Seasonal occurrence of Japanese pygmy octopus Octopus parvus in the intertidal zone

The Japanese pygmy octopus Octopus parvus is a small octopus that occurs commonly along the coast of southern Japan, and is caught using traditional fishing methods. To date, however, there have been no studies on the ecology of this species. In this study, we investigated the annual seasonal occurrence of O. parvus in the intertidal zone of Fukue Island, Nagasaki, Japan, and examined the growth, maturation, and feeding habits of this octopus. We accordingly found that the octopus inhabits the intertidal zone of the study site from August to January, during which time it appears to move from the high to low intertidal zone, and subsequently migrates to the subtidal zone. During low tide at night in the intertidal zone, we observed that the octopuses actively captured and fed on prey, such as fish, crabs, hermit crabs, shrimp, snails, and bivalves. Both males and females were found to be characterized by similar body sizes and growth, although gonadal development occurs relatively earlier in males. However, any mating or brooding behaviors were not observed during the course of the study. Our observations thus indicate that O. parvus uses intertidal zones as feeding grounds for rapid growth and maturation, and may thereafter move to the subtidal zone for spawning.