Recent ostracods as lagoonal paleoenvironmental indicators: application and limitations from a case study of the Ariake Sea, Japan

A total of 107 species belonging to 45 genera were identified from 26 sites in the Ariake Sea, Kyushu, Japan. Two biofacies were identified by both Q-mode cluster analysis. Redundancy analyses (RDAs) were computed on the standardized 71 species × 23 sites matrix data and 23 sites × 28 environmental data. The water temperature of February (WT2) is a valuable ecological factor to determine the distribution of 24 species from the Ariake Sea. Based on the results of RDA, WT2 correlated with 11 sites selected for MAT using 24 species and site 11 was applied by a recent site as a reference. The predicted WT2 was well matched (10.4°C) compared with actual WT2 (10.5°C). The morphological variation in the aperture ratio of a sieve-type normal pore canal at a homological location of Cytheromorpha acupunctata showed a good correlation with chlorophyll of September, sediment type, and the dissolved oxygen of February and helps reconstruct these three environments. The APR is especially a good index for reconstructing dissolved oxygen.