Lagoon Jellyfish (Mastigias papua)

Mastigias jellyfish still possess stinging cells, but the lake-dwelling forms have a sting that is usually too mild for most people to notice. Sensitive swimmers can still experience irritation, so describing them as completely stingless is misleading.

They migrate through the lake while tracking sunlight needed by the symbiotic algae living in their tissues. This daily movement also helps them avoid shaded areas and parts of the lake associated with predators such as sea anemones.

They obtain much of their energy from photosynthetic algae living inside their bodies, but they can also capture small plankton. Sunlight is therefore central to both their behavior and their unusually productive partnership with algae.

They are an isolated lake population related to the widespread Indo-Pacific species Mastigias papua. Long isolation produced distinctive traits, and the Palau form has often been treated as a local subspecies rather than an ordinary open-water population.