Story posted April 12, 2013
Chrstine Rholl presenting to other student fellows and Faculty advisors, July 2013 at the Coastal Studies Center
Continuing research by Tamara Perreault ‘12 and Julia Livermore ‘13, Christine Rholl ’14—a 2013 Summer Doherty fellow—hopes to better understand bioluminescent scale worms (Harmathoe imbricata) by testing their methods of survivorship against lobsters.
These particular scale worms are known for their reaction to predation. When in the presence of lobsters, the scale worms "will either flash, so their entire body will light up," Rholl explains, "or they will autotomize their scales and their tail and only their scales will light up and float around."
This bioluminescent display, and the particular randomness of the worm's autotomized floating scales, creates a decoy for the lobsters, oftentimes allowing the scale worms to escape the predators unscathed.
Rholl is trying to better understand the survivorship of these bioluminescent scale worms by replicating their light displays in the presence of both *blinded and unblinded lobsters to see if this affects their ability to catch the worms.
"Nocturnal predators" by natural design, the lobsters must be in completely dark conditions in order to evaluate the scale worm's survivorship and the effectiveness of their natural decoy when they self-autotomize. When blinded, the lobsters seem more likely to successfully prey on the scale worms. Without the natural light display of their autotomized scales, the lobsters are able to follow the chemical cues of the scale worms without being distracted.
Rholl has not had an easy time designing the experiment, or evaluating her findings.
"We can't have any extra light in the tank with the lobsters" Rholl explains, "they're nocturnal predators so they're in complete darkness."
Rholl’s biggest challenge so far has been replicating the exact darkness of a feeding lobster's natural environment while replicating the light display of the bioluminescent scale worms. First, in order to replicate the bioluminescent display, Rholl has programmed an LED light to display in a manner similar to the natural bioluminescence of the scale worms when their scales autotomize. Next, these lights will be introduced to the tanks containing both blinded and unblinded lobsters to test how each treatment (blinded or unblinded) affects the lobsters effectiveness at capturing their prey.
According to Julia Livermore’s research, the lobsters will be more successful at catching the scale worms when blinded because they will be responding instinctually, rather than being deterred by the natural decoy of the autotomized scales.
To test this finding, Christine explains, there needs to be no extra light in the tank with the lobsters.
"We found out that the backlight is not controllable." While her LED has been able to replicate the bioluminescent light display, the trials will not be valid if the backlight is present, as the lobsters will be able to see the prey.
Another hurdle Rholl has had to face are discrepancies between her findings and the findings of her predecessors. Livermore found that blinded lobsters were more often able to successfully kill their prey, whereas the unblinded lobsters would go after the decoy scales.
"So far, I haven't seen quite the same trends," Rholl explains. One possible explantion may be Livermore's small sample size. One main goal for me has been to finish up enough trials to make the research sample size big enough to make the findings statistically significant."
While there is still much to work through, Rholl’s research is on its way to offering a better understanding of the largely unknown behavior of bioluminescent marine life and the way their displays hinder or allow their survival.
Trevor Rivers, Doherty Postdoctoral Scholar in Marine Biology is Christine's advisor on this project. To learn more about this research, see Christine's presentation.
* The lobters were 'blinded' temporarily with nail polish that is shed during molting.