Florida Atlantic University is one of the leading local universities in producing top-notch marine biology research, especially in the field of sea turtle biology. Stephanie Kedzuf is a recent graduate of FAU, earning her Master’s of Science in Biology last December. She worked under the direction of Dr. Michael Salmon, a top sea turtle biologist and researcher. Stephanie’s work centered upon how sea turtles locate feeding grounds in the open ocean and then how they localize their behavior to find food. Specifically, she examined the turtles’ sense of smell and how they might use airborne odors to find areas with abundant food.
Sea turtles are known to make long-distance migrations across ocean basins, traveling between feeding and nesting areas and sometimes between different feeding areas as well. How they manage to navigate a seemingly featureless ocean is largely unknown. One hypothesis is that turtles use airborne odor cues as an “olfactory compass” to orient towards areas of high productivity and associated food resources. Highly productive areas in the ocean are characterized by high concentrations of a chemical called dimethyl sulfide (DMS), which smells like rotting seaweed.
Figure 1. Experimental tank set-up. (a) Introduction of airborne odors into the tank. A single
turtle was tethered inside of the test tank. Adjacent to the tank was a stimulus chamber
which contained a solution of DMS odor. A fan gently blew air over the odor, into the tank,
and exited the other side as indicated by the red arrows. (b) Introduction of waterborne odors
into the tank. For these experiments, three turtles were allowed to free swim inside of the
test tank. A perforated plastic ball was suspened at mid-depth in the water by plastic tubing.
A syringe with waterborne odor was attached at the other end of the tubing and the odor was
pushed into the tank, as shown by the blue arrows.
Although this stench might be repulsive to humans, other animals like many species of seabirds, use it as a cue to find food in the ocean. Loggerhead sea turtles have been shown to detect DMS odor in the air, but no one has tested their ability to orient upwind when it is present. Stephanie tethered young turtles that were just a few months old inside of a specially designed airflow tank (Figure 1a) and exposed them to airborne DMS odor.
Turtles did not show any reaction to the odor. Stephanie also tested the turtles with other odors that they might find more “interesting” such as shrimp, jellyfish, and squid.
Again, the turtles did not orient upwind when these odors were present. These results suggest that the turtles are not using airborne odors as a compass, but Stephanie wanted to examine if turtles use them to localize their feeding behavior once they do find their way to feeding grounds.
Previous studies have focused on sea turtles’ abilities to smell odors underwater. However, no studies have directly compared turtles’ responses to waterborne odors with their responses to airborne odors. Stephanie hypothesized that the turtles’ reactions to each odor type might be similar.
These experiments took place in a modified tank (Figure 1b) that allowed both airborne and waterborne odors to be introduced separately to free-swimming turtles.
These experiments also exposed the turtles to a small perforated ball that was suspended at mid-depth by plastic tubing (Figure 2). This item acted as a visual stimulus. Waterborne odors were introduced through the plastic tubing and diffused throughout the water in the tank.
When squid odor was introduced as an airborne odor, turtles bit the plastic ball in the tank, the tank walls, and other turtles in the tank. A similar, but stronger response was observed when waterborne squid odor was introduced.
Figure 2. A green sea turtle post-hatchling bites at the perforated ball during the introduction of waterborne odor into the tank.
Stephanie’s experiment provides support for the hypothesis that sea turtles use cues other than olfactory cues to locate food sources and possibly nesting beaches from far distances. It is likely that they use the Earth’s magnetic field to achieve this goal.
However, cues such as olfactory cues and visual cues are probably important in localizing their feeding behavior. For example, a female turtle might leave a nesting beach and use magnetic cues to reach a generalized feeding area.
Once near the feeding area, the turtle probably uses her sense of smell to tell her which direction food might be. Once she is heading in the correct direction to find that food, she can direct her behavior using visual cues to eat a tasty jellyfish that is swimming nearby.
Stephanie has presented her research at multiple biological meetings, including the International Sea Turtle Symposium and the Society for Integrative and Comparative Biology (Figure 3). She is currently employed at the Loggerhead Marinelife Center as their Field Coordinator.
In the summers, you can find her on the beach conducting additional research and collecting nesting data on south Florida’s local nesting populations of sea turtles.