A WSG-funded project unravels how moon jellyfish aggregations are causing ecosystem-wide impacts in Puget Sound
July 14, 2025
Seattle, WA – Moon jellyfish blooms are a stunning sight to see, their white and translucent colors making them appear light and delicate. However, these jellyfish are hidden predators lurking for their next meal. A research paper published in Marine Ecology Progress Series found that moon jellyfish (Aurelia labiata) are forming aggregations of thousands in Puget Sound during the summer months. Led by University of Washington oceanography graduate student Haila Schultz and funded by Washington Sea Grant, the study set out to understand the impacts moon jellyfish blooms have on zooplankton populations and the broader marine food web.
One focus of the study was copepods, a specific type of zooplankton (animal plankton). Copepods are integral to marine food webs, as they serve as a vital prey source for many fish species. The study sought to understand the dynamics of copepod populations by testing moon jellyfish predation and tracking oceanographic conditions. Through a combination of mesocosm (lab) and in situ (field) experiments, the researchers found significantly decreased copepod densities where jellyfish aggregated, demonstrating that jellyfish predation is a key driver of local copepod populations around jellyfish aggregations.
Moon jellyfish in Puget Sound. Photo by Haila Schultz.
The researchers also sampled microplankton and phytoplankton (photosynthesizing plankton), finding higher phytoplankton densities inside jellyfish aggregations. This finding suggests a potential trophic cascade effect: when the population of a predator impacts not only a prey species, but additional species as well. In this case, moon jellyfish reduce zooplankton, while phytoplankton populations increase from the lack of zooplankton predation. This directly interferes with local food webs and causes ecosystem-wide impacts.
The researchers seek to understand further ecosystem impacts by examining local fish populations. In collaboration with the NOAA Northwest Fisheries Science Center, the researchers plan to incorporate the study’s findings into NOAA’s Atlantis Ecosystem model to understand how fish populations, in particular forage fish and juvenile salmon, are impacted by jellyfish blooms. “Providing data to our collaborators for modeling is one of the best ways to predict ecosystem impacts. Setting up different future scenarios based on potential increases in jellyfish populations is the next important step to determine the state of future marine food webs,” explains Schultz.
Moon jellyfish aggregations have correlated with the warmer water temperatures associated with changing ocean conditions in recent years. For example, the “Blob,” as Schultz describes, was a short-term marine heatwave event that created a large mass of warm water in the Pacific Ocean. During this time, increases in jellyfish blooms were observed. This study helps to demonstrate the potential impacts of future ocean warming events like the Blob in Puget Sound and on a global scale. Increasing water temperatures not only help fast-growing jellyfish to thrive but place an additional stressor on zooplankton populations.
Future work on the project includes collecting more jellyfish samples to understand the spatial distribution of jellyfish throughout Puget Sound. “We found that most jellyfish aggregations were patchy throughout the Sound and need more data on the spatial distributions of jellyfish to understand how local environmental impacts scale up to regional impacts,” says Schultz. This research is important not only to scientists but also to local communities and Tribes throughout Washington who live among these moon jellyfish hotspots and their ecological impacts.
Learn more about the project here: wsg.washington.edu/research/26155-2-4/
CONTACT:
Haila K. Schultz, schulh2@uw.edu
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Washington Sea Grant, based at the University of Washington, helps people and marine life thrive through research, technical expertise and education supporting the responsible use and conservation of coastal ecosystems. Washington Sea Grant is one of 34 Sea Grant programs supported by the National Oceanic and Atmospheric Administration in coastal and Great Lakes states that encourage the wise stewardship of our marine resources through research, education, outreach and technology transfer.
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JUL
2025