AME prepress abstract  -  DOI:

Seasonal dynamics of heterotrophic and plastidic protists in the water column of Lake Biwa, Japan

Indranil Mukherjee, Yoshikuni Hodoki, Shin-ichi Nakano*


ABSTRACT: We followed seasonal changes in the vertical distribution of protistan community in Lake Biwa for 2 years. Heterotrophic and plastidic nanoflagellates (HNF and PNF) were enumerated from different depths and the seasonal community composition of protists was analyzed from the epilimnion and hypolimnion using 18S rRNA gene clone libraries. In the epilimnion, HNF were dominant during early summer and autumn, whereas PNF, which includes mixotrophs, had a higher contribution during the late summer and winter months. The changes in abundance of HNF and PNF differed and their peaks of abundance did not coincide, suggesting that these groups show contrasting responses to changes in environmental conditions. Protistan communities in the epilimnion and hypolimnion were represented mainly by cryptophytes and dinophytes, respectively, whereas cercozoans had a significant contribution in all libraries. We found high diversity and distinct protist communities in the epilimnion and hypolimnion, where the majority of the hypolimnion sequences had low similarity with the closely related sequences in the database. This indicates that protistan communities from deep freshwater lakes are less known and that further studies from deep waters are needed to understand the role of these organisms.