FASTFACTS

AREA COVERED:

0.3 miles, round-trip.

HABITAT:

Jellyfish Lake, Palau.

PREDATORS:

White sea anemone.

INDIVIDUAL HERD POPULATION:

13 million.

GOLDEN JELLYFISH IN-DEPTH

More from NationalGeographic.com

GOLDEN JELLYFISH (Mastigias papua)

The golden jellyfish is found only in Jellyfish Lake in Palau, an island nation near the Philippines. It technically belongs to the same species as the jellyfish found in nearby lagoons, but it has some key differences, including an almost complete lack of both spots and the clubs attached to the spotted jellyfish’s oral arms. One scientist has proposed designating it as a separate subspecies, Mastigias papua etpisoni. Golden jellyfish eat plankton, copepods, and fish larvae, but they also depend upon the algae-like zooxanthellae, which lives within their tissues and helps to nourish them. Though it has often been said, mistakenly, that the Jellyfish Lake is a predator-free environment, the endemic white sea anemone, Entacmea medusivora, has been observed eating jellyfish unfortunate enough to pass close by it.

In Jellyfish Lake, golden jellyfish migrate each day to follow sunlight, which they need to sustain the algae-like zooxanthellae in their tissues, upon which they partly depend for nourishment. They start in the western part of the lake at dawn and swim eastward toward the rising sun’s rays. After several hours, they reach the eastern rim of the lake, where they bask in the sun’s glow from midday. Then, in the afternoon, they follow the sun’s path westward, until they return to the spot where they began. The jellyfish tend to mass in spectacularly dense aggregations at the illuminated edge of shadows in the water.

Golden jellyfish’s role in the ecosystem is to contribute to the lake’s biomixing by churning the lake waters as they swim, which disperses nutrients. Scientists believe that the energy they contribute plays an important role in forming eddies, the ring-shaped currents that distribute nitrogen, carbon and other chemicals from one part of the lake to another.