Automation of species-specific cyanobacteria phycocyanin fluorescence compensation using machine learning classification

High-frequency cyanobacteria monitoring often uses in-situ fluorescence of phycocyanin (f-PC). However, f-PC must be calibrated for the dominant cyanobacteria species, and it cannot distinguish cyanobacteria taxa, which relies on conventional time-consuming cyanobacteria identification methods. This study proposes a framework to automate f-PC species-specific compensation through three components: (1) prediction of the dominant cyanobacteria species using data-driven models and routine environmental monitoring data; (2) determination of species-specific f-PC per biomass in controlled laboratory experiments; and (3) automation of f-PC species compensation. The framework was validated by applying it to Myponga drinking water reservoir in South Australia. Three machine learning techniques using only high-frequency water temperature data were compared to predict the dominant cyanobacteria species. The framework application to Myponga drinking water reservoir improved the agreement of f-PC with conventional cyanobacteria biovolume measurements, and provided rapid, low-cost identification of the dominant cyanobacteria species, which can support proactive species-targeted cyanobacteria management.     

The ecology of the visual pigments of snappers (Lutjanidae) on the Great Barrier Reef

The visual pigments in the retinal photoreceptors of 12 species of snappers of the genus Lutjanus (Teleostei; Perciformes; Lutjanidae) were measured by microspectrophotometry. All the species were caught on the Great Barrier Reef (Australia) but differ in the colour of the water in which they live. Some live in the clear blue water of the outer reef, some in the greener water of the middle and inshore reefs and some in the more heavily stained mangrove and estuarine water. All the species had double cones, each member of the pair containing a different visual pigment. Using Baker's and Smith's (1982) model to predict the spectral distribution of ambient light from chlorophyll and dissolved organic matter it was found that the absorption spectra of the visual pigments in the double cones were close to those that confer the maximum sensitivity in the different water types. Single cones contained a blue or violet-sensitive visual pigment. The visual pigments in the rods showed little variation, their wavelength of maximum absorption always being in the region 489–502 nm.Abbreviations DOC dissolved organic carbon - DOM dissolved organic material - MSP microspectrophotometry deceased     

Does pigment composition reflect phytoplankton community structure in differing temperature and light conditions in a deep alpine lake? An approach using HPLC and delayed fluorescence techniques1

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 a_DF672). 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 a_DF672 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.     

Global changes may be promoting a rise in select cyanobacteria in nutrient‐poor northern lakes

The interacting effects of global changes—including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes—are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient‐poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient‐poor Swedish lakes over 16 years (1998–2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon‐specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.     

Using an online phycocyanin fluorescence probe for rapid monitoring of cyanobacteria in Macau freshwater reservoir

Monitoring of cyanobacteria and their toxins are traditionally conducted by cell counting, chlorophyll-a (chl-a) determination and cyanotoxin measurements, respectively. These methods are tedious, costly, time consuming, and insensitive to rapid changes in water quality and cyanobacterial abundance. We have applied and tested an online phycocyanin (PC) fluorescence probe for rapid monitoring of cyanobacteria in the Macau Storage Reservoir (MSR) that is experiencing cyanobacterial blooms. The relationships among cyanobacterial abundance, biovolume, cylindrospermopsin concentration, and PC fluorescence were analyzed using both laboratory and in-the-field studies. The performance of the probe was compared with traditional methods, and its advantages and limitations were assessed in pure and mixed cyanobacterial cultures in the laboratory. The proposed techniques successfully estimated the species including Microcystis and Cylindrospermopsis, two toxic species recently observed in the MSR. During February–November, 2010, the PC probe detected high correlations between PC and cell numbers (R ² = 0.71). Unlike the chl-a content, which indicates only the total algal biomass, the PC pigment specifically indicates cyanobacteria. These results support the PC parameter as a reliable estimate of cyanobacterial cell number, especially in freshwater bodies where the phytoplankton community and structure are stable. Thus, the PC probe is potentially applicable to online monitoring of cyanobacteria.     

History of anthropogenically mediated eutrophication of Lake Peipsi as revealed by the stratigraphy of fossil pigments and molecular size fractions of pore-water dissolved organic matter

We investigated stratigraphic changes in fossil pigments and the molecular structure of the UV-absorbing fraction of pore-water dissolved organic matter in a sedimentary record from Lake Peipsi (Estonia/Russia) temporally covering the 20th century. The aims of the study were to define the onset of eutrophication in the lake and to track its course. An attempt was also made to reconstruct lake conditions before the intensive nutrient loading began. Fossil pigment analysis indicated that the eutrophication of the lake started in the 1960s and accelerated in the 1970s. Sedimentary pigments also indicate a continuing tendency of the lake ecosystem towards eutrophy in the 1980s and 1990s. However, changes in the molecular size structure of pore-water dissolved organic matter indicated that the contribution of autochthonous matter to the organic pool of the lake ecosystem had already started to increase around the end of the 1930s. We conclude that this rise was generated by a coincidence of several anthropogenic and natural factors. The pore-water data also show that a slight relative reduction in the autochthonous organic matter took place in the 1990s. A discordance in the paleodata obtained for the beginning of the 20th century complicates clear conclusions about earlier conditions in the lake. On the one hand, the qualitative characteristics of pore-water dissolved organic matter and the low concentration of chlorophyll a indicate that the phytoplankton biomass was low in Lake Peipsi during that period. On the other hand, the concentrations of marker pigments of specific phytoplankton groups are high, comparable with the values in the recent sediments. Possible reasons for the high levels of these pigments in the early 1900s sediments, such as a shift in the preservation conditions of organic substances and their transport from the lake’s catchment, are discussed.     

Transformation of algal turf by echinoids and scarid fishes on French Polynesian coral reefs

The respective roles of regular echinoids and scarid fishes in the transformation of turf algae, the main food resource for reef herbivores, were investigated on French Polynesian coral reefs. The role of one species of parrotfish (Scarus sordidus) was compared with that of four species of echinoids. The degree and ways of degradation of the algal matter were determined by the organic matter percentage, the composition of the sugar fraction, and the concentration and composition of chlorophylltype pigments as assayed by HPLC analysis. Chemical analyses were performed on anterior and posterior intestines for scarids, intestinal contents and faeces for echinoids, and on fresh algal turf as a control of initial food quality. A decrease in mean percentage of organic matter in gut content was observed from intestine (9.7%) to faeces (7%) in sea urchins, but not in parrotfishes. The total sugar fraction decreased from fresh algal turf (32% of total organic matter) to echinoid (28%) to scarid (18%) gut contents. The ratio of insoluble to soluble sugars (I/S ratios) was higher in echinoids (2.6) than in scarid gut contents (1.0). A decrease in the total pigment concentration was measured from fresh algal turf to echinoid and it was found to be even lower in scarid gut contents. Chromatograms showed that the composition of chlorophyll-type pigments in scarid intestines was very similar to fresh algal turf, with a dominance of native forms, mainly chlorophyll a and b. On the contrary, degraded pigment forms dominated in echinoids. The main degraded products were pheophorbides in sea urchins, and chlorophyllides in parrotfishes. These results provided evidence for differentiation in digestive processes occurring in the two types of grazers. Echinoids released higher degraded algal material than did scarids. Thus, these two types of grazers play different roles in the recycling of organic matter on coral reefs.     

Soil Cyanobacterial and Microalgal Diversity in Dry Mountains of Ladakh,NW Himalaya,as Related to Site,Altitude, and Vegetation

Although phototrophic microbial communities are important components of soils in arid and semi-arid ecosystems around the world, the knowledge of their taxonomic composition and dependency on soil chemistry and vegetation is still fragmentary. We studied the abundance and the diversity of cyanobacteria and eukaryotic microalgae along altitudinal gradients (3,700–5,970 m) at four sites in the dry mountains of Ladakh (Little Tibet, Zanskar Mountains, and Eastern Karakoram), using epifluorescence. The effects of environmental factors (altitude, mountain range, and vegetation type) on soil physico-chemical parameters (pH; texture; organic matter, nitrogen, ammonia, and phosphorus contents; and concentration of chlorophylls and carotenoids) and on the composition and biovolume of phototrophs were tested by multivariate redundancy analysis and variance partitioning. Phototrophs were identified in all collected samples, and phototroph biovolume ranged from 0.08 to 0.32 mm³ g⁻¹ dry weight. The dominant component was cyanobacteria, which represented 70.9% to 98.6% of the biovolume. Cyanobacterial species richness was low in that only 28 morphotypes were detected. The biovolume of Oscillatoriales consisted mainly of Phormidium spp. and Microcoleus vaginatus. The environmental factors accounted for 43.8% of the total variability in microbial and soil data, 20.6% of which was explained solely by mountain range, 7.0% by altitude, and 8.4% by vegetation type. Oscillatoriales prevailed in alpine meadows (which had relatively high organic matter and fine soil texture), while Nostocales dominated in the subnival zone and screes. Eukaryotic microalgae together with cyanobacteria in the order Chroococcales were mostly present in the subnival zone. We conclude that the high elevation, semiarid, and arid soils in Ladakh are suitable habitats for microbial phototrophic communities and that the differences in these communities are associated with site, altitude, and vegetation type.     

Inverse relationship of epilithic algae and pelagic phosphorus in unproductive lakes: Roles of N2 fixers and light

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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 phytoplanktonbiomass in oligotrophic lakes by marker pigments is comparedwith assessment by cell-counting biovolume estimates. Seasonalsamples from an oligotrophic alpine lake (Redon, Pyrenees) mostlyincluded species of chrysophytes, dinoflagellates, cryptophytesand chlorophytes. The chlorophyl a (Chl a) corresponding toeach algal group was estimated using HPLC pigment analyses andthe CHEMTAX program. Chl a estimates and biovolume showed asignificant correlation for all the groups during the ice-freeseason except for chlorophytes. However, some of the samplesfrom the initial phase of the ice cover presented a clear departurefrom the relationship during the ice-free period in most groups.On the other hand, the ratios between a specific marker pigmentand the biovolume of the marked algal group were significantlyconstant within the photic zone (>1% surface irradiance)for most of the pigments and groups, including chlorophytes.Nevertheless, the ratios increased and showed a large variabilityfor samples below the photic depth or below the ice cover. Theviolaxanthin-chrysophyte biovolume ratio presented an opposedtendency to other pigment-biovolume ratios, which increasedin inverse proportion to the depth of the sample. The resultsare discussed in terms of methodological limitations, acclimationresponses and species composition.     

Comparisons of optical pH and dissolved oxygen sensors with traditional electrochemical probes during mammalian cell culture

Small-scale upstream bioprocess development often occurs in flasks and multi-well plates. These culturing platforms are often not equipped to accurately monitor and control critical process parameters; thus they may not yield conditions representative of manufacturing. In response, we and others have developed optical sensors that enable small-scale process monitoring. Here we have compared two parameters critical to control in industrial cell culture, pH and dissolved oxygen (DO), measured with our optical sensors versus industrially accepted electrochemical probes. For both optical sensors, agreement with the corresponding electrochemical probe was excellent. The Pearson Correlations between the optical sensors and electrochemical probes were 98.7% and 99.7%, for DO and pH, respectively. Also, we have compared optical pH sensor performance in regular (320 mOsm/kg) and high-osmolality (450 mOsm/kg) cell culture media to simulate the increase in osmolality in pH-controlled cultures. Over a pH range of 6.38-7.98 the average difference in pH readings in the two media was 0.04 pH units. In summary, we have demonstrated that these optical sensors agree well with standard electrochemical probes. The accuracy of the optical probes demonstrates their ability to detect potential parameter drift that could have significant impact on growth, production kinetics, and protein product quality. We have also shown that an increase in osmolality that could result from controlling pH or operating the reactor in fed-batch mode has an insignificant impact on the functionality of the pH patches.     

EVALUATION OF PIGMENT EXTRACTION METHODS AND A RECOMMENDED PROTOCOL FOR PERIPHYTON CHLOROPHYLL a DETERMINATION AND CHEMOTAXONOMIC ASSESSMENT1

Many methods have been proposed to extract and quantify algal pigments. Comparative studies have found that pigment extraction efficiency varies among solvent and mechanical disruption protocols due to differential cellular resistance, thereby, leading to potential misinterpretation of pigment data. When the type or resistance of algae are unknown, a method is required that efficiently extract pigments from all taxonomic groups. The objective of this study was to develop a simple and efficient one stage periphyton pigment extraction protocol by comparing the extractability of four solvents (acetone, methanol, methanol/acetone, and methanol/acetone/N,N‐dimethylformamide), the effects of grinding, and the effects of freeze‐drying. The best overall extraction was obtained using freeze‐dried samples extracted with methanol/acetone/DMF/water (MAD). Eighty‐six percent more chlorophyll was extracted when the sample was freeze‐dried relative to fresh/frozen samples extracted with 90% acetone. Freeze‐drying greatly improved the extraction of both polar and non‐polar (lipophilic/hydrophobic) pigments while MAD increased the extractability of polar pigments and improved peak resolution of all pigments. Chemotaxonomic assessment differed between samples that were fresh/frozen or freeze‐dried before extraction. The relative abundance of cyanobacteria was greater for freeze‐dried material compared with fresh/frozen due to the improved extractability of cyanobacterial pigments. Based on the results of this study, the traditional approach of 90% acetone as a solvent is not recommended for periphyton samples containing cyanobacteria or when the composition of the mat is unknown. The combination of freeze‐drying and MAD was sufficient for the extraction of pigments from a periphyton mat containing filamentous cyanobacteria, green algae, and diatoms.     

The role of environmental parameters in the structure of phytoplankton assemblages and cyanobacteria toxins in two hypereutrophic lakes

We evaluated the variability of cyanotoxins, water chemistry, and cyanobacteria communities in two hypereutrophic drowned river mouth lakes (Spring Lake and Mona Lake; summer 2006) in west Michigan, USA. Even with considerable geographical and watershed similarity, local variations in nutrient concentrations and environmental factors were found to influence the differences observed in cyanobacteria assemblages and cyanotoxins levels between the two lakes. Limnothrix sp. dominated the phytoplankton community in Spring Lake (82% of biovolume) and was negatively correlated with total phosphorus (TP) concentrations. Although Spring Lake was treated with alum during the previous year, Limnothrix sp. was able to bloom in the lower P environment. In contrast, the N₂-fixing cyanobacterium, Anabaena flos-aquae, dominated the phytoplankton in Mona Lake (64% of biovolume). N₂-fixing cyanobacteria dominance in Mona Lake was correlated with higher TP lower dissolved nitrogen levels. Cylindrospermopsis raciborskii was found in both systems; however, the toxin-producing polyketide synthetase gene was not present in either population. The higher TP in Mona Lake appeared to account for the 3-fold increase in cyanobacteria biovolume. Restoration plans for both lakes should include assessments of internal loading and continued phytoplankton monitoring to track the temporal distribution of cyanobacteria species and cyanotoxin concentrations.     

Spectral fluorescence signatures in the characterization of phytoplankton community composition

Fluorescence spectral signatures from 28 algal cultures aredescribed.The cultures are split into four groups accordingto their accessory pigments. Phycocyanin and phycoerythrin,characteristic pigments of cyanobacteria, form groups I andII. The characteristic pigment found in group III is chlorophyllb (green and rasinophyte algae) and in group IV it is chlorophyllc (diatoms, dinophytes and some other algae).This preliminarycatalogue of spectral signatures was used to characterize fivenatural phytoplankton communities from brackish water environmentsas a comparison with phytoplankton species found in the samples.Accessory pigments such as phycocyanin and phycoerythrin, characterizinggroups I and II, can be used for identification without confusion.Distinguishing between groups III and IV is more complicated,because their accessory pigments do not have their own fluorescence.These groups can be characterized by increased fluorescenceof chlorophyll a induced by energy excited through chlorophyllb and c. The possibilities of applying the spectral fluorescencesignatures approach to the characterization of natural communitiesare discussed.     

A Spectrophotometric Analysis of Pigments in Apples

Methods of pigment extraction using traditional polar organic solvents (acetone or methanol) were compared to those employing a chloroform–methanol mixture. We found that, for spectrophotometric pigment analysis in the apple peel, the cuticular lipids must be preliminarily extracted from the samples with chloroform and MgO must be added during homogenization to prevent pigment degradation. The traditional extraction did not result in the complete extraction of intact pigments, and such extracts contained a considerable amount of light-absorbing impurities. The application of chloroform–methanol extraction allowed us to markedly reduce the content of such impurities and to increase the accuracy and sensitivity of the measurement of the content of chlorophylls and carotenoids. In addition, this extraction method proved useful for the analysis of phenolic substances (anthocyanins and flavonoids) in the water-methanol fraction of the extracts.     

Impact of chronic and pulse dilution disturbances on metabolism and trophic structure in a saline Mediterranean stream

Non-diatom benthic algae from 104 streams in southern California were studied. We present a novel method for quantification of non-diatom algae that seeks to improve upon two important aspects of existing methods: separate processing of macroalgae and microalgae to avoid sample blending and consequent loss of macroalgal integrity, and for better viewing, counting a well-mixed microalgal subsample on a standard microscope slide instead of using a counting chamber. Our method provided high-quality taxonomic and quantitative data with low uncertainty. A total of 260 algal taxa were recorded, 180 of which were identified to species level. The median total algal biovolume per site was 22.7 mm³ cm⁻² (range: <0.001–836.9 mm³ cm⁻²), the median species number was 11 (range: 2–43). Total algal biovolume and species number correlated with canopy cover (negative) and water temperature (positive), but not with measured water chemistry constituents. The proportion of heterocystous cyanobacteria and Zygnemataceae were strongly negatively correlated with nitrate concentrations and TN. The proportion of red algae was negatively correlated with TP. Species optima calculations combined with indicator species analysis identified >40 algal species as potential indicators of nutrient conditions. Proposed here is a practical tool for non-diatom algal quantification that enhances its application to stream bioassessment.     

PATTERNS OF EPIPELIC ALGAL DISTRIBUTION IN AN ACIDIC ADIRONDACK LAKE1

The biovolume and species composition of epipelic algae along sediment depth gradients were sampled seasonally in an acidic oligotrophic lake in the Adirondack Park in New York State. The epipelic algal community of Woods Lake (Herkimer Co., NY) was dominated by diatoms and cyanobacteria. Distinct depth zonation patterns of community composition were evident. Total algal biovolume increased with depth due to a dense cyanobacterial mat on the sediments in deeper water (5–8 m). This mat was dominated by a single species of cyanobacteria, Hapalosiphon pumilus (Kütz.) Kirchner, which accounted for the late summer maximum in total biovolume at 7 m. The shallower (1–4 m) epipelic communities were dominated by diatoms, which showed a spring maximum in total biovolume and were dominated by Fragilaria acidobiontica Charles, Navicula tenuicephala Hust. and N. subtilissima Cl.     

Change in cyanobacterial biovolume due to preservation by Lugol's Iodine

Cyanobacterial biovolume is used as a guide to the public health risk from these organisms for users of potable and recreational waters. Most routine surveillance programs preserve phytoplankton samples before analysis. We tested the effect of Lugol's Iodine, a common preservative, on the cell biovolume of four common freshwater cyanobacteria, Microcystis aeruginosa, Anabaena circinalis, Cylindrospermopsis raciborskii and Aphanocapsa incerta. Linear dimensions and cell area were measured with an image analyser. All four species shrank after preservation. The magnitude of shrinkage varied with species and preservation time but was not affected by Lugol's concentration. The maximum shrinkage in each species was a 30–40% reduction compared to the live cell biovolume. These results suggest shrinkage can be a greater source of uncertainty in estimating the biovolume of toxigenic cyanobacteria in aquatic environments than natural variability in the cell dimensions, instrument precision or cell counting. Standardised cyanobacterial biovolume lists based on agreed geometric shapes and formulae would improve the value of this information for public health risk assessment.     

A structured model for simulation of cultures of the cyanobacterium Spirulina platensis in photobioreactors: II. Identification of kinetic parameters under light and mineral limitations

A structured model for the culture of cyanobacteria in photobioreactors is developed on the basis of Schuster's approximations for radiative light transfer. This model is therefore limited to monodimensional geometries and kinetic aspects.Light-harvesting pigments play a crucial role in defining the profile of radiative transfer inside the culture medium and in controlling the metabolism, particularly the metabolic deviations induced by mineral limitations. Modeling therefore requires the biomass to be divided into several compartments, among which the light-harvesting compartment allows a working illuminated volume to be defined within the photobioreactor. This volume may change during batch cultures, largely decreasing as pigment concentration increases during growth but increasing as pigments are consumed during mineral limitation. This approach enables, in photobioreactors of simple parallelepipedic, geometries, kinetic parameters to be determined with high accuracy; this may then be extended to vessels of more complex geometries, such as cylindrical photobioreactors.The model is applied to controlled batch cultures of the cyanobacterium Spirulina platensis in parallelepipedic photobioreactors to assess its ability to predict the behavior of these microorganisms in conditions of light and mineral limitations. Results allowed the study of optimal operating condition for continuous cultures to be approached (c) 1992 John Wiley & Sons, Inc.     

Phytoplankton abundance and pigment changes during simulated in situ dilution experiments in estuarine waters: possible artifacts caused by algal light adaptation

I performed a dilution experiment during summer in mesohalineChesapeake Bay, comparing net growth rates of phytoplanktonbased on increases in accessory pigments with those based oncell counts of corresponding algal taxa. Fucoxanthin and peridininincreases were poor predictors of cell growth rates for diatomsand dinofiagellates, respectively, especially in the high dilutions(90% filtered seawater), while zeaxanthin predicted growth ratesof coccoid cyanobacteria closely. The insensitivity of microscopeestimates for rare, large phytoplankters may have contributedto the disparity between pigment and cell growth rates, butthis effect is argued to be small because all species presentat >1 cell ml^–1 were enumerated. Further experimentswith phytoplankton cultures suggest that light adaptation canlead to underestimates of growth when pigments are used as asurrogate for cell abundance in turbulent, eutrophic waterswhere the light field experienced by phytoplankton in Situ 5difficult to simulate.