications. The smaller cells have a lower velocity of sedimentation and are more efficient in terms of nutrient assimilation, growth, breathing and photosynthetic rate (Greisberger et al., 2008). This clearly shows the relative importance of the different size fractions that integrate a phytoplanktonic community, particularly in an ecosystem such as Lake Catalão, where a predominance of nanoplanktonic algae is found, especially Cyanobacteria and Chlorophyceae, in the low and high water periods of , respectively (Almeida and Melo, 2011. ...
Article
To evaluate the seasonal variation and isotopic composition of phytoplankton, water samples were collected monthly between October 2007 and November 2008 in Lake Catalão, a floodplain lake at the confluence between rivers Negro and Amazon. Analyses of total chlorophyll concentration and δ13C and δ15N isotopic abundances were made from particulate size fractions of 30-60, 10-30 and <10 μm in the littoral, pelagic, and floating meadows regions. Chlorophyll concentration was found to be inversely associated to lake depth, and high concentrations of chlorophyll in the floating meadows zone were significant. The fraction <10 μm was the most abundant representing in average more than 40 % of the particulate matter. The δ13C values were relatively constant during the study (-25.1 ‰ ~ -34.0 ‰), whereas the δ15N values showed strong variability (15.6 ‰ ~ 2.4 ‰), which has been attributed to the resuspension of sediments during mixing of the water column. Mixing associated to the sudden drop in temperature during the rising water period was an important event in the trophic and isotopic dynamics of the lake. Variations in chlorophyll content were generally associated with the dilution process, in which concentration was inversely correlated to the water level, whereas abundance was directly correlated to the water level.
... The size classifications of planktonic organisms, in relation to phytoplankton, have important physical and physiological implications. The smaller cells have a lower velocity of sedimentation and are more efficient in terms of nutrient assimilation, growth, breathing and photosynthetic rate (Greisberger et al., 2008). This clearly shows the relative importance of the different size fractions that integrate a phytoplanktonic community, particularly in an ecosystem such as Lake Catalão, where a predominance of nanoplanktonic algae is found, especially Cyanobacteria and Chlorophyceae, in the low and high water periods of , respectively (Almeida and Melo, 2011. ...
Article
Full-text available
To evaluate the seasonal variation and isotopic composition of phytoplankton, water samples were collected monthly between October 2007 and November 2008 in Lake Catalão, a floodplain lake at the confluence between rivers Negro and Amazon. Analyses of total chlorophyll concentration and δ13C and δ15N isotopic abundances were made from particulate size fractions of 30-60, 10-30 and <10 μm in the littoral, pelagic, and floating meadows regions. Chlorophyll concentration was found to be inversely associated to lake depth, and high concentrations of chlorophyll in the floating meadows zone were significant. The fraction <10 μm was the most abundant representing in average more than 40 % of the particulate matter. The δ13C values were relatively constant during the study (-25.1 ‰ ~ -34.0 ‰), whereas the δ15N values showed strong variability (15.6 ‰ ~ 2.4 ‰), which has been attributed to the resuspension of sediments during mixing of the water column. Mixing associated to the sudden drop in temperature during the rising water period was an important event in the trophic and isotopic dynamics of the lake. Variations in chlorophyll content were generally associated with the dilution process, in which concentration was inversely correlated to the water level, whereas abundance was directly correlated to the water level.
... Picocyanobacteria are photoautotrophs that, beside chlorophyll "a", also contain accessory pigments, such as phycocyanin and phycoerythrin, while their predominant carotenoid is zeaxanthin [63,64]. The abovementioned phycobiliproteins, including allophycocyanin, absorb the green and blue-green, through yellow-orange to red light, which significantly exceeds the spectrum of absorbance of chlorophyll "a" [65]. ...
Article
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Cyanobacteria of a picoplanktonic cell size (0.2 to 2.0 µm) are common organisms of both freshwater and marine ecosystems. However, due to their small size and relatively short study history, picoplanktonic cyanobacteria, in contrast to the microplanktonic cyanobacteria, still remains a poorly studied fraction of plankton. So far, only little information on picocyanobacteria toxicity has been reported, while the number of reports concerning their presence in ecosystems is increasing. Thus, the issue of picocyanobacteria toxicity needs more researchers’ attention and interest. In this report, we present information on the current knowledge concerning the picocyanobacteria toxicity, as well as their harmfulness and problems they can cause.
... Another major shortcoming is the high lower size limit (5 μm) of standard microscopy that does not allow determining the amount of autotrophic picoplankton (<3 μm) present [7,8]. The contribution of autotrophic picoplankton to total primary production may reach 50-90% in oligotrophic lakes and oceans [9] and 30-70% in meso/eutrophic lakes [10]. ...
Article
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Pigment-based chemotaxonomy and CHEMTAX software have proven to be a valuable phytoplankton monitoring tool in marine environments, but are yet underdeveloped to determine algal assemblages in freshwater ecosystems. The main objectives of this study were (1) to compare the results of direct microscopy and CHEMTAX in describing phytoplankton community composition dynamics in a large, shallow and eutrophic lake; (2) to analyze the efficiency of the pigment-based method to detect changes in phytoplankton seasonal dynamics and during rapid bloom periods; (3) to assess the suitability of specific marker pigments and available marker pigment:chlorophyll a ratios to follow seasonal changes in eutrophic freshwater environment. A 5-year (2009-2013) parallel phytoplankton assessment by direct microscopy and by CHEMTAX was conducted using published marker pigment:chlorophyll a ratios. Despite displaying some differences from microscopy results, the pigment-based method successfully described the overall pattern of phytoplankton community dynamics during seasonal cycle in a eutrophic lake. Good agreement between the methods was achieved for most phytoplankton groups - cyanobacteria, chlorophytes, diatoms and cryptophytes. The agreement was poor in case of chrysophytes and dinoflagellates. Our study shows clearly that published marker pigment:chlorophyll a ratios can be used to describe algal class abundances, but they need to be calibrated for specific freshwater environment. Broader use of this method would enable to expand monitoring networks and increase measurement frequencies of freshwater ecosystems to meet the goals of the Water Framework Directive.
... As described in the previous chapter, the lack of grazing control may be a good explanation for the extremely high planktonic picophytoplankton abundances; however, other factors could also contribute to the success of picophytoplankton. A high TSS concentration results in strong light limitation, and picophytoplankton have a selective advantage over larger phytoplankton under light-limited conditions [9,[45][46][47][48]. Shallow, turbid, saline lakes have been previously described as highly light-limited aquatic habitats: the average Z mix /Z eu ratio in these waters was 2.8, which still allowed net photosynthesis (the critical value is above 5-5.7), ...
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The extreme environmental conditions of the diverse saline inland waters (soda lakes and pans, hypersaline lakes and ponds) of the Carpathian Basin are an advantage for picophytoplankton. The abundance of picophytoplankton in these waters can be up to several orders of magnitude higher than that in freshwater shallow lakes, but differences are also found within different saline water types: higher picophytoplankton abundances were observed in hypersaline lakes compared to humic soda lakes, and their highest numbers were detected in turbid soda lakes. Moreover, their contribution to phytoplankton biomass is higher than that in shallow freshwater lakes with similar trophic states. Based on long-term data, their ratio within the phytoplankton increased with turbidity in the case of turbid soda lakes, while, in hypersaline lakes, their proportion increased with salinity. Picocyanobacteria were only detected with high abundance (>106–107 cells/mL) in turbid soda lakes, while picoeukaryotes occurred in high numbers in both turbid and hypersaline lakes. Despite the extreme conditions of the lakes, the diversity of picophytoplankton is remarkable, with the dominance of non-marine Synechococcus/Cyanobium, Choricystis, Chloroparva and uncultured trebouxiophycean green algae in the soda lakes, and marine Synechococcus and Picochlorum in the hypersaline lakes.
... For instance, the small-sized phytoplankton fraction (picophytoplankton: 0.2–2 lm) do best in resource-poor habitats in comparison with the larger size fraction (phytoplankton [2 lm) (Callieri 2008) for the same reason as bacteria (high surface to volume ratio). Therefore, picophytoplankton often dominates the summer production in oligotrophic clearwater lakes (Stockner 1991; Callieri et al. 2007) and in autumn in the mesotrophic, Alpine lake Mondsee in Austria (Greisberger et al. 2008). In addition, picophytoplankton seems to be pre-adapted to low levels of photosynthetically active radiation (PAR; Callieri et al. 1996; Gervais et al. 1997). ...
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The shallow Andean North Patagonian lakes are suitable environments for the evaluation of autotrophic and heterotrophic production under a scenario of high radiation in high dissolved organic matter (DOM) systems. We aimed to study the balance between primary and bacterial production in three shallow Andean lakes, in a summer sampling (high irradiance condition). Our hypothesis is that two factors would interact: high light and high DOM, affecting bacteria and algae. We carried out experiments of bacterial production (BP) by measuring [14C]-l-leucine incorporation and PP by 14C uptake in two fractions: picophytoplankton and phytoplankton>2μm. Cell abundance, chlorophyll a, nutrients, DOM, light, and temperature were also measured. The contribution of picophytoplankton to total primary production (PP) was, in general, very high exceeding 50%. Picophytoplankton was photosynthetically more efficient than the larger autotrophs in all lakes. We observed a decrease in PP at surface levels due the high solar irradiances, while BP was not affected. Changes in the PP:BP ratios were observed in relation to DOM content and light effect. Our data indicate that the amount of available DOM drives the balance between PP and BP. However, solar radiation should be included as an important factor since PP:BP ratio may decrease because of PP photoinhibition.
... Despite their small size and thus comparatively low total biomass, their contribution to primary production is far from negligible. Globally, APP have been estimated to be responsible for at least 10% of net primary production in aquatic habitats (Raven, 1998), and locally in lakes, they can contribute from 40 to 90% of total primary production (Belykh et al., 2006; Greisberger, Dokulil & Teubner, 2008; Peltomaa & Ojala, 2010). This is because the small-sized APP have higher growth rates and are more effective in nutrient and light acquisition than larger phytoplankton, especially under nutrient-and light-deficient conditions (Raven, 1998). ...
Article
1. The tiny non-motile autotrophic picoplankton (APP; size range 0.2–2 μm) occur in all types of aquatic habitats and are comprised of prokaryotic as well as eukaryotic taxa. In the Boreal Zone, the majority of lakes have high concentrations of coloured humic substances that can adversely affect lake light climate and cause steep summertime stratification resulting in epilimnetic nutrient depletion. APP are more effective in nutrient and light acquisition than larger phytoplankton and thus should be competitive in humic lakes. 2. Most lacustrine APP studies have been based on short sampling periods, and thus, interannual variation and its drivers are still unclear. We studied APP in the small, boreal, humic Lake Valkea-Kotinen during five open-water periods in 2002–06 to determine interannual variation and the importance of meteorological drivers for APP dynamics. 3. Total APP showed a bimodal annual pattern, but the timing and vertical location of the two maxima varied during the study. In general, APP thrived in warm water and the most important abiotic factor controlling APP was stability of the water column (Ns). On average, 82% of APP were found in the epilimnion or metalimnion during summertime stratification. 4. There was niche separation of APP and larger phytoplankton in the lake because, with only one exception, APP maxima occurred separately from the maxima of larger phytoplankton. 5. Two groups, solitary eukaryotic APP and colonial picocyanobacteria (Merismopedia warmingiana), responded differently to the abiotic factors. Solitary APP preferred high water colour and low pH, both of which occurred after heavy rain, whereas colonial APP did not fare well when water colour was high. Our findings suggest that when future climate change-related processes increase incoming allocthonous organic matter load from the catchment, solitary eukaryotic APP will be favoured.
... A lowlight-adapted APP strain can have a light-saturation parameter of as low as 3 μmol m -2 s -1 [43]. Based on fractionated photosynthesis measurements, APP was better acclimated to low light than larger-sized phytoplankton, which was confirmed by their higher light utilization parameter [44,45]. This low light acclimation of APP was particularly apparent in a shallow turbid alkaline pan [19]. ...
Article
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Autotrophic picoplankton (APP) abundance and contribution to phytoplankton biomass was studied in Hungarian shallow lakes to test the effect of inorganic turbidity determining the size distribution of the phytoplankton. The studied lakes displayed wide turbidity (TSS: 4–2250 mg l-1) and phytoplankton biomass (chlorophyll a: 1–460 μg l-1) range, as well as APP abundance (0 and 100 million cells ml-1) and contribution (0–100%) to total phytoplankton biomass. Inorganic turbidity had a significant effect on the abundance and contribution of APP, resulting in higher values compared to other freshwater lakes with the same phytoplankton biomass. Our analysis has provided empirical evidence for a switching point (50 mg l-1 inorganic turbidity), above which turbidity is the key factor causing APP predominance regardless of phytoplankton biomass in shallow turbid lakes. Our results have shown that turbid shallow lakes are unique waters, where the formerly and widely accepted model (decreasing APP contribu
... Mesoand oligotrophic conditions support the growth and colonisation of APP. The smaller cells are better able to cope with low nutrient concentrations due to their high surface:size ratio (Lavin & Lourenço, 2005;Greisberger et al., 2008) and can therefore outcompete larger plankton. Stockner et al. (2000) provide a possible explanation for the decline of the abundance of APP during summer by grazing. ...
Article
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In this study, we aimed to investigate the spatio-temporal distribution patterns of the picocyanobacterium Synechococcus, an important contributor to primary production in many freshwater lakes. Our study sites were four lakes with different trophic states within the Osterseen Lake District in Southern Germany. Flow cytometry counts and next-generation sequencing were used from April to October 2015 to analyse the occurrence of Synechococcus and heterotrophic prokaryotes in relation to physical and chemical habitat properties. Synechococcus was identified as the main representative of the autotrophic picoplankton, but cell counts varied widely. The Synechococcus taxa identified by flow cytometry were confirmed by sequencing data, but the comparison of the flow cytometry counts and sequence data revealed discrepancies for cells in the exponential phase. The eutrophic Lake Schiffhuettensee was dominated by algae and had the highest abundance of heterotrophic prokaryotes. The presence of distinct operational taxonomic units of Synechococcus varied seasonally and was lake-specific, indicating local niche adaptation. Our study sheds light on the ecology of these important primary producers in freshwater systems. Furthermore, the discrepancy observed with the direct comparison of the widely used methods of next-generation sequencing and flow cytometry should serve as a caveat for future data analysis.
... Lake Mondsee is an example of an originally ice-covered temperate lake undergoing a transition from a dimictic to a monomictic mixing pattern in the course of the ongoing lake warming (Ficker et al., 2017). Lake Mondsee is one of the best studied lakes in Austria with long-term phytoplankton datasets from the last 40 years (Findenegg, 1969;Dokulil & Skolaut, 1986;Dokulil & Jagsch, 1992;Greisberger et al., 2008;Dokulil & Teubner, 2012). Even longer records ([ 50 years) are available for some abiotic parameters such as Secchi depth . ...
Article
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Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community.
... Lake Mondsee is an example of an originally ice-covered temperate lake undergoing a transition from a dimictic to a monomictic mixing pattern in the course of the ongoing lake warming (Ficker et al., 2017). Lake Mondsee is one of the best-studied lakes in Austria with long-term phytoplankton data sets from the last 40 years (Dokulil and Skolaut, 1986;Dokulil and Teubner, 2012;Greisberger et al., 2008). The annual phytoplankton biomass in the upper 20 m of L. Mondsee is dominated by diatoms, cryptophytes, chrysophytes, and the cyanobacterium P. rubescens, which peaks below the thermocline (reaching up to 85% of total biovolume), whereas this species is almost absent in the epilimnion (Dokulil and Teubner, 2012). ...
Article
We combined profiling of the bloom-forming and potentially toxigenic cyanobacterium Planktothrix rubescens using a multiparameter probe equipped with a phycoerythrin sensor (in vivo fluorometry, IVL) in Lake Mondsee, Austria, with flow cytometric live analyses of discrete samples taken from several depths in the upper 20 m of the water column. Results obtained by IVL and acoustic flow cytometry (AFC) were compared to microscopic analyses of integrated (0-21 m) water samples using fixed material. This comparison was made because the integrated samples are used for the Austrian monitoring programme according to the EU Water Framework Directive. We demonstrate that AFC provides quantitative analyses of the filaments of P. rubescens that are significantly correlated to IVF and microscopic analyses, allowing rapid (within hours) and more precise calculation of P. rubescens biomass than estimates derived from IVL. Our analysis shows that vertically integrated water samples provide unreliable information on the concentration of P. rubescens in the upper surface waters and on the peak concentration of P. rubescens within the water column. We conclude that the protocol that we developed is superior to the current monitoring practice.
... In the frame of our work, the picoplanktonic members of Cyanobacteria were also detected. Due to their high surface-area-to-volume ratio, these bacteria usually prefer meso-and oligotrophic conditions [42]. Thus, with the decrease of trophy towards the Siófok Basin, the role of Synechococcus picoalgae in the total production increased (from 4% in the nutrient-dense Szigliget basin to 8-9% of the sequence reads in the middle and eastern basins). ...
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Lake Balaton is the largest European shallow lake, which underwent cultural eutrophication in the ‘70–80s. Therefore, strict pollution control measures were introduced and the water quality has become meso-eutrophic since the millennium. Due to the touristic significance and change in trophic levels of the lake, numerous ecological studies were carried out, but none of them was focused on both benthic and planktonic microbial communities at the same time. In our study, an attempt was made to reveal the spatial bacterial heterogeneity of the Lake Balaton and Zala River by 16S rDNA terminal restriction fragment length polymorphism fingerprinting and Illumina amplicon sequencing methods in the summer of 2017. According to the molecular biology results, mostly well-known freshwater microorganisms, adapted to nutrient-poor conditions were found in the pelagic water column. The LD12 subclade member Fonsibacter ubiquis, the cyanobacterial Synechococcus sp. and unknown Verrucomicrobia species were abundant in the less nutrient-dense basins, while the hgcI clade members showed various distribution. In the estuary and in the nutrient-dense western part of the lake, some eutrophic conditions preferring cyanobacteria (filamentous Anabaena and Aphanizomenon species) were also detectable. The benthic microbial community showed higher diversity, according to the observed appearance of microorganisms adapted to the deeper, less aerated layers (e.g. members of Desulfobacteraceae, Nitrosomonadaceae).
... This finding supports the model of APP biomass growth with decreasing phosphorus concentrations, as described by Stockner & Shortreed (1991) and Stockner et al. (2000). A possible explanation for the dominance of APP is the small size and hence low surface-size-ratio (Lavín & Lourenço, 2005;Greisberger et al., 2008). Due to this ratio, the organisms are able to absorb and transport nutrients inside their cells more effectively than larger competitors. ...
Article
Picocyanobacteria are important primary producers in freshwater; however, there is still a knowledge gap regarding their diversity at the strain level. For this reason, the microbial diversity of four lakes with different trophic states was investigated by sequencing of the 16S rRNA gene using universal primers. The study was performed in selected lakes of the Osterseen Lake District, Germany, from 2012 to 2014 (Lake Schiffhuettensee: eutrophic; Lake Ostersee: mesooligotrophic; Lake Groebensee: oligotrophic; Lake Lustsee: oligotrophic). It was determined that the bacterial community of each of these lakes was characterized by one or more specific phyla. Within the autotrophic plankton, the picocyanobacterium Synechococcus sp. dominated oligotrophic habitats, whereas eukaryotic algae prevailed in eutrophic lakes. The study focused on the occurrence of cyanobacteria, specifically the genus Synechococcus. Genetic analysis of the 16S rRNA gene revealed an extendend diversity of freshwater Synechococcus. The occurrence of the identified operational taxonomic units of Synechococcus did not correlate with the trophic state of their habitat, suggesting that the current, underestimated diversity of picocyanobacteria deserves increased consideration in assessments of microbial and freshwater biodiversity.
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Export Date: 8 January 2014, Source: Scopus
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This study investigated the performance of a spectral similarity index and a multivariate partial least-squares regression technique for detecting the presence of the gyroxanthin-diester-carrying toxic dinoflagellate Karenia mikimotoi from measurements of spectral light absorption. The methods were applied to fourth-derivative absorption spectra of K. mikimotoi mixed with the toxic dinoflagellate Prorocentrum minimum, which does not contain gyroxanthin-diester. Acclimating the cultures to different light and nutrient conditions allowed us to evaluate the sensitivity of the methods to changes in pigmentation and intracellular light absorption (pigment packaging) of the algae. Both methods were able to determine the fraction of K. mikimotoi and the gyroxanthin-diester concentration. However, whereas the partial least-squares predictions were almost insensitive to the induced variability in optical properties of the algae, predictions based on the similarity index differed significantly depending on the acclimation of the algae. Furthermore, discriminating K. mikimotoi from natural phytoplankton assemblages indicated a significant influence of cell-size composition, through pigment packaging, on the accuracy of the similarity index. Our results suggest that optical discrimination of phytoplankton species from spectral absorption signatures will improve significantly by applying the partial least-squares regression technique.
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Nine lakes in northern Wisconsin were sampled from February through September 1996, and HPLC analysis of water column pigments was carried out on epilimnetic seston. Pigment distributions were evaluated throughout the water column during summer in Crystal Lake and Little Rock Lake. The purpose of our study was to investigate the use of phytopigments as markers of the main taxonomic groups of algae. As a first approach, multiple regression of marker pigments against chlorophyll a (chl a) was used to derive the best linear combination of the main xanthophylls (peridinin, fucoxanthin, alloxanthin, lutein, and zeaxanthin). A significant regression equation (r2= 0.98) was obtained for epilimnion data. The good fit indicates that the chl a:xanthophyll ratios were fairly constant in the epilimnion of the nine lakes over time. Chlorophyll a recalculated from the main xanthophylls in each sample showed good agreement with measured chl a in epilimnetic waters. A second approach used the CHEMTAX program to analyze the same data set. CHEMTAX provided estimates of chl a biomass for all algal classes and allowed distinction between diatoms and chrysophytes, and between chlorophytes and euglenophytes. These results showed a reasonably good agreement with biomass estimates from microscope counts, despite uncertainties associated with differences in sampling procedure. Changes of pigment ratios over time in the epilimnetic waters were also investigated, as well as differences between surface and deep samples of Little Rock Lake and Crystal Lake. We found evidence that changes in the ratio of photoprotective pigments to chl a occurred as a response to changes in light climate. Changes were also observed for certain light-harvesting pigments. The comparison between multiple regression and CHEMTAX analyses for inferring chl a biomass from concentrations of marker pigments highlighted the need to take account of variations in pigment ratio, as well as the need to acquire additional data on the pigment composition of planktonic algae.
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Autotrophic picoplankton (APP) are distributed worldwide and are ubiquitous in all types of lakes of varying trophic state. APP are major players in carbon production in all aquatic ecosystems, including extreme environments such as cold ice-covered and/or warm tropical lakes and thermal springs. They often form the base of complex microbial food webs, becoming prey for a multitude of protozoan and micro-invertebrate grazers, that effectively channel APP carbon to higher trophic levels including fish. In this review we examine the existing literature on freshwater autotrophic picoplankton, setting recent findings and current ecological issues within an historic framework, and include a description of the occurrence and distribution of both single-cell and colonial APP (pi- cocyanobacteria) in different types of lakes. In this review we place considerable emphasis on methodology and ecology, including sampling, counting, preservation, molecular techniques, measurement of photosynthesis, and include extensive comment on their im- portant role in microbial food webs. The model outlined by Stockner of an increase of APP abundance and biomass and a decrease of its relative importance with the increase of phosphorus concentration in lakes has been widely accepted, and only recently con- firmed in marine and freshwater ecosystems. Nevertheless the relationship which drives the APP presence and importance in lakes of differing trophic status appears with considerable variation so we must conclude that the success of APP in oligotrophic lakes worldwide is not a certainty but highly probable.
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Two approaches may be utilized to explain the predominance of picocyanobacteria (Pcy) in oligotrophic lakes: the analysis of their interannual evolution in one single take and their relative importance in different lakes along a trophic gradient. Here we discuss results from field data on picocyanobacteria over several seasons from a deep oligotrophic subalpine lake - Lago Maggiore, and variables influencing their abundance. Comparing data from lakes along a trophic gradient, no simple relationship emerges between lake's trophic state and picocyanobacteria abundance and contribution to total phytoplanktonic biomass. That is, trophic state alone cannot explain the success/absence of picocyanobacteria that appear to be favored under P limitation, but seem more sensitive to grazing pressure and light. In some oligotrophic lakes, if light climate, grazing, and competition are favorable, picocyanobacteria can grow rapidly, out-compete competitors and become very abundant, but there are a host of factors that can influence the outcome of this competition, and ultimately influence Pcy success in lakes of all trophic types.
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Phytoplankton composition and community structure in the south-western Pacific Ocean were examined at sea using flow cytometry and epifluorescence microscopy to explore the relationships among distributions of picophytoplankton populations and a variety of nitrogen fixing cyanobacteria. The cruise track began in New Zealand, extended north via New Caledonia to 13°S, and continued east to 13.9°S 173.2°W. The track crossed a large bloom of the filamentous nitrogen-fixing cyanobacteria Trichodesmium centered around New Caledonia. Within Trichodesmium blooms, abundances of Synechococcus were elevated 10-fold; however, there was no significant enrichment of Prochlorococcus, picoeukaryotic algae, or heterotrophic bacteria. Unicellular coccoid cyanobacteria (> 2 μm), which resemble the nitrogen-fixing Crocosphaera spp., were observed in waters > 27 °C along the eastward track and were most abundant at the deep oceanic stations where Trichodesmium was absent or present at very low abundances. These Crocosphaera-rich, Trichodesmium-poor stations were characterized by lower dissolved iron concentrations compared to coastal stations where Trichodesmium tended to be more abundant. Given the apparent mutually exclusive distributions of these two groups of cyanobacteria, further examination of N2 fixation within the pico- and nanoplankton components of the phytoplankton community is needed.
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The scaling of metabolic rate with the size of algae has been discussed and researched at length. The observation that algae usually have exponents b in the equation R = a(.)W(-b) (where R is the specific growth rate, W is the organism [cell] biomass, and a and b are constants) equal to or higher than the value of -0.25 for many other organisms is generally related to resource-saturated (maximal) values of R. Recent work has shown that the exponent b for light-limited growth is more negative than -0.25. This was predicted from considerations of the package effect in photon absorption, as modulated by the volume-specific pigment content of the cells, and the photosynthetic unit size. Further work is needed to extrapolate these findings to fluctuating light environments. This minireview puts the recent work into a broader context and suggests how further work could quantify the roles of optical thickness and of spatial and temporal variations in the radiation field in determining metabolic rates.
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For 30 years, study after study has shown that respiration rates increase as similar to 0.75 of body size for organisms ranging from protozoans to mammals. However, a number of studies suggested that the respiration-size relationship for algae may be a rare exception to this general rule. Algal respiration may be almost proportional to cell size, such that the slope of the respiration-size relationship is closer to unity. The present study examined the effect of cell size and taxon on phytoplankton respiration, using data collected from the literature. To this end, we collected a data set of 178 observations of algal respiration and cell size representing six divisions-chlorophytes, chrysophytes, cyanophytes, euglenophytes, pyrrophytes and rhodophytes. The relationship between respiration (R, in pl O-2 cell(-1) h(-1)) and cell carbon content (C, in pg C cell(-1)) is described as R = 0.030C(0.93) and the exponent is significantly >3/4. When we expressed cell size in terms of volume, the exponent decreased to 0.88 but this is still significantly >3/4. Among the six divisions studied, chlorophytes, euglenophytes and rhodophytes seemed to differ significantly in their respiration-size relationship from other taxa. However, euglenophytes and rhodophytes have such small size ranges that no meaningful relationships can be developed for those groups alone. The chlorophyte respiration-size relationship has obvious patterns in its residuals which may indicate that significant sources of error were not controlled in these heterogeneous data. Thus, for the present, the general model seems most appropriate for the prediction of respiration rates of phytoplankton.
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Algal chlorophyll, carbon fixation and alkaline phosphatase activity were net-fractionated using 22-μm, and 75-μm screens in three lakes with contrasting zooplankton communities. Size distributions of algal biovolume were also determined through microscopic examination. Relatively good correspondence was found between size distributions obtained through net fractionation and those determined by microscopic examination. Biovolume-specific carbon fixation and chlorophyll decreased with increasing fraction size but no differences were observed among fractions for chlorophyll-specific carbon fixation. High algal standing stocks and low phosphorus deficiency in Tuesday Lake were attributed to low grazing pressure by small, inefficient zooplankton and possible limitation by nutrients other than phosphorus. Algal standing stocks were low and phosphorus deficiency was high in Peter and Paul Lakes, in which the zooplankton was dominated by large grazers. Different algal size fractions experienced differing degrees of phosphorus deficiency. These size fraction differences in P-deficiency in Peter and Paul Lakes were attributed to differences in algal species composition and to differing levels of zooplankton grazing pressure and nutrient regeneration. A unimodal relationship between relative nanoplankton biovolume and zooplankton biomass was found and reflects the positive (nutrient regeneration) and negative (grazing mortality) effects of zooplankton on the algal community.
Picoplankton consists of those organisms found in the open waters of seas and lakes which are capable of passing through a filter with 2 μ m pores but not through one with 0.2 μ m pores. Cells in this size range are well adapted to planktonic life in that they sink extremely slowly and are more efficient than larger forms in taking up nutrients and absorbing radiant energy. Picophytoplankton includes coccoid cyanobacteria and a variety of eukaryotic algal forms. Strains studied in the laboratory have all been found to show maximum growth at relatively low irradiances, the eukaryotic forms being more efficient than the cyanobacteria in utilizing the blue light which predominates at the bottom of the photic zone in clear oceanic waters. Oceanic strains of coccoid cyanobacteria, however, are characterized by high concentrations of phycoerythrin, which appears to function as a nitrogenous reserve as well as an accessory pigment in photosynthesis. The seasonal and spatial distribution of picophytoplankton seems explicable in terms of these physiological characteristics. Numbers of coccoid cyanobacteria have shown a striking correlation with temperature in a number of different situations. Heterotrophic bacteria are also included in the picoplankton, and a review of the information concerning them suggests that they form a highly dynamic population subsisting on dissolved organic matter liberated by living phytoplankton and zooplankton and by decomposition of dead matter. The productivity of this population in the euphotic zone approaches that of the phytoplankton. Both the picophytoplankton and the bacterioplankton are preyed on by phagotrophic flagellates. Both bacteria and flagellates are active in regeneration of mineral nutrients. Regardless of the salinity, temperature or nutrient status of the water, the numbers of heterotrophic bacteria, picophytoplankton and flagellates tend to be around 106, 104 and 103 organisms per millilitre respectively. It is suggested that these populations form a basic, self-sustaining and self-regulating community in all natural waters. From present information, it seems that little of the energy which passes through this community finds its way into the larger planktonic organisms, but the role of picoplankton in recycling nutrient elements is of great importance in the marine ecosystem.
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Ahstruct Competition at different levels of phosphorus availability was observed in continuous cul- tures of freshwater phytoplankton communities. Although dilution rates ranged lo-fold in all, the outcome of competition was usually similar among cultures and resulted in dominance of the small diatom Synedra acus. Species growth rates decreased significantly with increas- ing cell, or colony, size among the 16 speci.es examined. A variable internal stores model of algal growth, combined with functions relating its species-specific parameters to cell size, correctly predicted the observed inverse correlation between cell size and competitive ability. The model's predictions, and the empirical correlation between size and growth, were poor at low dilution rates (
Article
Discovery of minute (0.2-2.0 mu m) algal picoplankton in the late 1970s in both marine and freshwater ecosystems has led to a resurgence of research activity throughout the world, addressing questions related to taxonomy, distribution and abundance, physiology and biochemistry, and ecological considerations of their role in aquatic food webs. To many, their discovery provided the 'missing link' in the controversial carbon supply-demand question in the world's oceans and gave further credibility to the emerging new paradigm on the importance of microbial food webs in energy transfer and nutrient recycling in aquatic systems. -from Authors
Article
Acidification and bubbling was found superior to membrane-filtration for post-incubation treatment of 14C-productivity samples. The method eliminates errors associated with filtration. Results are compared with those of conventional and corrected filtration procedures, and application of the method is discussed.
Article
Size-fractionated phytoplankton biomass and primary production, together with net community metabolism, were measured in a coastal ecosystem (Ria de Vigo, NW-Spain) during a full annual cycle (July 2001-July 2002). On a seasonal scale, this ecosystem was characterized by two distinct oceanographic conditions, namely upwelling and downwelling favourable seasons. During the upwelling season, total chlorophyll a (Chl a) and particulate organic carbon production rates (POC-pr) were in the range 36-129 mg Chl a m(-2) and 89-834 mg C m(-2) h(-1), respectively, and were mainly accounted for (> 80%) by the microphytoplankton size fraction (> 20 pm). During the downwelling season, total Chl a and POC-pr were much lower (< 27 mg Chl a m(-2) and < 97 mg C m(-2) h(-1), respectively), and the pico- (< 2 mu m) and nano-(2-20 mu m) phytoplankton size fractions significantly increased their contribution to total Chl a (46-87%) and POC-pr (30-86%). The seasonal and short-time scale variability in the hydrographic conditions, in particular upwelling intermittency, provides a feasible explanation for the continuous dominance of large-sized phytoplankton during the upwelling period. Shelf water intrusions, continuous vertical mixing and the size-dependent limitation in light acquisition (package effect), suffered in a higher degree by larger phytoplankton, were likely to account for the shift in phytoplankton size structure during the downwelling period. During the upwelling season, community respiration represented a minor fraction of gross primary production (15-30%), which highlights the large export potential of organic matter by this ecosystem. On the contrary, community respiration accounted for a major fraction of primary production (85%) during the downwelling period, which suggests that most of the photosynthesised organic matter was remineralised within the ecosystem. Although the microbial plankton community of the Rfa de Vigo exhibits a net autotrophic functioning throughout the year, the magnitude of the carbon flows and budgets seems to be dependent on phytoplankton size structure. (c) 2005 Elsevier Ltd. All rights reserved.
Article
Direct counts of coccoid cyanobacteria were made by the autofluorescence technique over a period of two years in the waters of the Menai Straits and western Irish Sea. In both situations there was a seasonal fluctuation, from low numbers of around 103 cells ml-1 in winter to high numbers of around 105 cells ml-1 in summer. Numbers in the Straits were not affected by the strong tides in these waters but were correlated with water temperature. Three size classes of cyanobacterial cell were distinguished and of these the two smallest, having dimensions of 0·5-0·7×0·8 μm and 0·7-0·9×1·0-1·2 μm, preponderated in both inshore and offshore waters, together making up 75–80% of the total. A third group, 1-1·2×1·4-2·2 μm, was more abundant in inshore waters in which it occasionally equalled the smallest size group in abundance. Hydrographic sections across a tidal mixing front in the western Irish Sea showed that coccoid cyanobacteria were abundant in surface stratified, bottom stratified and mixed waters but tended to be most numerous in the surface stratified water in summer when they sometimes accumulated in a surface patch adjacent to the front.
Article
Against a background of controversy concerning the absolute magnitude of biological productivity in the oligotrophic, tropical ocean1–4, evidence is accumulating for the existence there of a population of minute, unicellular organisms collectively known as picoplankton5,6. In the tropical Pacific, it has been estimated recently7 that cells passing a 1-µm screen (picoplankton) make a very substantial contribution to the rate of turnover of phytoplankton biomass. On the other hand, previous work in the tropical Atlantic8 led to the conclusion that particles in the size class ≲3 µm are fragments of larger cells and metabolically inert. We present here the first data on the photosynthetic characteristics of picoplankton collected at sea. This new evidence from the tropical North Atlantic supports the argument that the picoplankton contains a significant, metabolically-active, autotrophic component, capable of supplying about 60% of the total primary production hi an open-ocean ecosystem.
Article
Allometric relations between physiological processes and cell volume and surface area are combined with the variable-internal-stores model of growth to predict the ability of hypothetical phytoplankton to compete for phosphorus at equilibrium. The analysis shows that for spherical cells, smaller cells are better competitors than large ones. For cells that are very elongated in shape, however, large cells are often better competitors than small ones. The cells predicted to be the best competitors compare favorably in size and shape with the species observed to dominate in phosphorus-limited chemostats at equilibrium.
Article
1. Pigment composition was measured in natural phytoplankton samples from Lake Kinneret, Israel. From March through June 1998, the dinoflagellate Peridinium gatunense Nygaard mostly contributed more than 95% of the algal biomass. Peak densities were found in April, close to the water surface, with >109 cells m−3, chlorophyll (Chl) a concentration of 380 mg m−3 and areal Chl-a density of >1300 mg m−2. 2. Cellular concentrations of Chl-a changed between 201 and 282 pg cell−1, but did not show a defined temporal fluctuation. 3. The mass ratio of Chl-c to Chl-a changed from March to June between 0.16 and 0.22, and the peridinin to Chl-a ratio changed from 0.25 to 0.41. Neither ratio showed a clear pattern of seasonal change. Conversely, there was a progressive increase in diadinoxanthin and β-carotene ratios to Chl-a through the season, parallel to the increase in photon flux impinging upon the lake surface. The diadinoxanthin to Chl-a ratio changed from 0.11 to 0.28 and the β-carotene to Chl-a ratio varied from 0.03 to 0.08 from March through June. 4. Diatoxanthin was not detected in natural samples. However, it was present in experiments with P. gatunense cultures, when concentration of diatoxanthin increased rapidly, concurrent with a decrease in diadinoxanthin and β-carotene concentrations, while Chl-c and peridinin ratios to Chl-a were almost stable with photon flux increase. 5. The seasonal variation in cellular pigmentation of P. gatunense in Lake Kinneret suggests that accumulation of photoprotective pigments is essential for optimisation of photosynthetic activity of this large dinoflagellate.
Article
The phytoplankton community structure of a hypertrophic lake was quantitatively determined with the aid of flow cytometry. The flow cytometry signals were calibrated to obtain cell-specific information, such as the chl a content and the biovolume per cell. The reliability of this method was tested with laboratory cultures. The results of the phytoplankton structure in a hypertrophic lake with respect to chl distribution in the different algal groups obtained by flow cytometry were compared with the results from HPLC pigment fingerprinting. Both methods yield the percentage contribution of the different algal groups to total chl a. The chl a specific absorption coefficient of the phytoplankton (a*Phy) was determined via visible (VIS) spectroscopy of samples taken from a hypertrophic lake (Auensee) in 2003. The results indicated that a*Phy of the total cell suspension is dependent on the phytoplankton structure as well as on environmental factors. The linear relationship between a*Phy at 675 nm and the product of the chl a content per cell and the biovolume offered the possibility to normalize phytoplankton absorption spectra to acquire the taxon-specific a*Phy. The estimated a*Phy (675 nm) values were used to normalize single cell absorption spectra at this wavelength to obtain the a*Phy between 400 and 750 nm for representatives of the major algal groups. Our measurements show that the absorption coefficient for the whole phytoplankton community varies within the season. Finally, we used the a*Phy and the chl a distribution to calculate the light absorption of each algal group in the hypertrophic lake.
Article
The seasonal abundance and composition of photosynthetic picoplankton (0.2-2 μm) was compared among five oligotrophic to mesotrophic lakes in Ontario. Epilimnetic picocyanobacteria abundance followed a similar pattern in all lakes; maximum abundance (2-4 × 10⁵ cells · ml⁻¹) occurred in late summer following a period of rapid, often exponential increase after epilimnetic temperatures reached 20 °C. In half of the lakes picocyanobacteria abundance was significantly correlated with temperature, while in other lakes the presence of a small spring peak resulted in a poor correlation with temperature. In all lakes there was a significant correlation between epilimnetic abundance and day of the year. Correlations with water chemistry parameters (soluble reactive phosphorus, total phosphorus, particulate C: P and C: N) were generally weaker or insignificant. However, in the three lakes with the highest spring nitrate concentrations, a significant negative correlation with nitrate was observed. During summer stratification, picocyanobacteria abundance reached a maximum within the metalimnion and at or above the euphotic zone (1% of incident light) in all lakes. These peaks were not related to nutrient gradients.
Article
Autotrophic picoplankton communities were examined in eleven oligotrophic lakes from a broad geographic region of western Canada, representing a variety of physico-chemical and biological conditions. During our study, several of the lakes were treated with additions of inorganic nitrogen and phosphorus fertilizers. Picoplankton communities in most lakes were dominated (>70%) by unicellular or colonial coccoid cyanobacteria, provisionally identified by morphological and autofluorescence properties as Synechococcus. Also common in some lakes were red-fluorescing cyanobacteria and Chlorella-like eucaryotes. Autotrophic picoplankters contributed from 36-63% to total chlorophyll, from >2-26% to total phytoplankton carbon, and from 29–53% to total photosynthesis. Average populations ranged from >5-10,000 cells·ml−1 in winter and early spring to 65-75,000 cells · ml−1 in summer and fall. Peak densities in most lakes occurred in August-September and most populations were within the epilimnion or metalimnion/hypolimnion boundary. Subsurface peaks were prevalent only in untreated, strongly stratified lakes. Eucaryotic picoplankters became dominant in acidic (pH < 6.2), humic lakes. Colonial picoplankters were more common in more productive interior lakes in August, and though present, were uncommon in coastal systems. Picoplankton populations exhibited large increases under ice in a Yukon lake, and their abundance and seasonal distribution showed little relation to temperature or to light. Fertilization of lakes resulted in picoplankton population increases (>2x) and the elimination of subsurface peaks. Nutrients were considered to be one of the major factors controlling population abundance in these oligotrophic lakes with average pH < 6.5.
Article
The significance of photoautotrophic picoplankton (APP) was investigated for three years in the eutrophic Lake Belau. Using epifluorescence microscopy with green excitation, the abundance of APP was found to vary seasonally with maximum values reaching 1.7* 106 cells ml−1 in June and July. Above a threshold of 12°C, cell numbers of APP in the epilimnion were strongly correlated with the water temperature (r = 0.837 > r(34;0.001) = 0.526). The horizontal distribution varied by a factor of 1.1 to 3.3. All stations in the different parts of the lake, including the littoral zone, exhibited a similar seasonal pattern. Photoautotrophic picoplankton accounted for up to 54% of the total picoplankton carbon content (bacteria and photoautotrophic picoplankton) and averaged 8% over the entire year. It contributed <1–29% to the total phytoplankton carbon in the pelagic zone and up to 47% in the littoral. Size fractionated primary productivity determinations revealed that APP contributed between 13% and 17% to the total primary production in the pelagic zone during the period of its peak abundance and between 6% and 37% in the littoral zone. The annual averages were 6% and 7%, respectively. These results support the assumption that the average contributions of APP to phytoplankton biomass and primary production decrease as the trophic state of the lake increases. However, the individual timepoints show that APP sometimes contributes significantly to the primary producers in eutrophic systems, particularly in the littoral zone.
Article
In vivo delayed fluorescence (DF) and HPLC/CHEMTAX pigment analyses were used to investigate seasonal and depth distributions of phytoplankton in a deep alpine mesotrophic lake, Mondsee (Austria). Using chl a equivalents, we determined significant relationships with both approaches. Community structure derived from pigment ratios of homogenous samples was compared with microscopic estimations using biovolume conversion factors. An advantage of the HPLC/CHEMTAX method was that it gave good discrimination among phytoplankton groups when based on a pigment ratio matrix derived from multiple regression analysis. When a single algal group was dominant, such as epilimnetic diatoms or hypolimnetic cyanobacteria in the deep chl maxima, HPLC/CHEMTAX results were significantly correlated with microscopic estimations (diatoms: r = 0.93; cyanobacteria: r = 0.94). Changes in the composition of photosynthetically active pigments were investigated with DF and benefited from excitation spectra that considered all light-harvesting pigments, which made it possible to assess the enhancement of accessory photosynthetically active pigments relative to active chl a (chl aDF672). Changes in similarity index, based on normalized DF spectra, confirmed compositional shifts observed by microscopy. At chosen wavelengths of DF spectra, 534 and 586 nm, we generally observed a significantly inverse relationship between normalized DF intensities and temperature and light along both seasonal and depth gradients. The relative increase in photosynthetically active pigments other than chl aDF672 under low light and temperature was caused by an increasing dominance of diatoms and/or phycobilin-rich cyanobacteria and Cryptophyta. DF spectra provided a more accurate picture of community pigments acclimated to light and temperature conditions than the β-carotene:chl a ratio derived from HPLC.
Article
The hypothesis that both photosynthesis and pigment pattern are more reflective of size related strategies than taxonomic composition of the assemblages was tested under natural conditions in alpine lakes during fall 1999. The small size fraction (< 10 μm) in Lake Lucerne, Mondsee and Traunsee and in an additional incubator experiment contributed 55-67 % to the total integral of chlorophyll-a and photosynthesis per m2. The photosynthetic depression induced by UV-A in Lake Lucerne, measured during the 7th GAP-workshop, markedly increased to 65 % with PAR up to 500 μmol m-2 s-1. At super-saturating light intensities near the surface, UV-A inhibition further increased marginally to 69 %. Effects of light acclimation and pigment adaptation on photosynthetic rates and efficiencies of phytoplankton indicated size related strategies that were more important than the taxonomic composition of the assemblage measured in Traunsee and Mondsee. Algal communities and small size fractions (<10 μm), that had a high maximum light utilisation coefficient (*) were adapted to low light by high ratios of chlorophyll-a to photo-protective -carotene. Algae at high solar radiation and of large size (>10 μm) were photosynthetically less efficient but high light adapted having low ratios of chlorophyll-a to -carotene. In contrast to low light adapted small cells the high light adapted large-cells increased their relative proportion of photo-protective carotenoids above saturating light levels. At light limitation in deeper water layers lipophilic accessory photo-synthetic versus photo-protective pigments increased for all fractions.
Article
Picoplankton (plankton 3 m) biomass was determined by flow cytometry in three European estuarine systems (Krka Estuary in Croatia, Rhne Delta in France, and Lena Delta and Laptev Sea in Russia). The size of natural phytoplankton groups was obtained by a calibration curve, with different picoplankton's strains (from 1.6 to 3.4 m), measured by a Coulter counter (size) and a flow cytometer (light-scattering). Two natural groups of picoplankton were identified by flow cytometry in the three systems: Synechococcus sp and picoeukaryotes. Picoplankton cells abundance ranged between: 2800 and 42000, 5000 and 37000, 1000 and 50000 cells ml–1 in the Krka estuary, in the Rhne delta and in the Lena-Laptev system, respectively. In the Krka estuary, picoplankton biomass ranges between 11 and 68 gC l–1. It can make up as much as 88% of the total photosynthetic plankton population and 50% of total organic particulate carbon. Picoplankton biomass was greater in the summer than in the autumn. At the halocline layer this biomass can attempt ca. 390 gC l–1during the summer cruise. In the Rhne delta, a lower picoplankton biomass (6–39 gC l–1) was observed at the end of the winter. These biomass represented between 0.4 and 22% of the particulate organic carbon, which could reach 71% of the total photosynthetic plankton biomass at the marine station. In the Lena-Laptev system, picoplankton biomass varied between 6 and 56 gC l–1 in surface waters. Picoplankton biomass decreased with depth, but picoeukaryotes were still observed in deep samples (20, 30 m) in the Laptev Sea, showing a considerable autotrophic activity in spite of low temperatures (0–1 C). Although the widely dispersed estuary geographic distribution and their different estuarine characteristics, the data point out that these small organisms can also play an important role in the transfer of organic carbon from rivers to oceans and that flow cytometry can be able to detect these small cells in turbid systems.
Article
Autotrophic picoplankton (APP) were studied in Chilko Lake, a large, deep ultra-oligotrophic pre-alpine lake (elevation: 1172 m) in the south central coast mountains of British Columbia. Data from 1985 (untreated) and 1990 (treated) were used to compare and contrast APP community response to a whole-lake fertilization experiment. The APP communities of Chilko Lake were dominated by the coccoid cyanobacteria Synechococcus and its colonial morph which comprised about 99% of the APP community of Chilko Lake. Chlorella-like eukaryotic picoplankters and small cyanobacteria were rare, comprising < 1 % of the APP community. In 1990 autotrophic picoplankters contributed an average of 73% to total chlorophyll, and 54% to total photosynthesis. Average APP abundance ranged from lows of 4,000–5,000 cells ml-1 in winter and spring to highs of 50000–150000 cells ml-1 in early August with no apparent autumnal increase. APP populations were uniformly distributed in the epilimnion, but during calm periods in August often formed a peak near the metalimnion/hypolimnion boundary. Seasonal and vertical distribution patterns of APP showed little relation to temperature or to light. When nutrients were added to the lake in 1990, APP populations doubled within 3 wk of addition and average abundance (6.16 × 104 cells · ml-1) was twice 1985 APP numbers. Bottom-up control by scarce nutrient supplies is considered the primary factor regulating community composition and abundance during the initial population growth phase (June, July) with top-down control by grazing during nutrient colimitation periods when the epilimnion is deplete of both nitrogen and phosphorus (August, September).
Article
Allometric relationships of phytoplankton communities were studied on the basis of a five-year data-set in a deep oligotrophic alpine lake in Austria. The seasonal phytoplankton succession in Mondsee is characterised by diatoms during winter mixing and a distinct metalimnetic population of Planktothrix rubescens during stratification in summer. The variation of phytoplankton photosynthetic efficiency between seasons was assessed using in situ carbon-uptake rates (5 years data) and Fast Repetition Rate Fluorometry (FRRF) (2 years data). The light-saturated, chlorophyll-specific rate of photosynthesis (P*max), irradiance at the onset of saturation (E k) and maximum light-utilisation efficiency (α*) were determined for winter mixing and summer stratification. Fluorescence-based parameters as the functional absorption cross section of Photosystem II (σ PSII) and the photochemical quantum yield (F v/F m) were additionally analysed in 2003 and 2004 to study the underlying physiological mechanisms for the variability in photosynthetic performance. Beyond their sensitivity to changing environmental conditions like thermal stratification, phytoplankton populations differ in their photosynthetic behaviour according to their size structure. Therefore Photosynthesis vs. Irradiance (P/E)-relationships were analysed in detail within a 1-year period from size fractionated cell counts, chlorophyll-a and carbon-uptake.
Article
Phytoplankton samples from 7 different lakes were processed in 2 intercalibration series using Utermöhl's sedimentation method. Total biomass volumes obtained by most of the investigators give reliable results in respect to the mean. Numbers of individuals and mean volumes of selected species obtained by the different participants were compared and show larger variations than the overall results. Therefore a certain delimitation of particular sources of errors was tried in the 2nd intercalibration series by giving recommendations for the different steps of the whole procedure.
Article
Size-fractionated phytoplankton biomass and primary production, together with net community metabolism, were measured in a coastal ecosystem (Ría de Vigo, NW-Spain) during a full annual cycle (July 2001–July 2002). On a seasonal scale, this ecosystem was characterized by two distinct oceanographic conditions, namely upwelling and downwelling favourable seasons. During the upwelling season, total chlorophyll a (Chl a) and particulate organic carbon production rates (POC-pr) were in the range 36–129 mg Chl a m−2 and 89–834 mg C m−2 h−1, respectively, and were mainly accounted for (>80%) by the microphytoplankton size fraction (>20 μm). During the downwelling season, total Chl a and POC-pr were much lower (<27 mg Chl a m−2 and <97 mg C m−2 h−1, respectively), and the pico- (<2 μm) and nano- (2–20 μm) phytoplankton size fractions significantly increased their contribution to total Chl a (46–87%) and POC-pr (30–86%). The seasonal and short-time scale variability in the hydrographic conditions, in particular upwelling intermittency, provides a feasible explanation for the continuous dominance of large-sized phytoplankton during the upwelling period. Shelf water intrusions, continuous vertical mixing and the size-dependent limitation in light acquisition (package effect), suffered in a higher degree by larger phytoplankton, were likely to account for the shift in phytoplankton size structure during the downwelling period. During the upwelling season, community respiration represented a minor fraction of gross primary production (15–30%), which highlights the large export potential of organic matter by this ecosystem. On the contrary, community respiration accounted for a major fraction of primary production (85%) during the downwelling period, which suggests that most of the photosynthesised organic matter was remineralised within the ecosystem. Although the microbial plankton community of the Ría de Vigo exhibits a net autotrophic functioning throughout the year, the magnitude of the carbon flows and budgets seems to be dependent on phytoplankton size structure.
Article
Algal picoplankton are a ubiquitous component of the microbial plankton communities of both marine and freshwater ecosystems. They contribute significantly to the total biomass of phyto- plankton communities, and in oligotrophic oceans and lakes can be responsible for up to 80-90% of the total daily or annual carbon production. As part of the "microbial loop," they are thought to be grazed by flagellates, ciliates, rotifers, copepods, and other metazoans, and contribute to the flow of energy to higher trophic levels. This presentation highlights their discovery, distribution, physiology, production, and contribution to pelagic food webs in marine and freshwater systems.
Article
1. Picophytoplankton are planktonic photosynthetic O2-evolvers that can pass through 2 μm-diameter pores; they include prokaryotic (eubacterial) and eukaryotic members and occur in freshwater and marine habitats. There are no photosynthetic reproductive and dispersal stages of benthic macrophytes of picoplanktonic size. The picophytoplankton condition appears to be derived and polyphyletic in both prokaryotes and eukaryotes. 2. Picophytoplankton are among the smallest free-living cells, despite having to contain the photosynthetic apparatus, which occupies about half of the cell volume, as well as core cellular machinery. The size of the smallest prokaryotic (0·6 μm diameter) and eukaryotic (0·95 μm diameter) picophytoplankton are close to the minimum possible size estimated from the occurrence of non-scalable essential components such as the genome and plasmalemma and other membranes. 3. Picophytoplankton cells have advantages relative to larger phytoplankton cells in terms of resource acquisition and the subsequent use of the resources in catalysing cell growth and reproduction. The smaller package effect in light harvesting means smaller resource (energy, C, N, Fe, Mn, Cu) costs of photon harvesting and transformation into chemical energy in small than in large cells. The smaller diffusion boundary layer around small cells, coupled with smaller nutrient fluxes per unit plasmalemma area needed to attain a given fraction of the maximum specific growth rate in smaller cells, increases the availability of low concentrations of nutrients to small relative to larger cells. If the supply of CO2 to the core photosynthetic carboxylase ribulose bisphosphate carboxylase-oxygenase is purely by diffusion then smaller cells could satisfy their catalytic requirements with less of this enzyme whose synthesis has high energy, C and N costs. Overall, resources can be acquired, and used in growth, more effectively in smaller than in larger cells. 4. Some factors work against the conclusion in (3.) but, in most habitats, do not negate these conclusions. Examples related to non-scalable essential cell components are the use of energy, C, N and P in the genome and of energy, C, N, P and Fe in the plasma membrane. Transport-related factors include the increased potential cell volume-specific leakage of accumulated resources, and the greater cell volume-specific energy costs of motility at a given speed, in smaller than in larger cells. The smaller package effect in smaller cells involves a greater potential for photodamage by both photosynthetically active radiation and by UV-B. 5. Picophytoplankton occurrence is also a function of factors which lead to cell loss. Factors such as sinking out of the euphotic zone and parasitism by eukaryotes such as chytrids are less significant for picophytoplankton than for larger cells, whereas viral parasitism and grazing by appropriately sized grazers are likely to be at least as great for picophytoplankton as for larger cells. 6. The totality of the effects mentioned in (3.) above suggests that picophytoplankton should generally have higher specific growth rates (probably) in resource-saturated (photons, C, N, P, Fe, etc.) and (certainly) in resource-limited environments than do larger cells. The distribution of picophytoplankton is certainly consistent with their ability to capitalize on resource-limited environments: they contribute a larger fraction of biomass and productivity relative to larger cells in low-nutrient than in high-nutrient environments, and in low-light (e.g. the deep chlorophyll maximum) than in high-light environments. 7. Sexual reproduction is apparently rare in picophytoplankton, with implications for species definition. There are probably relatively few species (hundreds or thousands) with very wide biogeographical ranges in marine or in freshwater habitats. The small size and (probably) low biodiversity means large numbers of individuals worldwide, e.g. c.1026 individuals of the commonest species of the marine cyanobacterium Synechococcus. Picophytoplankton contribute at least one-tenth (i.e. in excess of 3 Pg C per year) to global aquatic net primary productivity.
Book
Preface to the third edition Part I. The Underwater Light Field: 1. Concepts of hydrologic optics 2. Incident solar radiation 3. Absorption of light within the aquatic medium 4. Scattering of light within the aquatic medium 5. Characterizing the underwater light field 6. The nature of the underwater light field 7. Remote sensing of the aquatic environment Part II. Photosynthesis in the Aquatic Environment: 8. The photosynthetic apparatus of aquatic plants 9. Light capture by aquatic plants 10. Photosynthesis as a function of the incident light 11. Photosynthesis in the aquatic environment 12. Ecological strategies References and author index Index to symbols Index to organisms Index to water bodies Subject index.
Article
SUMMARY 1. Biomass and production of picophytoplankton, phytoplankton and heterotrophic bacterioplankton were measured in seven lakes, exhibiting a broad range in water colour because of humic substances. The aim of the study was to identify environmental variables explaining the absolute and relative importance of picophytoplankton. In addition, two dystrophic lakes were fertilised with inorganic phosphorus and nitrogen, to test eventual nutrient limitation of picophytoplankton in these systems. 2. Picophytoplankton biomass and production were highest in lakes with low concentrations of dissolved organic carbon (DOC), and DOC proved the factor explaining most variation in picophytoplankton biomass and production. The relationship between picophytoplankton and lake trophy was negative, most likely because much P was bound in humic complexes. Picophytoplankton biomass decreased after the additions of P and N. 3. Compared with heterotrophic bacterioplankton, picophytoplankton were most successful at the clearwater end of the lake water colour gradient. Phytoplankton dominated over heterotrophic bacteria in the clearwater systems possibly because heterotrophic bacteria in such lakes are dependent on organic carbon produced by phytoplankton. 4. Compared with other phytoplankton, picophytoplankton did best at intermediate DOC concentrations; flagellates dominated in the humic lakes and large autotrophic phytoplankton in the clearwater lakes. 5. Picophytoplankton were not better competitors than large phytoplankton in situations when heterotrophic bacteria had access to a non-algal carbon source. Neither did their small size lead to picophytoplankton dominance over large phytoplankton in the clearwater lakes. Possible reasons include the ability of larger phytoplankton to float or swim to reduce sedimentation losses and to acquire nutrients by phagotrophy.
Article
This is the first study using flow cytometry to characterize the population dynamics of freshwater autotrophic picoplankton (APP) over a full seasonal cycle, the goal of which was to accurately quantify and qualify the natural APP populations in relation to major environmental parameters. In particular, we wanted to test current assumptions about the seasonal succession of prokaryotic and eukaryotic picoplankton cells, including the relationship between solitary picocyanobacteria and microcolonies. Using flow cytometry, we were able to efficiently characterize the abundances of 4 lake APP assemblages in Lake Mondsee, including that of a solitary picocyanobacterial population exhibiting high "side scatter" values. Such cells were not readily enumerated by epi-fluorescence microscopy. Unlike Lakes Constance and Maggiore, we found no evidence of a spring peak in solitary picocyanobacteria - we propose that the lack of a spring peak in Lake Mondsee was due to weak stratification in March-April and relatively deep vertical mixing. Since summer declines in the abundance of solitary picocyanobacteria were associated with extended periods of reduced light availability, it is likely that such declines were in part due to low relative growth rates, Finally, we argue that the formation of microcolonies by picocyanobacteria is unlikely to be a strategy for more efficient nutrient recycling (e.g. Stockner & Antia 1986). Rather, we suggest that microcolonies reach high concentrations in surface and near-surface waters due to the production of a photosynthate-rich mucilage resulting from active photosynthesis during periods of severe nutrient deficiency.
Article
Thesis (doctoral)--Universität Konstanz, 1993. Includes bibliographical references (p. 149-168).
Article
In principle, allometric relationships for algal growth can be applied to biomass size spectra to yield estimates of primary productivity. In practice, reported values of the scaling exponent of algal growth are variable, perhaps reflecting differences in the expression of cell size or phyletic differences or small sample size. The present study established the relationship between algal growth and size with a larger set of literature data than has been used previously, and assessed the effects of expression of cell size and of gross taxonomic differences on that relationship. I was able to collect a data set consisting of 127 observations of daily growth rate and cell size from three algal divisions (Chlorophyta, Chrysophyta, Pyrrophyta) and five classes (Bacillariophyceae, Chlorophyceae, Chrysophyceae, Dinophyceae and Prymnesiophyceae). Growth rate (μ, in divisions day−1) varies with cell carbon content (pg C cell−1) as μ &equals; 3.45C−0.21. The size effect (as reflected by the exponent) is smaller if algal size is expressed as cell volume, reflecting changes in cell composition with size. The exponent is not affected by taxonomic affiliation, but growth rates of Pyrrophyta and Dinophyceae (a class within Pyrrophyta) were significantly lower than those of other divisions and classes. However, pyrrophytes have such a small size range in this data set that no meaningful growth-size relationship can be developed for that group alone.
Article
Data from three cruises (Arabesque 1 and 2 cruises in the Arabian Sea and the Vancouver Island cruise) were examined to assess the importance of species composition and accessory pigments in modifying specific absorption coefficients. The three cruises differed widely in their phytoplankton assemblages with small cells dominating the Arabesque 2 cruise and large diatoms the Vancouver Island cruise. Absorption spectra from each cruise were decomposed into 13 Gaussian bands representing absorption by the major chlorophylls and accessory pigments. The maximum specific peak height $${P}_{m}^{*}$$ for each Gaussian band was obtained by regressing Gaussian peak heights against the concentration of the pigment responsible for the absorption band. This relationship was generally non-linear and was fitted with a rectangular hyperbolic function. Changes in the maximum specific peak heights between cruises reflect changes in the packaging effect, which were most apparent at Gaussian bands of high absorption (400–490 nm), but were close to zero at the Gaussian band centered around 623 nm, associated with chlorophyll a (Chl a). The maximum specific peak height of this Gaussian band, $${P}_{m}^{*}$$ (623), may be used to obtain reliable estimates of Chl a for any phytoplankton assemblage, unaffected by variations caused by the package effect. Comparing the Arabesque 2 peak heights with the Vancouver data, an apparent flattening effect of 0.42 at 440 nm and 0.62 at 676 nm was found for the Vancouver data relative to the Arabesque 2 data (assuming a zero flattening effect for the latter). Multiple linear regression analysis suggested that 29–42% of the variability in the specific absorption coefficient of phytoplankton at 440 nm was due to changes in pigment composition, while the remaining 58–71% was due to changes in the package effect. An inverse relationship was found between the proportion of non-photosynthetic pigments (NPC) and ambient Chl a concentration, suggesting that small cells (generally found in oligotrophic waters) had higher proportions of photoprotective pigments.
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Plankton autotrophs vary greatly in size and shape. Computation of surface/volume ratios for biomass units of 27 coexisting phytoplankton species in a tropical lake indicates that these ratios are conserved within a range much narrower than expected by random choice of shapes. Conservation of surface/volume ratios suggests new explanations for the shapes of phytoplankton biomass units.