Severe damages will result in human society, when several different critical natural phenomena coincide. One example relates to the resting cysts of Alexandrium species (dinoflagellates that cause paralytic shellfish poisoning), which are preserved in surface sediments throughout Osaka Bay, Japan. These cysts have been found to accumulate particularly densely in shallow areas in the inner parts of Osaka Bay, where a tsunami caused by an earthquake could occur any time. Damage by a tsunami could cause a change of the coastal ecosystems at Osaka Bay including the resuspension of surface sediments containing resting Alexandrium tamarense cysts and the subsequent redistribution of the cysts in newly deposited sediment. Under certain environmental conditions, these cysts could germinate and form dense blooms, leading to paralytic shellfish poisoning. Such a scenario could also affect other coastal areas, including the southern coast of the Korean Peninsula.

Ground arthropods are abundant in urban ecosystem, but our understanding on their ecological traits is little. The aim of this study is to clarify the effect of urbanization on ground arthropod communities. Ground arthropods were monitored once a week from April to December 2005 in 6 sites: Yamato River riverbank (Site 1), Daisen Park (Site 2), Oizumi forest area (Site 3), Osaka Prefecture University campus (Site 4), Paddy field (Site 5), and Satoyama (Site 6). A total of 221,000 individuals of ground arthropods belonging to 19 orders were collected in 6 sites. Isopoda including Porcellionidae and Armadillidiidae was the 1st dominant and 195161 individuals were collected, representing 88.3% of the total. Mean density of ground arthropods in Site 1- 4, urbanized areas, was much higher than in paddy field and Satoyama. Pattern of ground arthropod community in riverbank did not differ with those of urban park, urban forest area, and campus. Our finding showed that ground arthropods in urban area tend to increase biomass and specific groups in area disturbed and urbanized by human activities.