Since the 1997-1998 El Niño, Coral Reef Research Foundation has monitored the jellyfish population, weather patterns and water quality to understand how climate variation can affect Jellyfish Lake. The most recent 2015-2016 El Niño brought on a drastic change in the lake, leading to the disappearance of the golden jellyfish medusa population. During this time, CRRF has increased frequency of field additional instruments to monitor the lake on a finer time scale. This update covers data we collected from May-July 2017, as a follow up to the April 2017 update provide to Koror State Government.

Weather Programs

Rain: Rainfall from May-July 2017 ranged from 10-14 inches. Rain is very important for the lake as it helps to cool the lakes water and keeps the lake at a lower salinity than the ocean. It also washes important nutrients from the land into the lake.
Wind: Average wind speeds in May and June were 5-7 mph with a predominant east wind. In the first two weeks of July, Avergae winds were 6mph and shifting from easterly to westerly. In the last week, average wind speed has increased to 9 mph with a predominant west wind. Wind is very important for the lake because it helps the lake cool by mixing cooler, freshwater from the rain, mixes deep, warmer layers and also produces evaporative cooling. If the current weather condition (Strong winds with rain) continues, the lake temperature will decrease.

Lake Water Profile

Temperature: Average lake water temperature for 0-12m depth increased after March 2017, and stayed consistent at 32.1-32.7 degrees Celsius until July 2017. This average temperature is warmer than usual (31.5 degrees Celsius) for this time of the year, and is in art, due to the delayed westerly winds.
Salinity: Average salinity for 0-12mm has steadily decreased from the highest record of -31 ppt in April 2016, during the driest time of that year. Avergae salinity for 0-12m for the months of May-July 2017 was -29.5 ppt, which isw slightly higher than normal (28ppt).

Jellyfish Population

The golden jellyfish population remains low since March 2017. From May-July, we did not catch any ephyra, or baby jellyfish, in our net hauls, indicating that there has been no recent strobilation or production of baby jellyfish. During a swim around the whole perineter of the lake, Emilio Basilius recorded only 25 large golden jellyfish (5-23 cm in bell diameter) one positive update from our monthly monitoring is that two moon jellies (Aurelia sp. – 13 and 20cm diameter) were sightd; they have nt been recorded in OTM by us since 2009.


Since the drought in 2016, Jellyfish Lake continues to recover. Rainfall has added freshwater and nutrients into the lake. However, the delay in strong westerly winds has contributed to the water warm temperatures during May-July 2017, which in turn, affected the strobilation or production of Baby jellies. The golden jellyfish population has not increased significantly in the last three months, but the sighting of two moon jellies is positive news for a native species that has not been in jellyfish in the last eight years. The weather of the last week (strong winds) may help decrease lake water temperatures may decrease to levels favorable for strobilation. It may take 4-12 months before we see a significant increase in the golden jellyfish population, dependiing on thr weather and ocean temperature.                

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