The Golden Jellyfish of Palau, known as the “Jilly Bug,” is a unique marine creature found in the isolated waters of Jellyfish Lake. This species, Mastigias papua, is non-stinging to humans. Millions of these jellyfish inhabit the lake, a natural spectacle in the Pacific island nation.
Understanding the Jilly Bug
The Jilly Bug (Mastigias papua etpisoni) has a translucent, hemispherical bell, typically 3 to 10 centimeters in diameter. Its coloration varies from greenish-blue to olive green, often with yellow, white, or brown oval spots. This appearance is due to symbiotic algae called zooxanthellae.
These algae reside within the jellyfish’s tissues, performing photosynthesis to produce nutrients. This symbiosis provides a significant portion of its food, supplementing its diet of zooplankton. To maximize photosynthetic activity, the jellyfish undertake a daily migration. They follow the sun across the lake, moving horizontally and rotating their bodies for even sunlight exposure.
The Unique Habitat of Jilly Bugs
Jilly Bugs thrive in Jellyfish Lake (Ongeim’l Tketau) on Eil Malk island in Palau. This marine lake formed 12,000 to 15,000 years ago when rising sea levels isolated a limestone depression from the ocean. Connected to the ocean through underground fissures, the lake’s isolation created a distinct ecosystem.
The lake is meromictic, meaning its water is stratified into layers that do not mix. It features an oxygenated upper layer supporting the jellyfish, and a lower anoxic layer (around 15 meters deep) devoid of oxygen and containing high hydrogen sulfide concentrations. This unique, stable, and isolated environment contributed to the reduction or loss of the golden jellyfish’s stinging capabilities.
Interacting Safely with Jilly Bugs
Golden jellyfish in Jellyfish Lake are largely harmless to humans, a result of long-term isolation and reliance on symbiotic algae. Over millennia, in the absence of predators, they have significantly reduced their nematocysts (stinging cells). While some may retain a mild, often undetectable sting, it poses no threat to human skin.
Swimming with these creatures is popular, but responsible interaction is necessary to protect the delicate ecosystem. Visitors should move gently, avoiding aggressive splashing or sudden movements that could harm the jellyfish. Using reef-safe sunscreen or sun-protective clothing helps prevent harmful chemicals from entering the lake, preserving its pristine conditions.
Conservation and Environmental Factors
The Jilly Bug population, while abundant, is vulnerable to environmental changes. Significant declines have occurred, notably during strong El NiƱo events (e.g., 1998 and 2016). These events can lead to increased water temperatures and altered rainfall, disrupting the lake’s balance and affecting the symbiotic algae crucial for survival.
Despite severe decline, the population has shown resilience and recovered, often due to the survival of polyps in the lake’s deeper, more stable environments. Conservation efforts, including strict tourism regulations and scientific monitoring, protect this unique ecosystem. These measures safeguard the Jilly Bug population against climate change and other environmental pressures.