If you have ever been snorkeling in Florida or the Caribbean, or pretty much any warm shallow tropical or subtropical water, you may have been lucky enough to see the charming and eccentric upside-down jellyfish (Cassiopea spp.). Unlike most jellies, these animals sit bell-side down on the sandy or rocky bottom and raise their oral arms into the water column. Cassiopea have a symbiotic relationship with microscopic algae called Symbiodinium, which typically live within the tissues of the animal. This symbiotic relationship allows Cassiopea to get the majority of its energy and nutrition from the sun, but they retain their ability to capture prey using stinging cells, called nematocytes, which are found within all cnidarians (jellies, sea anemones, corals, hydra, etc). Their sting is fairly mild to moderate for humans, but can be painful depending on various environmental factors yet to be established.
For instance, if you have been a less than fortunate snorkeler, you may know you don’t need to touch these adorable jellies to feel their sting. Through a phenomenon known as “stinging water,” Cassiopea jellies release mucus full of stinging cells into the water column.
Despite the unusual, indirect sting mechanism noted by frequent mangrove snorkelers, there is no formal description of the stinging contents of this mucus or the ecological role it might play. This raises numerous interesting questions about this unique behavior. What types of stinging cell types are present in Cassiopea mucus? How concentrated are the stinging cells in the mucus? And how do they get embedded in the snot?
A team of researchers and volunteers in the AquaRoom (wet culture lab) of IZ have been trying to answer these questions over the past few years, and we have discovered something totally unexpected in Cassiopea mucus: strange microscopic structures composed of nematocytes. No information about these odd structures could be found in the current literature, only anecdotal reports noted in tourist guidebooks about stinging water in mangroves, where these jellies are commonly found. Our initial questions were soon replaced with new ones. What are these structures and what other kinds of cells are they composed of? What is their function? How are they made? And in terms of stinging power, how potent are they?
For answers to most of these questions, stayed tuned for a scientific publication we are preparing on these novel structures comprising Cassiopea mucus!
What I can share now, however, is a little bit of the analytical techniques I learned during the month of July. I proposed to complete ultrastructural analyses (using various forms of microscopy to determine what cells types and cellular components were present or absent in the mucus) coupled with functional analysis (determine various activities of the stinging components in the mucus) in order to infer how this mucus might be used in the jellies’ environment. For the ultrastructure, I was trained on the epifluorescence scope at the NMNH by Scott Whittaker, manager of the SEM Imaging Lab. Using a newly developed microfluidic device, I could image and observe the contents in a more holistic context, and reduce some of the potential resolution issues inherent in trying to image mucus squashed onto a slide. I could also introduce brine shrimp into these chambers to see how they behaved in the presence of the stinging snot.
If you go back to the anecdotal reports of Cassiopea stinging mucus, there are two claims that are largely assumed: 1) the mucus contains stinging cells (as opposed to soluble proteases or other toxins) and 2) the mucus appears to be used both in predation and defense. Our findings corroborated that the mucus itself does contain large, penetrant stinging capsules with barbed shafts and long threads. These capsules are called rhopaloids, because they have a distinct, barbed shaft, e.g., birhopaloids have two distillations, or bumps, along the shaft, while euryteles have only one. Rhopaloids range from 8-15 um long, or 8/100ths to 15/100ths of a millimeter.
In the mucus, I often found these cells in groups of 3-4, some discharged, others not. Finding these stinging capsules in both states is important, since it could be argued if all of the stinging cells were in their discharged state, these stinging capsules could simply be ejected from the tissue after being fired. This would mean the stinging of the mucus is an artifact of discarded stinging cells that may release some of the toxic contents instead. Since we also find undischarged capsules seemingly stuck in the released mucus, these capsules have the potential to envenomate prey and predators when encountered some distance from the jellyfish that produced them.
It is also interesting to note that I mainly found large penetrant capsules in the mucus, and just a few of the two other types of Cassiopea stinging capsules: O-isorhizas and a-isorhizas. These nematocyst types are generally smaller, do not have a barbed shaft, but are found throughout the tissue of Cassiopea. This may suggest an adaption to releasing these larger stinging cells over the others, but the reasons are not totally clear. Do these larger penetrant cells have different toxins that are absent in the other stinging cell types? The variation in venom profiles of different stinging cell types is another major question I hope to address in future research. For more photos of some of the stinging cells I have been imaging, check out my blog post: Stinging Cells from the Summer.
In all of my excitement, I never introduced myself! That tends to happen when you get me started talking about jellyfish and venoms. My name is Anna Klompen, and in the fall I will begin my second-year as a graduate student in Ecology and Evolutionary Biology at the University of Kansas in Dr. Paulyn Cartwright’s lab. I have been fascinated with jellyfish for almost a decade now, and feel extremely lucky to work with these animals. I am interested in venom evolution and diversity within jellyfish, and the relationship between venom composition, function and the ecological roles these venoms play within the complex life histories of many cnidarians. The start of my jellyfish research career actually began here at the NMNH two years ago as a NOAA Hollings Scholar. It was even in the same lab I am working in now, supervised by Dr. Allen Collins.
Now as a visiting scholar, I have returned to this project that was started two years ago with several high school interns I worked with in the AquaRoom. I have loved being able to spend my July exploring a new jellyfish system, learning new techniques in microscopy, and working in the museum I loved two years ago.
This research was completed under a Visiting Researcher Fellowship at the National Museum of Natural History, Smithsonian Institution. The project was funded by the Lerner-Gray Memorial Funding for Marine Science from the American Museum of Natural History and a Graduate Studies Research Support Award from the University of Kansas. A huge thank you to Dr. Cheryl Ames, NRC Postdoctoral Fellow, for the mentorship on this project, as well as Kade Muffet and Mehr Kumar, who began this project as high school interns in 2016. And for all the laughs and jellyfish nerdiness, thank you to everyone in the AquaRoom this summer for making me so happy to be working on these adorable animals!
By Anna Klompen
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