Intertidal crustaceans use seaweed-derived chemical cues to mitigate predation risk

© 2017, Springer-Verlag Berlin Heidelberg. Abstract: As predation is a primary driver of mortality, the need to minimize predation risk can shape prey behavior, influencing habitat selection and investment in vigilance. As structurally complex habitats can reduce predation risk, prey within heterogeneous environments may have evolved sensory abilities to locate them. In temperate rocky intertidal systems, fucoid seaweeds are a main source of structural complexity and can provide shelter for small organisms. This study examined the effects of predation risk on habitat selection in a tide pool-dwelling shrimp, Palaemon affinis, specifically testing whether predation risk drives preferences for fucoid seaweeds and if shrimps use chemical cues to locate fucoid-rich habitats. While tide pools with and without fucoids were equally abundant, P. affinis densities were >3 times higher in pools containing fucoids. The relationship between P. affinis and fucoids appears to be related to predation risk with P. affinis exhibiting a preference for fucoid microhabitats when a potential predator was present. Shrimps could distinguish between olfactory signatures from tide pools with and without fucoids and the odor of fucoids from other marine algae, suggesting that chemical cues are used to identify these structurally complex habitats. In addition to reducing predation risk, fucoid-rich habitats may provide better access to essential resources and reduce exposure to other biotic and abiotic stressors. This study shows that prey organisms can rapidly modify habitat use based on ambient predation risk, with olfactory cues used to identify the shelter characteristics of different habitats. Significance statement: Predation is the major source of mortality for most animal species. For this reason, animals may have evolved ways to minimize predation risk by modifying their behavior. In this study, we show that small tide pool-dwelling shrimps modify their habitat use in response to predators, using chemical cues to locate and identify structurally complex habitats that could reduce predation risk when this risk is high.