Adaptive coloration, behavior and predation vulnerability in three juvenile north Pacific flatfishes

Abstract

Adaptive color change in flatfish has long been of interest to scientists, yet rarely studied from an ecological perspective. Because color change can take a day or so in some species, movement between sediments with differing color or texture may render fish more conspicuous to predators. We conducted laboratory experiments to test the following hypotheses related to adaptive color change in flatfish: 1) fish which do not cryptically match sediment will be more vulnerable to predation, 2) fish will reduce activity and bury to minimize conspicuousness when on a sediment they mismatch, and 3) fish will choose a sediment they match when given a choice. Experiments were conducted using three co-occurring north Pacific juvenile flatfishes: English sole Parophrys vetulus, northern rock sole Lepidopsetta polyxystra and Pacific halibut Hippoglossus stenolepis. As per expectations, juvenile flatfish were more vulnerable to visual predators when they mismatched sediment. Mismatched fish tended to behave differently than fish which matched the sediment. Rather than burying and becoming inactive, they became more active and less likely to bury, perhaps contributing to their predation vulnerability. This increased activity may have represented search for better matching sediment, a stress response, or conspicuousness-related density dependent behavior. Fish which had acclimated to light colored sediment preferred light over dark sediment in choice trials. In contrast, fish acclimated to dark sediment demonstrated no preference. These experiments demonstrate that adaptive coloration is an integral part of the flatfish detection minimization strategy and that movement between habitats can increase risk of predation.