Planktonic oyster larvae optimize settlement decisions in complex sensory landscapes

The settlement of pelagic larvae constitutes a pivotal phase in the life cycle of benthic aquatic species. The choice of settlement location is critical for the recruitment to established populations and the colonization of unoccupied habitats. Consequently, the cues governing settlement decisions in larvae become particularly pertinent for human activities such as habitat restoration, mariculture, or biofouling prevention. Our study aims to enhance our comprehension of the underlying principles of how larvae optimize settlement decisions when exposed to multiple natural chemical cues simultaneously. Through a series of laboratory experiments, we investigate settlement patterns of Pacific oyster Magallana gigas larvae when exposed to different combinations of attractant and repellent cues. Our findings reveal additive increases in settlement rates in the presence of attractant cues originating from conspecifics and biofilms. Conversely, settlement attraction by conspecific water-borne cues was reduced in the presence of repellent cues emanating from predators. Notably, when repellent predator cues were presented alongside attractant cues linked to substrates (biofilms or shells from conspecific adults), the repellent effect was nullified.