Activity patterns of the New Zealand cancrid crab Cancer novaezelandiae (Jacquinot) in the field and laboratory

Abstract

The activity patterns of the sublittoral crab Cancer novaezelandiae (Jacquinot) were investigated in the laboratory and field. Subtidal and intertidal potting surveys showed that timing of foraging activity in the field is influenced by daily and tidal variables. Subtidally, catches of crabs were greatest during night-time fishing periods. Catch rates also appeared to vary with timing of high tide relative to the diel period. Crabs were only caught in the intertidal zone during night high tides, indicating that their response to the tidal stimuli that initiate migration is strongly modulated by the light-dark (LD) cycle. When subjected to a normal LD cycle in the laboratory crabs confined most of their activity to the “night-time” with hourly activity values highest just after “dusk”. Under constant laboratory conditions crabs exhibited an endogenous, circadian, nocturnal locomotor rhythm, with little evidence of a circatidal component within the pattern of activity. Lack of an endogenous tidal oscillator was also indicated by the stable phase-angle relationship between initial onset of activity to time of expected sunset, regardless of daily timing of high tides. Results indicate that tide-related activity in the field is based entirely upon a direct responsiveness to tidal stimuli and illustrate the importance of both exogenous and endogenous factors in regulation of timing of activity of epifaunal crustaceans.