We use nets to catch jellyfish at 15 different stations equally spaced in the lake, from one end to the other. At each station, we drop the net to 15m, and slowly pull it up towards the surface to catch jellyfish. At the end of each run (all 15 stations), we count the number of jellyfish we caught and measure their bell diameter. We complete three runs in one day. We use the mean of our catch for the day, multiplied by the area of the lake, to estimate how many Golden jellyfish are in the lake.

The Golden jellyfish follow the sun. In the morning, the Golden jellyfish will swim from the west to the east. As the sun passes over, the Golden jellies will turn around and swim from the east to the west. This migration happens on sunny days, but on cloudy days, with no sun as a cue, the Golden jellyfish will not migrate and will be spread throughout the lake.

Another factor to consider is the time of the year, because the jellyfish respond to changes in the angle of the sun that changes as the Earth revolves around the sun. The general pattern is:
• October–March: Golden jellyfish migration will be closer to the south edge.
• May–August: Golden jellyfish migration will be closer to the north edge.
• April & September: Golden jellyfish migration will be towards center of lake.

One thing to look out for during the months of May–July: You can find the Golden jellyfish right next to the dock in the late afternoon, around 3pm.

Lake water temperature is the primary factor influencing Golden jellyfish abundance. When the lake starts warming up, fewer Golden jellyfish are present and bleached jellyfish are observed. Once the lake becomes too warm, no new jellyfish are produced, and the old ones eventually die. When the lake is cool, we see more smaller Golden jellyfish (0.5cm–2cm) in the lake.

Changes in weather and climate can affect the lake and the Golden jellyfish. Drought can increase salinity (how much salt is in water) in Jellyfish Lake. Heavy rainfall can a result in a freshwater lens from the surface to 5m, and with little to no wind, this can lead to an increase in water temperature at 6m. Wind energy can help cool the lake down. These changes in lake conditions can lead to changes in jellyfish abundance.

We use data on:

• • Temperature, salinity and oxygen of Jellyfish Lake and jellyfish abundance (collected during monitoring visits).
  • Rainfall and wind speed collected by our weather station on Ngeanges Island.
  • Lagoon water temperature and water pressure (proxy for sea level) collected by loggers in Malakal Harbor.
  • Season – time or month of the year.
  • 3 Month Forecast from Palau’s National Weather Service for predictions on rainfall, water temperature, and El Niño Southern Oscillation (ENSO) events (El Niño/La Niña).

Scuba diving in Jellyfish Lake is prohibited for visitor safety. Jellyfish Lake is a stratified lake, meaning its water column is made up of distinct layers that do not mix. The upper layer, from the surface to about 12 m, contains oxygen and supports the Golden jellyfish and other life. Below that, from 13 m to the bottom at 30 m, there is no oxygen. Instead, the deeper layer contains high concentrations of hydrogen sulfide, a deadly poisonous gas. Exposure to hydrogen sulfide can have adverse effects, including death at high concentrations. For this reason, visitors must stay above 12 m in Jellyfish Lake.

We can all do our part in protecting Jellyfish Lake, by doing the following:

• • • SUPPORT our monitoring research: your donations will help protect Jellyfish Lake!
    • Empty your pockets. Do not carry anything from the ocean into the lake, including rocks and shells.
    • Use reef-safe sunscreen and apply it 30 minutes before entering the lake.
    • Swim gently in the lake to make sure you do not damage the jellyfish.