Sensory environments, larval abilities and local self-recruitment

Models of larval dispersal rarely incorporate the behavior of larvae, yet many potential settlers of marine invertebrates and fishes may navigate toward suitable settlement sites by responding to gradients of environmental stimuli. Accordingly, a variety of stimuli may be used for navigation (directed movements to the source of stimuli) and partial navigation (e.g., migration to a current that may favor transport to a settlement site) in the pelagic environment. A broad diversity of taxa have senses that allow them to detect variation in: water chemistry (biotic sources, e.g., amino acids and abiotic sources, e.g., salinity), sound and vibration (biotic sources, e.g., grunting fishes, abiotic sources, e.g., waves breaking), white light gradients and images, polarized light, current direction, magnetism and water pressure. Some organisms can detect multiple stimuli (e.g., decapods and fishes) and integrated sensory responses are likely to be common; many potential settlers of these taxa are good swimmers. Demonstrations of strong orientation to stimuli and navigation over short (centimeters to meters) and broad spatial scales (tens of meters to tens of kilometers) are most common for these groups. Partial navigation, involving vertical migration, is common for invertebrate larvae. A consequence of vertical migration can be transportation that favors movement to suitable settlement habitat. Navigation over a range of spatial scales may use stimuli that are very predictable regardless of location (e.g., water pressure, gravity). The gradients of other stimuli may be more useful for environment-specific signals and even the location of natal habitats, locations and conspecifics (e.g., using sound or smell of specific taxa). We argue that some larvae may use a hierarchy of sensory cues to find suitable settlement sites and that some of the same types of stimuli may be used at more than one spatial scale (as demonstrated for adult salmonid fishes). There are good demonstrations of the use of cues for orientation and navigation at small spatial scales (less than a few meters). More information, however, is required at spatial scales that are relevant to navigation over kilometers before behavior can be incorporated more accurately into models of larval dispersal.