Chrysophytes and other protists in High Arctic lakes: molecular gene surveys, pigment signatures and microscopy

Abstract

Microscopic analysis of the phytoplankton and other protist communities in High Arctic lakes has shown that they often contain taxa in the Chrysophyceae. Such studies have been increasingly supported by pigment analysis using high-performance liquid chromatography (HPLC) to identify the major algal groups. However, the use of 18S rRNA gene surveys in other systems indicates that many protists, especially small heterotrophs, are underreported or missed by microscopy and HPLC. Here, we investigated the late summer protist community structure of three contrasting lakes in High Arctic polar desert catchments (Char Lake at 74°42′ N, Lake A at 83°00′ N and Ward Hunt Lake at 83°05′ N) with a combination of microscopy, pigment analysis and small subunit 18S ribosomal RNA gene surveys. All three methods showed that chrysophytes were well represented, accounting for 50–70% of total protist community biomass and 25–50% of total 18S rRNA gene sequences. HPLC analysis supported these observations by showing the ubiquitous presence of chrysophyte pigments. The clone libraries revealed a greater contribution of heterotrophs to the protist communities than suggested by microscopy. The flagellate Telonema and ciliates were common in all three lakes, and one fungal sequence was recovered from Char Lake. The approaches yielded complementary information about the protist community structure in the three lakes and underscored the importance of chrysophytes, suggesting that they are well adapted to cope with the low nutrient supply and strong seasonality that characterize the High Arctic environment.