I spent much of this week capturing video of Pleurobrachia. I ran into a slight road block early in the week when I realized that some of the Pleurobrachia I had collected where not in good enough shape to be videotaped. This was due to a large amount of parasitism by marine amphipods. I have since learned that there are two main species of amphipods that parasitize Pleurobrachia; Hyperoche mediterranea and Hyperoche medusarum (Laval 1980). I’m not completely sure, but I think the Pleurobrachia that I had were parasitized by H. mediterranea. I found that I could remove the parasites by careful pulling them off with forceps under the dissecting microscope, but this still left the parasitized jellies in bad shape. Of the five that were parasitized, only one retained its full swimming ability after the parasites had been removed. One died very quickly and the other three became largely inactive before eventually dying. This left me without four organisms that I needed to reach my intended sample size of 15 individuals. To remedy this, I went jelly fishing a lot this week. I learned from Marco, a Ph.D. candidate in the lab, that most jellyfish undergo a diurnal vertical migration in which they migrate to the surface at night. Therefore, I went fishing for jellies at night a few times this week and was able to collect the four Pleurobrachia that I needed. During these night fishing expeditions, I saw huge aggregations of another jellyfish called Clytia, which was amazing to witness.
In the end, I was able to collect video of all 15 Pleurobrachia in my sample this week, which is really exciting! Although, I am a bit sad that I won’t be collecting any more video of these wonderful organisms as I have quite enjoyed watching them swim. The next steps for me will be to collect raw data from all 15 videos, which I have already started, and then process that data to get the values that I can make into plots and other figures. Collecting raw data from the videos can be quite time consuming, especially the swim speed data, but I am hoping to get the data processed by the end of next week. If all goes well, I’ll soon be running statistical analyses on the data and will have some cool graphs to show y’all.
The data for my main question is coming along nicely, so I’ve been able to start working on some of the sub questions that I am interested in addressing during my project. In addition to looking at how beat frequency affects swimming speed of Pleurobrachia, I also want to address whether the ratio between body size and the length of the ctenes, as well as the ratio between body size and the spacing of the ctenes, is consistent across the size range of these organisms. I have been measuring the body length, the average length of the ctenes, and the average ctene spacing for each organism in an effort to investigate that. I think this data will give some valuable insight into how Pleurobrachia are able to maintain swimming performance across their size range. I am also interested to see whether there is a consistent inflection point on the ctenes and how the feathering of the ctenes contributes to swimming performance. I have been collecting data on where the average inflection point occurs, as a percentage of total ctene length, for each organism. I also have been collecting stills of ctene feathering over the course of a beat to illustrate my descriptions of that aspect of ctene movement.
Top Row: Stills showing how feathering of the ctenes changes over the course of a beat. Bottom Row: Stills indicating approximate inflection points on two ctenes.
Furthermore, I am interested in collecting some observational data about how the ctenes behave during forward swimming, reverse swimming, and turning. There isn’t much in the literature that describes how the ctenes move during the various swimming behaviors of Pleurobrachia so I hope to describe that aspect of their swimming in detail.
Thanks for following along with me on this journey so far. I have made a lot of progress during this past month and I’m excited to start sifting through my data to see what I can learn about Pleurobrachia swimming performance.
Laval, P. (1980). Hyperiid Amphipods as Crustacean Parasitoids Associated with Gelatinous Zooplankton. Oceanography and Marine Biology: An Annual Review, 18(1), 11-56.
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.