Abstract
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.
Highlights
Chrysophytes, known as golden algae or goldenbrown algae, usually form an essential part of algal communities in cool, high-latitude, oligotrophic lakes, such as the majority of lakes in Finland (Eloranta, 1995; Sandgren et al, 1995)
scanning electron microscope (SEM) images of some of the most common cyst types found in Finland are shown in Online Resource 1
Unornamented cyst surfaces form the majority of all cyst ornamentation types in lake sediments from Finland, their relative occurrence ranging between 31% and 71% per sample, with an average of 54% of cysts counted per sample
Summary
Chrysophytes, known as golden algae or goldenbrown algae (classes Chrysophyceae and Synurophyceae), usually form an essential part of algal communities in cool, high-latitude, oligotrophic lakes, such as the majority of lakes in Finland (Eloranta, 1995; Sandgren et al, 1995). All chrysophytes produce siliceous resting stages, often previously referred to as statospores, but more properly called stomatocysts or cysts, to ensure the survival of the population under unfavourable environmental conditions in the form of a seed bank. Only a small percentage of chrysophyte stomatocysts have successfully been linked with their vegetative stages. This shortcoming led to the development of an artificial naming system created by the International Statospore Working Group (Cronberg & Sandgren, 1986). These guidelines have been extensively modified and revised in subsequent taxonomic treatments (Duff et al, 1995; Wilkinson et al, 2001)
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