According to the introduction of the Total Pollutant Load Control System for Ise Bay, a part of the water quality has gradually improved, although the demarsal fish production including shellfishes at the bay has been declining until recently. The richness of the bay existed before 1960s has been lost as well as the other water basin in Japan. The Japanese government initiated the work for restoring clean and rich ocean as a countermeasure for this situation. A research project by Mie Prefecture in Japan was then carried out in this movement and the richness of the marine organisms of every trophic level in the ecological pyramid was studied, mostly through literature surveys. This article reports a part of the survey results and describes the variation of macrobenthos community in the bay over the years. The study elucidated the large population increase in the phylum annelida and the substantial population decrease in the phylum crustaceans that had happened from 1940s to the late 1960s. This incident caused the reduction of the mean individual wet weight and then brought a miniaturization into the macrobenthos community at the bay, similar to the miniaturization phenomena seen in the phytoplankton and the zooplankton community in Ise Bay as described by the author [14][15]. The study also revealed the occurrence of the catastrophic event that reduced the macrobenthos population to near extinction at the summer of 2016 and the recovery process from that. The relation between these drastic changes in the macrobenthos community and the emergence of the hypoxic water mass was described in detail. The geograpfhical difference of the biological diversity of macrobenthos community in the bay was also studied and a method to evaluate richness of macrobenthos community by the number of species and the biological diversity was examined.