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.

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.

Modern Archaeomonadaceae from the land-fast ice off Adélie Land, East Antarctica: a preliminary report

The land-fast ice and the platelet ice layer off Adélie Land are inhabited by a dense and diversified diatom community. Along with Bacillariophyceae, Archaeomonadaceae sensu Deflandre are present and relatively abundant. These modern siliceous nanostructures are similar to the nanofossils described by geologists in marine sediments from upper Cretaceous to Pliocene, Pleistocene and recently in Holocene and modern sediments, and are probably related to chrysophyte cysts. The two most abundant taxa were Achaeomonas cf areolata Deflandre and Litheusphaerella cf spectabilis Deflandre. The other taxa were not common. Despite the taxonomic uncertainty of immature forms, the diversity of archaeomonads was high. Three new species of Archaeomonas are described. The morphology of A. cf areolata is highly variable, showing a possible diversification over geologic time. Litheusphaerella cf spectabilis also shows some differences between fossil and modern specimens. Recent studies confirm that archaeomonads are extant in diverse marine water bodies and recent sediments. There is growing evidence that these siliceous structures represent possible reliable proxies of sea ice extent, even if their presence in geologic time is not always linked exclusively to sea ice. Further studies are needed to elucidate the exact origin of these cysts and their real taxonomic affinities.

Fossil Rotifers and the Early Colonization of an Antarctic Lake

Early Holocene sediments from a continental Antarctic lake (Ace Lake, Vestfold Hills, East Antarctica) contained abundant fossil rotifers of the genus Notholca. The fossil is similar to specimens of Notholca sp. present in modern-day Ace Lake and other fresh and brackish lakes of the Vestfold Hills. Cyanobacteria and protists (chrysophyte cysts, dinoflagellate cysts, and rhizopod tests) were also recovered from the core samples. These sediments were deposited early in the freshwater phase of Ace Lake, soon after deglaciation of the area. The occurrence of this trophically diverse assemblage of organisms at an early stage in the evolution of the lake suggests either that they were part of an endemic Antarctic flora and fauna which pre-dated the last glacial maximum and survived in glacial refugia or that efficient intercontinental dispersal had occurred.

Chrysophycean stomatocysts from freshwater habitats of the Strømness Bay area, South Georgia, Antarctica

The chrysophycean stomatocyst flora of freshwater samples from the Strømness Bay area, located in the northern part of the Sub-Antarctic Island of South Georgia, was investigated, using scanning electron microscopy. A total of 59 stomatocyst morphotypes were recorded. Thirty-one of them were previously observed and 28 are described as new, following guidelines of the International Statospore Working Group. Since this is only the second study of chrysophyte cysts from South Georgia, this large number of new morphotypes is not surprising. The cyst flora show only a small resemblance to the stomatocyst flora found on mosses of the same area.Key words: chrysophyte stomatocysts, South Georgia, Sub-Antarctica.