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

Abstract

The Japanese pygmy octopus, Octopus parvus, is a small octopus that commonly occurs along the coast of southern Japan; however, the ecological information is limited. This study investigated the annual seasonal occurrence of O. parvus in the intertidal zone of Fukue Island, Nagasaki, Japan, and examined its growth, maturation, and feeding habits. We found 140 individuals in the intertidal zone from August to January, and zero from March to July. During the emergence period, they appear to move from the high to low intertidal zone, and subsequently migrate 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, gastropods, and bivalves. The body size of collected individuals increased significantly from summer to winter. Both males and females were found to be characterized by similar body sizes and growth, although gonadal development occurred earlier in males. However, no mating or brooding behaviors were 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.