Humans Distracting Hermit Crabs: How Noise Pollution Affects Decision-Making

Animals, including humans, perceive their environments using multiple types of sensory systems, which can include visual, auditory, tactile, chemical, or electric senses. They integrate sensory information gathered from different systems and use it to make decisions that will best help them to survive and reproduce. However, animals can also perceive sensory information that is not relevant to the decisions they must make, which complicates the decision-making process. This is demonstrated by the “distracted prey hypothesis” which states that in the presence of noise, animals may not react normally to predator cues because they must divide their limited attention between the predator and the distraction (Chan et al. 2010b).

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Tidau and Briffa (2019) studied the effect of noise pollution on integration of sensory information and decision making in hermit crabs. In particular, they looked at how ship noise, a source of anthropogenic noise pollution in coastal marine environments, altered the shell-assessing behavior of European hermit crabs (Pagurus bernhardus). Hermit crabs typically integrate visual and tactile information when assessing empty shells and use it to determine whether or not to leave their current shell to enter the new shell. Shell size is important for growth and reproduction, so typically the more shell size hermit crabs stand to gain by switching to a new shell, the more likely they are to switch. However, they are also vulnerable to attack while changing shells, so the presence of predators influences shell-assessing behavior. Tidau and Briffa hypothesized that the presence of anthropogenic noise would impact the ability of hermit crabs to integrate multimodal sensory information and therefore alter the crabs’ decisions on whether or not to enter a new shell.

To test their hypothesis, the authors observed the shell-assessing behaviors of European hermit crabs in the lab under control conditions with ambient noise and no predator cues, and under experimental conditions with ship noise, with a simulated visual predator cue, or with both. Their results showed that ship noise did influence shell-assessing behavior. As expected, under ambient noise conditions and no predator cue, hermit crabs that started in smaller shells (and therefore had more shell size to gain) showed shorter decision times than those that started in larger shells. When a visual predator cue was present, hermit crabs that started in smaller shells were more cautious and showed longer decision times. However, the crabs did not show this effect in the presence of ship noise and a visual predator cue, demonstrating that the anthropogenic noise disrupted their ability to integrate multiple types of sensory information and react appropriately.

This study was one of the first to examine the effects of anthropogenic noise pollution on the integration of multimodal sensory information, as opposed to on the processing of only one type of sensory information. It demonstrates that in addition to things like habitat destruction and chemical pollution, noise pollution is another way in which humans are negatively impacting the ability of other organisms to survive and reproduce in their environments. Since shell assessment behavior in hermit crabs is important for growth, reproduction, and avoiding predation, anthropogenic noise pollution directly impacts the fitness of hermit crabs and could therefore have disastrous effects on hermit crab populations, as well as entire ecosystems.

References

Svenja Tidau, Mark Briffa, Distracted decision makers: ship noise and predation risk change shell choice in hermit crabs, Behavioral Ecology, Volume 30, Issue 4, July/August 2019, Pages 1157–1167, https://doi.org/10.1093/beheco/arz064