The role of bacterivorous flagellates in the phosphorus cycling in Lake Biwa, Japan

Article信州大学理学部附属諏訪臨湖実験所報告 9: 53-60(1995)departmental bulletin pape

Protistan grazing and viral lysis losses of bacterial carbon production in a large mesotrophic lake (Lake Biwa)

Published online: 18 April 2014The grazing and lysis mortalities of planktonic bacteria were estimated using the modified dilution method and respiratory quinone (RQ) analysis in mesotrophic Lake Biwa, Japan. The planktonic bacterial assemblages in the lake consisted of various RQ subgroups with different growth and mortality rates. The sum of total bacterial mortalities due to protistan grazing and viral lysis accounted for 96.6 % (range 89.0–107.2 %) of daily total bacterial production. This is the first report that successfully demonstrates a balanced relationship between bacterial production and losses using the modified dilution method in a lake. The growth rates of ubiquinone (UQ)-containing bacteria were faster than those of menaquinone-containing bacteria. Especially the dominant and fastest growing bacterial groups in the present study were the bacterial groups containing UQ-8 or UQ-10. The sum of their production and loss accounted for 60 % of carbon fluxes within the microbial loop. Thus, a large portion of the carbon cycling through the bacterial community in Lake Biwa can be explained by the carbon fluxes through dominant bacterial groups

Phylogenetic diversity of the picocyanobacterial community from a novel winter bloom in Lake Biwa

In Lake Biwa, picocyanobacteria blooms usually occur during the summer-autumn thermal stratification period. Intriguingly, a novel bloom was detected in winter 2015-2016, in which picocyanobacterial cell density increased by one order of magnitude despite lower water temperature, suggesting the possibility that "cold-water-preference" species dominate in the picocyanobacterial community. In the present study, we investigated the phylogenetic diversity of picocyanobacteria in Lake Biwa by analyzing the 16S rRNA gene. We found that the picocyanobacterial community were highly diverse in Lake Biwa, with eight Synechococcus-related operational taxonomic units (OTUs) detected in different seasons. These OTUs fell into distinct phylogenetic groups, and the majority were closely related to clusters reported previously. Notably, OTU04, detected during the winter bloom, was highly affiliated with sequences found in a variety of lakes, such as Tibetan lakes and Lake Superior, where the water bodies generally have a low trophic state and temperature, and different concentrations of total dissolved solids. Thus, we inferred that the group containing OTU04 may be a psychrotolerant lineage that is widely distributed in oligotrophic water systems with low-intermediate salinity

Introduction of Biodiversity Observation Network in the Asia Pacific Region

Article信州大学山地水環境教育研究センター研究報告 6: 11-12(2010)departmental bulletin pape

Influence of potential grazers on picocyanobacterial abundance in Lake Biwa revealed with empirical dynamic modeling

Picocyanobacteria in lakes generally occur as single cells (single-celled picocyanobacteria; SPcy) or colonies (colonial picocyanobacteria; CPcy), and the latter form has been considered an adaptation to grazing pressure. In addition to direct effects of grazing, grazers may also have important indirect effects on picocyanobacteria, such as those from nutrient regeneration and trophic cascades. Interactions between picocyanobacteria and their grazers in lakes can thus be complex and difficult to predict. To evaluate the influence of various grazers on SPcy and CPcy in Lake Biwa, Japan, we followed seasonal changes in their abundances and potential grazers at 2-week intervals over 2 years. The data collected were analyzed using empirical dynamic modeling (EDM), a model-free, nonlinear time-series method. We found that heterotrophic nanoflagellates (HNF), rotifers (Keratella, Polyarthra, and Trichocerca), cladocerans, and copepods played important and differing roles in controlling the abundances of SPcy and CPcy. Notably, HNF had an apparent positive influence on SPcy abundance, despite being considered major consumers of SPcy. This result suggested that the enhancement of SPcy growth due to nutrient regeneration by HNF might exceed losses from mortality due to grazing by HNF. EDM also suggested that colony formation by picocyanobacteria may be unidirectional, with SPcy tending to form CPcy. Our findings show that the seasonal dynamics of SPcy and CPcy in Lake Biwa are influenced by a variety of grazers, which may play differing ecological roles in the aquatic food web