Pyrodinium bahamense var. compressum (Pbc) is one of the causative species of Paralytic Shellfish Poisoning (PSP). Incidents of PSP and red tides caused by Pbc are increasing, as well as the geographic distribution of Pbc expanding in Southeast Asia, where it has recently occurred in several areas that previously have not experienced blooms, such as Ambon Bay and Lampung Bay in Indonesia. Five factors including anthropogenic activities, natural activities, visual realization with red tide discoloration, development of techniques like RNA sequence and ELISA toxin kits, and the establishment of a regular monitoring system have been suggested to have led to the increase in reports of dinoflagellate blooms. Occurrence of dinoflagellate cysts in sediments has been used as evidence to which species of vegetative cells occurred in the water column. In this study, the vertical distribution of dinoflagellate cysts in sediments was investigated to confirm the first occurrence of Pbc cysts and to examine the floral changes of dinoflagellate cysts in Ambon Bay and Hurun Bay, Indonesia. In Ambon Bay, Pbc cysts first occurred in ca. 1850 and the cysts were continuously observed since ca. 1870. In Hurun Bay, Pbc cysts were found at 50-52 cm depth, and also at 42-44 cm depth. Cysts of Pbc first occurred at least in 1883, using depositional age calculated from the historical eruption of Mt. Krakatau. Cysts of Pbc have continuously occurred since ca. 1910, and the cyst densities rapidly increased in ca. 1960. Based on these findings, we consider that anthropogenic activities such as ballast water and transportation of shellfish seeds probably did not cause the introduction of Pbc in both bays.

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Trichodesmium biovolume and its distributional pattern were investigated in spring in the East China Sea. It showed surface-biased distribution at all stations where it was detected. The maximum biovolume in each water column was 0-4.4×10⁷ μm³L^-1, and it was sometimes larger than that of coccoid cyanobacteria (8.9×10⁶-2.0×10⁷ μm³ L^-1). Horizontal distribution of Trichodesmium around the boundary between continental shelf water and Kuroshio water showed different patterns between a large-sized fasciculated form and other forms; the former was more abundant on the Kuroshio side and the latter, small-sized fasciculated form or separate filamentous form, more abundant on the continental shelf side, while the abundance of all types varied temporally. Considering that the large fasciculated form may develop from the separate filamentous form or the small fasciculated form, and it may be more efficient for N₂-fixation under an aerobic conditions, this contrastive horizontal distribution might reflect an adaptive enlargement process in Trichodesmium colonies accompanied with passive transport from continental shelf water to more oligotrophic Kuroshio waters.

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Abundance and community structure of chaetognaths were studied based on the vertical stratified zoo-plankton samples from the epipelagic through abyssopelagic zones (maximum: 5,000-5,800 m) at four stations in the western North Pacific (44°N, 39°N, 30°N, and 25°N) and one station each in the Japan Sea, Okhotsk Sea, and Bering Sea. Chaetognath standing stocks (indiv. m^-2) were greatest at subarctic stations (44°N, Okhotsk Sea, and Bering Sea). Vertically, chaetognath density (indiv. m^-3) was the greatest in the shallowest depths, and decreased with increasing depth. Chaetognaths occurred down to 4,000-5,000 m at subarctic stations, while chaetognaths were not found below 3,000 m at subtropical stations (30°N and 25°N). The number of chaetognath species was the greatest (22 representing 14 genera) at the transition station (39°N), and the least (1 species) at the station in the Japan Sea. Species diversity indices (H ') were low at subarctic stations, but high at subtropical stations. Vertical profiles of H ' varied also between these stations; it peaked at the mesopelagic zone at subarctic stations, and at the epipelagic zone at subtropical stations. Cluster analysis separated chaetognath communities of the study region into 5 groups (A-E) characterized by discrete spatial distribution: group A; the mesopelagic zone at subtropical and transition areas, group B; the epipelagic zone at subtropical and transition areas, group C; the bathy- and abyssopelagic zone (except the Japan Sea), group D; all depths in the Japan Sea, and group E; the epi- and mesopelagic zones in the subarctic area. For the four most abundant species at the subarctic stations, allometric data showed greater head width to total length ratios, and greater hook length to total length ratios for deeper-dwelling species. Relatively larger head width (i.e. large mouth) and longer hooks of deep-sea chaetognaths are considered to be an adaptation significant to the successful capture of prey zooplankton in resource limited deep-sea environments.

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We investigated the benthic fauna of the inner part of Ariake Bay in August 2006. We set 45 sampling stations including at 28 mud and 17 sand bottoms in subtidal areas. In each station, sediment samples were taken once with a Smith-McIntyre grab. The sediment samples were sieved with a 1 mm mesh, and the residue was fixed with 10% formalin solution. In the laboratory, benthic organisms were sorted, identified and weighed by their wet weight. The data obtained were compared to the samples collected in 1989. In both mud and sand bottoms, benthic fauna in 2006 was dominated by bivalves and polychaetes as in 1989. However, the abundance of polychaetes, bivalves, ophiuroidea, and the other taxa except crustaceans significantly or nearly significantly decreased from that in 1989 irrespective of bottom types, leading to an overall decrease in macrobenthos. The biomass of mud bottoms tended to decrease from that in 1989, though did not differ in the sand bottom. The distribution of bivalves dominating in 1989 also drastically decreased. The cause of the drastic decrease in macrobenthos may represent the consequence of the frequent occurrence of hypoxia in summer and/or change in sediment grain size, both of which have recently occurred in the inner part of Ariake Bay.

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Cobbled shores in subtropical Japan are small and disturbed by sand transported from terrestrial runoff. How benthic organisms live in such a harsh environment has been seldom studied. On a cobbled shore at Ishigaki Island, the present study investigated the life-history traits of the gastropod, Nerita squamulata Le Guillou 1841. Seasonal quadrat samplings showed that the neritid density decreased when and where sand covered cobbles, indicating impact of sand on the neritid. Monthly frequency histograms of the shell width suggested that the neritid lives less than 2 years and recruits as individuals of 1-4 mm shell width in both May-August and February. With the possible short longevity and frequent recruitments, the neritid population may quickly recover after the disturbance by sand.

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