As spring edges closer to summer, residents, cottagers, and visitors dream about summer days, swimming and boating under a blue sky with the sun shining. Most likely, those daydreams do not include sharing the waters with tiny little jellyfish. But whether you have seen them or not, they swim among us!
First reported in the Great Lakes around 70 years ago, peach blossom jellyfish or common freshwater jellyfish (Craspedacusta sowerbii) are an introduced species to North America (and to many other parts of the world). While most jellyfish species are marine dwellers, peach blossom jellyfish are one of just a few species of jellyfish in the world that live in freshwater.
International Traveler
Peach blossom jellyfish are indigenous to the Yangtze River Valley region of China, where they inhabit shallow freshwater pools and slow-moving waters. Having spread from their native range, peach blossom jellyfish have now been found on every continent except Antarctica. In North America, they can be found in calm, shallow waters, such as lakes, reservoirs, man-made impoundments, and algae-filled ponds and rivers.
The pathway for their spread is unknown, but there are many possibilities. Likely modes of transport include in bilge water, in bait buckets, attached to boats, on the feet or bills of birds, and/or transported on ornamental aquatic plants. No matter how they travelled here, it is likely that they spread while in their polyp lifestage.
The diagram below from Winata et al. (2024) shows the complex life cycle of peach blossom jellyfish: (A) Mature medusae; (B) planula larva; (C) primary polyp; (D) two-polyp colony; (E) polyp budding medusae; (F) frustule; (G) podocyst. Learn more by reading the open access article, “Life Cycle Transitions in the Freshwater Jellyfish Craspedacusta sowerbii”.
During their polyp stage, peach blossom jellyfish are only about one millimeter in size, making them very difficult to detect. Polyps are easy to accidentally transport, as they attach themselves to surfaces such as submerged wood debris, rocks, and aquatic plants. In addition, polyps spread rapidly, reproducing asexually to form colonies of 2-12 polyps.
As an added challenge, polyps can enter dormancy as resting bodies called podocysts. Podocysts form a protective membrane which allows them to survive extreme conditions. When conditions become more favourable, the podocysts turn back into polyps, which can then bud into medusae (jellyfish). It is usually not until they bud into jellyfish that peach blossom jellyfish are detected. They can remain undetected in waterbodies for years as polyps.
A Rare Sight
While easier to detect than polyps, adult peach blossom jellyfish are still a rare sighting in the Great Lakes region. Medusa blooms (the sudden appearance of lots of jellyfish) typically occur in late summer to early fall, when waters warm up. But warm temperatures alone do not always result in jellyfish blooms. The exact combination of environmental factors that trigger polyps to bud into medusae is still unknown. Furthermore, they only live for one to two weeks in their adult life stage.
How Do I Look?
In their adult medusa stage, peach blossom jellyfish are only about 5-25 mm in diameter and are translucent with a white or greenish tinge. They have five opaque-white canals and a variety of long and short tentacles. They use their shorter tentacles to eat and their longer tentacles to provide stability while they swim. The number of tentacles varies, but one jellyfish can have over 500 tentacles!
The good news is that these tiny jellyfish are not a threat to people, as they are too small for their stings to pierce human skin!
More Research Needed
Not much research has been done yet in Canada on their ecological impacts. Studies in the United States have not yet found significant ecological harm from peach blossom jellyfish. As medusae, they eat mostly zooplankton (tiny floating aquatic animals, such as copepods). It is possible that large blooms of jellyfish could have cascading impacts on aquatic ecosystems if they were to compete with native species for zooplankton. More research is needed to determine the extent of the spread of peach blossom jellyfish and their potential impacts.
Report Your Observations
If you spot jellyfish in Georgian Bay or any other waterbody, the best thing you can do is snap a picture of them and report your observation to iNaturalist.org. iNaturalist is a free community science database that shares observations of plants and animals with researchers around the world. Reporting observations to iNaturalist will help researchers to properly map the distribution of peach blossom jellyfish, so that they can better understand their impact on freshwater ecosystems.
You can help prevent the spread of peach blossom jellyfish and other non-native aquatic species by always making sure to clean, drain, and dry your boat! Follow these tips from Invasives Canada:
CLEAN: Inspect your boat, trailer, paddles, fishing gear, and boots for mud, plants, or small critters. Remove and dispose of anything you find before leaving the water.
DRAIN: Empty all standing water from your boat, live wells, ballast tanks, bilge, and gear. Even tiny droplets can transport microscopic invaders!
DRY: Let all equipment dry completely between trips. Sun and air naturally help eliminate aquatic invaders before they spread.
