The influence of fluctuating light intensities on species composition and diversity of natural phytoplankton communities

The influence of fluctuating light intensities on phytoplankton composition and diversity was investigated for 49 days under semi-continuous culture conditions with sufficient nutrient supply, using phytoplankton assemblages from Lake Biwa, Japan. Light conditions were either periodically changed from high intensity (100 µmol photons m^-2 s^-1) to low intensity (20 µmol photons m^-2 s^-1) at intervals of 1, 3, 6 and 12 days, or fixed to constant intensities (permanent high and low light levels). All treatments additionally experienced a day:night cycle of 16:8 h. Phytoplankton abundance increased and reached a saturation level on day 19 of the treatment with permanent high light, but increased continuously until the end of the experiment (day 49) in the treatment with permanent low light intensity. In treatments with periodically changing light intensities, the phytoplankton abundance reached saturation levels between these dates. Under phytoplankton abundance saturation, chlorophytes predominated in the treatment with permanent high light, while either cyanophytes or diatoms were abundant under permanent low light intensity. Treatments with changing light supply had chlorophyte- and cyanobacteria-dominated replicates as well as replicates with balanced proportions of both. Furthermore, species diversity, measured by the Shannon index, was low in cultures under permanent light intensity, while slow fluctuating light at the scale of 3 -12 days resulted in an increased diversity index. These results indicate that species composition and diversity of the phytoplankton were affected by the periodically changing light regime in the order of days, and suggest that temporal changes in weather conditions are a major impediment to competitive exclusion of phytoplankton species in nature.     

Pigment signatures reveal temporal and regional differences in taxonomic phytoplankton composition off the west coast of Ireland

The composition of phytoplankton assemblages in April, 1998in Galway Bay and during a summer phytoplankton bloom occurringsouthwest of Ireland in August, 1998, was characterized by pigmentsmeasured by high-performance liquid chromatography. Pigmentdata reflecting phytoplankton assemblages dominated by diatomsin Galway Bay and dinoflagellates in the southwest of Irelandwere compared to phytoplankton cell counts. Significant relationshipswere found between the fucoxanthin concentrations and the diatomcell numbers (P < 0.0002 r² 0.63) during April, and betweenfucoxanthin (P < 0.0001 r² 0.79), 19'hexanoyloxyfucoxanthin(P < 0.0001 r² 0.77) concentrations and Gyrodinium aureolumcell numbers during the summer bloom.     

Phytoplankton communities in the littoral zone of lakes: Observations on structure and dynamics in oligotrophic and eutrophic systems

Summary The structure and seasonal dynamics of phytoplankton communities in the littoral zone were compared between oligotrophic and eutrophic lakes in the southeastern United States. Differences in diversity and species composition between lakes could be ascribed to long-term variation in nutrients corresponding to trophic status. However, significant within-lake variation could not be accounted for by microstratification of nutrients or other abiotic variables. Local biotic factors, perhaps dominated by the spawning activities of centrarchid fishes, resuspend periphyton and generate tychoplankton which becomes a persistent and integral part of the phytoplankton community in eutrophic systems. The patchy distribution of these biotic factors and resultant tychoplankton may lead to the observed variation. Grazing by herbivorous zooplankton was considered to be the major factor affecting the relative abundance of phytoplankton in the littoral zone, completely overriding the effects of nutrient concentration and biotic interactions between phytoplankton species during spring and summer.The relative importance of tychoplankton and grazing as regulatory factors operates independently of the trophic status or geographical location of a lake, making comparisons of different studies difficult and perhaps meaningless if traditional analyses based only on nutrients and interactions between species of phytoplankton are used. Limnetic as well as littoral components must be considered in future studies of phytoplankton communities in the littoral zone.     

The influence of water circulation on chlorophyll-turbidity relationships in Lake Okeechobee as determined by remote sensing

The spatial distribution of phytoplankton can be difficult toassess in shallow, productive aquatic systems due to frequentalgal blooms, high turbidity and sediment-resuspension events.We conducted a study to assess the distribution of suspendedparticles in Lake Okeechobee, Florida, utilizing both Landsat(1974–75) or Advanced Very High Resolution Radiometer(AVHRR) (1987) satellite remote sensing. Surface water sampleswere collected by helicopter to determine in situ chlorophyll-aand turbidity levels at 20 stations on four dates in 1974–75and six dates in 1987. Remotely sensed reflectance values agreedwell with in situ particle densities at the 20 in-lake stations(average R²: Landsat = 0.81, AVHRR = 0.53) and independent,synoptic boat mapping of algal blooms (r² = 0.79, P < 0.01).Basin-wide maps of chlorophyll and turbidity, as well as additionalspatial sampling, both indicated that these parameters are notnecessarily coupled in Lake. Our data concur with the hypothesisthat the spatial distributions of chlorophyll and turbidityare shaped by different forces. The highest concentrations ofchlorophyll occurred in the vicinity of tributary nutrient inputsat the lake's perimeter, while turbidity increased towards thecenter of the lake, reflecting predominant water circulationpatterns. ²Present address: Department of Biology & Romberg TiburonEnvironmental Center, San Francisco State University, San Francisco,CA 94132, USA ³Present address: Idaho Division of Environmental Quality, 1420North Hilton, Boise, ID 83706-1260, USA ⁴Present address: 5642 Santiago Circle, Boca Raton, FL 33433,USA     

Application of the lognormal equation to assess phytoplankton community structural changes induced by marine eutrophication

A methodological approach was developed for the quantification of the structural changes of phytoplankton communities induced by marine eutrophication. The lognormal equation assigning species abundance to doubling intervals (octaves) of individuals formed the basis of the proposed methodology and the field validation process was based on phytoplankton enumeration and classification data characteristic of eutrophic, mesotrophic and oligotrophic waters. Five octave sets with different sizes were tested for goodness of fit against field data and the set with the smallest size of doubling intervals was selected for further consideration. The application of the lognormal equation was evaluated statistically with field data and it was considered satisfactory at the 87% level. The changes in the shape of the lognormal equation induced by eutrophication were expressed by three characteristic parameters of the equation: the number of the modal octave, the number of species in the modal octave, and the shaping factor. Significant differences were observed for the three parameters among eutrophic, mesotrophic, and oligotrophic waters; the number of the modal octave was high in eutrophic and mesotrophic waters, the number of species in the modal octave has shown a trend of low values under mesotrophic conditions and the shaping factor has shown a considerable increase from eutrophic to oligotrophic waters. Handling editor: L. Naselli-Flores     

2006年秋季东海陆架浮游植物群集

根据2006年11月19日—12月24日在东海陆架海域（24.0°—32.0°N,120.0°—127.0 °E）进行的综合采样调查,对调查海域浮游植物的群集特征进行了研究.本次调查共发现浮游植物4门64属145种（包括未定名种）,其中硅藻是该调查海区浮游植物的主要功能群,其次为甲藻.主要的优势种为菱形海线藻、圆海链藻、丹麦细柱藻、斯氏几内亚藻、尖刺伪菱形藻和铁氏束毛藻等.浮游植物细胞丰度为0.09～5.11 cells·ml^-1,平均值为4.92 cells·ml^-1,秋季东海陆架浮游植物细胞丰度的平面分布主要由浮游硅藻刻画,其高值出现在调查区的北、东部离岸海域,细胞丰度大于30 cells·ml^-1.浮游植物及硅藻和甲藻的细胞丰度垂直变化趋势基本上都是随着水深增加,丰度逐渐减小.各个断面细胞丰度密集区主要集中在表层,个别站位的中层和底层也出现浮游植物密集区.调查区浮游植物的多样性指数平均值为2.80,其高值位于调查区东北和东南部,物种均匀度指数平均值为0.81,其高值位于调查区中部,生物多样性的分布与细胞丰度的分布一致.从Pearson相关性指数来看,亚硝酸盐、溶解态有机氮(DON)和温度显著影响调查区浮游植物的生长.     

Light absorption by phytoplankton: development of a matching parameter for algal photosynthesis under different spectral regimes

A spectral matching parameter (absorption efficiency, A_e) wasdeveloped to quantify the relationship between the light absorptionspectra of phytoplankton communities and the spectral irradianceof their ambient light field. A_e was defined as the ratio betweenthe amount of radiation absorbed by the phytoplankton in situand the amount absorbed in a spectrally flat light regime. Thisapproach was applied to our measurements of spectral absorptionfor the phytoplankton communities in six lakes in High ArcticCanada that spanned a range of bio-optical conditions. A_e valueswere calculated for the light spectrum down through the watercolumn and for 11 types of artificial light source. Spectralmatching varied among lakes and with depth. There was a significantlinear relationship between the relative change in A_e with depthand the diffuse attenuation coefficient K_d (r² = 0.52, P = 0.012for K_d for the 400–700 nm waveband; r² = 0.78, P = 0.0003for K_d at 440 nm). The tabulated values for the matching parameterA_e allow the comparison of photosynthesis versus irradiance(P versus E) curves among studies using different light sources.A_e estimates also facilitate the evaluation of chromatic adaptationin natural waters, and the calculation of spectrally adjusted,in situ primary production down through a water column fromP versus E relationships under a single spectral regime.     

A rapid Utermohl method for estimating algal numbers

The standard method for counting phytoplankton requires 24–48h of settling (Utermöhl, 1931). The modified Utermöhlmethod (plunger) described here reduces settling time to 2 h.Estimates of counts for phytoplankton using the plunger methodplotted against counts from the Utermöhl method yield agood correlation (r² = 0.97), and 95–100% of species (>2µm) recorded in the Utermöhl method were recordedwith the plunger method.     

A model of phytoplankton production in the lower River Rhine verified by observed changes in silicate concentration

The production of phytoplankton in the three main branches andsedimentation areas of the River Rhine in the Netherlands wasanalyzed using a simulation model describing the carbon andsilicate metabolism. This model is based on data derived froma sampling programme in which river water was followed duringdownstream transport. A ‘plug-flow model’ was developed,including sky irradiance and light attenuation in the water,and integrating photosynthetic rates determined in the laboratory.On the basis of the silicate content of diatom-dominated phytoplanktonand silicate regeneration in the river bottom, changes in silicateconcentrations were simulated and found to match observed changesin dissolved silicate. Low sìlicate concentrations wereshown to restrict the maximum population density of diatoms.Depth- and time-integrated rates of photosynthesis were shownto permit multiplication of the phytoplankton at a rate of upto one doubling day^–1 In the primary production periodApril-August 1988. values of 0.48–6.33 g C m^–2 day^–1,close to the few values reported for highly eutrophic riversand lakes, were observed. Model runs, including phytoplanktonproduction and losses, such as respiration, sedimentation andplanktonic grazing, were carried out to simulate the downstreamdevelopment of phytoplankton biomass. These simulations confirmthe view that a substantial part of the phytoplankton biomassand production is grazed or settles in the river delta despiteresidence times of only 52–97 h.     

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.     

Carbon dynamics in the 'grazing food chain' of a subtropical lake

Studies were conducted over a 13 month period at four pelagicsites in eutrophic Lake Okeechobee, Florida (USA), in orderto quantify carbon (C) uptake rates by size-fractionated phytoplankton,and subsequent transfers of C to zooplankton. This was accomplishedusing laboratory ¹⁴C tracer methods and natural plankton assemblages.The annual biomass of picoplankton (<2 µm), nanoplankton(2–20 µm) and microplankton (<20 µm averaged60, 389 and 100 µg C 1^–1 respectively, while correspondingrates of C uptake averaged 7, 51 and 13 µg C1^–1h^–1. The biomass of microzooplankton (40–200 µm)and macrozooplankton (<200 µm averaged 18 and 60 µgC 1^–1, respectively, while C uptake rates by these herbivoregroups averaged 2 and 3 µg C 1^–1 h^–1. Therewere no strong seasonal patterns in any of the plankton metrics.The ratio of zooplankton to phytoplankton C uptake averaged7% over the course of the study. This low value is typical ofthat observed in eutrophic temperate lakes with small zooplanktonand large inedible phytoplankton, and indicates ineffectiveC transfer in the grazing food chain. On a single occasion,there was a high density (<40 1^–1) of Daphnia lumholrzii,a large-bodied exotic cladoceran. At that time, zooplanktoncommunity C uptake was <20 µg C 1^–1 h^–1and the ratio of zooplankton to phytoplankton C uptake was near30%. If D.lumholrzii proliferates in Lake Okeechobee and theother Florida lakes where it has recently been observed, itmay substantially alter planktonic C dynamics.     

Production biology of copepods and cladocerans in three south-east Sri Lankan low-land reservoirs and its comparison to other tropical freshwater bodies

Production, biomass and productivity of the microcrustacean zooplanktonpopulations of three low-land reservoirs, Tissawewa (eutrophic), Ridiyagama(moderately eutrophic), and Muruthawela (mesotrophic) in South-east SriLanka were studied. The temporal variation of zooplankton production wasstudied in Tissawewa on basis of fortnightly sampling on five fixed samplingstations for 2 years. Zooplankton production was relatively high, mainlybecause of high copepod production predominantly realised due to twocalanoid copepods, Phyllodiaptomus annae and Heliodiaptomus viduus. Abouthalf of the copepod production was contributed by the naupliar instarstages, whereas the contribution of the eggs was generally much smaller(<20%). In contrast, the cladoceran production consisted for ca50–70% of egg production. The results of this study werecompared with those from more than twenty other tropical and subtropicalwaterbodies reported in the literature by deriving empirical relationshipsbetween mean phytoplankton biomass and mean zooplankton biomass andproduction. Mean zooplankton biomass and annual zooplankton production werefound to be positively related to mean phytoplankton biomass, and meanphytoplankton biomass proved to be a good predictor of mean zooplanktonbiomass (r² = 0.58) and a moderate good predictor ofannual zooplankton production (r² = 0.43). However,the relationships between the mean phytoplankton biomass and zooplankton P/Bwere not significant neither for small-bodied and large-bodied cladoceransnor for copepods.     

Phytoplankton biomass and distribution in a shallow eutrophic lake (Lake George,Uganda)

Summary Lake George, a shallow lake in western Uganda, supports a permanent and dense crop of phytoplankton, and may be regarded as eutrophic although the ambient concentrations of inorganic nitrogen and phosphorus are low. The figures for the annual nutrient loadings (Viner and Smith, 1973) would suggest, however, a eutrophic lake when analysed on the scheme of eutrophication proposed by Vollenweider (1968).The horizontal distribution of chlorophyll a shows a concentric pattern, with the maximum values occurring towards the center. This horizontal variation is thought to reflect water movements, and a general pattern of water flow is proposed.The majority of the species show no seasonal variation but populations of both Anabaena and Melosira show annual variations. These two species also have a horizontal distribution pattern which is the reverse of other species. This pattern is used to support the proposed movements of water.Phytoplankton generation times are discussed in relation to the diurnal cycle occurring in Lake George.     

Phytoplankton composition and pigment concentrations as indicators of water quality in the Rybinsk reservoir

Long-term changes in phytoplankton (1954–1981) and chlorophyll (1969–1984) and their spatial distribution in summer 1989 were studied in the Rybinsk reservoir (second largest reservoir of the Volga River, North-West Russia). Estimation of trophic status and saprobity of the reservoir was based on phytoplankton biomass and species composition and chlorophyll content. The most eutrophic waters were found to occupy the peripheral areas in littoral zone and river inflows of the reservoir, while the waters in the central part of the basin were less eutrophic. Long-term changes of the phytoplankton biomass, chlorophyll, chlorophyll/biomass-ratio and saprobity index observed in the central part of the reservoir were analyzed by statistical methods. An increase in saprobity and an inverse relationship between chlorophyll/biomass-ratio and water transparency demonstrate progressive eutrophication in the central part of the reservoir. Two distinct periods (1954–1970 and 1971–1984) could be discerned on the basis of annual mean phytoplankton biomass values. For the earlier period a relationship between biomass and climatic factors (solar radiation and wind velocity) could be established, but no such correlation could be found for the latter period. There was no significant increase in the phytoplankton biomass during the monitoring period, but a definite increase in the proportion of small-sized species of centric diatoms, cryptomonads and blue-greens. These forms are considered as r-strategists in the community, and their increase is interpreted as a sign of eutrophication.     

Measuring the intensity of disturbancein zooplankton communities of Mediterranean salt marshes using multivariate analysis

The possibility of using multivariate analysis for measuringdisturbance intensity in fluctuating ecosystems is discussed.As an example, two variables derived from the results of correspondenceanalysis of aquatic invertebrate samples from the Aiguamollsde l'Empordà (NE Spain), Mediterranean salt marshes,are proposed as measures of the severity and intensity of disturbance.The behaviour of these variables allows us to discuss severaltopics of disturbance theory, such as the relationship betweendisturbance intensity and the distribution of planktonic biomassby size, stability and diversity. A better adjustment to a curve(r²= 0.743) is obtained when testing Connell's intermediatedisturbance hypothesis when evenness and severity are used tomeasure diversity and disturbance, respectively. This hypothesismay be expressed as follows: at intermediate severity, the maximumlinks between present species are found. These measurementsare simple to obtain and may be useful tools for the managementof Mediterranean ecosystems. Although they cannot be directlyapplied to other ecosystems, a relationship between multivariateresults and measurements of disturbance might be observed insimilar ecosystems if analogies between some multivariate resultsand the flux of external energy are investigated.     

Long-term dynamics of phytoplankton assemblages: Microcystis-domination in Lake Taihu, a large shallow lake in China

Long-term phytoplankton assemblages in a large shallow Chineselake, Lake Taihu, were presented using the monthly monitoringdata from October 1991 to December 1999. Earlier research results(1960, 1981 and 1988) were applied to discuss the differenttrophic stages of the lake. The species composition in the lakewas more closely related to eutrophication level than to lake-size,shallowness, or turbidity. Each summer, a single peak of phytoplanktonbiovolume appeared in Meiliang Bay. The results of principalcomponents analysis showed a distinct temporal shift in speciescomposition between summer and winter. A clear spatial differencein phytoplankton occurred between Meiliang Bay and the lakecentre. Wind speed and direction affected the horizontal distributionof phytoplankton, especially Microcystis, in the lake. Temperature,underwater light climate, nutrients and grazing by zooplanktonand by fish were discussed to explain the overwhelming dominanceof Microcystis. Four nutrient-phytoplankton stages were identifiedin the lake: an oligo-mesotrophic stage with low algal biomassuntil 1981, a eutrophic situation with blooms of Microcystisduring 1988–1995, hypertrophic conditions with the dominanceof Planctonema and total phosphorus up to 200 mg m^-3 from 1996to 1997 and the restoration period after 1997. The wax and waneof the phytoplankton assemblages were mainly controlled by temperature,wind and turbidity while long-term biomass dynamics were influencedby the level of nutrients.     

Seasonal variations of phytoplankton photosynthate partitioning in two lakes of different trophic level

The aim of this study was to compare vertical and seasonal variationsof inorganic carbon allocation into macromolecules by the phytoplanktonpopulation in a eutrophic lake (Lake Aydat) and an oligo-mesotrophiclake (Lake Pavin). Biochemical fractionation was conducted byconsecu tive differential extractions in order to separate proteins,polysaccharides, lipids, and low molecular weight compounds(LMW). The ratio of light absorption at480 and 665 nm by acetoneextracts of phytoplankton pigments was used as an indicatorof the nutritional statusof natural phytoplankton populations.Our results show that in Lake Aydat, the main photosyntheticend productswere poly saccharides, whereas in Lake Pavin, radioactivitywas predominantly incorporated into the protein fraction. Moreover,the seasonal cycles of mixing and stratification in these twolakes affected the pattern of ¹⁴C incorporation into LMW andmacromolecules. An increase in the relative synthesis of proteinsoccurred during stratification periods. It was linked to anincrease in temperature and nutrient limitation further complicatedby the shift in species composition of the populations. Differences recorded both between the two lakes of different trophicstatus and between seasons confirm that the proportion of carbonincorporated into proteins might be a useful indicator of thephysio logical status of phvtoplankton communities.     

Limnology of Heart Lake,Ontario

Heart Lake, a small dimictic lake in Southern Ontario shows classical characteristics of eutrophy: high phytoplankton populations, blooms of blue-greens, predominently Aphanizomenon flos-aquae, in summer, a shallow photic zone decreasing seasonally in response to dense phytoplankton crops and a hypolomnion which is deoxygenated from early summer to fall turnover. Large decreases occur in TDP and SRS in particular, but also in TDN from spring to summer.The distribution of individual species of algae with depth in the epilimnion was seldom uniform but, more commonly conformed to a definite pattern. The simultaneous existence of different patterns in different species provides evidence of spatial heterogeneity (niche diversification) in the epilimnion, which could lessen any interspecific competition.Diatom stratigraphy in a 70 cm core revealed that the lake has been eutrophic throughout but may have gone through 3 periods; of these, the most recent one was the most eutrophic and was preceeded by a period of unusually low water levels.     

Phytoplankton biomass is mainly controlled by hydrology and phosphorus concentrations in tropical hydroelectric reservoirs

Phytoplankton is widely recognized as being regulated mainly by resources (nutrients and light) and predation by higher trophic levels. In reservoirs, these controls also can be modulated by hydrology, for example through the influence of flow pulses generated by the operation of the dam. In this study, we tested the influence of light, nutrients, and zooplankton grazing pressure, and also hydrology (as water residence time) on the phytoplankton biomass in eight tropical hydroelectric reservoirs, which differ in size, morphometry, location, trophic state, and water residence time. Our hypothesis was that, as these reservoirs are used for hydroelectric purposes, the control that would otherwise be exerted on phytoplankton biomass primarily by resource availability and grazing will also be modulated by hydrology. Low phytoplankton biomass (range of system medians = 12–299 μg C l⁻¹) occurred in most systems, except for one highly eutrophic reservoir (median = 1331 μg C l⁻¹). Our data showed that phosphorus was more often likely to be the limiting nutrient in these systems, as assessed through nutrient limitation indexes (nitrogen and phosphorus), based on concentrations and ratios. For most reservoirs, excluding the eutrophic system with high cyanobacteria biomass, seasonal water residence time was the variable that best explained phytoplankton variation among the several environmental variables analyzed in this study (P < 0.0001; adjusted r ² = 0.38). Hydrology was an important and additional factor modulating phytoplankton in these tropical reservoirs, directly removing phytoplankton populations and their potential zooplankton grazers by washout, and also affecting nutrient availability.