Local Species: Moon Jellies

This post is part of an occasional series on local marine species compiled and photographed by New England Aquarium aquarist Peter Gawne. When he's not diving locally for these posts or researching coral reefs in Belize, Peter takes care of the touch tank's sharks and rays and the jellies exhibit.

Moon jelly (Aurelia aurita) can be found off the New England coast.
They belong to the phylum Cnidaria, and the class Scyphozoa.

Moon jellies are found throughout the Atlantic Ocean, and are a common sight in New England waters. Like all cnidarians, moon jellies possess stinging cells (nematocysts), but the sting of moon jellies is mild enough to be imperceptible to most humans. Moon jellies are comprised of 95 percent water, and lack anything resembling a heart or brain.  Despite their lack of substance, moon jellies are carnivorous, and use their fine, fringe-like tentacles to capture prey and transport it to their oral arms for digestion.

Moon jellies provide a source of food for a variety of animals, including sea turtles, ocean sunfish, other jellies, birds, and even humans.  Jellies, including moon jellies, have long been on the menu in Asian cuisines.  The United States helps to satisfy the demand for edible jellies, which are dried and then cut into noodle-like strips.  Following the first official commercial season in 2013, jelly fishing became the third largest fishery in the state of Georgia.  Commercial plants in Georgia are able to process more than 5 million pounds of jellies per week.  The entire catch is exported to Asian markets.

The life cycle of moon jellies is similar to that of most scyphozoan jellies, but that makes it no less extraordinary.  Adult moon jellies are either male or female, with the occasional hermaphrodite.  The males release sperm strands, which are ingested by female moon jellies.  Once ingested, the sperm strands fertilize the female's eggs.  These two genetic-halves combine, resulting in a planula.  Unlike most scyphozoan jellies, which simply release their eggs into the water column, female moon jellies brood planulae beneath their oral arms.  Once the planulae are fully formed, they are released from the brooding sacs to swim, via small hairs called cilia, until they reach a suitable substrate.  When a spot has been found, the planula hooks onto the substrate, and begins its first metamorphosis into a polyp.

Tiny moon jelly polyps cling to a rock. The polyp farthest to the right is in the initial stages of strobilation.

Polyps are the benthic (ground-associated) stage of the jelly life cycle. Jelly polyps resemble the adult form of their relatives, sea anemones, in that they possess a point of attachment to a hard surface, and a crown of tentacles at the opposite end. Polyps can survive months or even years, by using their tentacles to capture small prey from the water column.

When environmental conditions are right, a metamorphosis begins with a process called strobilation. The strobilating polyp begins to undergo morphological changes, where the animal’s body becomes segmented, transforming it into a sequence of disks.  Each of these segments will eventually detach from one another and become a free-swimming phase, called an ephyra.  Thus one polyp can generate multiple free-swimming individual animals.  Typically, a portion of the polyp remains adhered to the seafloor, where it regenerates the body and prepares to strobilate anew.

Pictured above is a moon jelly ephyra cultured at the New England Aquarium. A 2014 National
Institute of Health-funded program made advances in tissue engineering by emulating jellyfish
ephryae cultured at the New England Aquarium (original study, video).

The ephyra is the free-swimming precursor to the final stage of the jelly life cycle.  Ephyrae pulse about through the water column, capturing prey, and growing.

Showing up in staggering numbers, smacks (a term for a group of jellies) of moon jellies can dominate New England harbors and estuaries in the summer months. The benthic polyp stage slows or becomes dormant during the coldest months of the year. Water temperatures, sunshine, and plankton increase in the spring, propelling the polyps into action. The polyps, all driven by the same environmental cues, begin to produce ephyrae en masse.  This mass influx of jellies into the environment often leads to incredible “blooms” of jellies, where thousands of adult jellies can be found in huge aggregations.

In a matter of weeks to months, the ephyrae will have grown, and gathered enough energy, to develop into their adult form—the medusa. The jelly medusa is final phase of the jelly life cycle, and the most recognizable form. These adult jellies will drift though the seas for up to a year or more, reproducing and beginning their extraordinary life cycle anew.

Large plastic sheets are kept as optimal growth sites for moon jellies at the New England Aquarium. 

Not all ephyrae released from polyps become juvenile jellies; some may drop to the sea bottom and develop into new polyps, which will eventually bud off their own ephyrae. Before strobilating, and when conditions for growth are good, polyps may bud off new polyps. Polyps may live for years, so densities in areas favorable for growth can be quite high.  It should be noted that all polyps are either male or female, and all ephyrae produced from a single polyp are genetically identical, and thus the same gender.

Each year, New England Aquarium staff culture and raise thousands of sea jellies. They can be found on display at the New England Aquarium’s Jellies exhibit. In 2014 alone, the New England Aquarium supplied more than 1,000 jellies to other public aquariums around the globe, including institutions in Las Vegas, Dubai and Australia.

Learn more about moon jellies:

• Here's a primer: Sea Jellies 101
• Read the species profile of moon jellies
• Flame jellies debuted at the Aquarium this winter 
• These tiny jellies are springtime visitors to Boston Harbor 
• What do jellies eat? Sometimes other jellies