The presence and status of harmful algal blooms (HABs) in Japan are reviewed, revealing a decrease in red tides; however, toxic blooms are found to be increasing in western Japan. Environmentally friendly control strategies against HABs are also compared with integrated agricultural pest management. Very high densities (10⁵–10⁸ CFU/g) of algicidal and growth-inhibiting bacteria were found in biofilm on seagrass and seaweed surfaces and in surrounding coastal seawater. The situation in freshwater ecosystems is similar to coastal seas for toxic cyanobacterium,Microcystis aeruginosa, and aquatic plants. These findings offer new insights into the ecology of influential bacteria and harmful algae, suggesting that protection and restoration of native seagrasses and seaweeds in coastal marine environments should be implemented to suppress HABs. Diatom blooms were successfully induced with bottom sediment perturbation to prevent the occurrence of harmful flagellates such asChattonellaspp. andAlexandrium catenellain the Seto Inland Sea; however, this method requires robust and reproducible verification. “Sato-Umi” is a helpful concept for HAB control in the sea and freshwater ecosystems when adequately managed by people (e.g., appropriate bottom perturbation; protection and restoration of seaweeds, seagrasses, and aquatic plants; application of polycultures of fish, seaweeds, etc.).

Ishii K.-I., Iwataki M., Matsuoka K. and Imai I. 2011. Proposal of identification criteria for resting spores of Chaetoceros species (Bacillariophyceae) from a temperate coastal sea. Phycologia 50: 351–362. DOI: 10.2216/10-36.1 Chaetoceros is a large, ecologically important genus of marine planktonic diatoms. Many species of Chaetoceros form resting spores to survive environmental stress. Species identification based on morphological characteristics of resting spores is difficult. In the present study, we proposed a flow diagram for the identification of Chaetoceros species based on morphology. Resting spores of 18 Chaetoceros species were identified in water and sediment samples from southern Japan and the East China Sea based on morphological characteristics of resting spores and/or the vegetative cells containing them. A single ring of puncta was found to be the most important morphological feature of resting spores for species identification, by which the positions of primary and secondary va...

Questiomycin A (1) along with three new compounds, questiomycins C–E (2–4), were isolated from culture of Alteromonas sp. D, an algicidal marine bacterium, guided by algal lethality assay using the raphidophyte, Chattonella antiqua, one of the causative organisms of harmful algal bloom. The structures of 1–4 were assigned on the basis of their spectrometric and spectroscopic data. Compounds 1 to 4 exhibited algicidal activity against C. antiqua with LC₅₀ values ranging from 0.18 to 6.37 M. Co-cultivation experiment revealed that 1 was produced only when the microalgae and the bacterium are in close contact, suggesting that some interactions between them trigger the biosynthesis of questiomycins. These results suggested that the algicidal bacteria such as Alteromonas sp. D can control microalgae chemically in marine ecosystem.