Diversity and adaptive strategy of submarine cave faunas

点击翻译按钮获取中文摘要

This study aims to clarify the diversity and adaptive strategy of cryptic faunas (especially cavernicolus molluscs) in a wide area of the tropical western Pacific from Japan to Micronesia and Polynesia. Research of several domestic caves and indoor studies of domestic and foreign samples (living organisms and substrates obtained from numerous caves) have been carried out with this Grant-in-Aid.As the result of our observation and identification of minute molluscs, species composition of bivalves in each cave and their geographic distribution were elucidated. More than 100 cavernicolous bivalves were identified. Remarkable and unique features of these bivalves are the minute size, paedomorphosis, K-selection, similarity to deep-sea species, large egg size, low fecundity, dominance of brooding species, and ecological primitiveness.These features are certainly related to one another and could have resulted from a common adaptive strategy to cavernicolous environments. Low food levels must be the most important controlling factors. Though many problems (especially the process of speciation and migration) remain unsolved, the characteristics of cave bivalves generally suggest the type of adaptive strategy that could be advantageous, when extreme oligotrophic conditions prevail in the world.