Experimental study of filtration activity in Ditrupa arietina (Annelida Polychaeta) using an automated image analysis system

An automated image analysis system designed to assess the activity of benthic organisms is described. This system is used to study filtration in the serpulid polychaete Ditrupa arietina. The video sensor of the system is composed of a black and white charged coupled device, a microprocessor, a memory and an interface board. It is driven by real-time routines, which are downloaded in permanent memory prior to each experiment. These routines control picture acquisition frequency and compute the differences in grey levels between the image recorded at a given time and a reference image (corresponding to no filtration in the case of D. arietina). These differences are used to detect numerical objects, which are stored in the memory board. At the end of each experiment, these objects are uploaded to a microcomputer where they are analysed using a second set of programs. This procedure involves several parameters, namely. the minimal object surface which is indicative of a real difference between two images (minimal surface), the research area (search radius), the research sites, and the definition of a set of conditions relating differences between images with a true filtering activity by D. arietina. These parameters were determined by comparing the results obtained using: 1) the automated system, and 2) classical frame by frame videotape analysis. They were then validated on several batches of worms by comparing total filtering durations per worm measured using the as previously calibrated automated system with those obtained using classical video observations. This step showed that the automated system is suitable for studying filtering activity in D. arietina. Our first results show that inter-individual variability is high, which has important consequences on experimental plans designed to assess the effects of environmental factors on filtration.