Feeding and metabolism in the mussel Mytilus edulis L.

Three levels of metabolism have been identified in the mussel Mytilus edulis L. Standard Metabolism is attained after prolonged starvation. On feeding, there is an initially elevated metabolic rate, termed active metabolism, which is characterised by increases in oxygen uptake, ventilation rate and filtration rate. After three days feeding, oxygen consumption decreases to a value intermediate between standard and active levels; this is defined as routine metabolism. Integrated measurements of ingested ration, assimilated ration and metabolic rate provide an estimate of energy balance which is a useful index descriptive and predictive of the effects of sublethal stress. Growth efficiency increases hyperbolically with increasing ration to reach a maximum after which efficiency decreases as ration is further raised. The optimum ration for efficient growth is an increasing; function of mussel weight. Gametogenesis in Mytilus edulis occurs in winter when food is scarce, Energy for gonad maturation is obtained from reserves built up during summer when food is abundant. The mantle and digestive gland are particularly important storage sites. The digestive gland also regulates the flow; of assimilated material to other tissues, During prolonged stress the digestive tubules become considerably degenerate but the tissue possesses the capacity to recover after such periods of stress. Lipid, carbohydrate and protein are synthesised in summer and metabolic rate is low. During winter, gametogenesis results in an inflated metabolic rate and turnover of metabolic pools is rapid as reserves are utilized. Sublethal stress also leads to catabolism of energy reserves but it is not possible to define the degree of stress in terms of biochemical parameters such as the carbohydrate: protein ratio because they tend to be regulated to similar values which are independent of the severity of the stress experienced.