food produced by tiny plants called zooxanthellae; zooplankton
average size is 4 inches (10 cm) in diameter, but can grow to about 12 inches (30 cm)
blue jelly; Family: Magistiidae
South Pacific Ocean, Hawaii and Puerto Rico
This species is also known as a "lagoon jelly" because it lives in bays, harbors and lagoons in the South Pacific. The spotted jelly has a rounded bell and four clumps of oral arms with clublike appendages that hang down below. Instead of a single mouth, it has many small mouth openings on its oral arms that capture small animal plankton. In addition, the jelly grows a crop of symbiotic algae in its tissues, which gives it a greenish-brown color and produces food for the jelly to harvest.
The number of spotted jellies in some lakes on Palau island (part of Micronesia in the Western Pacific) declined dramatically in 1998. After studying the lakes, scientists think the jellies disappeared because of changes in the lake water due to the very severe El Niño of 1997-98. The temperature of the lakes rose, as did the saltiness, creating an unhealthy environment for the jellies. By the year 2000, jelly numbers were on the rise.
Some of the larger spotted jellies actually have small fishes living with them. The fishes use the inside of a jelly's bell as protection from larger predators until they reach maturity.
During the day, the spotted jelly will travel upward, orienting its body to absorb maximum sunlight.