Monday, September 28, 2020

Living Like Larry: Spiny Lobster Homing

Hey everyone! My name is Coral Holt, and I am a senior biology major in the Childress Lab. I have been in the lab since the fall of 2019 working on the spiny lobster homing project with Dr. Childress. I am working toward a Departmental Honors thesis and manuscript this year, and I hope to be able to present a poster presentation as well if the state of the COVID-19 pandemic allows.

In this post, I want to talk a little bit about the data I am working on this semester. To start, I want to give a brief explanation of my project. Homing is an organism's ability to find its way back to its home shelter if displaced. Lobsters have been identified as a type of animal capable of this, and it is thought that they navigate utilizing an internal organ sensitive to earth's magnetic fields, like a compass! Previous studies have looked at adult lobsters' ability to home using acoustic telemetry. This tracking technique involves setting up a grid of receptors and placing acoustic tags on lobster subjects. The tags send out frequent acoustic signals, and depending on when they are detected by different receivers in the grid, a precise location can be triangulated.

In the specific studies I am working on, we look at a species called the Caribbean Spiny Lobster, Panulirus argus, a species found in the Florida Keys ecosystems our lab focuses on. This specific species of lobster has been found to be especially good at homing. However, until last year, only adult lobsters were utilized in the studies. The studies I am working on look at juvenile lobsters to see if they have a similar ability to their adult counterparts. If they do, this may suggest homing is an innate ability rather than learned.

Last year, I worked on a data set from a study conducted near Lower Matecumbe Key. We found that control/nondisplaced lobsters tended to move in larger areas than the experimental/displaced lobsters on the night following displacement. We speculated that this could be due to nondisplaced lobsters moving in a more meandering pattern, creating a circular area of activity, as opposed to a more directional and linear area of activity in displaced lobsters as they try to find their way back to their dens. We also found that the displaced lobsters were visually and statistically accurate at homing in regards to both direction and displacement. Take a look at my poster presentation from this spring!

This year, I am looking at another two data sets from experiments conducted in Lower Matecumbe Key and Coral Gardens in the summer of 2020. In the end, I plan to combine them with the data set from last year to write up a manuscript for publication and my Departmental Honors project. Here is how we go about conducting the studies and analyzing the results:

We first set up the field experiment over the summer. The acoustic telemetry receptor array is set up first. Then, lobsters are caught and tagged before they are released either at their original den (control) or at another location (displaced). The lobsters are then left to move about for a period of about three weeks before the field study is concluded.

Then, we take the location data collected from the field study and organize it into an Excel spreadsheet. First, I cut the data to include only night time location points, from 10pm-10am, and I also cut out any data points in which the number of receivers that detected the tag is below 3 (this is because an accurate location cannot be triangulated without three receptors!). I make a separate CSV file for each day of movement for each lobster, and I upload each CSV into Google Earth to visualize the movement. In Google Earth, I use a color template to make the first point of the day red, all of the intermediate points orange, and the last point yellow. This helps me in making measurements in ImageJ!

Next, I upload the Google Earth images into ImageJ to measure the distance and angle of movement from beginning to end (red to yellow) and area of activity by making a convex polygon around the data points. Finally, with the distance and angle measurements, I create vector diagrams that compare the distance and angle displaced (black arrow) to the distance and angle of movement on the day following displacement (orange arrow) for each lobster. Perfect homing would be represented by an orange arrow pointing 180 degrees away from the black arrow and extending all the way to the border of the circle. As you can see in the above diagrams, the lobsters are pretty accurate!

We also create graphs and conduct statistical analyses on the distance and area of movement of control and displaced group lobsters on the few days following displacement. That is how we found last year that the control group lobsters moved in larger areas on the day following displacement, and that this difference was statistically significant.

You may be wondering, “So what does this all have to do with marine conservation?” Well, while lobsters have this ability to find their way back home if they are displaced, most other marine organisms do not. Therefore, anthropogenic disruptions to marine ecosystems are very detrimental. In addition, lobsters’ ability to home does not make them immune from disruption. If displaced too far from their home dens, perhaps by capture-and-release practices, they may not be able to find their way back. Also, even if they are not displaced, just being captured and handled stresses them out and causes them to move around more, as we found in last year’s study. Lastly, environmental disruptions such as man-made magnetic fields, such as those created by submarine power cables, can disrupt the mechanism by which lobsters navigate, discussed earlier, and negatively affect their ability to home.

Thank you for giving me the opportunity to tell you a little bit about the research I am working on! I am excited to see what this year has in store, and I am looking forward to giving some cool updates in the future! Until then, keep living like Larry :)