Loggerhead sea turtle response to terrestrial-related odors

Loggerhead sea turtles (Caretta caretta) exhibit natal homing and feeding site fidelity following long-range migrations, a navigational phenomenon of returning to localized areas that is not yet fully understood. Previous studies suggest that sea turtles use earth’s magnetic field to relocate their approximate natal regions, but it is likely they use additional cues, such as olfactory stimuli, in combination with other navigation methods to localize specific islands and beaches. Such olfactory stimuli may come from land-based volatile organic compounds in coastal plants or ammonia. Previous studies demonstrate sea turtles are able to detect air and water-based odors related to foraging. However, it is not yet known if sea turtles are able to detect and respond to coastal plant odors, nor is it known the detection threshold at which turtles are able to distinguish odorant concentrations. From previous work, it has been established that turtles exposed to a biologically relevant odor spend significantly more time with their nares out of the water and take a higher number of breaths. In this study turtles were placed in an experimental arena and exposed to a variety of terrestrial-related olfactory stimuli: airborne odors of loblolly pine needles (in-tact, and crushed needles), food (positive control) and seawater (negative control) odors. Analysis suggests that turtles do not spend significantly longer with their nares out of the water or take a higher number of breaths in response to loblolly pine needle odors. Unpublished data from a 2021 study showed that turtles were likely able to detect and respond to odors of airborne ammonia in concentrations of 1e-5M NH4OH and 1e-7M NH4OH. Sea turtles used in the study in this paper were exposed to odorants of airborne ammonia (in concentrations of 1e-6M NH4OH, 1e-9M NH4OH and 1e-11M NH4OH). Analysis showed turtles did not respond significantly differently to odors of airborne ammonia than a control of DI water. It appears that sea turtles did not detect and respond to airborne loblolly pine or ammonia odors. Thus, these land-based odor cues may not be an innate cue. Juvenile turtles may learn or reinforce recognition of these terrestrial-related odors while spending time in nearshore feeding grounds. These land-based odorants may be a navigation cue used later in life to locate nesting or foraging grounds.