Mini-workshop on Microcystis bloom studies

An introduction of the project “Ecophysiology, phylogeography and environmental sociology on water blooms of the globally distributed cyanobacterium Microcystis aeruginosa”

Shin-ichi Nakano (CER, Kyoto Univ.)

Blooms of freshwater cyanobacterium, Microcystis aeruginosa, are a serious symptom of eutrophication and have harmful effects on lake ecology and human beings. We aim to elucidate transport, growth and genetic diversity of the cyanobacterium, together with the dynamics of its toxic strains, using large experimental systems and the most sophisticated molecular biological/ecological techniques. We also clarify the relationship between Microcystis blooms and human activities conducted around the lakes with the blooms. The present study will contribute the success in the Millennium Development Goals, ODA, demonstrating the raison d’etre of the Japanese Government.

Microcystis bloom in an experimental pond: ecological, microbiological and molecular biological approaches to understand Microcystis dynamics

Yoshikuni Hodoki, Yuki Kobayashi, Kako Ohbayashi (CER, Kyoto Univ.)

1) Changes in microbial abundance and composition during Microcystis bloom in an experimental pond (Kobayashi & Hodoki)

2) Genetic diversity of the genus Microcystis observed in an experimental pond using 16S to 23S internal transcribed spacer (ITS) region (Hodoki & Ohbayashi)

In the Microcystis project as above, we conducted bloom-forming experiment using experimental ponds at Center for Ecological Research, Kyoto University. We collected condensed natural plankton (CNP) of Lake Biwa using a plankton net and prepared three systems: large CNP addition, small CNP addition and no addition. We added mixed nutrients into the ponds almost every two weeks to stimulate Microcystis growth. Remarkable growth of Microcystis was detected only in the large CNP addition system, while phytoplankton biomass increased in all systems. We determined abundance and physiological activity of cyanobacteria dominated by Microcystis, together with abundance and composition of heterotrophic bacteria and protists. In the present talk, we will introduce the data thus collected and discuss ecophysiology of Microcystis in the pond where Microcystis bloom occurred.

Diversity of waterbloom forming cyanobacteria in Chinese waters

Renhui Li (Wuhan Institute of Hydrobiology)

Environmental problems caused by cyanobacterial blooms in eutrophic lakes, rivers and drinking water reservoirs have been increasingly documented. Toxins produced by cyanobacterial blooms, directly threading to human health through drinking water systems, have been attracted more attention and extensively studied. This talk will focus on molecular diversity and phylogenetic analyses in several major groups of water bloom forming cyanobacteria of Chinese waters: Microcystis, Planktothrix/Planktothricoides, Anabaena/Aphanizomenon, Cylindrospermopsis/ Raphidiopsis, and cyanotoxin production related to these groups will also be reported.

Competition between macrophytes and phytoplankton under different nutrient levels in shallow lake

Guoxiang Wang (Nanjing Normal Univ.)

Submerged macrophytes have been regarded to play a key role in sustaining the clear water state by mechanisms like competing with algae for nutrients and light, enhancing denitrification, or providing a refuge for zooplankton, directly reducing phytoplankton and periphyton growth by releasing allelopathic substances. However, severe eutrophication resulted in gradual increases of phytoplankton biomass and epiphytic layers that cover macrophytes and lead to disappearance of most submerged macrophytes. Several submerged plants, such as winter-type Potamogeton crispus and Elodea nuttallii, summer-type Vallisneria natans, Hydrilla verticillata and others, were introduced and cultured in different enclosures and different seasons. The results will reveal the follwing issues: Whether macrophytes could be restored in shallow eutrophic lakes with high nutrient loading? How about the competition between macrophytes and phytoplankton under different nutrient levels in shallow lakes.