I’d like to start this week by telling you a bit more about the details of my research project and the direction that it is currently heading. Last week, I mentioned that I would like to study to what extent the beat frequency of the comb rows determines the swimming speed of Pleurobrachia. I am interested in studying this primarily because it seems to be a fundamental aspect of this organism’s swimming performance, however, the previously published research on Pleurobrachia does not, to my knowledge, address this topic. How beat frequency affects Pleurobrachia at the level of the comb plates has been well described, for example we know the relationship between beat frequency and the angular velocity of a comb plate (Barlow and Sleigh 1993) as well as the relationship between beat frequency and the power output of a comb plate (Dauptain et al. 2008). However, I have not seen any empirical data that shows how beat frequency affects Pleurobrachia at the level of the organism. I hope to address this gap in the literature by assessing the relationship between beat frequency and swimming speed.
This week I have been focusing on designing an experimental setup and protocols to address my primary research question. I have collected 15 Pleurobrachia using a combination of plankton tows and dipping them from the surface. They have since been living happily in the sea table in our lab.
I am using what is called a dark field setup to take high speed video of my jellies. This setup involves a dark room and a camera pointed at a glass tank containing a solitary Pleurobrachia. Behind the tank is a light absorbing cloth and the tank is illuminated from the top by fiber optic lights.
This allows the camera to capture a clear image of a translucent organism, such as Pleruobrachia. Using this setup, I can zoom in on the organism and take video in 60 frames per second that has a high enough resolution such that the comb plates are well resolved. I can then view the video frame by frame using a program called ImageJ. Viewing the video frame by frame allows me to manually count the beat frequency of the comb plates over a certain length of time. ImageJ also allows me to measure the dimensions of the organism’s body as well as the distance that the organism moves from frame to frame. Knowing the distance the organism moved between frames and the time between the frames gives me a measurement of swimming speed since velocity is simply distance over time.
I am currently planning to take two 15 minute videos of each jelly that I have. Each video will give me 15 measurements of beat frequency and swimming speed, so a total of 30 measurements per organism. Now that you have the details, I hope you will enjoy looking at some test stills that I shot this week. The comb plates are iridescent, which makes these jellies look quite beautiful when they move. It’s hard to get a camera to focus on a translucent organism so please excuse any blur.
Barlow, D., & Sleigh, M. A. (1993). Water Propulsion Speeds and Power Output by Comb Plates of the Ctenophore Pleurobrachia Pileus Under Different Conditions. Journal of Experimental Biology, 183(1), 149–164.
Dauptain, A., Favier, J., & Bottaro, A. (2008). Hydrodynamics of ciliary propulsion. Journal of Fluids and Structures, 24(8), 1156–1165. https://doi.org/10.1016/j.jfluidstructs.2008.06.007
My name is Wyatt Heimbichner Goebel and I am a marine biology major at Western Washington University. I love biology, specifically marine mammal ecology and biomechanics. I’m always up for conversations about music, poetry, and weird biology facts.