Feeding physiology of infaunal (Mulinia edulis) and epifaunal (Mytilus chilensis) bivalves under a wide range of concentrations and qualities of seston

Abstract

A comparative study was carried out on the functional feeding behavior of the infaunal clam Mulinia edulis and the epifaunal mussel Mytilus chilensis from Yaldad Bay, southern Chile, in response to broad fluctuations in quantity and quality of seston. A number of physiological variables were quantified and compared, including clearance, filtration and ingestion rates; pseudofeces production and pre-ingestive selection efficiency. Relative sizes of the ctenidia and labial palps were measured for both species to determine if the size of the organs was related to their capacity for filtration and pre-ingestive particle selection. Both species showed high rates of clearance at lower seston concentrations (<3 to 5 mg l -1 ). Above these concentrations, both species regulated both the quantity and quality of material ingested. When the seston concentration was relatively low and/or its quality high, regulation of food ingested was accomplished primarily by reduction in clearance rate, while at high seston concentrations and/or low quality, this parameter was regulated primarily by the expulsion of pseudofeces with a lower content of organic matter. Ingestion regulation was higher in M. chilensis. In general, both species showed a capacity for pre-ingestive particle selection, which increased with seston concentration and the proportion of organic matter present. In diets containing more than 60 % organic matter, selection efficiency in M. chilensis became slightly reduced, while in M. edulis it remained stable; this observation is explained by the larger relative size of the labial palps in Mulinia edulis. Generally, feeding rates of M. chilensis were higher than those of M. edulis; this may be attributable to the former's larger-sized ctenidia, which are able to filter more food.