New Chrysophycean cyst morphotypes and their ecology in Finland

Despite multiple studies on chrysophyte stomatocysts globally, detailed surveys of these resting stages have remained scarce in Northern Europe. This is the first description of new chrysophyte cyst morphotypes in concordance with the International Statospore Working Group guidelines, based on scanning electron microscope images from lake sediment material in Finland. A nationwide chrysophyte cyst survey revealed 18 new cyst morphotypes with different surface ornamentation types. Environmental background information on the locations and the quantitatively calculated optimums and tolerances for electric conductivity, pH, total phosphorus and ice-free period are also provided.

Biogeography and ecology of freshwater chrysophyte cysts in Finland

The occurrence of various chrysophyte cyst morphotypes is unknown in Finland, with the exception of a few isolated lake studies. We set out to chart which cyst types are found in Finland and what their ecological preferences are, focusing on cyst-air temperature relationships that could be further utilized in reconstructing past winter/spring air temperatures and ice-free periods from sedimentary cyst assemblages. Surface sediment samples from lakes across Finland were analysed for their chrysophyte stomatocyst assemblages. Multivariate ecological techniques (e.g. canonical correspondence analysis, principal component analysis) were used to identify the environmental variables that most strongly affected the distribution of the cysts. This survey expanded the known geographical range for several cyst types. Lake water pH and ice-free periods (surrogate for air temperature) explained the statistically significant distribution and composition of the cyst assemblages studied. The results broaden our knowledge of cyst biogeography and strengthen the findings of previous studies of the environmental factors contributing to the occurrence of cysts. Highly variable and rich chrysophyte cyst assemblages in Finland are clearly associated with temperature, pH, electrical conductivity and total phosphorus, with good potential in contemporary and retrospective environmental assessment.

Influence of inter-annual environmental variability on chrysophyte cyst assemblages: insight from a 2-years sediment trap study in lakes from northern Poland

<p>Quantitative paleonvironmental studies using transfer functions are developed from training sets. However, changes in some variables (<em>e.g</em>., climatic) can be difficult to identify from short-term monitoring (<em>e.g.,</em> less than one year). Here, we present the study of the chrysophyte cyst assemblages from sediment traps deployed during two consecutive years (November 2011-November 2013) in 14 lakes from Northern Poland. The studied lakes are distributed along a W-E climatological gradient, with very different physical, chemical and morphological characteristics, and land-uses. Field surveys were carried out to recover the sediment trap material during autumn, along with the measurement of several environmental variables (nutrients, major water ions, conductivity, pH, dissolved oxygen and chlorophyll<em>-a</em>). During the study, one year experienced mild seasonal changes in air temperature (November 2011-November 2012; TS1), typical of oceanic climate, while the other year was characterized by colder winter and spring (November 2012-November 2013; TS2), and higher summer temperatures, more characteristic of continental climate. Other environmental variables (<em>e.g</em>., nutrients) did not show great changes between both years. Multivariate statistical analyses (RDA and DCA) were performed on individual TS1 and TS2 datasets. Water chemistry and nutrients (pH, TN and TP) explained the largest portion of the variance of the chrysophyte data for the individual years. However, analyses of the combined TS1 and TS2 datasets show that strong changes between summer and autumn (warm period, ice-free period with thermal stratification) and winter and spring (cold period, ice-cover period) play the most important role in the inter-annual variability in the chrysophyte assemblages. We show how inter-annual sampling maximizes ecological gradients of interest, particularly in regions with large environmental diversity, and low climatic variability. This methodology could help to identify distinct seasonal and inter-annual changes of biological communities to improve its application in paleoclimate studies.</p>

Seasonality of chrysophyte cyst and diatom assemblages in varved Lake Nautajärvi – implications for palaeolimnological studies

Phytoplankton species composition is strongly affected by seasons, which should be taken into account in palaeolimnological studies. Although chrysophyte cysts and diatoms are widely used as palaeobioindicators in palaeolimnological studies, only recently have attempts been made to use their modern deposition from sediment trap data to provide more detailed, seasonal-based environmental reconstructions. In this study sediment traps were used to record seasonality of chrysophyte cysts and diatoms during two climatically different years 2009 and 2010 in an annually laminated Lake Nautajärvi, Finland, and this seasonal data was then compared with the fossil record derived from the surface sediment of the lake. The overall changes in cyst and diatom assemblages between years and seasons are subtle. For both groups, no clear connection to any particular season could be detected in the sediment surface. Despite the climatological differences between the study years, the inter-annual accumulation rates of both algal groups were surprisingly similar, whereas the intra-annual accumulation rates differed substantially. This and the high amount of taxa occurring during all seasons in the trap samples implies that primary producers are more dependent on prevailing seasonal limnological conditions than on rapid, shortly lived episodes. Redundancy analysis (RDA) revealed that chrysophyte cyst assemblages from the spring sediment trap are mainly controlled by the spring discharge intensity, a surrogate variable of spring weather conditions, whereas precipitation and air temperature have the strongest impact on the summer assemblages. However, only discharge explains statistically significantly the variance in the cyst data. Precipitation and air temperature have the strongest impact on the diatom summer samples, whereas the spring sediment trap sample of the snowy and harsh winter of 2010 was strongly correlated with the spring discharge. However, none of the measured environmental variables explains the variance in the diatom data statistically significantly. The similarity between the algae found in the sediment traps and surface sediment sample suggests that within small and shallow lakes without any extreme environmental settings the surface sediment sample represents well the lake´s overall algal composition and can thus be used in palaeolimnological studies.

Stomatocyst 29 Cabała is a pollen grain, not a chrysophyte cyst

Stomatocyst 29 Cabała was described from the Żabie Oko lake in the Tatra Mts, Poland, in 2005 as a chrysophycean stomatocyst new to science. The examination of the recently found specimens in the Dwoisty Staw Gąsienicowy lake in the Tatra Mts, including their chemical composition, showed that stomatocyst 29 is not a cyst, but a pollen grain.