Predator presence affects activity patterns but not food consumption or growth of juvenile corkwing wrasse (Symphodus melops)

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Abstract: Indirect effects of predators can manifest themselves as changes in prey behaviour and physiology. Reduced prey activity is a common behavioural response to predation risk, generally resulting in reduced foraging and growth. Given that digestion requires energy, it has been suggested that prey will choose to eat smaller meals under predation risk to reserve a larger portion of the aerobic metabolic scope they have available for energetically demanding tasks more critical than digestion, such as

escape. To test this prediction, we quantified food consumption and growth of juvenile corkwing wrasses (Symphodus melops) over 11 days in the presence or absence of a predator (Atlantic cod, Gadus morhua). We then quantified behaviour and food consumption of the same wrasses in behavioural arenas with a predator present. All food consumption data were examined in the context of the aerobic scope that would have been available during the digestive period. Overall, there was no effect of

predator exposure on food consumption or growth, yet predator-exposed wrasses were more consistent in their daily food consumption, lending some support to our prediction of prey bet-hedging on meal size under predation risk. The lack of a clear pattern may have resulted from a relatively low percentage of aerobic scope (~20-27%) being

occupied by digestion, such that fish retained ample aerobic scope for activities other than digestion. In the subsequent behavioural trials, predator-exposed wrasses were

more active and spent more time near the cod than predator-naïve wrasses, suggesting the former had habituated to predation threat and were more risk-taking.

Our results highlight the complex and often counter-intuitive effects that predator presence can have on prey populations beyond direct consumption.