Jellyfish Lake

A marine lake on Eil Malk island in the southern Rock Islands, cut off from the sea since the last ice age and reached by a short climb over a limestone ridge from the boat landing. Snorkelers cross water thick with golden jellyfish (Mastigias papua etpisoni), an endemic subspecies that lost most of its sting in isolation and pulses across the lake each day to keep its symbiotic algae in sunlight. Moon jellyfish drift through the same surface layer. Scuba is banned: exhaled bubbles lodge under the bells and harm the animals, and a hydrogen sulfide layer below 15 m is dangerous to breathe near. Golden jellyfish numbers swing with climate, from tens of millions in good years to near total collapse and back.