An actograph and its use in the study of foraging behaviour in the benthic polychaete, Nereis virens Sars

An automated device has been developed for recording burrow emergence in the benthic polychaete, Nereis virens Sars. A description of the apparatus (an actograph) designed to study the diel activity rhythm underling the feeding behaviour of this polychaete is presented. The actograph consists of a series of U-shaped tubes mounted into the base of an aquarium where the tubes act as artificial burrows for the experimental animals. Infrared (IR) light beam switches from optocouplers continuously monitor the openings of all burrows where a signal is recorded each time any beam is broken as the animals emerge. The signal is relayed to a data logger, which simultaneously triggers the recording of the event with a time-lapse video recorder and infrared sensitive camera. Video analysis of the emergence behaviour shows that the time spent and distance travelled in foraging excursions closely correlate with the actographic recording, as does frequency of emergence events. Out-of-burrow activity in N. virens is restricted to the hours of darkness, and activity away from the burrow entrance is concentrated in the period just after lights-off when feeding is greatest. During the course of the scotophase, the distance of individual forays is reduced as is the total number of foraging events whilst the time 'out-of-burrow' remains constant. The adaptive significance of such a response is explained in terms of minimizing relative out-of-burrow risk to predation. Overall, the actograph has provided a very robust means of quantifying foraging activity and will allow for a rapid and robust elucidation of the photoperiodic mechanisms of this and other tube dwelling polychaetes. (C) 2002 Elsevier Science B.V. All rights reserved.