Pacific sea nettles off the coast of Carmel, California

An illuminated bloom. Pacific sea nettles off the coast of Carmel, California, USA

Jellyfish may be observed in all the world's oceans in an array of shapes and sizes. There are about 2,000 different species of jellyfish, and they all lack hearts, bones and brains. Pacific sea nettle jellyfish, seen here, are known for their vibrant golden-brown bell and long tentacles, and inhabit the coastal waters of California and Oregon. Moon jellyfish are pale and have short tentacles, and in an unexpected but somewhat appropriate twist, they ventured into space aboard the space shuttle Columbia in 1991 to help scientists study their unique biology. No matter the species, jellyfish play a vital role in the ocean's food chain, as they are the primary food source for many seawater animals, including sea turtles. Jellies are threatened by climate changes, marine pollution and overfishing, and damage to their populations has reverberating effects on the sea life that depends on them.