Predator presence alters prey diet composition but not quantity in tide pool fish interactions

Abstract

Understanding species interactions and how they change in the presence of a predator or competitor is a fundamental goal for ecologists. We tested such interactions in an intertidal soft sediment pool system where both the sand goby Favonigobius lentiginosus and post-settlement whiting Sillago spp. consume meiofaunal prey, but F. lentiginosus also consumes Sillago spp. We quantified changes in fish gut content volumes and composition (i.e. meiofaunal group diversity and abundances) in response to the presence of a predator/prey and to different fish densities (two, four or six total individuals) in experimental aquaria. We found no significant density-dependent effects on either the predator or prey species, likely due to meiofaunal prey oversupply; however, the diet composition of the prey species Sillago spp. changed significantly in the presence of their potential predator. We conclude that lower consumption of meiofaunal amphipods in the presence of gobies suggests that whiting perhaps maintain their gut fullness by preferentially targeting larger amphipods.