Jellyfish
Craspedacusta sowerbii
"Peach Blossom Jellyfish Clones"
On the topic of jellyfish in general, even a small amount of research produces a sense of awe for these small creatures. According to the website oneearth.org there are about 300,00 species of jellyfish and they have existed for some 700 million years. Comprised mainly of water and with no brain, their existence is summed up by "oneearth.org" in the following text excerpt:
“Before the dinosaurs, trees, or even fungi, there were jellyfish. They are the oldest multi-organ animal, surviving all five of Earth’s mass extinction events. “
Previously on this website information concerning the freshwater jellyfish in Hotel Lake was limited to an October 2020 article in the Harbour Spiel which you can now find in the library by clicking here.
This webpage presents information on this small freshwater jellyfish called Craspedacusta sowerbii or as it is more popularly dubbed: "Peach Blossom Jellyfish Clones”
To understand a bit more about the history and naming of this jellyfish we refer to the following explanation, quoted from a recent paper by Professor Evgeny Pakhomov and Dr. Florian Luskow:
"In ancient Chinese, there are four dialects or local names of FWJ [freshwater jellyfish]: 士淑水母: The pronunciation of this name is similar to ‘dead-water jellyfish’ in the Hangzhou dialect where it was found; 马鼻子 – Horse nose or horse nasal mucus; 桃花扇 – Peach Blossom Fan; 桃花鱼 – Peach Blossom Fish. The last one, 'Peach Blossom Fish' is the most common name. It is unknown who first coined these names. Old notes mention these FWJ were found at the time of peach bloom, and the jellyfish look like falling petals of the flowers. Kimura (1937) reviewed ancient Chinese literature – some dating back to the Song dynasty in the year 1250. Despite centuries-old written proof of existence, FWJ were kept aside as an 'abnormality' by many GZ researchers and limnologists."
The freshwater jellyfish, Craspedacusta sowerbii, is now thought to inhabit every continent except Antarctica. This jellyfish is indigenous to the Yangtze River Valley in China and experts theorize that it has made its way around the world on the hulls of boats, through aquarium dumping, in bait buckets and by hitching rides on stocked fish, aquatic plants, and even waterfowl. Because this tiny jellyfish has very little mobility in the water and spends most of its time slowly ascending or descending through the water column, it has been categorized as zooplankton.
In BC, sightings of freshwater jellyfish in lakes have been concentrated in the Lower Mainland and Vancouver Island areas. On the Sunshine Coast, the first reports of Peach Blossom Jellyfish Clones in Hotel Lake date back to 2001.
From here, we delve into the spread, and life cycle of the Peach Blossom Jellyfish as well as an update on current research efforts to understand its impact on our ecosystem.
Hotel Lake Jellyfish video taken in August 2024
The medusa feeds on zooplankton including water fleas and copepods. To catch and digest this prey, the jellyfish has tentacles lining the rim of the bell and a large stomach structure (manubrium) hanging down from the centre of the inside of the bell with a mouth-opening and four frilly lips. The many tentacles each contain thousands of cells called cnidocytes which are the source of barbs and venom. Dangling its tentacles, the jellyfish drifts along until prey touches a tentacle.The prey is then stung, paralyzed, coiled by a tentacle and brought to the mouth. Food is taken into the mouth opening, digested in the stomach and waste is finally expelled through the same opening. This sounds like a water fleas’ worst nightmare.
So, if freshwater jellyfish eat zooplankton, what eats jellyfish? It is believed that fish avoid jellyfish. Turtles and crayfish are mentioned as the only interested predators.
What we see in Hotel Lake in the warmth of July, August and September is the medusa, a whitish, translucent bell that is approximately one inch in diameter. Composed of at least 90% water the medusa have no lungs, heart or brain. Oxygen is absorbed through their thin skin. They have no blood for a heart to pump. The nerve net found just below the epidermis allows them to respond to changes in their environment.
A group of jellyfish, which can be in the thousands, is called a bloom, a swarm or a smack of jellyfish. Except for the warmest summer months, the freshwater jellyfish exists as a polyp found underwater attached to vegetation, rocks or even tree stumps. Often existing in small colonies, they are cylindrical in shape and look much like like tiny bowling pins. These “bowling pins” have one end fixed to the ground, and the other end extending up into the water with a ring of tentacles surrounding its mouth/anus. In this phase, the jellyfish polyp has a fully developed digestive system and is able to catch prey and feed itself efficiently.
According Professor Pakhomov: "Polyps are very small, usually around a millimetre in size, and it is challenging to locate them. They inhabit shallow areas and can be found on rocks and submerged wood debris. Hence, we usually know about jellyfish introduction when we see the floating medusa form produced by polyps appear in the water, which appear only when water temperature is higher than 21degrees Celsius —so polyps could be in many more lakes without us knowing about it. We do not know how and when introduction of the species occurred, but it was likely through medusa-producing polyps carried on recreational boats or on the bills or feet of birds when feeding.” It seems that locating polyps in Hotel Lake is the next big task, one that will advance our understanding of our local jellyfish.
In the coldest months of the year, or in other harsh environmental conditions such as drought, polyps can shrink into tiny dome shaped bodies known as podocysts. This resting, dormant stage allows jellyfish to survive detrimental conditions for lengthy periods and rebound when circumstances become more favourable.
Freshwater jellyfish have three major stages: egg, polyp, and medusa.
Sexual reproduction happens when medusae release sperm and eggs into the water. Asexual reproduction is more common and occurs when polyps “bud”. The complexity and adaptability of this life cycle play significant roles that contribute to 700 million years of survival for this resilient jellyfish. However, this life cycle still has a few question marks that we cannot answer. Future work and study in this area will likely provide greater understanding.
The tentacle’s stinging cells are used for paralyzing very tiny prey and have not been proven to have the capacity to pierce human skin. Recently concern has been expressed for allowing freshwater jellyfish to get close to our eyes (e.g accidentally being scooped up in googles) or near open wounds as has happened in a couple of incidents. On Vancouver Island, two children needed to go the hospital and undergo a week or so of antibiotic treatment.
Craspedacusta sowerbii and other freshwater jellyfish hold a place of special interest for the scientific community. Jellyfish are known as an indicator species, meaning changes in their populations represent greater changes in the ecosystem. Around the world today, jellyfish are thriving in record numbers.
A local zoologist Dr. Florian Lüskow, became interested in freshwater jellyfish when they were reported in Killarney Lake near Victoria. Later, working with Professor Evgeny Pakhomov at UBC the aim of their research was to understand the distribution and impacts of the jellyfish on lake ecosystems in B.C. An initial study analyzed polyp and medusa responses to different temperatures. In our library, you can read the article: “Increasing Temperature Facilitates Polyp Spreading and Medusa Appearance of the Invasive Hydrozoan Craspedacusta sowerbii “ by clicking here.
Recognizing that medusae bloom in the warmth of July, August and even September the possibility exists that climate change will affect both life cycle stages and their food web impacts. Luskow surmises that increases in temperature due to environmental warming “will favour the expansion of the species in the future to higher latitudes.”
Many researchers emphasize how much can be learned with help from citizen scientists who work under supervision to find and document samples and data. Even casual observers can share the place, time, conditions and if possible, even a picture of the jellies on iNaturalist.
Researchers lament that many questions remain and much is not known and just as important, “The ecological impacts of this non-native species are unclear”. Some of the questions revolve around the concerns that non-native species with few predators can outcompete the local residents for food. If these jellyfish were to cause a major decline in planktonic organisms, algae, and other organisms that form the basis of aquatic food chains, they might indeed have an indirect impact on populations of fish and other larger animals.
In the summer of 2022, we were seeing these jellyfish in Hotel Lake and decided to publish this webpage. We initially contacted Dr. Florian Lüskow at UBC for information. Over time, Dr Lüskow and Professor Evgeny Pakhomov, at UBC, outlined a research study of freshwater jellyfish that would require the help of local volunteers. We floated the idea and happily six local Hotel Lake volunteers came forward to assist in the summer of 2023. This project began with Dr. Lüskow and Professor Pakhomov visiting Hotel Lake to provide training to the 6 volunteers. The 2023 project involved 17 sorties out onto the lake to collect data and samples; these sorties dubbed “Stations” took place every 4 days. At each station volunteers conducted a number of measurements and sample-taking and associated processing for later analysis. In 2024, the local volunteers assumed the mantle: “Hotel Lake Stewards” and this project continued to evolve with new protocols. 2024 proved to be a very active year as a great many jellyfish samples and other data were collected. By 2025 we had 9 volunteers and were operating year-round with the addition of work towards a level-3 lake study for Min Env.
TROPHIC ECOLOGY OF THE INVASIVE FRESHWATER JELLYFISH
CRASPEDACUSTA SOWERBII, REVEALED THROUGH STABLE ISOTOPE
ANALYSIS
by
JOHANNA MARINA MARSHALL
We are very happy to be able to share a recently published (2026) thesis by Johanna Marshall, one of the UBC students who has been working on the Hotel Lake jellyfish research project.
Above, we add a few supporting charts from her thesis and below Johanna has graciously provided the following "Lay Abstract”. Johanna's thesis has been placed in our website's library where you can access it at any time, by Clicking Here.
Lay Abstract
Hotel Lake is home to many native plants and animals, but often hosts large blooms of the Peach Blossom Jellyfish (Craspedacusta sowerbii), a freshwater jellyfish considered invasive in Canada. Despite the high densities of jellyfish that often appear throughout the summer, very little is known about the role they play in the lake’s food web or the impact they have on native species. My research aims to answer two questions: What are the jellyfish eating, and which native animals are they competing with for food?
To investigate this, I collected jellyfish, zooplankton, stickleback, and larval midges from Hotel Lake throughout the summer of 2025. Then, I analyzed the ratios of naturally occurring carbon and nitrogen isotopes in their tissues. Moving up the food chain, isotope ratios change in predictable ways, which allows scientists to trace feeding relationships and map out food webs.
The results showed that Peach Blossom Jellyfish feed on zooplankton, as expected, but that they also consume tiny microzooplankton and small particles of algae and organic matter. This diet is distinct from that of sticklebacks and larval midges, which may allow them to coexist in Hotel Lake. By determining the role of Peach Blossom Jellyfish in the Hotel Lake food web, this research helps better predict their influence on the lake’s ecosystem.
Johanna
Research Poster
Craspedacusta sowerbii (Peach Blossom Jellyfish) study at Hotel Lake, B.C.
Presented in Cork, Ireland July 2026
In, July 2026, at the International Jellyfish Blooms Symposium in Cork, Ireland, a "research poster" was presented by UBC student, Dana Halay. This poster is based on 2023-2024 research conducted in a University of British Columbia study by Dana Halay, Johanna Marshall, Dr. Florian Luskow, and Dr. Evgeny Pakhomov (in collaboration with the Hotel Lake Stewards).
The research poster highlights some preliminary results of UBC's Craspedacusta sowerbii (Peach Blossom Jellyfish) study at Hotel Lake, showing that the jellyfish medusae may significantly reduce zooplankton abundance during high medusae bloom years. This has potential cascading trophic impacts on lower levels (zooplankton and phytoplankton) and upper trophic levels (freshwater fish, ex. Cutthroat trout).
This study also shows that the presence of jellyfish may impact ecosystem services for the local community through eutrophication (potential impact on swimming) and reduction of fish populations (impact on fishing). To view a high res version of this poster, click here:
2024 article by Invasive Species of BC: https://bcinvasives.ca/news/freshwater-jellyfish/
2022 article from Delta Optimist, Why climate change could mean more jellyfish for B.C. by reporter, Stefan Labbe.
2020 . October edition article from Harbour Spiel, titled: Local lakes Included in Study of Invasive Freshwater Jellyfish