宮古諸島下地島の海底洞窟に棲息する海綿動物

抄録

Submarine caves are widely known for their unique biodiversity and peculiar ecosystem. In the submarine caves around the Ryukyu Islands, sponges are the most abundant and diverse organisms. These sponges are considered to play an important role for the coral reef ecosystem in terms of supplying food resources to other organisms. An overview of the features of submarine cave sponge fauna especially at the “Akuma-no-Yakata” cave in Shimoji Island, Miyako Islands, Okinawa is presented herein. Sponges in “Akuma-no-Yakata” are roughly categorized into three types based on their distribution pattern inside the cave. The first category is sponges living around entrance of the cave, which are conspecific with species attached on underside of overhangs and interstices of coral reef. These species are considered as species just favoring cryptic habitats. The second category is sponges living around the mid part of the cave, some of which are closely related to species found in the deep-sea fauna. Lastly, the third category is sponges living in innermost part of the cave, which possibly have strong tolerance to low salinity water. The environment of second and third category is affected by fresh water infiltrated through calcareous ground of the island, and can be regarded as anchialine habitat, where the sponge fauna is very unique.