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In February 1976, I lucked into an assignment in Australia for Eastman Kodak. En route, I stopped in Auckland, New Zealand, to visit the local operations. My host invited me to sail in the harbor, with plans for a swim and a cookout. The swim was abruptly canceled when we looked overboard to see the water covered with thousands of moon jellyfish.
Fifty years later, beachgoers in Casco Bay are witnessing a similar, albeit more alarming, natural phenomenon. Large, rust-colored jellies have been spotted in our waters and on our shores. From 5-foot-wide specimens reported on Willard Beach in South Portland to 18-inch specimens my wife photographed while kayaking near the Salt Cod Cafe, the lion’s mane jellyfish (Cyanea capillata) is making its presence known.
The largest jellyfish species on Earth, the lion’s mane is a marvel of biology. It is an apex predator, an essential link in the northern ocean’s food web, and a key indicator of how oceans are affected by climate change. It is named for its cluster of trailing, hair-like tentacles and frilly, dark-brown oral arms, which resemble a lion’s mane.
These jellies are adapted to cold water, and their size varies dramatically depending on where they live. In the frigid, nutrient-rich waters of the Arctic Ocean, the bell of a lion’s mane can reach 8 feet in diameter, with tentacles extending up to 120 feet — longer than a blue whale. In warmer latitudes, their bells rarely exceed 20 inches. Young jellies are pink or yellow, gradually darkening into brown, orange and crimson as adults.
The lion’s mane has a complex, biphasic life cycle that alternates between a bottom-dwelling (benthic) asexual phase and an open-ocean (pelagic) sexual phase. Despite living just one year, they achieve incredible size. Adult females, known as medusae, brood fertilized eggs in their frilly oral arms. Upon hatching, the tiny planulae drift to the ocean bed and attach to hard surfaces.
The planulae transform into sessile polyps and feed upon zooplankton. The polyps can persist on the seabed for multiple seasons if environmental conditions are unfavorable. With seasonal temperature changes, normally arriving in early spring, the polyp begins to segment. The segments separate into star-shaped juvenile jellyfish.
The jellies consume huge quantities of food to transition into the free-swimming adult medusa stage by summer. While the lion’s mane can move by pulsating in the water (jet propulsion), its movements are dictated by the sea.
The thick web of sticky tentacles functions as a drift net to collect food — a mix of zooplankton, fish and fish eggs, plus other jellies. When prey contacts a tentacle, microscopic stinging cells called nematocysts discharge a paralyzing cocktail of neurotoxins. The jellyfish’s highly maneuverable oral arms then sweep the prey into the mouth on the underside of the bell.
Conversely, the massive bell of the lion’s mane may shelter marine life. Fish species such as cod and butterfish have a natural immunity or manage to avoid the tentacles and avoid other predators.
Lion’s mane jellies are a primary food for leatherback sea turtles. These reptiles migrate thousands of miles to gorge on jellyfish blooms, keeping the jelly population in check.
Lion’s mane venom is rarely fatal to healthy individuals, but a sting is painful and can cause redness, severe burning, cramping and respiratory distress in sensitive or allergic individuals. In extreme cases, it may cause anaphylactic shock, loss of consciousness or cardiac distress that could lead to drowning.
Please note that detached tentacles or dead jellies on the beach can still sting. The nematocysts remain active even days after the jellyfish has died or dried out.
If you are stung, safety guidelines suggest scraping off any remaining tentacle fragments with a clean object (like a plastic card), rinsing the area thoroughly with water, and seeking medical attention if serious symptoms develop.
While rising ocean temperatures threaten the survival of many fish, corals and marine mammals, research indicates that jellyfish may prosper as climate change continues on its current arc. The Alfred Wegener Institute developed computer models that project lion’s mane jellyfish nearly tripling their habitat range since they thrive in low-oxygen waters. This allows them to outcompete fish that struggle in such ocean conditions.
The lion’s mane jellyfish is a beautiful and complex inhabitant of our coldest seas. From its dual-phase life cycle to its ecological role as both a lifeline for juvenile fish and a feast for endangered sea turtles, it illustrates the intricate balance of cold-water marine environments.
