Morejón-Arrojo, Ramón D., Florian Lüskow, Alfredo Fernández-Alías, Humberto Ramírez, and Aldo Cróquer. "First Record of a Cannonball Jellyfish Bloom (Stomolophus sp.) in Venezuelan Waters." Journal of Marine Science and Engineering 13, no. 4 (2025): 689.

 What They Did

While on a diving trip off the coast of Venezuela, one of the researchers encountered several unusual jellyfish. These were photographed and identified as cannonball jellyfish, genus Stomolophus, and were found at eight other locations over 120 km of the coast. Observed population densities were about 3 jellyfish/m³. Based on information from local fishers and divers, the researchers determined that the population bloom had begun on March 5, 2024, and it continued through late April of that year.

They downloaded environmental data from monitoring organizations for the period from September 2023 to August 2024 and examined environmental conditions at the time the bloom occurred and the likely time of stroblilation (the process by which one or more immature free-living jellyfish bud off of a stationary polyp). The researchers found that the period of likely strobilation was correlated with decreasing water temperature, high chlorophyll a in the water, high rainfall, and low salinity. Cooler temperatures are known to trigger strobiliation, and the large amount of chlorophyll likely meant that food was abundant for the immature jellyfish. The large amount of rain could have increased nutrient runoff into the water, further increasing food availability, and also decreased the salinity.

It therefore seems likely that strobilation occurred between November 2023 and January 2024, as would be predicted from the time of the bloom.  The authors note, however, that polyps for this genus have not been observed in the wild, so it is also possible that the immature jellyfish may have migrated from elsewhere.

 

Further Exploration

I was surprised to learn that the polyps haven’t been observed in the wild. Apparently, members of the genus are bred from polyps in captivity (see https://www.raisingpetjellyfish.com/blue-cannonball), so we know they exist. Cannonball jellyfish aren’t typically found on the coast of Venezuela, however, being more common along the Gulf of Mexico and the southern Atlantic coast of the United States.

They’re frequently eaten in Asia and are becoming an income source for fishers during the off-season for vertebrate fish species. The jellyfish are typically sold partially dried, then soaked and rinsed before eating. They’re described as both crunchy and chewy in texture but lacking much flavor, instead absorbing the taste of any added sauces (see https://www.seaaroundus.org/magazines/2011/INFOFISHInternational_AreJellyfishTheFoodOfTheFuture.pdf).

The researchers suggest that the range of cannonball jellyfish might be increasing, possibly due to heating of the ocean: the Caribbean has warmed by 0.5 °C every decade since the 1980s, which would mean an increase of about 2.5 °C by now. That’s a scary statistic considering the U.N. goal of keeping atmospheric warming to 1.5 °C (see https://www.un.org/en/climatechange/science/climate-issues/degrees-matter.) Water has a higher specific heat than air, meaning it takes more energy to heat water the same number of degrees. The ocean has been absorbing a lot of the heat from the greenhouse effect (see https://unric.org/en/global-warming-90-of-emissions-heat-absorbed-by-the-ocean/), but it can’t do that forever, and doing so affects the ocean ecosystems. I’m not clear on how increasing the ocean temperature would expand the range of the jellyfish from cooler to warmer areas, but that’s a rabbit hole for another day!   

Image Credit: Cape Hatteras National Seashore, public domain

https://commons.wikimedia.org/wiki/File:Cannonball_jellyfish_washed_ashore_near_Ramp_59._It%27s_not_common_to_see_Cannonball_Jellyfish_around_this_time_of_year_-_this_one_may_have_been_cold-stunned._(51759006613).jpg