Habitat complexity alters lethal and non-lethal olfactory interactions between predators and prey

Abstract

Habitat complexity often modifies rates of prey capture by visual predators, but little is known about how structural features affect non-visual olfactory consumers. Laboratory studies indi- cate that turbulent water flow over complex bedforms mixes chemical information in ways that con- fuse some olfactory foragers but improve the odor-tracking abilities of burrowing gastropods (whelks Busycon spp.). We augmented bottom roughness in a soft-sediment estuary to test the hypothesis that turbulent mixing of chemical attractants in the field increases whelk predation on hard clams Merce- naria mercenaria. Thin flat layers of shell fragments around the perimeter of experimental clam plots increased turbulent mixing of prey odors relative to those emanating from control plots. Assessment of prey mortality after 4 wk of exposure revealed that whelk predation on clams surrounded by shells was significantly higher than on clams surrounded by natural sediment. A second set of experiments showed that open prey plots containing a centrally caged (non-lethal) whelk experienced lower mor- tality due to avoidance responses of prey, but surrounding those plots with shells counteracted the non-lethal predator effect and led to significantly greater consumption by naturally foraging whelks. Shell treatments did not increase prey feeding or reduce predator interference. Results suggest that whelks hunt more successfully when bottom roughness increases turbulent mixing of prey chemicals or disrupts prey abilities to detect and respond to predator odors. When integrated over time, habitat- related differences in chemical transfer and olfactory behavior could have important implications for populations of both predators and prey.