MEPS 498:161-171 (2014)  -  DOI: https://doi.org/10.3354/meps10627

ABSTRACT: Terrestrial insect predators and parasitoids commonly use volatile plant compounds released during grazing to find living herbivorous prey (i.e. tritrophic signaling). Because few studies have tested for tritrophic signaling in marine organisms, it is unclear if marine predators commonly use these fluid-borne cues to find living herbivore prey, especially under realistic settings. Such interactions might occur in the ocean because marine predators often use chemosensory-based foraging, and herbivore-induced production of defensive chemistry is common in some algal taxa. To examine the ability of predators to find live herbivores using waterborne chemical cues from grazed algae, we tested the responses of marine predators to several baits using in situ trapping and video experiments. We tested the attractiveness of chemical cues released by (1) Macrocystis pyrifera and Ulva sp. actively grazed by herbivores for short- or long-term periods, (2) crushed herbivores, (3) positive controls containing fish carrion, or (4) negative controls. Most predators trapped and filmed were spiny lobsters Panulirus interruptus. Under realistic field conditions, chemical cues from actively grazed algae with live herbivores failed to attract predators, but chemical cues from crushed herbivores and fish carrion were highly attractive. Thus, while marine predators like lobsters may utilize fluid-borne chemical cues to find dead or injured prey, such cues appear less important for finding live herbivore prey. Our literature review of 142 terrestrial studies revealed that tritrophic cues were unrelated to diet breadth of predators or herbivores and that most examples of terrestrial tritrophic signaling contained parasitoid predators. We additionally found that similar field studies in natural, non-agricultural settings such as ours are lacking even in better-studied terrestrial food webs, where they represent only 3% of manipulative experiments.

KEY WORDS: Tritrophic interactions · Chemically mediated · Predator foraging · Subtidal