Amphipod choice for seaweeds under predator cues: Should I stay or should I go?

Abstract

Marine herbivores may alter their behavior regarding habitat and food source choice according to the presence or absence of chemical cues from predators. To assess whether an amphipod species can detect and react to different water-soluble cues, individuals of Ampithoe marcuzzii were tested through a 2-current choice flume. Dual-response choice experiments were conducted in which the animals selected water flowing from one of 2 different sources. Comparisons among sources were tested using seawater (control), water with cues from different seaweeds (Dictyopteris delicatula , Gracilaria cervicornis or Gelidium coarctatum) , water with cues from potential predators (Abudefduf saxatilis , Sparisoma sp., Haemulon plumieri , H. aurolineatum and Holocentrus adscensionis) and water mixtures with seaweed and predator cues. The amphipods were able to avoid predator cues and to distinguish and actively choose between the water-soluble cues of different seaweeds. The animals preferred D. delicatula cues over those of G. cervicornis and G. coarctatum . The amphipods also selected more G. cervicornis cues than those of G. coarctatum . When predator cues were mixed with D. delicatula cues, amphipods changed their initial choice for G. cervicornis . However, when predator cues were added to G. cervicornis , the animals maintained their preference for this seaweed’s cues over those of G. coarctatum . Our findings demonstrate that A. marcuzzii exhibits a preference for brown seaweeds that draw fewer predators. The choice of seaweed changes according to predation risk perception based on water-soluble chemical cues. This ability to distinguish water-soluble chemical cues and base their habitat decisions on them is a fundamental adaptive behavior for this group.