Measuring feeding and absorption in suspension-feeding bivalves: an appraisal of the biodeposition method

Abstract

In this paper we analyse methods that have been used to quantify the different physiological processes involved in food acquisition and absorption by suspension-feeding bivalves. In particular, we have considered those methods that have been used for determining food processing rates under ambient conditions of food availability. During the last few years, an increasing number of studies has been performed using the biodeposition method, which estimates feeding and absorption rates through measurements of suspended particles and biodeposit production. The main assumption of this method is that ingested particulate inorganic matter can be used as an inert tracer of feeding and digestive processes, i.e. that secretion or absorption of inorganic matter across the gut wall is negligible. There are several points that have to be taken into account when applying this method: a) the method assumes that sampled suspended particles and those retained by the gill are of similar organic content; b) faeces and pseudofaeces collection must be quantitative and separate and particle sedimentation must be controlled, if not avoided; c) where particulate food availability or composition is expected to fluctuate, the time lag for particles being captured and processed before they appear in the form of biodeposits must be evaluated to provide a proper reference value for available food. The biodeposition method and more conventional procedures provide equivalent results for estimating clearance rates. Moreover, predictions of scope for growth obtained with this technique also seem to be compatible with directly measured growth rates.