Phytoplankton Biovolume Research Articles

Picophytoplankton predominance in hypersaline lakes (Transylvanian Basin, Romania).

The occurrence and importance of photoautotrophic picoplankton (PPP, cells with a diameter <2 μm) was studied along a trophic and salinity gradient in hypersaline lakes of the Transylvanian Basin (Romania). The studied lakes were found to be rich in PPP, with abundances (maximum 7.6 × 10(6) cells mL(-1)) higher than in freshwater and marine environments of similar trophic conditions. The contribution of PPP to the total phytoplankton biovolume did not decrease with increasing trophic state as it was generally found in other aquatic environments. Regardless of the trophic conditions, the contribution of PPP could reach 90-100 % in these hypersaline lakes. We hypothesized that the PPP predominance might be the result of the low grazing pressure, since heterotrophic nanoflagellates (the main grazers of PPP) were absent in the studied samples. There were significant differences in community composition among the lakes along the salinity gradient. CyPPP predominated in less saline waters (mainly below 5 %), while EuPPP were present along the entire salinity range (up to 18.7 %), dominating the phytoplankton between 3 and 13 % salinity. Above 13 % salinity, the phytoplankton was composed mainly of Dunaliella species.

Determination of ecological status and ecological preferences of phytoplankton using multivariate approach in a Mediterranean reservoir

The European Union Water Framework Directive includes phytoplankton as one of the mandatory five biological indicators to be used to assess the ecological status of surface waters. The objective of the study was determination of ecological status and ecological preferences of phytoplankton from April 2012 to June 2013, using multivariate approach in Alleben Reservoir in the southeast Turkey. The reservoir showed a warm monomictic stratification pattern (stratification in April–October 2012 vs. mixing in November 2012–March 2013). The reservoir was meso-eutrophic according to phosphorus, chlorophyll a, and transparence values. Phytoplankton biovolume reached remarkable peaks in autumn and spring. Phytoplankton species belong to functional groups of A, D, E, J, LO, LM, MP, P, and Y as descriptor. Phytoplankton trophic index (PTI) and assemblage index (Q) indicated the overall medium ecological status of Alleben Reservoir. PTI and Q indices may be appropriate phytoplankton metrics to assess the ecological status of the reservoir. Changes in environmental gradients significantly influenced the ecological preferences of species and phytoplankton abundance in the reservoir. Canonical correspondence analysis (CCA) confirmed that phytoplankton species were sensitive to environmental variability, with the first two axes of CCA able to explain 92.8% of the total variation and 37.1% of the cumulative percentage variance in the phytoplankton assemblage structure. Most effective explanatory factors (e.g., salinity, conductivity, pH, and temperature) played significant role (P = 0.002) in the seasonality of species.

Phytoplankton trends in the Great Lakes, 2001–2011

We describe recent trends in phytoplankton composition and abundance in the Laurentian Great Lakes using synoptic spring (April) and summer (August) sampling events from 2001 through 2011, a period of rapid shifts in pelagic food webs and water quality. Data analysis identified qualitative and quantitative changes in algal densities, biovolume, and taxonomic composition of assemblages. Since 2001, Lake Superior has changed subtly with an increase in small-celled blue-green algae in spring and a recent decline in summer centric diatoms, possibly a result of lake warming and changes in water quality. Spring phytoplankton declines mainly attributed to diatoms occurred in Lakes Huron and Michigan, a probable result of invasions by non-native dreissenids that have reduced pelagic nutrients and selectively consumed certain taxa. The decline in Lake Huron's spring phytoplankton biovolume was earlier and more severe than that in Lake Michigan, despite a faster and more abundant dreissenid invasion in Lake Michigan. Lake Erie's central basin had a notable increase in spring centric diatoms (largely Aulacoseira), while the whole of Lake Erie shows a summer increase in cyanobacteria, complementing that found in coastal regions. The composition of Lake Ontario's species assemblage shifted, but little overall change in algal abundance was observed with the exception of higher summer densities of cyanophytes. Additional mechanisms for shifts in the pelagic primary producers are described or hypothesized in the context of concurrent shifts in water quality and invertebrate populations. Tracking these trends and explaining driving factors will be critical to the management of lake conditions.

Influence of re-flooding on phytoplankton assemblages in a temperate wetland following prolonged drought

Wetlands can experience drying and flooding cycles which influence the dynamics of the phytoplankton assemblages. The aim of our study was to evaluate changes in the phytoplankton structure during a drought/flood period in a warm-temperate wetland. We hypothesized that fluctuations in water level and development of macrophytes favour the development of fast-growing algae with adaptations to low light conditions. We studied algal and cyanobacterial colonization and succession in the nascent planktonic habitat in a wetland in the Southern Hemisphere (Argentina). We assessed changes in phytoplankton biovolume, chlorophyll aconcentration (Chl a), richness, diversity, and evenness throughout a drought/flood period. Phytoplankton species were classified into ecological functional groups (FG). Multivariate analysis (RDA) showed that water level, conductivity and percentage macrophyte cover of the site surface (PCSS) explained the variability in the phytoplankton assemblage structure in terms of classes and FG. Particularly, FGs T and LM responded to the changes during the drought/flood cycle, probably due to light constraints and stability of the water column induced by the development of emergent and freefloating macrophytes. Our study expands the knowledge of phytoplankton species composition and ecological FG succession under freefloating macrophyte cover in a re-flooding episode. We conclude that water depth and development of macrophytes are the key factors in shaping phytoplankton species structure in a temporary wetland.

Modifying the PEG model for Mediterranean lakes – no biological winter and strong fish predation

Summary The widely cited Plankton Ecology Group (PEG) model of plankton seasonal succession is often used as a template to explain the seasonal changes in plankton communities outside the cold temperate zone, where it was developed, but this may be inappropriate for lower‐latitude lakes. Lower‐latitude lakes have high light availability in winter and less pronounced seasonal variations in fish predation on zooplankton. We might therefore expect higher phytoplankton crops in winter and much more predation on zooplankton by fish than in colder lakes. This might lead to less grazing in summer and relatively higher phytoplankton crops. We compared data on phytoplankton biovolume, zooplankton biomass and body size from 18 German and 6 Greek lakes to test these hypotheses.

Effects of an extensive Prymnesium polylepis bloom on breeding eiders in the Baltic Sea

The effects of an extensive bloom of the potentially toxic Prymnesium polylepis (Haptophyta) on breeding eiders (Somateria mollissima) in the Baltic Sea were analysed. Increasing abundances of the alternate stage P. polylepis was detected by a marine monitoring programme in the autumn 2007. The bloom peaked between March and May 2008 in the southern, central and northwestern Baltic Proper and abundances of up to 5×106cells l−1 were recorded. At several sites P. polylepis constituted between 30 and 90% of the total phytoplankton biovolume. The flagellate was only recorded in low numbers in the northeastern Baltic Proper and Gulf of Finland. The abundances were low in 2007, 2009 and 2010. In 28 eider colonies situated in the southern and central Baltic Proper, sharp and synchronous declines in the number of nesting eiders were observed from 2007 to 2008. In colonies on Gotland in the central Baltic Proper, a 76% decrease, from 6650 nests to 1620 nests, was followed by increases in 2009 and 2010, although not up to numbers observed in 2007. At Utklippan and Ertholmene in the southern Baltic Proper, the observed decreases of 55%, from 144 to 65 nests, and 36%, from 1660 to 1060 nests, respectively, between 2007 and 2008, were followed by increases in 2009 and 2010 up to the level observed in 2007. By contrast, no general decline of the number of nesting eiders was observed from 2007 to 2008 in 75 colonies in the northeastern Baltic Proper and Gulf of Finland. Hence, the spatial distribution of the P. polylepis bloom in 2008 closely matched the observed distribution of extensive non-breeding of female eiders. We suggest that the intensive spring bloom of P. polylepis, either through a toxic or non-toxic pathway, affected the main benthic food of eiders, i.e. blue mussels (Mytilus trossulus × Mytilus edulis), at pre-breeding foraging sites close to the breeding sites, and, subsequently, the body condition of adult female eiders and their breeding propensity.

Phytoplankton and suitability of derived metrics for assessing the ecological status in a limno-reservoir, a Water Framework Directive nondefined type of Mediterranean waterbody

“Limno-reservoirs” are small waterbodies constructed in the riverine zone of large Mediterranean reservoirs to preserve a constant water level, with the goal of mitigating the undesirable effects of reservoir operation, including those related to water level fluctuations. The Pareja limno-reservoir was among the first limno-reservoirs, and its purposes are both environmental and recreational. Phytoplankton is one of the compulsory biological indicators used to estimate ecological status in lakes and reservoirs in accordance with the European Union Water Framework Directive (WFD). Chlorophyll a (Chl-a) and phytoplankton biovolume in the Pareja limno-reservoir were studied between spring 2008 and winter 2011. Phytoplankton composition was analyzed employing the functional group approach. The suitability of several phytoplankton metrics to assess the ecological status of the limno-reservoir was verified, including Chl-a, total biovolume, cyanobacteria contribution and absolute biovolume, IGA (Índex de grups algals), MedPTI (Mediterranean Phytoplankton Trophic Index), Assemblage (Q) Index, and PTI (Phytoplankton Trophic Index). Phytoplankton composition was dominated by centric diatoms from functional group B, although they were replaced by other groups in some periods as a response to environmental changes. Checking the response of the phytoplankton metrics to a trophic gradient in addition to Chl-a, we determined that total biovolume, Q Index, and especially PTI were the most appropriate metrics to assess the ecological status of the Pareja limno-reservoir. This approach has relevant management implications for Mediterranean limno-reservoirs. Ecological status assessment may not yet be mandatory in countries such as Spain, but considering environmental and recreational goals, performing such assessments is advisable.

Weekly flow cytometric analysis of riverine phytoplankton to determine seasonal bloom dynamics

Understanding the relative role of anthropogenic and environmental drivers on the timing, magnitude and composition of algal and cyanobacterial blooms is vitally important for the effective management of river catchments. Whilst taxonomic identification and enumeration of algal species can provide valuable insights, the time and specialist skills needed for this approach makes it prohibitive for high frequency and multiple-site studies. Other proxies for phytoplankton, such as total chlorophyll concentration provide little information on community composition. Here we demonstrate the use of flow cytometry (FCM) as a viable alternative approach for monitoring the changing seasonal patterns of abundance, composition and biovolume of phytoplankton in rivers. A FCM assay was set up and calibrated using a range of pure algal cultures and then applied to a year-long, weekly sampling campaign on the River Thames at Wallingford, UK. Ten groups of phytoplankton representing diatoms, chlorophytes, cryptophytes and cyanobacteria were monitored over the course of the year and examined in relation to river physiochemical parameters. Major diatom blooms occurred in spring and autumn, correlating with depletion of soluble reactive phosphorus and dissolved silicon concentrations and we also observed a significant and sustained cyanobacteria bloom between July and October. Pico-chlorophytes (0.2-2.0 μm in diameter) dominated the community throughout the summer period but were not detected using traditional colorimetric chlorophyll analysis, suggesting underestimates of actual phytoplankton standing stocks by traditional methods. We demonstrate high resolution sampling and FCM as a sensitive method for river ecosystem monitoring and that FCM data may be used as an indicator of riverine health.

How does interannual trophic variability caused by vertical water mixing affect reproduction and population density of the Daphnia longispina group in Lake Iseo, a deep stratified lake in Italy?

Lake Iseo is a deep meromictic lake located in Italy. During the past 20 years (1993–2013), the lake has experienced complete mixing of the water column only in spring 2005 and 2006. The full overturn episodes in these 2 years resulted in an increase in nutrients in both years, but an increase in phytoplankton biovolume occurred in the surface layers only in 2005. Our study examined if the magnitude of vertical mixing and the resulting increase in concentrations of epilimnetic total phosphorous (TP) can help predict reproduction and abundance of the main primary consumers, the cladocerans. We investigated the lake for 9 years (2001–2009) and compared annual changes in the Cladocera community and reproduction of the Daphnia longispina group between years of full and partial mixing. During the complete vertical mixing years (2005 and 2006), the taxonomical composition of Cladocera did not change, and density relationships among taxa shifted slightly toward an increase in the population density of Daphnia spp. Phytoplankton biovolume was significantly related to Daphnia mean clutch size. The increase in TP subsequent to the complete vertical mixing during late winter–early spring also seemed to predict reproduction and population density of Daphnia species. To our knowledge, this is the first long-term field study highlighting the importance of vertical mixing depth and TP concentrations on Daphnia abundance and phenology in a meromictic–oligomictic deep lake.

Key drivers for phytoplankton composition and biomass in an Ethiopian highland lake

We studied the temporal phytoplankton community pattern of the deep crater Lake Hayq in the highlands of Ethiopia from October 2007 to October 2008. Earlier sporadic surveys indicated that the phytoplankton community was predominantly characterized by heavy diatoms, which characteristically suffer from rapid sedimentation. The trophic status of Lake Hayq was reported to have changed from oligotrophic to eutrophic in 1992. The present study addresses the potential reasons for the diatom dominance as well as causes of the trophic change. Net and integrated water samples were used for determination of physico-chemical parameters and phytoplankton biovolumes. Our results revealed that diatoms and chlorophytes dominated during most of the study period in Lake Hayq and seem to be favored by the mixing regime of the water body, which can be described as partial atelomixis with daily mixing of the epilimnion maintaining the algae within the euphotic depth via regular re-suspension. However, the epilimnion may be decoupled from the hypolimnion by a seasonal chemocline. Nutrients were not limiting in the lake with an overall mean concentration of soluble reactive phosphorus of 22 μg L−1 and total phosphorus of 58 μg L−1 and of dissolved inorganic nitrogen of 305 μg L−1, with ammonium being the primary form. In the 1940s only diatoms were reported, but since the 1990s other phytoplankton groups and taxa have become relevant. Canonical correspondence analysis showed that chlorophytes were mainly associated with nutrients and rainfall, euglenophytes with elevated alkalinity and the diatoms with silica and zooplankton. Chlorophyll a as measure of total phytoplankton biomass was significantly influenced by seasonality and underwater light supply, reflecting the significant role of atelomixis in persistent occurrence of heavy taxa in the epilimnion. The lake is still categorized as a eutrophic system, demonstrating that the trophic change reported in 1992 was not short-lived. In addition to changes in the catchment the eutrophication process was probably primarily triggered by a previous introduction of Tilapia in the lake, causing a cascading effect in the food–web interactions. This implied that the phytoplankton composition and biomass of this tropical deep tropical lake can be controlled through biomanipulation, as has been demonstrated for temperate lakes.

Climatic Influence on the Phytoplankton Communities of the Upper Reaches of the Southern Bug River (Ukraine)

ABSTRACT A total of 98 taxa of algae were observed in phytoplankton, sampled monthly, from the Khmelnitsky monitoring station in the Southern Bug River, Ukraine, between April 2010 and March 2011. Chlorophyta species are the richest taxonomic group with 46 taxa, followed by Bacillariophyta, Euglenophyta, Cyanoprokaryota, Dinophyta, Chrysophyta, Streptophyta, and Xanthophyta. Seasonal dynamics of species distribution in taxonomic divisions shows that the role of Bacillariophyta in communities was high in January-March, which were replaced by greens in March-September. Euglenoids were developed in February-December and bluegreen algae in summer communities only. Strong positive correlations between temperature and species richness was observed. Abundance and biovolume of phytoplankton were maximal in summer, caused mostly by Dolichospermum flos-aquae (Lyngb.) Wacklin, Hoffmann and Komarek and Ceratium hirundinella (O. Müll.) Bergh. The river ecosystem has two periods of trophic levels - high at summer and low at winter. Bioindication characterizes the river as low alkaline and low mineralized with a moderate organic pollution level, revealed aspects of seasonal changes and revealed the main source of organic pollution as flowing from the catchment area during ice melting and rains. Organic pollution indices fluctuate within narrow limits suggesting relative stability of the river ecosystem that is shown also by Shannon indices. The calculated indices, comparative statistics, CCA, and bio-indication analysis exhibits a low pollution level in the Khmelnitsky monitoring station that can be used as a model of aquatic community dynamics under seasonal fluctuation in the southern boreal province climate, applicable for monitoring of the Southern Bug River.

Diel responses of phytoplankton of an Amazon floodplain lake at the two main hydrological phases

AIM: This study examines the short-term changes of phytoplankton in an oxbow lake on the floodplain of the Acre River, Amazonia, Brazil. METHODS: Samples were taken with a Van Dorn bottle, at three depths (surface, middle and bottom), in two periods (low waters and high waters), for seven consecutive days in two schedules, night and morning. RESULTS: Phytoplankton was represented by 198 taxa and the Class Euglenophyceae, with 62 taxa, was the best-represented group in both periods. There were abrupt changes in the community during the high waters (potamophase). During this period, in conditions of partial atelomixis, we recorded higher values of phytoplankton biovolume and dominance of Gonyostomum semen (Ehr.) Dies. (Raphidophyceae). CONCLUSIONS: In the low waters (limnophase), conditions in the lake were more stable, the diversity and rate of change in the community were lower, and the frequent periods of stratification and mixing were responsible for the dominance of Geitlerinema sp. (Cyanobacteria).

&lt;b&gt;Spatial and temporal fluctuation of phytoplankton functional groups in a tropical reservoir&lt;/b&gt; - doi: 10.4025/actascibiolsci.v35i3.12988

Along the horizontal axis of reservoirs are generally recognized three zones (fluvial, transition and lacustrine) with distinct hydrodynamic and physical, chemical and biological properties. Quarterly samplings were conducted in 2002, in the limnetic region from each zone, at different depths of a tropical reservoir. To test the hypothesis that highest biomass (biovolume) of phytoplankton are found in the transition zone, the PERMANOVA analysis was realized. 106 taxa were recorded. Significant differences between biovolume values of the three zones were not verified (pseudo F = 0,89; p = 0,55). Higher values of biomass were obtained in lacustrine and transition zones of the reservoir. The functional group (FG) N (Cosmarium spp.) was dominant in these zones, in rain period, and related to low phosphorus concentration, high transparency and water column stability. Low biovolume values in reservoir characterized oligotrophic conditions in all zones of the reservoir, most of the period. The dominance of FGs Y, Lo, E, P and A, as evidenced by the CCA, was associated with low light availability and higher nutrients concentrations.

The allelopathic capacity of submerged macrophytes shapes the microalgal assemblages from a recently restored coastal wetland

We have tested the efficiency of isolated and combined submerged macrophyte cultures to inhibit, through allelopathy, the natural phytoplankton growth. Both plants and microalgae come from the same wetland, a recently restored area in Albufera de València Natural Park (Spain). The need to replant the area under restoration with submerged macrophytes makes this information essential for wetland management. The selection and culture of the submerged macrophytes used in that restoration (four charophytes: Chara hispida, Chara vulgaris, Chara baltica, Nitella hyalina, and one angiosperm: Myriophyllum spicatum) provided a good opportunity to test in the laboratory the allelopathic effect of macrophyte assemblages on environmental phytoplankton communities. Three experiments were carried out using spring communities: in Experiment 1, a diverse phytoplankton assemblage (29% of biomass Chlorophyceae, 26% Cryptophyceae, 19% diatoms and 9% cyanobacteria) was cultivated with exudates from monocultures of C. hispida, N. hyalina and M. spicatum. Experiment 2 proved the allelopathic effect of a macrophyte assemblage exudate (C. hispida, C. baltica, C. vulgaris, N. hyalina and M. spicatum in a mixed culture) on two different phytoplankton communities (one diverse: 53% biomass of diatoms, 27% cyanobacteria, 18% chlorophytes and another dominated by small chlorophytes). The response variables were Chl a concentration, phytoplankton biovolume and main algal groups’ biovolumes. When phytoplankton grew in water with exudates from monocultures, microalgal biomass was from 4 to 6 times lower than in the control after 5 days and Chl a concentration was up to 4 times lower. The inhibitory effect of C. hispida was greater than that of M. spicatum. Mixed macrophyte assemblages resulted in even stronger allelopathic effects than monocultured macrophytes; the biomass was reduced by 7 fold after 5 days using the mixed exudates and Chl a concentration was between 3 and 5 times lower. The experiments demonstrate that macrophytes are particularly effective in inhibiting the growth of both small diatoms and the least desirable phytoplankton component in these wetlands (filamentous cyanobacteria), but not chlorophytes (reduction by 37–69, 7–14 and 1–7 fold for diatoms, cyanobacteria and chlorophytes, respectively). The predictions are that spring macrophytes might enhance microalgae that are suitable for grazing (mostly small chlorophytes) and will decrease non-edible filamentous taxa. Thus, restoration managers should replant with the mixture of submerged native macrophytes that provide the most harmful allelopathic effects to promote benefits on aquatic communities in two synergistic ways: by directly reducing microalgal biomass and by indirectly enhancing grazing, which in turn, would promote a clear-water phase. We present replanted macrophytes as ecosystem engineers, i.e. organisms that directly or indirectly modulate the availability of resources for the wetland food webs, by causing changes in primary producer assemblages.

Spatial heterogeneity of diatom silicification and growth in a eutrophic reservoir

Summary Diatoms are one of the most important phytoplankton groups. As they grow, diatoms use silicon to produce a siliceous frustule, which protects the cell. During April–November 2011, at 1–3 week intervals, we estimated diatom silicification rates at two distinct sites along the longitudinal profile of the canyon‐shaped eutrophic Římov Reservoir (Czech Republic): (i) a nutrient‐depleted lacustrine zone near the dam and (ii) a nutrient‐rich transition zone upstream near the river inflow. Diatom silicification was estimated using the 24‐h in situ incubation of natural phytoplankton assemblage with a fluorophore 2‐(4‐pyridyl)‐5‐{[4‐(2‐dimethylaminoethyl‐aminocarbamoyl)methoxy]phenyl}oxazole (PDMPO) which fluorescently stains the newly synthesised diatom frustules. Diatoms contributed an average c. 40% to the total phytoplankton biovolume in the lacustrine zone, but only c. 20% in the transition zone where a cyanobacterial bloom developed during summer. Asterionella formosa and Fragilaria crotonensis were the most abundant diatom species, while Aulacoseira italica, Nitzschia acicularis, Synedra acus and Stephanodiscus sp. were less important. Silicification rates of all diatom species were significantly higher in the transition zone than at the dam. The intensity of PDMPO fluorescence per diatom cell was tightly related to the growth rates of three diatom species calculated from changes in cell counts during the incubation. The PDMPO technique can thus be used as a proxy for diatom growth. Growth rates of the two most abundant diatom species were positively correlated with daily light exposure but not with nutrient concentrations.

An empirical modeling approach to predict and understand phytoplankton dynamics in a reservoir affected by interbasin water transfers

[1] In this paper, we use empirical modeling to predict and understand phytoplankton dynamics in a reservoir affected by water transfers. Prediction of phytoplankton biovolume is central to the management of water resources, particularly given the significant impacts on quality of the water-quantity oriented management of transfers between reservoirs. A novel tree-based iterative input variable selection algorithm is applied for the first time in an ecological context, and identifies a maximum of eight driving factors out of 77 candidates to explain the biovolume of chlorophytes, cyanobacteria and diatoms. The stepwise forward-selection to iteratively identify the most important inputs leads to a physically interpretable model able to infer the physical processes controlling phytoplankton biovolume. Reservoir inflows and outflows are found to exert a strong control over diatom and chlorophyte dynamics while water temperature, nitrate and phosphorus determine the biovolume of cyanobacteria. Following the selection of the most relevant inputs, the 1 week ahead predictions of four different data-driven model classes, i.e., neural networks, extra trees (ETs), model trees and linear regressions, are compared based on performance indices and statistical tests. ETs are found to outperform the other models by providing accurate predictions of cyanobacteria, chlorophyte and diatom biovolume by explaining 66.6%, 66.9%, and 80.5% of the variance, respectively. The methodology is applicable to different environmental studies and combines the strength of empirical modeling, i.e., compact models and accurate predictions, with a good understanding of the physical processes involved.

Changes in the phytoplankton community and dominance of Cylindrospermopsis raciborskii (Wolosz.) Subba Raju in a temperate lowland river (Ponjavica, Serbia)

Species composition and seasonal succession of phytoplankton were analyzed in a lowland river located in South Banat (Ponjavica, Serbia). As a result of human activity, a network of irrigation channels was built on the Ponjavica River’s upper and lower courses. These channels reduce the water level in the river and help to create favorable conditions for accelerated eutrophication processes. Eight phytoplankton divisions with 444 taxa were present. Physical and chemical testing of water, phytoplankton abundance and biomass, as well as chlorophyll a concentration showed a high level of eutrophication. Cyanobacterial biomass developed in 2002 with dominance of Microcystis aeruginosa and Aphanizomenon flos-aquae. Changes in phytoplankton composition were observed during 2008, characterized by the appearance and dominance of Cylindrospermopsis raciborskii when this species accounted for more than 85% of the total phytoplankton biovolume. The change in dominant phytoplankton functional groups was observed: codons H1 and M characterizing summer in 2002 were replaced by codons SN and S1 in 2008. This study compares the presence of C. raciborskii with other phytoplankton species in relation to water quality parameters. High abundance of this species correlated positively with biochemical oxygen demand and turbidity, and negatively with NO3-N concentrations during the study period.

Seasonal variation of the phytoplankton community structure in the São João River, Iguaçu National Park, Brazil

The limnological characteristics and the phytoplankton community of the pelagic region of the São João River, tributary of the Iguaçu River, Iguaçu National Park were analyzed from August 2008 to July 2009. 221 taxa were identified and the Bacillariophyceae class was the most representative. Bacillariophyceae and Chrysophyceae were the dominant classes in density and Bacillariophyceae in biovolume. According to the DCA carried out for phytoplankton density and biovolume, significant differences were identified between the periods, and between the sites and study periods, respectively. The highest richness of species reached 40 taxa in September 2008 at station 1. The Shannon-Wiener diversity indexes and evenness, calculated from the density of phytoplankton, were temporally heterogeneous and spatially similar. In general, the significant temporal variations in the composition of the phytoplankton community were due to variations in limnological conditions, mainly temperature, transparency and nutrients. Spatially the structure was more similar due to the proximity among the stations. Moreover, the similarity of the distribution of communities in lotic environments were due to the unidirectional flow.

Cell biovolume and surface area in phytoplankton of Mediterranean transitional water ecosystems: methodological aspects

1 - A series of experimental researches highlighted the role of morphometric parameters of phytoplankton guilds as descriptors of the ecological status of transitional water ecosystems (TWs). 2 - However, at present, standardized or common methodologies for their use do not exist. In this work, we develop a procedure for the determination of biovolume and surface area in phytoplankton guilds of Mediterranean TWs. 3 - Phytoplankton biovolume and surface area are included among the most studied morphometric descriptors. They can be estimated by associating the algae with similar geometric forms and determining the volume of these by measuring the linear dimensions required for its calculation under the light microscope. 4 - Here, a set of geometric models is suggested for calculating the cell biovolumes and surface area of 235 phytoplankton genera, deriving from the analysis of 869 phytoplankton species, found in transitional water ecosystems of the Mediterranean Ecoregion. The equations were designed to minimize the effort of microscopic measurements. 5 - The similarities and differences between the geometric models here proposed and previously published are discussed.

Long-term seasonal effects of dreissenid mussels on phytoplankton in Lake Simcoe, Ontario, Canada

The invasion of dreissenid mussels to Lake Simcoe coincided with notable changes in the ecosystem, including a period of lower phytoplankton biovolume, particularly at shallower sites. Dreissenid grazing effects are typically most prominent during the summer season in the nearshore areas of lakes. Grazing effects in the winter are small because dreissenid filtration rates, especially those of zebra mussels (Dreissena polymorpha), decrease in cold temperatures. Phytoplankton dynamics in the winter season are poorly characterized, particularly in lakes that experience ice cover. The purpose of this study was to examine the effects of dreissenids on the seasonality of phytoplankton dynamics in the nearshore waters of the lake using long-term monitoring data from unchlorinated water treatment plant (WTP) intake pipes. The long-term dataset from the WTPs showed significant and sustained declines in phytoplankton biovolumes and chlorophyll a (Chl-a) concentrations in the 12-year period following the invasion of dreissenid mussels to Lake Simcoe. The decline was smallest during the ice-covered winter months (Jan–Mar). The fall phytoplankton peak observed in the pre-dreissenid years shifted to a smaller peak during the winter in post-dreissenid years. We hypothesized that reduced dreissenid grazing pressure during the winter, and possible improved under-ice light conditions that we attribute to climate change, may be contributing to this shift. Phytoplankton biovolume data collection continues to be important in Lake Simcoe as a measure of phytoplankton biomass. Our results also indicate that winter phytoplankton biovolumes should be considered when managing lakes experiencing both climate change and dreissenid mussel effects.