2021 Volume 76 Pages 39-49
Thirty-six sediment samples were collected from Lake Hamana, on the Pacific coast of central Japan, from 2013 to 2018 for research on ostracod assemblages. The distributions of living species were determined and compared with the results of a previous study conducted in the latter half of the 1970s. The diversity of living species had decreased in the central part of the lake (from 20 species of 19 genera to 9 species of 7 genera) but increased in the Shonai branch lake (from 10 species of 10 genera to 14 species of 10 genera). The overall lake species diversity was maintained (from 24 species of 23 genera to 22 species of 13 genera). However, the number of sampling stations at which living individuals were found had decreased from 25 to 17. The systematic diversity (diversity of taxa higher than species) also decreased. Furthermore, the area over which brackish- and freshwater species were distributed had particularly reduced. In contrast, there was an increase in species diversity, due to the inward migration of marine species along with the connection with the sea.
