THE PALEOECOLOGY OF A SUBMARINE CAVE IN OKINAWA, JAPAN FOR THE PAST 7000 YEARS

A submarine cave is a unique environment, which is dark, food-limited, semi-isolated from the outside, and sheltered from wave actions. However, our knowledge on the long-term change in submarine cave ecosystem remains limited. Here we document how the Holocene development of a submarine cave, Daidokutsu, in Okinawa, southern part of Japan, has caused gradual changes in its ecosystem. Using microfossil ostracods in the sediment cores obtained from the cave as a model system, the past 7000-year faunal changes are reconstructed. The abundance of cave-endemic species shows gradual increase for the last 7000 years, reflecting the gradual development of the cave during the Holocene. It is consistent with the gradual decrease in abundance of open shallow marine species (e.g. Xestoleberis spp., Loxoconcha japonica) during the same period. Based on multi-dimensional scaling and cluster analysis, the environmental changes inside the cave can be divided into 3 stages, reflecting the gradual reduction of connectivity with external open-water environment due to the cave development for the past 7,000 years.