Predatory fish sounds can alter crab foraging behaviour and influence bivalve abundance

Abstract

The risk of predation can have large effects on ecological communities via changes in prey behaviour, morphology and reproduction. Although prey can use a variety of sensory signals to detect predation risk, relatively little is known regarding the effects of predator acoustic cues on prey foraging behaviour. Here we show that an ecologically important marine crab species can detect sound across a range of frequencies, probably in response to particle acceleration. Further, crabs suppress their resource consumption in the presence of experimental acoustic stimuli from multiple predatory fish species, and the sign and strength of this response is similar to that elicited by water-borne chemical cues. When acoustic and chemical cues were combined, consumption differed from expectations based on independent cue effects, suggesting redundancies among cue types. These results highlight that predator acoustic cues may influence prey behaviour across a range of vertebrate and invertebrate taxa, with the potential for cascading effects on resource abundance.

Keywords: bioacoustics; invertebrate; non-consumptive effect; predation; trophic cascade.

Figure 1.

Evoked potentials for an individual crab in response to 200 Hz sound presentation of tonal bursts at several sound levels. Sound levels are shown in terms of both particle acceleration and acoustic pressure. (a) Evoked potentials as a function of time from stimulus presentation. Vertical scale bar represents 1.0 μV amplitude. Inset: experimental crab on wooden sling prior to placement in the tank for the sound presentation. (b) Evoked potentials as a function of frequency (FFT of traces in (a)). Vertical scale bar represents 0.05 μV amplitude. (Online version in colour.)

Figure 2.

Evoked potential audiograms in terms of (a) acoustic pressure and (b) acoustic particle acceleration, showing the lowest sound level that produced a detectable evoked potential. Eight crabs were tested at all frequencies. Lower values for thresholds and particle accelerations indicate greater sensitivity. Error bars represent ±1 s.e.

Figure 3.

Crab foraging responses to predatory cues. (a) Effects of predator and non-predator acoustic cues. Crab foraging activity (proportion of clams consumed) varied in response to both predator and non-predator cues compared with the silent cue control. (b) Effects of predator acoustic cues and predator chemical cues. Crab foraging activity decreased in response to short-term catfish acoustic cues, persistent water-borne catfish cues and their combination. Consumption rates in the combined cue treatment were greater than the expectation calculated with the multiplicative risk model (black circle). Letters indicate significant differences based on Tukey post hoc tests. Error bars represent ±1 s.e. Line drawings by T. Rogers.