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25The seagrasses are known to have allelopathic activity to reduce the growth of phytoplankton. We 26 found growth-inhibiting bacteria (strains E8 and E9) from Zostera marina possessing strong activities 27 against the toxic dinoflagellate Alexandrium tamarense. The strain E9 markedly inhibited the growth of 28A. tamarense even with the initial inoculum size as few as 2.9 cells ml -1 . This bacterium also had 29 78we report some characteristics of growth inhibiting activities of these bacteria. 80 Materials and Methods 81Algal cultures 82Microalgal species used in this study were presented in Table 1. They were all axenic and maintained 92Sterilized sea water (200 ml) was added to the bottle containing the Z. marina sample and the bottle 93 was shaken 500 times by hand to obtain its easily-detaching biofilm. The seawater with the suspended 94 biofilm was used for enumerating algicidal and/or growth-inhibiting bacteria described in detail in 2.3. 96Isolation of the growth-inhibiting bacteria active against A. tamarense 97The growth-inhibiting bacteria against A. tamarense were enumerated using the MPN method [24, 25]. 98The cultures of A. tamarense at the late logarithmetic phase were diluted with the SWM-3 culture 99 medium to 3.3 x 10 3 cells ml -1 , and 0.5-ml aliquots were added to the wells of 48-well microplates. The 106showed roundish form without thecal plates, and were broken were scored as "positive". Sterilized 107seawater was inoculated into five wells with assay cultures as controls. From the "positive" wells, 0.5-ml 108 aliquots were added to the culture of A. tamarense in the wells (6.0 x 10 3 cells ml -1 ), and the activity of

12As a basis for analyzing development of six large grazing copepods (Eucalanus bungii,

The distribution of growth-inhibiting bacteria (GIB) against the toxic dinoflagellate Alexandrium catenella (Group I) was investigated targeting seagrass leaves and surface waters at the seagrass bed of Akkeshi-ko Estuary and surface waters of nearshore and offshore points of Akkeshi Bay, Japan. Weekly samplings were conducted from April to June in 2011. GIBs were detected from surface of leaves of the seagrass Zostera marina in Akkeshi-ko Estuary (7.5 × 105–4.7 × 106 colony-forming units: CFU g−1 wet leaf) and seawater at the stations in Akkeshi Bay (6.7 × 100–1.1 × 103 CFU mL−1). Sequence analyses revealed that the same bacterial strains with the same 16S rRNA sequences were isolated from the surface biofilm of Z. marina and the seawater in the Akkeshi Bay. We therefore strongly suggested that seagrass beds are the source of algicidal and growth-inhibiting bacteria in coastal ecosystems. Cells of A.catenella were not detected from seawaters in Akkeshi-ko Estuary and the coastal point of Akkeshi Bay, but frequently detected at the offshore point of Akkeshi Bay. It is suggested that A.catenella populations were suppressed by abundant GIBs derived from the seagrass bed, leading to the less toxin contamination of bivalves in Akkeshi-ko Estuary.

11Short-term changes in vertical distributions of copepods during the spring 12 phytoplankton bloom were analyzed based on day and night vertically stratified 13 sampling (9 strata between 0-1000 m) with a fine-mesh (60 µm