A QUALITATIVE AND QUANTITATIVE STUDY OF PLASTOQUINONE A IN TWO THERMOPHILIC BLUE-GREEN ALGAE1

The thermophilic blue-green alga Synechococcus lividus strain Y52 was shown to have plastoquinone (PQ) types A, B, and C. The values PQA per cell and chlorophyll a per cell are presented with the changes in the ratio of PQA to chlorophyll a for cells grown at different light intensities.     

Some allometric and non-allometric relationships between chlorophyll-a and abundance variables of phytoplankton

We analysed data from three Bulgarian reservoirs, with trophic status from meso to eutrophic. Two kinds of relations (non-allometric and allometric) of chlorophyll with phytoplankton density, biovolume and surface area were investigated. The non-allometric relationships compare these phytoplankton variables with chlorophyll-a concentration, while the allometric ones include comparisons of average individual volume (AIV) of phytoplankters with chlorophyll-a content per individual (Chl.N^–1), per unit biovolume (Chl.BV^–1) and per unit surface area (Chl.SA^–1).Maximum values of the rank correlation of the three non-allometric relationships were found in the eutrophic reservoir. The highest allometric correlation coefficients were observed in the mesotrophic reservoir. Two non-allometric relationships, Chl with N and Chl ith BV calculated on unified data from all three reservoirs showed lower significance and a non-linear character. Chl-SA relationship was always statistically significant and varied from linear to slightly non-linear when calculated on weighed values. Two allometric relationships, AIV with Chl.BV^–1 and AIV with Chl.N^–1 seem to be linear. A third AIV and Chl.SA^–1 was described by a polinomial of the second degree, indicating that the smallest and largest phytoplankton individuals have a similar chlorophyll content per unit surface area. At the highest trophy, the Chl.SA^–1 seemed lowest.The frequently investigated relationship between chlorophyll-a and biovolume ranged from statistically not significant in the mesotrophic to highly significant in the eutrophic reservoir. This tendency was generalized by obtaining a statistically significant rank correlation between the levels of significance of chlorophyll-biovolume correlations and the corresponding chlorophyll-a concentrations. The non-linear character of the chlorophyll-biovolume relationship over a wide range of trophy was probably caused by changes in surface area-biovolume ratio.Deceased.     

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

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

Comparison of chlorophyll a spectra in wild-type and mutant barley chloroplasts grown under day or intermittent light

The absorption (640–710 nm) and fluorescence emission (670–710 nm) spectra (77 K) of wild-type and Chl b-less, mutant, barley chloroplasts grown under either day or intermittent light were analysed by a RESOL curve-fitting program. The usual four major forms of Chl a at 662, 670, 678 and 684 nm were evident in all of the absorption spectra and three major components at 686, 693 and 704 nm in the emission spectra. A broad Chl a component band at 651 nm most likely exists in all chlorophyll spectra in vivo. The results show that the mutant lacks not only Chl b, but also the Chl a molecules which are bound to the light-harvesting, Chl a/b, protein complex of normal plants. It also appears that the absorption spectrum of this antenna complex is not modified appreciably by its isolation from thylakoid membranes.Abbreviations Chl chlorophyll - DL daylight - ImL intermittent light - WT wildtype - LHC light-harvesting Chl a/b protein complex - S.E. standard error of the mean DBP-CIW No. 763.     

Deep-water aquatic plant communities in an oligotrophic lake: physiological responses to variable light

1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer. 2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level. 3. There was evidence that the deep-water community consisting of Chara corallina had adapted physiologically to low-light conditions. Net light saturated photosynthesis (CO₂ exchange) per unit chlorophyll a (Chl a) was reduced to 1.7 μg C (μg Chl a)^?1 h^?1 at the lower boundary, half of that recorded at 5 m. The concentration of Chi a per gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chl a (g dry wt)^?1 at 16 m vs. 4 mg Chl a (g dry wt)^?1 at 5 m]. Chl b also increased with depth and there was no change in the ratio of Chl a and Chl b with increasing depth. The saturation light intensity (I_k) of the community at the lower boundary was only 78 μmol photons m^?2 s^?1. Photosynthetic parameters (I_k and α) as well as the Chl a content remained relatively constant throughout the seasonal and short-term changes in radiation. 4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep-water community would be sensitive to any further changes in underwater light availability.     

Spatial and temporal photosynthetic compartments during summer in Antarctic Lake Kitiesh

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

Formyl group modification of chlorophyll a: a major evolutionary mechanism in oxygenic photosynthesis

We discuss recent advances in chlorophyll research in the context of chlorophyll evolution and conclude that some derivations of the formyl side chain arrangement of the porphyrin ring from that of the Chl a macrocycle can extend the photosynthetic active radiation (PAR) of these molecules, for example, Chl d and Chl f absorb light in the near‐infrared region, up to ～750 nm. Derivations such as this confer a selective advantage in particular niches and may, therefore, be beneficial for photosynthetic organisms thriving in light environments with particular light signatures, such as red‐ and near‐far‐red light‐enriched niches. Modelling of formyl side chain substitutions of Chl a revealed yet unidentified but theoretically possible Chls with a distinct shift of light absorption properties when compared to Chl a.     

Chlorophyll b accumulation and grana formation in low intensities of red light

Abstract When dark grown leaves of wheat (Triticum aesivum L.) were given a brief irradiation, there was an immediate onset of chlorophyll (Chl) b synthesis in the dark. This synthesis led to a rather slow accumulation of Chl b, which ceased when the Chl b/Chl a ratio had reached a value of about 0.1. The Chl b synthesis occurred also when the seedlings were treated with the herbicide SAN 9789. Leaves grown under different intensities of red light accumulated Chl b and Chl a, resulting in a ratio Chl b/Chl a which depended on the light intensity. If the light intensity was low, Chl a accumulated to a level about ten times the level of PChlide of the dark grown leaves. This occurred without any increase in the Chl b/Chl a ratio. There was no difference between SAN 9789-treated seedlings and water controls in this respect. Above a certain threshold of irradiance, the Chl b/Chl a ratio in the control leaves increased rapidly with the irradiation intensity. The increase in Chl b/Chl a ratio coincided with formation of grana in the plastids. This increase was not found and grana formation was completely absent in the seedlings treated with SAN 9789. The possibility of two different stages in the Chl b synthesis is discussed.     

An automatic device for in vivo absorption spectra acquisition and chlorophyll estimation in phytoplankton cultures

In order to aid the study of photoacclimation, a new programmable deviceis described which provides automatic on-line acquisition of in vivo cellabsorption in phytoplankton cultures. The system was used for a long-termstudy of Rhodomonas salina grown at constant photon flux density ina nitrate-limited continuous culture with different dilution rates. Particulate absorption measured at the red chlorophyll a (Chl a)maximum was not a good proxy of biomass, because of the large variabilityof cellular chlorophyll induced by nitrogen limitation. However, thedevice is well suited to automatic assessment of Chl a andphycoerythrin (PE) concentrations in phytoplankton cultures, if algal cellsize and concentration are measured in parallel to correct the packagingeffect. The effects of nitrogen limitation on Chl a and PE contentsand particle absorbance are discussed.     

The Formation and Dynamics of Deep Bacteriochlorophyll Maximum in the Temperate and Partly Meromictic Lake Verevi

Vertical distribution of phytoplankton and the formation of deep chlorophyll maximum (DCM) in the metalimnion of a small stratified and partly meromictic temperate lake was studied in 1999 and 2000. During summer DCM usually occurred on the borderline of H₂S and oxygen-containing waters. At the depths where the bacteriochlorophyll (Bchl) maxima were observed, the sulphide concentration was usually relatively low compared to the bottom layers, where its concentration reached as high as possible saturation level. In April 2000, DCM was formed at the depth of 3.5 m, and lowered thereafter slowly to 6.5 m by October. The concentration of Bchl d reached the highest values (over 1000 μg l⁻¹) just before the water column was mixed up in autumn. In December and April Bchl d was detectable only near the bottom of the lake. The concentration of chlorophyll a yielded by the spectrophotometric phaeopigment corrected method and by HPLC (high pressure liquid chromatography), fit rather well in the upper layers. In deeper water layers chlorophyll a concentration (Chl a) measured by spectrophotometry was overestimated about 47 times if compared to HPLC values because of the high Bchl d in that layer. In most cases vertical profiles of primary production (PP) did not coincide with the vertical distribution of the pigment content; the maximum values of PP were found in the epilimnion. In some cases PP had notably high values also at the depth of DCM. In the upper layers Chl a usually did not exceeded 20 μg l⁻¹ in spring and 10 μg l⁻¹ in summer_. The moderately high Chl a in the epilimnion in spring was significantly reduced after the formation of thermocline most probably because of the establishment of the nutrient limitation in epilimnion. Decreasing Chl a concentration in the epilimnion led to increased water transparency and better light conditions for photosynthetic bacteria in metalimnion.     

Spectral analysis on origination of the bands at 437 nm and 475.5 nm of chlorophyll fluorescence excitation spectrum in Arabidopsis chloroplasts

Chlorophyll fluorescence has been often used as an intrinsic optical molecular probe to study photosynthesis. In this study, the origin of bands at 437 and 475.5 nm in the chlorophyll fluorescence excitation spectrum for emission at 685 nm in Arabidopsis chloroplasts was investigated using various optical analysis methods. The results revealed that this fluorescence excitation spectrum was related to the absorption characteristics of pigment molecules in PSII complexes. Moreover, the excitation band centred at 475.5 nm had a blue shift, but the excitation band at 437 nm changed relatively less due to induction of non‐photochemical quenching (NPQ). Furthermore, fluorescence emission spectra showed that this blue shift occurred when excitation energy transfer from both chlorophyll b (Chl b) and carotenoids (Cars) to chlorophyll a (Chl a) was blocked. These results demonstrate that the excitation band at 437 nm was mainly contributed by Chl a, while the excitation band at 475.5 nm was mainly contributed by Chl b and Cars. The chlorophyll fluorescence excitation spectrum, therefore, could serve as a useful tool to describe specific characteristics of light absorption and energy transfer between light‐harvesting pigments. Copyright © 2015 John Wiley & Sons, Ltd.     

Widespread occurrence and unexpected diversity of red-shifted chlorophyll producing cyanobacteria in humid subtropical forest ecosystems

Discovery of red-shifted chlorophyll d and f in cyanobacteria has opened up new avenues to estimate global carbon fixation driven by far-red light. Shaded habitats in humid subtropical forest ecosystems contain an increased proportion of far-red light components relative to residual white light. After an extensive survey of shaded ecosystems within subtropical forests, wide occurrence of red-shifted chlorophyll-producing cyanobacteria was demonstrated by isolated Chl f-producing and Chl d-containing cyanobacteria. Chl f-producing cyanobacteria were classified into the genera of Aphanocapsa and Chroococcidiopsis and two undescribed genera within Leptolyngbyaceae. Newly isolated Chl d-containing Acaryochloris sp. CCNUM4 showed the closest phylogenetic relationship with Acaryochloris species isolated from marine environments. Acaryochloris sp. CCNUM4 produced Chl d as major photopigment, and Chl f-producing cyanobacteria use Chl a under white light conditions but Chl a + f under far-red light conditions. Their habitats are widely distributed in subtropical forest ecosystems and varied from mosses on limestone to macrophyte and freshwater in the streams and ponds. This study presents a significant advance in the knowledge of distribution and diversity of red-shifted chlorophyll-producing cyanobacteria in terrestrial ecosystems. The results suggest that Chl f-producing and Chl d-containing cyanobacteria might be important primary producers in far-red light dominant niches worldwide.     

Adaptation of epiphytic bryophytes in the understorey attributing to the correlations and trade-offs between functional traits

This study explores adaptive strategies of epiphytic bryophytes in the understorey by investigating the photosynthetic characteristics, pigment concentrations and nutrient stoichiometry, as well as other functional traits of three trunk-dwelling bryophytes in a subtropical montane cloud forest in SW China. The results showed that their light-saturated net photosynthetic rate (A_nmax?L), light saturation point (I_sat), light compensation point (I_c) and dark respiration rate (R_d) were ca 0.55, 106.72, 4.17 and 0.25?μmol?m^?2?s^?1, respectively. Furthermore, the samples demonstrated photosynthetic down-regulation under high irradiance. These photosynthetic characteristics can be explained by higher total chlorophyll concentrations, specific leaf area, chlorophyll per unit leaf N (Chl/N), lower ratio of chlorophyll a to chlorophyll b (Chl a/b) and photosynthetic nitrogen-use efficiency. We suggest that the bryophytes adapted to the shaded understorey microhabitats through a series of correlations and trade-offs between functional traits.     

NONDESTRUCTIVE TRACING OF MIGRATORY RHYTHMS OF INTERTIDAL BENTHIC MICROALGAE USING IN VIVO CHLOROPHYLL A FLUORESCENCE1,2

In vivo chlorophyll (Chl) a fluorescence was measured in undisturbed intertidal sediments with the purpose of tracing the vertical migratory rhythms of benthic microalgae. A pulse amplitude fluorometer, an instrument which does not require physical contact with the sample, was used, thus allowing successive measurements to be taken on the same sample without causing any type of disturbance to the sediment structure. The basis of the method is the possibility to detect changes in the Chl a concentration near the sediment surface caused by the vertical movement of the microalgae. This requires the verification of two conditions: the possibility to follow changes in the sediment Chl a content from fluorescence intensity, and a sediment photic depth smaller than the vertical distances covered by the moving microalgae. Both conditions were experimentally verified in intertidal muddy sediments of the Tagus estuary, Portugal. In vivo fluorescence was shown to vary linearly with the sediment Chl a content, and the sediment photic depth was estimated to reach 0.27 mm, a value clearly smaller than the reported depths for microalgal migrations. Sediment samples kept under in situ conditions exhibited large hourly Variations (over 400%) in the Chl a fluorescence intensity, which were closely synchronized with the daytime periods of emersion. The rhythmic fluctuations in Chl a fluorescence were confirmed further to represent microalgal migration by (1) its endogenous nature (fluorescence continued to follow diurnal and tidal cycles after removal of environmental stimuli), (2) its dependence on the vertical distribution of the microalgal population within the sediment (vertically homogenized samples failed to display fluorescence variations), and (3) the lack of significant temperature and light effects on the fluorescence emission under in situ conditions (tested in three species representative of the main groups found in the studied microphytobenthic communities—the diatom Phaeodactylum tricornutum (Böhlin), the cyanobacterium Spirulina maxima (Setch. et Gard.), and the euglenophyte Euglena granulata (Klebs) Lemm.). The results obtained indicate that, in spite of the potential concurrent effects of factors other than the Chl a concentration on the fluorescence intensity, in vivo Chl a fluorescence can be used to trace nondestructively the migratory behavior of benthic microalgae.     

The Adaptation of Plankton Algae

The variation in Skeletonema cells grown at 3 klux continuous illumination and 20°C is reported. Four different types of lamps gave no difference in the photosynthetic characteristics. The average diameter of the cells decreased from 8–3.5 μ during their six months vegetative period. The ratio between the pigment content in the largest and the smallest cells was about 2:1. A good correlation between cell volume and chlorophyll a content was found for this species. The content of chlorophyll c generally varied between 4 and 17 per cent of the chlorophyll a content. — A distinct correlation between the chlorophyll a content and the rate of photosynthesis per unit of cells at low light intensity was found. The rate of photosynthesis, in mg C per mg chlorophyll a and hour at 1 klux, varied between 0.40 and 0.70 for all 60 experiments with an average value of 0.56. The corresponding value for cells deficient in phosophorus was 0.19 and for cells deficient in nitrogen 0.09. — The material also showed a good correlation between the rate of photosynthesis per cell at 1 klux and the light-saturated rate of photosynthesis. I_k varied between 7 and 13 klux.     

Changes in the antenna size of Photosystem I and Photosystem II in Synechococcus sp. strain PCC 7942 grown in the presence of SANDOZ 9785 — a Photosystem II inhibitor

SANDOZ 9785, also known as BASF 13.338, is a pyridazinone derivative that inhibits Photosystem II (PS II) activity leading to an imbalance in the rate of electron transport through the photosystems. Synechococcus sp. strain PCC 7942 cells grown in the presence of sublethal concentration of SANDOZ 9785 (SAN 9785) for 48 hours exhibited a 20% decrease in Chl a per cell. However, no changes were observed in the content of phycocyanin per cell, the size of the phycobilisomes or in the PS II:PS I ratio. From an estimate of PS II electron transport rate under varying light intensities and spectral qualities and analysis of room temperature Chl a fluorescence induction, it was deduced that growth of Synechococcus PCC 7942 in the presence of SAN 9785 leads to a redistribution of excitation energy in favour of PS II. Though the redistribution appears to be primarily caused by changes affecting the Chl a antenna of PS II, the extent of energetic coupling between phycobilisomes and PS II is also enhanced in SAN 9785 grown Synechococcus PCC 7942 cells. There was a reduction in the effective size of PS I antenna based on measurement of P700 photooxidation kinetics. These results indicate that when PS II is partially inhibited, the structure of photosynthetic apparatus alters to redistribute the excitation energy in favour of PS II so that the efficiency of utilization of light energy by the two photosystems is optimized. Our results suggest that under the conditions used, drastic structural changes are not essential for redistribution of excitation energy between the photosystems.Abbreviations APC Allophycocyanin - Chl a chlorophyll a - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DCMU 3-(3,4-dichlorophyenyl)-1,1-dimethyl urea - DCIP 2,6-dichlorophenolindophenol - F_o fluorescence when all the reaction centres are open - f_m fluorescence yield when all the reaction centres are closed - F_v variable chlorophyll fluorescence - HEPES N-2-Hydroxyethylpiperazine-N-2-ethanesulphonic Acid - I₅₀ concentration that causes 50% inhibition in activity - MV methyl viologen - pBQ para benzoquinone - PBS phycobilisome - PC phycocyanin - PS I, PS II Photosystem I, Photosystem II - P700 reaction centre Chl a of PS I - SAN 9785 SANDOZ 9785 i.e. 4-chloro-5-dimethylamino-2-phenyl-3 (2H) pyridazinone, also known as BASF 13.338     

Relative binding affinities of chlorophylls in peridinin–chlorophyll–protein reconstituted with heterochlorophyllous mixtures

Peridinin–chlorophyll–protein (PCP), containing differently absorbing chlorophyll derivatives, are good models with which to study energy transfer among monomeric chlorophylls (Chls) by both bulk and single-molecule spectroscopy. They can be obtained by reconstituting the N-terminal domain of the protein (N-PCP) with peridinin and chlorophyll mixtures. Upon dimerization of these “half-mers”, homo- and heterochlorophyllous complexes are generated, that correspond structurally to monomeric protomers of native PCP from Amphidinium carterae. Heterochlorophyllous complexes contain two different Chls in the two halves of the complete structure. Here, we report reconstitution of N-PCP with binary mixtures of Chl a, Chl b, and [3-acetyl]-Chl a. The ratios of the pigments were varied in the reconstitution mixture, and relative binding constants were determined from quantification of these pigments in the reconstituted PCPs. We find higher affinities for both Chl b and [3-acetyl]-Chl a than for the native pigment, Chl a.     

Antarctic marine bacterioplankton subpopulations discriminated by their apparent content of nucleic acids differ in their response to ecological factors

Bacterial abundances determined in Drake Passage and Bransfield and Gerlache Straits (Antarctica) in the Austral summer ranged from 0.78 to 9.4×10⁵ cells ml⁻¹, and were positively correlated with standing stocks of Chl a. Two bacterial subpopulations were discriminated based in their different levels of green fluorescence and wide angle light scatter (SSC) per cell after SYTO-13 staining for the first time in Antarctic waters. High nucleic acid (HNA) and low nucleic acid (LNA) subpopulations differed considerably in their response to changes in environmental variables. The apparent content of nucleic acids per cell for the HNA subpopulation (FL1-HNA) showed vertical profiles similar to those of Chl a, including the presence of a maximum at the subsurface chlorophyll maximum. FL1-HNA was positively correlated with Chl a. No similar trends were observed for the LNA fraction. HNA and LNA subpopulations differed in the response of the wide angle light scatter signal to environmental factors as well. SSC-HNA decreased strongly with depth and was positively correlated with Chl a. Again, no similar trends were observed for the LNA subpopulation. The percentage of HNA cells (%HNA) ranged between 35.0 and 76.7% and showed a general tendency to increase with depth. This increase seemed to be larger when the stratification of the water column was higher. Differences in grazing pressure could be responsible of the unexpected vertical distribution of HNA cells. Our results shows that in situ LNA and HNA bacterioplankton subpopulations are under different ecological controls and likely to play different trophodynamic roles in Antarctic waters.     

Seasonal variation in pigmentation of the dinoflagellate Peridinium gatunense (Dinophyceae) in Lake Kinneret, Israel

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.     

Relative effects of Daphnia and Ceriodaphnia on phosphorus-chlorophyll relationships in small urban lakes

Empirical models based on zooplankton biomass were used to predict mean summer chlorophyll a (Chl a) and to examine how zooplankton influenced the total phosphorus (TP) - Chl a relationship. Four years of data were analyzed for three lakes having similar TP concentrations but varied abundances of Daphnia and Ceriodaphnia. Mean TP did not correlate significantly with mean Chl a during the study period, although mean Daphnia density was a good predictor of Chl a concentration (p > 0.001). Both residuals from the TP - Chl a relationship (p > 0.001) and Secchi depth (p > 0.007) were negatively correlated with Daphnia abundance. Ceriodaphnia abundance was positively correlated with Chl a (p > 0.002) and Secchi depth (p > 0.001). Mean size of Daphnia during spring was the best predictor of the Daphnia-Ceriodaphnia shift in mid-summer. Early establishment of a large-sized Daphnia cohort may prevent their summer elimination by Chaoborus and intensify competition with Ceriodaphnia. These results imply an important link between Daphnia and Ceriodaphnia thereby limiting the utility of Chl a - TP model predictions in these small, urban lakes. This linkage and the differential effect of these two zooplankton species on planktonic algae deserve further consideration in similar lakes where phytoplankton and zooplankton tend to be tightly coupled.