MARINE BIOGEOGRAPHICAL MICRO-PROVINCES — JAPAN 497 



Distribution Type of the Fauna as a 

 Regional Characteristic 



In the establishment of biogeographical provinces, the taxonomic 

 list of fauna has been the material of the first importance to be con- 

 sulted. From the standpoint of ecology and production biology for our 

 economic life, however, the regional characteristics of biomass and dis- 

 tribution types of fauna are no less important than the presence or 

 absence of a particular species or a group of species. 



In respect to biomass, our study of bay communities has revealed 

 that within the Japanese Islands the productivity has closer relation- 

 ships with specific characteristics or individuality of bays such as the 

 mean depth, influents and other ecological factors, than with geograph- 

 ical regions with different submarine climates. 



The distribution types of benthic animals differ, on the contrary', 

 in bays of the Pacific and Japan Sea sides. On the Pacific coast, con- 

 tinental molluscan elements have a relatively narrow zonal arrangement 

 in the inmost part of the bay, and the remaining larger area extending 

 from the mouth to the inner part is occupied by the coastal elements of 

 the open sea, showing more or less clear boundary between these two 

 communities. On the Japan Sea side, continental elements occupy most 

 of the area, and only a few open sea elements invade the bay. Further- 

 more, the continental elements are segregated into two zonal commu- 

 nities: i) the animals which are indices of strong embayment and dis- 

 tributed in the inmost part, and ii) those of moderate embayment 

 occupying the remaining area. 



Some of the molluscs of the continental and open sea systems ap- 

 pearing in Japanese bays may be classified as follows: 



a) Continental coastal elements which appear in the inner part 

 of bays of both Pacific and Japan Sea sides. They are used as indices 

 of strong embayment. 



Theora luhrica, Raeta pulchella, Pahia undulata and Fluvia hunger- 

 jordi. 



b) Continental coastal elements which are quite common in the 

 central and mouth parts of bays of the Japan Sea side, but are rare or 

 absent on the Pacific side. They are the indices of moderate embay- 

 ment. 



Veremolpa micra and Alvenius ojianus. 



c) Coastal elements of open sea under the influence of the warm 

 Kuroshio Current. They are common in bays of the Pacific coast of 

 southern Japan, but are less prosperous in bays of the Japan Sea and 

 tlie Pacific coast of northern Japan. They are the indices of weaker 

 embayment. 



