THE CIRCADIAN BEHAVIOURAL REGULATION OF THE SHRIMP, PROCESSA CANALICULATA LEACH, 1815 (DECAPODA, PROCESSIDAE) IN RELATION TO DEPTH, ONTOGENY, AND THE REPRODUCTIVE CYCLE

Marine endobenthic decapods (i.e., burrowers and buriers) are a good model of reference for the study of circadian regulation in relation to day-night cycles of different intensity at different depths. Their behavioural rhythms can be efficiently studied with bottom trawling, repeated at different times of the day. In this study, fluctuations in the number of sampled Processa canaliculata as recorded by a temporally scheduled bottom trawl sampling on the shelf (100-110 m) and the slope (400430 m), in October (i.e., autumn equinox) and June (i.e., Summer solstice), were used to characterize the species' circadian regulation and its modulation over depth and season. A surface density of sampled animals (no. km(-2)) was computed for each haul and resulting time series were screened by waveform and periodogram analysis. Light intensity measures were also taken by CTD between consecutive catches. Marked catchability patterns were reported at both depths according to light intensity cycles, the amplitude of which varies several orders of magnitude. At 100-110 m, results showed a crepuscular rise in captures in autumn, while a nocturnal rise in captures was reported during the spring-sui timer. In autumn, these peaks in catches were diurnal at 400-430 m, showing a shift in their timing as a function of depth. In June, the phenomenon was also reported although the peaks in the catches shifted toward sunset. To assess whether a differential phase in activity rhythms was taking place upon ontogeny, sex, or stage of the reproductive cycle, surface density estimates at each catch were recomputed separately for juveniles, adults, berried females, non-berried females, and males. Resulting time series were screened by waveform and periodogram analyses. Juveniles and adults showed similar rhythmicity, whereas the patterns of capture for females were arrhythmic when these were berried. The present data are discussed considering that P canaliculata is an endobenthic species with burying activity.