Moon Jelly Fish Bloom in Howe Sound & Deep Cove

In 2022 there was a significant moon jellyfish bloom in Howe Sound & Deep Cove, on the Pacific West Coast of Canada. The jellies stayed in the area for weeks and they grew to be bigger than dinner plates and hundreds of thousands deep. As a kayak instructor in the area for over 30 years I had never seen anything like it. 2022 was a "triple dip la nina" year where the northern hemisphere had three consecutive years of warmer than usual temperatures. Does increased jellyfish populations like in 2022 have a big effect on the population of zooplankton? It is my understanding that jellyfish are naturally resilient to climate change by being able to adapt to pollution, increased temperatures, and acidity. I wonder if large blooms of jellyfish will become the norm, and will this have a cascading effect on the sea life food chain in the future. Also, I am curious whether there have been similar jellyfish blooms in other parts of the oceans around the world?

LEO Network Says:

Thank you Desiree for sharing. Jellyfish blooms are a popular topic in LEO Network, and we are always interested in learning more. We have provided some similar observations from around the north, along with an analysis (below) and summary of the articles. We are also copying Dr. Tom Okey, a LEO Network member and Principal of Ocean Integrity Research, for his comments on this event.

Comment by Tom Okey:

One dynamic related to jellyfish blooms that does not appear to be covered in LEO observations thus far, but which Desiree alludes to, is interactions with fish fauna. Exploratory simulations that I conducted at the UBC Fisheries Centre in Vancouver using the Prince William Sound Ecopath with Ecosim food web model during 1998-1999 indicated that jellyfish populations can explode when multiple small pelagic fish ("forage fish") species are overfished, even without changes in oceanographic conditions that favor jellyfish blooms. These fish are considered competitors of jellies for zooplankton prey, but ichthyoplankton (early life) stages of many fish species are also consumed by jellies and fish. Consumption of ichthyoplankton by jellies would lead to alternate stable states dominated by jellies with very few fish if jelly blooms were not so episodic and spatially patchy. However, if ocean conditions do trend toward those that favor jellies over key interacting fish species, then yes it is plausible that those marine ecosystems would shift to more jellyfish dominated systems, espeically if such dynamics and trends are not accounted for by fisheries managers who would need to reduce or eliminate catches on small palagic fish species to increase the resiliency of these systems to regional trends in global environmental changes. A good literature has emerged on these topics related to jellyfish blooms since those early simulations, and the reader is encouraged to refer to those published scholarly journal articles for more information.

Pacific herring are famously overfished in BC, though DFO might deflect some blame to oceanography. Capelin, sandlance, surf smelt are otherwise forage fish in the region that could be adversely affected to industrial and city-related pollution in the Vancouver area. Mackerel are occasional visitors from the south when water warms (like this season), and they are voracious predators on the smaller forage fish species, and some life stages and species of salmon, which are forage fish species when small and outmigrating, and various other factors can affect their populations such as watershed health, adult escapement of fisheries. Anchovies show up episodically, but have also been much more abundant at certain points in the past.

Comment from GPT 5:

The related posts attached here show that large jellyfish aggregations—and their effects—have been observed in many regions and with multiple species, offering some context for your questions:

• Zooplankton and food-web effects: In the Sea of Japan, large Nomura’s jellyfish “consume large amounts of plankton,” and that post notes resulting declines in fish populations and damage to nets (Large jellyfish threaten fisheries in the Sea of Japan). While that is a different species and ecosystem, it illustrates a potential pathway by which high jellyfish biomass can exert strong grazing pressure on zooplankton with cascading effects.

• Possible drivers and whether blooms may become more common: Two posts link increased jellyfish presence to warm conditions and prey availability: increased sightings of moon jellies in Alaska were associated with “warm ocean temperatures and an abundance of zooplankton” (Alaska residents to see increased jellyfish sightings), and warming temperatures were suggested as a factor in more lion’s mane jellyfish in the U.S. Northeast (Jellyfish the size of dinner plates on Northeast beaches). At the same time, other posts emphasize that causes can be uncertain, with speculation ranging from changing currents to warmer water (Abundant Jellyfish Disrupt Commercial Salmon Fishery). Bloom-and-bust dynamics are also noted; a large bloom of northern sea nettles in Alaska was followed by a die-off, and NOAA reported shifts in jellyfish size classes in a regional ecosystem assessment (Large Northern Sea Nettle Die-off).

• Similar blooms elsewhere: Reports span the North Pacific, North Atlantic, and Nordic seas, involving moon jellies, lion’s mane, sea nettles, and Nomura’s jellyfish. Impacts range from stings and recreation concerns to fisheries disruption and even infrastructure problems (e.g., intake clogging at a power plant in Scotland) (Jellyfish attack nuclear power plant).

Related posts in context:

• Alaska residents to see increased jellyfish sightings — Moon jellies increased with warm ocean temperatures and abundant zooplankton in Juneau, Alaska (2019).

• Large Northern Sea Nettle Die-off — Bloom-and-die-off of Chrysaora melanaster in Alaska; NOAA noted shifts toward smaller-bodied jellies in a regional assessment (2019).

• Abundant Jellyfish Disrupt Commercial Salmon Fishery — High sea nettle abundance fouled nets and threatened boats in Sand Point, Alaska; causes uncertain, with speculation about currents or warmer water (2016).

• Jellyfish the size of dinner plates on Northeast beaches — Lion’s mane blooms on U.S. Northeast beaches; warming temperatures were suggested as a factor in increased spawning (2020).

• "Startlingly Large" Jellyfish Washes Up on Maine Beach — Very large lion’s mane observed in Maine; researchers note size variability and advise caution around stinging tentacles (2020).

• Manet invasion in the Oslo Fjord — Dense jellyfish affected swimmers and reduced shrimp catches in Norway (2020).

• Venomous jellyfish invading west Swedish beaches — Lion’s mane sightings increased along Sweden’s west coast, raising sting concerns (2025).

• Large jellyfish threaten fisheries in the Sea of Japan — Nomura’s jellyfish consuming plankton led to fish declines and gear damage; monitoring and mitigation efforts described (2021).

• Jellyfish attack nuclear power plant — Jellyfish clogged seawater intakes at a Scottish nuclear plant, disrupting operations (2021).

Taken together, these posts document that large jellyfish events recur across regions and species, with multiple hypothesized links to warm conditions and prey availability in some cases, uncertainty about drivers in others, and a range of ecological and human impacts noted in the observations cited above.