AN AUTOMATIC TECHNIQUE FOR RECORDING GRAZING ACTIVITY OF LIMPETS

The foraging activity of intertidal chitons and gastropods livingon rocky shores has been investigated by many authors by usingmicrophones or piezoelectric transducers to obtain audio-recordingsof radular grazing on various algae. However, the lack of automaticdevices for recording the noise associated with radular activityhas made the assessment of the spatial and temporal organizationof foraging of these animals difficult and labour intensive.A new technique is described that permits automatic recordingon computer and the analysis of grazing noises produced by limpetswhile foraging. The apparatus consists of three parts: a transducingpre-amplifying section (on limpets, or free in the field asa reference); an amplifying, filtering and digital-encodingsection (a free standing device) and a data acquiring and storingsection (on computer). Recordings of Patella caendta Linnaeusobtained in the laboratory during spring and summer 1993–1994,were analysed using a standard procedure to investigate grazingactivity. Each grazing bout is recorded on computer as a sequenceof 2–6 unit events, lasting about 0.4–0.8 sec, separatedby 1–3 sec. Each foraging phase consisted of a sequenceof several grazing bouts (maximum frequency about 1500–2000grazing bouts per hour), concentrated during high tides, witha distinct preference for nocturnal periods. The results ofthe automatic analysis were consistent with those obtained bydirect audiblescoring of the corresponding audio-recordings.The software used also permitted discrimination of true grazingactivity from other noises produced by the limpets, such asshell rubbing on the substrate while moving. This new techniquehasa number of advantages with respect to previous methods. Themost important characteristic is that the apparatus is ableto resolve automatically the grazing activity of shelled molluscsat different time scales, from msec to hours and days, accordingto an integrating constant that can be set on the apparatus. (Received 27 October 1994; accepted 28 December 1994)