The Nocturnal Emergence Activity Rhythm in the Cumacean Dimorphostylis asiatica (Crustacea)

The crustacean Dimorphostylis asiatica inhabits the sublittoral zone and actively swims in the water at night. Males are positively phototaxic, and can be collected on the surface by using a light at night. The timing of this emergence was investigated in the field. Nearshore collections of males have demonstrated a clear rhythmic pattern, with emergence synchronized with both day-night and tidal cycles. The remarkable feature of this record was that the tidal aspect of the pattern was modified seasonally. While emergence was strongly synchronized with high tide during the winter and spring, tidal synchrony was scarcely detected in summer and autumn. Environmental factors that affect the seasonal modification of the activity pattern are still unknown.