Life history and zonation dynamics of the cirolanid isopod, Eurydice nipponica Bruce & Jones, on an intertidal sand flat in western Kyushu, Japan

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A dense population of the cirolanid isopod, Eurydice nipponica Bruce & Jones, inhabited an intertidal sand flat in western Kyushu, Japan. Newly-ovigerous female groups occurred twice yearly, during March to June and August to October, generating two major recruitment groups: June to July (summer group) and September to November (autumn group). The summer group became ovigerous after 2 mo, with most of the early recruits to the group dying out after breeding (3-5-mo life span). Some of the later summer recruits overwintered to have their second brood, dying out during spring to summer. Members of the autumn group overwintered to have their first brood during late spring to mid-summer, some of them surviving longer to have their second brood just before dying (12-13-mo life span). The life history pattern for males was not as clear as for females owing to the successive merging of the newly-recruited individuals into the older ones with smaller asymptote body sizes. The center of distribution of the population along the elevation gradient on the sand flat was generally located around the MLWS level, with the breeding components mostly concentrated there. Most probably part of the overwintering population migrates to the subtidal zone to avoid the harsh conditions of the winter months.
日本甲殻類学会の論文