Small actions, big costs: the behavioural energetics of a commercially important invertebrate.

Anthropogenic disturbance of farmed animals can be detrimental by adversely affecting behaviours and metabolic rate, potentially reducing their commercial value. However, relatively little is known about the normal behavioural time budgets and associated metabolism of many such species, particularly for example pectinid bivalves, which use anaerobic metabolism during periods of short-burst activity. In the present study, we used the accelerometry technique to measure scallop overall dynamic body acceleration in combination with respirometry in order to obtain and compare the behavioural time budgets and associated metabolism of 10 scallops, Pecten maximus, in an aquaculture hatchery and 10 in the wild. Scallops in the wild typically spent only 0.1 per cent of the time moving (less than 2 min d(-1)), yet, on average, the estimated metabolism of such movement represented 16.8 per cent of daily energy expenditure. Furthermore, owing to their reliance on anaerobic pathways during such activity, movement resulted in the wild scallops having a raised metabolic rate for, on average, an estimated 7.8 per cent of the time, during which oxygen debts accumulated during movement were paid off. Hatchery scallops also typically spent only 0.1 per cent of the time moving but estimated metabolism of such movement represented 41.8 per cent of daily energy expenditure. Estimated mean daily metabolism of scallops in the hatchery was significantly higher than scallops in the wild (169.1 versus 120.7 mg O(2) d(-1)) because anthropogenic disturbance in the hatchery caused energetically costly non-feeding behaviours. Consequently, hatchery scallops also spent a far greater amount of time with a raised metabolic rate (an estimated 26.6% of the time) than wild scallops. While short-term bursts of movement in pectinid bivalves may appear innocuous, they result in large expenditures of energy and an oxygen debt that is paid off over long periods of time that together limit further movement. These findings have implications for the farming industry; mitigating anthropogenic disturbances to farmed colonies may minimize non-feeding behaviours and hence maximize growth rates by reducing the costs of such movements and increasing the opportunity to feed.