Synura Petersenii Research Articles

Rapid diversification of a free-living protist is driven by adaptation to climate and habitat

Microbial eukaryotes (protists) have major functional roles in aquatic ecosystems, including the biogeochemical cycling of elements as well as occupying various roles in the food web. Despite their importance for ecosystem function, the factors that drive diversification in protists are not known. Here, we aimed to identify the factors that drive differentiation and, subsequently, speciation in a free-living protist, Synura petersenii (Chrysophyceae). We sampled five different geographic areas and utilized population genomics and quantitative trait analyses. Habitat and climate were the major drivers of diversification on the local geographical scale, while geography played a role over longer distances. In addition to conductivity and temperature, precipitation was one of the most important environmental drivers of differentiation. Our results imply that flushing episodes (floods) drive microalgal adaptation to different niches, highlighting the potential for rapid diversification in protists.

Morphological and Molecular Characterizations of Three Species of the Genus Synura (Synurales, Chrysophyceae) from China

Three species of the genus Synura from China are described here. Morphological observations and molecular phylogenetic analyses were conducted for three specimens collected at different locations in China. The described morphological features included cell size, scale size, spines, keels, and struts. Molecular analyses based on multiple genetic markers (SSU and LSU rDNA and internal transcribed spacer rDNA) were used to determine the phylogenetic positions of the three Synura species. Morphologically, specimen GZ201017 collected in Guizhou Province was characterized by a well-developed keel and lanceolate scales; specimen SX210304 collected in Shanxi Province was characterized by a less-developed keel and poor silicification; and specimen GD201126 collected in Guangdong Province was characterized mainly by spines with blunt ends or two small teeth on the tips. The morphotypes GZ201017, SX210304, and GD201126 corresponded to the original descriptions of Synura petersenii, S. glabra, and S. longitubularis, respectively. This discovery laid a foundation for the molecular phylogeny of the genus Synura and an enhanced understanding of Synura diversity and distribution in China.

When you Like Other Algae: Adglutina synurophila gen. et sp. nov. (Moewusinia, Chlorophyceae), a Clingy Green Microalga Associated with Synura Colonies

Unicellular green biflagellates of the order Volvocales (Chlorophyceae, Chlorophyta) are common inhabitants of various types of habitats, and can also form peculiar interspecific relationships. Most of their morphological diversity has historically been assigned to the two prominent genera Chlamydomonas and Chloromonas. Ongoing reclassification of these algae, aided by molecular phylogenetics, has resulted in numerous newly proposed genera, but there are certainly brand-new taxa awaiting recognition. In this study, based on morphological and ultrastructural observations together with sequence data of the nuclear 18S and ITS2 rDNA and the plastid rbcL gene, we describe Adglutina synurophila gen. et sp. nov., a volvocalean biflagellate isolated from colonies of the golden-brown alga Synura petersenii (Chrysophyceae). Phylogenetic analyses placed Adglutina in the phylogroup Moewusinia as a sister lineage to the acidophilic "Chlamydomonas" species. It is characterised by having oval to broadly ellipsoidal cells with a low keel-shaped papilla and a cup-shaped chloroplast lacking a pyrenoid, but possessing a lateral eyespot of a variable position. The unique set of features, together with its Synura-loving nature, anchor Adglutina as a well distinguishable phylogenetic lineage within the Moewusinia. The novel alga has a widespread distribution; it has been found in three European countries to date.

Silica-Scaled Chrysophytes from the Ukrainian Polissia

We investigated the silica-scaled chrysophyte flora from the Ukrainian Polissia by means of electron microscopy. Overall, 49 taxa were recorded, including three species each of Chrysosphaerella Lauterborn and Paraphysomonas De Saedeleer emend. Scoble & Cavalier-Smith, one unidentified Lepidochromonas Kristiansen taxon, two Spiniferomonas E.Takahashi species, 28 Mallomonas Perty taxa and 12 Synura Ehrenb. taxa. Only six species have previously been reported from this region and 29 of the taxa encountered in this study are reported for the first time from Ukraine. Two taxa, Synura petersenii f. columnata Siver and S. korshikovii Kapustin & Gusev were found for the second time since their original descriptions. We hypothesize that the latter species is an endemic of Polissia, however, to test this idea it would be necessary to sample the water-bodies from the adjacent territories of Belarus and Russia.

Substantial intraspecific genome size variation in golden-brown algae and its phenotypic consequences.

While nuclear DNA content variation and its phenotypic consequences have been well described for animals, vascular plants and macroalgae, much less about this topic is known regarding unicellular algae and protists in general. The dearth of data is especially pronounced when it comes to intraspecific genome size variation. This study attempts to investigate the extent of intraspecific variability in genome size and its adaptive consequences in a microalgal species. Propidium iodide flow cytometry was used to estimate the absolute genome size of 131 strains (isolates) of the golden-brown alga Synura petersenii (Chrysophyceae, Stramenopiles), identified by identical internal transcribed spacer (ITS) rDNA barcodes. Cell size, growth rate and genomic GC content were further assessed on a sub-set of strains. Geographic location of 67 sampling sites across the Northern hemisphere was used to extract climatic database data and to evaluate the ecogeographical distribution of genome size diversity. Genome size ranged continuously from 0.97 to 2.02 pg of DNA across the investigated strains. The genome size was positively associated with cell size and negatively associated with growth rate. Bioclim variables were not correlated with genome size variation. No clear trends in the geographical distribution of strains of a particular genome size were detected, and strains of different genome size occasionally coexisted at the same locality. Genomic GC content was significantly associated only with genome size via a quadratic relationship. Genome size variability in S. petersenii was probably triggered by an evolutionary mechanism operating via gradual changes in genome size accompanied by changes in genomic GC content, such as, for example, proliferation of transposable elements. The variation was reflected in cell size and relative growth rate, possibly with adaptive consequences.

Increased relative abundance of colonial scaled chrysophytes since pre-industrial times in minimally disturbed lakes from the Experimental Lakes Area, Ontario

A top–bottom paleolimnological analysis of 30 undisturbed lakes in the Experimental Lakes Area (ELA) in northwest Ontario showed marked increases in the relative abundance of colonial scaled chrysophyte taxa in most lakes since pre-industrial times. The increase in abundance of colonial taxa was primarily driven by Synura sphagnicola in small, high-nutrient, and warm lakes. The colonial taxa Synura petersenii and Synura echinulata also increased in the deeper study lakes. Detailed analysis of sediment cores from six lakes revealed that these changes occurred in the early to mid-1900s. Based on the modern distribution of scaled chrysophytes relative to lake physicochemical data, we propose multiple processes that may be contributing to these changes, such as changes in lake thermal properties and historical changes in the flux of important particles and solutes to lakes. Additional mechanisms that may contribute to the observed changes are discussed, including trophic interactions and changes in limnetic pCO2. Because the ELA is relatively undisturbed, our findings provide important information on the drivers responsible for increases in colonial chrysophyte abundance, which have been documented in studies of lakes in central Ontario and northeast United States.

The Diversity of Chrysophycean Algae in an Arctic Zone of River and Sea Water Mixing, Russia

According to the results of studies in the region of lower Yenisei River to the Kara Sea shelf in September 2009, the flora of chrysophyte algae in the zone of river and sea water mixing comprises 43 species of the classes Chrysophyceae and Synurophyceae. Most of them are cosmopolitan and widespread, but four rare species have also been recorded. The most frequent species are Synura petersenii f. petersenii, S. petersenii f. kufferathii, Spiniferomonas takahashii, Mallomonas acaroides, and M. crassisquama. The composition of chrysophyte flora in the study region is similar to that in some lakes of the Taimyr Peninsula. It has been found that the diversity of chrysophytes in the zone of river and sea water mixing depends on water salinity, with a group of species occurring at increased salinity levels. It includes Chrysosphaerella coronacircumspina (5.2‰), Kephyrion spirale (5.2‰) and Mallomonas crassisquama (8‰). These data contribute to knowledge of how the distribution of chrysophytes responds to changes in ecological conditions such as water salinity, turbidity, pH, and concentrations of oxygen and mineral phosphorus.

Morphological delineation and distribution patterns of four newly described species within the Synura petersenii species complex (Chrysophyceae, Stramenopiles)

The Synura petersenii species complex represents a common, cosmopolitan and highly diverse taxon of autotrophic freshwater flagellates. In this paper, we describe and characterize four new species (S. borealis, S. heteropora, S. hibernica and S. laticarina) that have been identified during our extensive sampling of freshwater habitats in 15 European countries. Morphometric analyses of siliceous scales led to the significant phenotypic differentiation of all four newly described species, and their separation from other related species of the S. petersenii complex. Two of these newly described species (S. hibernica and S. borealis) can be clearly distinguished by characteristic large colonies consisting of elongated, lanceolate-shaped cells. Development of strongly elongated, narrow cells in S. hibernica could be explained by the adaptation of this species to oligotrophic conditions. Though morphologically distinct, S. borealis possesses an exceptionally high degree of genetic diversity, possibly indicating recent speciation and evolutionary diversification within this taxon. Three of the four newly described species exhibit restricted biogeographic distribution. The evolutionarily related S. borealis and S. laticarina occur only in Northern Europe, and seem to be adapted to colder areas. The most remarkable distribution pattern was observed for S. hibernica, which has a geographic distribution that is restricted to western Ireland.

The stabilizing effects of genetic diversity on predator-prey dynamics

Heterogeneity among prey in their susceptibility to predation is a potentially important stabilizer of predator-prey interactions, reducing the magnitude of population oscillations and enhancing total prey population abundance. When microevolutionary responses of prey populations occur at time scales comparable to population dynamics, adaptive responses in prey defense can, in theory, stabilize predator-prey dynamics and reduce top-down effects on prey abundance. While experiments have tested these predictions, less explored are the consequences of the evolution of prey phenotypes that can persist in both vulnerable and invulnerable classes. We tested this experimentally using a laboratory aquatic system composed of the rotifer Brachionus calyciflorus as a predator and the prey Synura petersenii, a colony-forming alga that exhibits genetic variation in its propensity to form colonies and colony size (larger colonies are a defense against predators). Prey populations of either low initial genetic diversity and low adaptive capacity or high initial genetic diversity and high adaptive capacity were crossed with predator presence and absence. Dynamics measured over the last 127 days of the 167-day experiment revealed no effects of initial prey genetic diversity on the average abundance or temporal variability of predator populations. However, genetic diversity and predator presence/absence interactively affected prey population abundance and stability; diversity of prey had no effects in the absence of predators but stabilized dynamics and increased total prey abundance in the presence of predators. The size structure of the genetically diverse prey populations diverged from single strain populations in the presence of predators, showing increases in colony size and in the relative abundance of cells found in colonies. Our work sheds light on the adaptive value of colony formation and supports the general view that genetic diversity and intraspecific trait variation of prey can play a vital role in the short-term dynamics and stability of planktonic predator-prey systems.

The stabilizing effects of genetic diversity on predator-prey dynamics.

Heterogeneity among prey in their susceptibility to predation is a potentially important stabilizer of predator-prey interactions, reducing the magnitude of population oscillations and enhancing total prey population abundance. When microevolutionary responses of prey populations occur at time scales comparable to population dynamics, adaptive responses in prey defense can, in theory, stabilize predator-prey dynamics and reduce top-down effects on prey abundance. While experiments have tested these predictions, less explored are the consequences of the evolution of prey phenotypes that can persist in both vulnerable and invulnerable classes. We tested this experimentally using a laboratory aquatic system composed of the rotifer Brachionus calyciflorus as a predator and the prey Synura petersenii, a colony-forming alga that exhibits genetic variation in its propensity to form colonies and colony size (larger colonies are a defense against predators). Prey populations of either low initial genetic diversity and low adaptive capacity or high initial genetic diversity and high adaptive capacity were crossed with predator presence and absence. Dynamics measured over the last 127 days of the 167-day experiment revealed no effects of initial prey genetic diversity on the average abundance or temporal variability of predator populations. However, genetic diversity and predator presence/absence interactively affected prey population abundance and stability; diversity of prey had no effects in the absence of predators but stabilized dynamics and increased total prey abundance in the presence of predators. The size structure of the genetically diverse prey populations diverged from single strain populations in the presence of predators, showing increases in colony size and in the relative abundance of cells found in colonies. Our work sheds light on the adaptive value of colony formation and supports the general view that genetic diversity and intraspecific trait variation of prey can play a vital role in the short-term dynamics and stability of planktonic predator-prey systems.

The stabilizing effects of genetic diversity on predator-prey dynamics

Heterogeneity among prey in their susceptibility to predation is a potentially important stabilizer of predator-prey interactions, reducing the magnitude of population oscillations and enhancing total prey population abundance. When microevolutionary responses of prey populations occur at time scales comparable to population dynamics, adaptive responses in prey defense can, in theory, stabilize predator-prey dynamics and reduce top-down effects on prey abundance. While experiments have tested these predictions, less explored are the consequences of the evolution of prey phenotypes that can persist in both vulnerable and invulnerable classes. We tested this experimentally using a laboratory aquatic system composed of the rotifer Brachionus calyciflorus as a predator and the prey Synura petersenii , a colony-forming alga that exhibits genetic variation in its propensity to form colonies and colony size (larger colonies are a defense against predators). Prey populations of either low initial genetic diversity and low adaptive capacity or high initial genetic diversity and high adaptive capacity were crossed with predator presence and absence. Dynamics measured over the last 127 days of the 167-day experiment revealed no effects of initial prey genetic diversity on the average abundance or temporal variability of predator populations. However, genetic diversity and predator presence/absence interactively affected prey population abundance and stability; diversity of prey had no effects in the absence of predators but stabilized dynamics and increased total prey abundance in the presence of predators. The size structure of the genetically diverse prey populations diverged from single strain populations in the presence of predators, showing increases in colony size and in the relative abundance of cells found in colonies. Our work sheds light on the adaptive value of colony formation and supports the general view that genetic diversity and intraspecific trait variation of prey can play a vital role in the short-term dynamics and stability of planktonic predator-prey systems.

Toward a revision of the genus Synura, section Petersenianae (Synurophyceae, Heterokontophyta): morphological characterization of six pseudo-cryptic species

Škaloud P., Kynčlová A., Benada O., Kofroňová O. and Škaloudová M. 2012. Toward a revision of the genus Synura, section Petersenianae (Synurophyceae, Heterokontophyta): morphological characterization of six pseudo-cryptic species. Phycologia 51: 303–329. DOI: 10.2216/11-20.1Morphological data, based on transmission and scanning electron microscopy of silica scales, are provided for six genetic lineages of the Synura petersenii species complex as revealed by multiple genetic markers (internal transcribed spacer rDNA, psaA, rbcL and cox1). The morphology allows clear distinction of all six lineages, as well as their separation from all other taxa in section Petersenianae. The lineages are redefined or described as new species in accordance with previously published molecular and morphometric evidence as S. petersenii, S. glabra, S. truttae comb. et stat. nov., S. americana sp. nov., S. macropora sp. nov. and S. conopea sp. nov. The section Petersenianae further includes nine taxa with well-known ultrastructural characteristics. Four have status of species (S. australiensis, S. longisquama, S. macracantha and S. obesa), and five have been described as different formae of S. petersenii sensu lato (S. petersenii f. asmundiae, S. petersenii f. bjoerkii, S. petersenii f. columnata, S. petersenii f. praefracta and S. petersenii f. taymyrensis). All 15 taxa can be distinguished by the shape of the body scales, scale dimensions, keel shape, number of and distance between struts, degree of interconnections between struts, and the size of base plate pores, keel pores, and base plate hole. A key to species is provided. The biogeography of newly defined taxa is discussed based on the morphological data obtained from previously published reports.

Growth characteristics of two bloom-forming synurophytes (Mallomonas elongata and Synura petersenii) at different nitrate and phosphate concentrations

Two dominant planktonic bloom-forming algal species in a small shallow eutrophic pond were identified as Mallomonas elongata and Synura petersenii by electron microscopy. Their growth requirements were investigated as uni-algal cultures in a laboratory study. The maximum population growth and maximum growth rate of M. elongata occurred at concentrations of 24 μM nitrate (NO3) and 5 μM phosphate (PO4) at a temperature of 15°C and a pH of 6. Synura petersenii grew maximally and exhibited the highest growth rate at a NO3 concentration of 24 μM and a PO4 concentration of 2 μM. Mallomonas elongata and S. petersenii had similar nutrient requirements for optimum growth, suggesting that the biomass of these two species can be controlled by nutrient gradients.

Effect of temperature on size and shape of silica scales in Synura petersenii and Mallomonas tonsurata (Stramenopiles)

Synurophytes are planktonic protists whose cells are covered with silica scales. According to the temperature-size rule, protists decrease in size with increasing temperature. Here, we showed that inorganic silica scales responded to increasing temperature in the same way as the cells did. Two species, Mallomonas tonsurata and Synura petersenii, were cultivated at five temperature levels (5, 10, 15, 20 and 25°C) and the methods of geometric morphometrics were applied for scale size and shape data analyses. We observed that the shape of the scales was significantly affected by the cultivation temperature. The overall shape change from rounded, circular scales to oval or more elongated scales seemed to be a general feature in synurophytes and may be considered a consequence of rising temperature. Moreover, the difference in shape remained significant even if the effect of size (allometric effect) was separated. Finally, we compared the level of the scales’ morphological variation among all temperature treatments. The results indicated that the cultivation temperature of 25°C negatively affected cellular processes involved in scale biogenesis. The use of the scale shape data has potential in palaeoecological research.

Evidence for the occurrence of photorespiration in synurophyte algae

The fluxes of CO(2) and oxygen during photosynthesis by cell suspensions of Tessellaria volvocina and Mallomonas papillosa were monitored mass spectrometrically. There was no rapid uptake of CO(2,) only a slow drawdown to compensation concentrations of 26 μM for T. volvocina and 18 μM for M. papillosa, when O(2) evolution ceased, indicating a lack of active bicarbonate uptake by the cells. Darkening of the cells after a period of photosynthesis did not cause rapid release of CO(2), indicating the absence of an intracellular inorganic carbon pool. However, upon darkening a brief burst of CO(2) was observed similar to the post-illumination burst characteristic of C(3) higher plants. Treatment of the cells of both species with the membrane-permeable carbonic anhydrase inhibitor ethoxyzolamide had no adverse effect on photosynthetic rate, but stimulated the dark CO(2) burst indicating the dark oxidation of a compound formed in the light. In the absence of any active accumulation of inorganic carbon photosynthesis in these species should be inhibited by O(2). This was investigated in four synurophyte species T. volvocina, M. papillosa, Synura petersenii, and Synura uvella: photosynthetic O(2) evolution rates in all four algae, measured by O(2) electrode, were significantly higher (40-50%) in media at low O(2) (4%) than in air-equilibrated (21% O(2)) media, indicating an O(2) inhibition of photosynthesis (Warburg effect) and thus the occurrence of photorespiration in these species.

Complex phylogeographic patterns in the freshwater alga Synura provide new insights into ubiquity vs. endemism in microbial eukaryotes.

The global distribution, abundance, and diversity of microscopic freshwater algae demonstrate an ability to overcome significant barriers such as dry land and oceans by exploiting a range of biotic and abiotic colonization vectors. If these vectors are considered unlimited and colonization occurs in proportion to population size, then globally ubiquitous distributions are predicted to arise. This model contrasts with observations that many freshwater microalgal taxa possess true biogeographies. Here, using a concatenated multigene data set, we study the phylogeography of the freshwater heterokont alga Synura petersenii sensu lato. Our results suggest that this Synura morphotaxon contains both cosmopolitan and regionally endemic cryptic species, co-occurring in some cases, and masked by a common ultrastructural morphology. Phylogenies based on both proteins (seven protein-coding plastid and mitochondrial genes) and DNA (nine genes including ITS and 18S rDNA) reveal pronounced biogeographic delineations within phylotypes of this cryptic species complex while retaining one clade that is globally distributed. Relaxed molecular clock calculations, constrained by fossil records, suggest that the genus Synura is considerably older than currently proposed. The availability of tectonically relevant geological time (10⁷-10⁸ years) has enabled the development of the observed, complex biogeographic patterns. Our comprehensive analysis of freshwater algal biogeography suggests that neither ubiquity nor endemism wholly explains global patterns of microbial eukaryote distribution and that processes of dispersal remain poorly understood.

The scaled chrysophyte flora from the Pinelands National Preserve of southern New Jersey, U.S.A.

The distributions of scaled chrysophytes relative to physical and chemical conditions are described for waterbodies of the Pinelands National Preserve in southern New Jersey, U.S.A. The Pinelands represent the northern end of the Atlantic Coastal Plain and contain waterbodies that are largely shallow, acidic, poorly buffered, dilute and highly colored from high concentrations of iron and dissolved organic matter. The Pinelands sites are rich in scaled chrysophytes with 55 species representing the six genera, Mallomonas, Synura, Chrysodidymus, Chrysosphaerella, Spiniferomonas and Paraphysomonas. On average, 19 species were found per waterbody and several localities harbored 22 or more scaled chrysophyte taxa. Although the genus Mallomonas contained the most organisms with 41 species, scale counts of Mallomonas and Synura taxa were equally abundant. Synura echinulata, followed by Chrysodidymus synuroideus, Synura sphagnicola, Mallomonas punctifera, Synura petersenii and Synura spinosa were the most abundant species, each found in over 80 % of the study sites. Many of the species found in the Pinelands sites, including Mallomonas acaroides var. muskokana, M. canina, M. calceolus, M. hindonii, M. paludosa, M. pugio and M. wujekii, are acidobionts known to inhabit acidic localities. Taxa in the genera Chrysosphaerella, Spiniferomonas and Paraphysomonas were present, but rare. The biogeographies of selected taxa are discussed relative to other regions along the Atlantic Coastal Plain.

INORGANIC CARBON ACQUISITION BY CHRYSOPHYTES(1).

Twelve species, representing 12 families of the chrysophytes sensu lato, were tested for their ability to take up inorganic carbon. Using the pH-drift technique, CO2 compensation points generally varied between 1 and 20 μmol · L(-1) with a mean concentration of 5 μmol · L(-1) . Neither pH nor alkalinity affected the CO2 compensation point. The concentration of oxygen had a relatively minor effect on CO2 -uptake kinetics, and the mean CO2 compensation point calculated from the kinetic curves was 3.6 μmol · L(-1) at 10-15 kPa starting oxygen partial pressure and 3.8 μmol · L(-1) at atmospheric starting oxygen partial pressure (21 kPa). Similarly, uptake kinetics were not affected by alkalinity, and hence concentration of bicarbonate. Membrane inlet mass spectrometry (MIMS) in the presence and absence of acetazolamide suggested that external carbonic anhydrase in Dinobryon sertularia Ehrenb. and Synura petersenii Korschikov was either very low or absent. Rates of net HCO3 (-) uptake were very low (∼5% of oxygen evolution) using MIMS and decreased rather than increased with increasing HCO3 (-) concentration, suggesting that it was not a real uptake. The CO2 compensation points determined by MIMS for CO2 uptake and oxygen evolution were similar to those determined in pH-drift and were >1 μmol · L(-1) . Overall, the results suggest that chrysophytes as a group lack a carbon-concentrating mechanism (CCM), or an ability to make use of bicarbonate as an alternative source of inorganic carbon. The possible evolutionary and ecological consequences of this are briefly discussed.

Factors contributing to cucumber odor in a northern USA reservoir

Episodic occurrences of cucumber odor caused by the alga Synura petersenii in Meander Creek Reservoir (MCR), northeastern Ohio, USA, are partly attributed to increased water transparency resulting from decreased phosphorus and suspended solids loading from the watershed. The first documented occurrence of nuisance odor levels was in 1984, 52 years after the reservoir was filled. This indicates that previous environmental factors constraining the growth of S. petersenii have been relaxed, probably from changes in the physical–chemical environment in the reservoir caused by changes in land use in the catchment. Reduction in farming since 1950, and diversion of sewage around the reservoir in 1977, reduced suspended solids and total phosphorus loading into the reservoir during the time that the cucumber odors occurred. These observations support the hypothesis that increased transparency of the reservoir, resulting from decreased sediment loading and reduced productivity, has permitted the occasional occurrence of nuisance densities of S. petersenii. Based on available data, pH, iron, and silica do not appear to be key factors regulating growth of S. petersenii in MCR. The transition to lower turbidity and total phosphorus concentrations from catchment restoration actions may increases the risk of S. petersenii blooms and cucumber odor episodes. While the overall benefits of cleaner raw water for water supply may outweigh this risk, it is desirable to understand the factors that promote nuisance growths and take actions to control them.

Ecological distribution of scaled-chrysophyte assemblages from the sediments of 54 lakes in Nova Scotia and southern New Brunswick, Canada

Chrysophyte scales have been used in several paleolimnological studies to track long-term environmental change, however little data exist for the many lakes in the Maritime provinces of eastern Canada. As part of a multi-disciplinary investigation of acidification and other environmental stressors in the Maritimes, chrysophytes scales were identified and enumerated from the sediments of 52 lakes from Nova Scotia and two lakes from New Brunswick. A total of 25 chrysophyte taxa were identified from the surface sediments, reflecting the modern-day chrysophyte assemblages. The dominant species included Mallamonas duerrschmidtiae and Mallomonas acaroides. Taxa of the genus Synura were present in some lakes, but mainly in the more southern sites. In general, the floras were less diverse than those recorded from similar studies in other temperate regions. This may be related to the fact that the calibration lake set contained only a relatively short limnological gradient, and the assemblages reflect the acidic to circumneutral conditions of these lakes. Synura petersenii, a taxon that has been linked to imparting taste and odor problems to lakes, and had been shown to increase in the recent sediments of many other Canadian lakes, was only rarely present. In contrast to other studies, scaled chrysophytes were very rare in the pre-industrial sediments, with substantial nineteenth century populations only present in four relatively deep (>19 m) lakes. Detailed stratigraphic analyses of eight sediment cores revealed that scaled-chrysophyte assemblages increased dramatically during the latter part of the twentieth century. Limnological changes associated with climate (e.g. increased thermal stratification due to a 1.5°C temperature increase since ~1850) may have influenced chrysophyte distributions in these lakes.