Early life history in marine benthic crustaceans often includes externally brooded eggs that hatch into free-swimming planktonic larvae. These larvae are relatively strong swimmers, and movement in the vertical plane provides a number of advantages, including modulation of horizontal transport and assurance of favorable predator–prey interactions. Swimming behavior in larval crustaceans is regulated by predictable external cues in the water column, primarily light, gravity, and hydrostatic pressure. Light-regulated behavior depends upon the optical physics of seawater and the physiology of light-detecting sensory structures in the larvae, which overall vary little with ontogeny. Swimming in response to light contributes to ecologically significant behaviors in planktonic crustacean larvae, including shadow responses, depth regulation, and diel vertical migration. Moreover, the photoresponses themselves, and in turn the evoked behaviors, change with the needs of larvae as development progresses. Regarding other sensory modalities, crustacean embryos and larvae respond to chemical cues using bimodal sensilla (chemosensory and mechanosensory) as contact receptors, and aesthetascs for detection of water-soluble cues. Processes and behaviors are stimulated by larval detection of chemical cues throughout ontogeny, including egg-hatching, avoidance of predators during free-swimming stages, and, ultimately, settlement and metamorphosis in juvenile habitats. The latter process can also involve tactile cues. The sensory-mediated behaviors described here for crustacean larvae have parallels in numerous arthropod and nonarthropod taxa. Emerging directions for future research on sensory aspects of behavior in crustacean larvae include multimodal sensory integration and behavioral responses to changing environmental stressors.
Barnacle biology before, during and after settlement and metamorphosis: a study of the interface