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Aquarium of the Pacific - Online Learning Center - Species Print Sheet

Conservation Status:  Safe for Now

Climate Change:  Uncertain

Aquatic SpeciesSpotted Lagoon Jelly

Mastigias papua CnidariansSea jellies

spotted lagoon jelly | Robin Riggs
spotted lagoon jelly - popup
Robin Riggs

Species In-Depth | Print full entry

At the Aquarium

The habitat for our spotted lagoon jellies is in the Tropical Pacific gallery, where there is also signage about the golden jelly that inhabits Palau’s Jellyfish Lake.

Geographic Distribution

Lagoon jellies subspecies are found in the Indian Ocean, Red Sea, and China Sea to Japan and the Fiji Islands, and as far west as the Indo-Pacific. They were more recently in the southwest Atlantic Ocean.


These jellies live in lagoons, bays, and lakes, where they move in the water column to find light for their zooxanthellae.

Physical Characteristics

The bell of the spotted lagoon jelly has a translucent, hemispherical shape with eight oral arms that end in a club-like appendage. Instead of a single mouth, this jelly has multiple mouths on its oral arms. The mouths are on the clubs and along the length of the arm that is toward the bell. The arms hang down below the bell margin. The bell is usually greenish-blue to olive green with yellow, white, and/or brown oval, granular spots over the exumbrella. Color variation is attributed to the symbiotic zooxanthellae living in the gelatinous mesoglea between the bell’s exterior and interior layers.


Bell average diameter 10 centimeters (4 inches), but may grow to about 30 centimeters (12 inches). Oral arms total length can be about the diameter of the bell.


M. papua primarily derives energy from the carbon fixed by its symbiotic zooxanthellae. This energy is directly absorbed from the algae that live within the jellyfish’s tissues. About 30 percent of the jelly’s nutritional needs are obtained from prey it captures, such as zooplankton, phytoplankton, and tiny invertebrates.


The spotted jelly is a true jelly. It has a two-phased reproduction cycle, sexual and asexual. They also respond evolutionarily to their specific habitats. Medusas are either male or female. Breeding season is from May to June. Males release sperm that swim toward the eggs within the female where fertilization takes place. The female may brood the fertilized eggs in her brood filaments within the oral arms and disk until they hatch into free swimming planulae (larvae).

After hatching, the planulae search for a suitable hard surface to attach upside-down. The search can take a few hours or several days. The attached larva becomes a polyp that feeds on prey floating by until it grows large enough to reproduce asexually either by budding non-motile clones of itself, or going through strobilation, in which yellow-green ephyrae that will mature into adult medusae are produced. M. papua requires specific temperature, salinity, and exogenous cues for proper strobilation to occur. It can occur only during cooler water temperatures since warmer water temperatures cause the symbiotic zooxanthallae needed for energy to die.


The lagoon jelly’s primary source of energy is the zooxanthellae that live in its tissue; however, 30 percent comes from the prey it captures with its oral arms (most other jelly species use tentacles). The multiple mouths in the oral arms engulf the food that is then transferred to the gastovascular cavity via through its mouths on the oral arms and sends it to the body via canals along the arms.


The sting of an individual jelly is mild, but encounters with large aggregations may cause itching and burning for people who are more sensitive to their sting.

The spotted jelly has adapted its lifestyle to become a “sun worshipper” in order to give its symbiotic zooxanthellae access to the light needed for photosynthesis. The jelly moves up in the water column with the sunrise, and back down in the water column as the sun sets.


Longevity in the wild is estimated to be about three months.


These jellies saw a marked decline during the 1997-98 El Niño. Palau lake water temperature and saltiness increased, causing a massive drop in jelly populations. Even though medusae died, hardy polyps survived the event, enabling populations to start recovering in 2000.

Today there is concern about impacts of climate change and also the invasion of a non-native sea anemone (Aiptasia), with its mutualistic algae. The anemone, which preys on lagoon jellies, is flourishing in the shallower waters of Jellyfish Lake.

Special Notes

In 2003 scientists identified a population of lagoon jellies in a Puerto Rico lagoon and in 2009-2010 a population in a quarry in the Florida Keys. Records showed that both of these populations had been present for many years, as long as 20 years in the case of the quarry jellies.

There are considerable morphological differences among the many subspecies of lagoon jellies. Scientists use four main morphological features together with DNA analysis to differentiate between the subspecies: number and shape of the lappets (flaps) on the bell, length of the mouth arms relative to bell diameter, length of the arms terminal clubs relative to bell diameter, and color.