Behavioural mediation of the costs and benefits of fast growth in a marine fish

Trade-offs between the costs and benefits of growth are thought to be mediated by behaviour, whereby rapid growth is associated with greater predation mortality because of increased foraging effort. We tested this hypothesis by collecting young Pomacentrus amboinensis using light traps and settling them onto patch reefs where their behaviour and survivorship were monitored for 24 h. One month later, individuals of the same cohort were collected from shallow reefs and released onto patch reefs where their behaviour and survivorship were monitored for 6 days. At settlement young fish suffered high (60% in 24 h) mortality that preferentially removed larger, faster-growing individuals. However, we could find no evidence that foraging behaviour contributed to this selective mortality. In contrast, 1 month later the same cohort underwent negative size-selective mortality where the smallest, slower-growing fish were preferentially removed by predators. Larger fish spent more time foraging, were more aggressive, swam greater distances and chased more fish than smaller individuals. Thus, consistent individual differences in behaviour contributed to patterns of mortality, but in a way that involved no apparent trade-off with growth. For P. amboinensis, consistent variation in growth may be maintained by spatial and temporal differences in the selective regime within the reef environment.