Jellyfish Lake is connected to the ocean through fissures and tunnels in the limestone of ancient Miocene reef.
However, the lake is sufficiently isolated and the conditions are different enough that the diversity of species in the lake is greatly reduced from the nearby lagoon. The golden jellyfish, Mastigias cf. papua etpisoni, and possibly other species in the lake have evolved to be substantially different from their close relatives living in the nearby lagoons. – Zack Travel
Two species of scyphozoan jellyfish live in Jellyfish Lake, moon jellyfish and the golden jellyfish.
The moon jellyfish were identified as Aurelia aurita by Hamner. Addition to the three species of Aurelia there are at least six other cryptic species in the Aurelia genus. Three of the cryptic species identified were from Palau. One of these cryptic species is common to four of Palau’s marine lakes with jellyfish populations including Jellyfish Lake.