The thimble jellyfish--unlike other jellyfish and most other creatures on Earth--has a "grocery store" of algae growing inside it. So why does it continually bother to shop for animal plankton?
Because it cannot live by photosynthesis alone, USC biologist Patricia Kremer reported last week at a meeting of the American Society of Limnology and Oceanography in New Orleans. Specifically, she said, the jellyfish cannot get enough nitrogen-containing compounds without consuming the plankton.
The thimble jellyfish is a pulsating drifter that thrives in the shallow sunlit waters off the Bahamas. Like sea anemones and reef-building corals, it has algae, single-celled plants called dinoflagellates, living symbiotically inside it. "The algae photosynthetically meet most of the thimble jellyfish's need for energy-producing carbon," Kremer said, "but animals also need nitrogen. It's essential for growth and reproduction."
Complete details of the thimble jellyfish's energy budget, she said, "would give scientists an understanding of why the creature does so well in its habitat" and will also help researchers learn "how ocean ecosystems work and how the various organisms adapt to their environment."