Effects of seston concentration on feeding, digestion and growth in the mussel Mytilus edulis

Abstract

Mussels Mytilus edulis L. were fed a mixing diet comprising 2 algal species and ashed silt at a range of concentrations simulating natural conditions both above and below the level at which pseudofaeces were produced. Rates of ingestion increased to an asymptotic value at the highest concentration tested. Although gut passage times declined with increasing ingestion rate, efficiencies of food absorption remained relatively constant, probably signifying a balance between total gut contents and the rate of production of digestive enzymes. Measured physiological rates were similar to those recorded for mussels in the natural habitat. Respiration rates increased exponentially with increased rates of absorption, and the scope for growth was linearly related to absorbed ration, reaching a maximum value at the highest ration concentrations tested. The metabolic costs of feeding and growth represented 16% of the absorbed ration at twice the maintenance requirement, and increased to 22% at 4 .times. maintenance. Despite these increased respiratory losses, we conclude that the limits to growth are set primarily by constraints on feeding behaviour, particularly on the processes of digestion and absorption.