The density of meiofauna, a benthic animal whose size measures from 0.031mm to 1mm (Fig. 1) can be 1 million/1㎡ in the sediment of a tideland or a beach.Meiofauna is an important element of seabed ecosystems. We have investigated the following two subjects on meiofauna.

• Influences that environmental changes caused by large benthic animals exert on meiofauna living in tideland. We have been investigating influences that the small spaces such as burrows (Fig.2) of the large benthic animals; e.g., crabs or nereides in tidelands, have on species diversity of meiofauna communities.
• Spatiotemporal variations of species diversity and community structure of bathybic harpacticoids.
  “Why is diversity high in the deep-sea though the environment is seemingly consistent?”
  In order to solve this great mystery, we have investigated the spationtemporal variations of community structures and species diversities of harpacticoids which belong to the dominant group of deep-sea meiofauna, and also environmental factors that control them.