Marine Lakes Research

Our ongoing research is looking at the effects of natural climate conditions and hundreds of tourists entering Jellyfish Lake daily.


Our current marine lakes research program began in 1994 when CRRF started working in Palau and graduate students of Bill Hamner (UCLA), Drs. Laura Martin and Mike Dawson, were carrying out their PhD research here at the same time.  Overall the program emphasizes the origins, ecology, and evolution of marine lakes, including how their species vary through time due to regional variation in the ocean and climate. This research became particularly important when the jellies in Jellyfish Lake disappeared in 1999 following a strong El Niño, and continues as we have documented extreme changes linked with the 2015-2016 El Niño and put these in the context of longer-term dynamics.

At monthly intervals since 1999 the Coral Reef Research Foundation (CRRF) has been monitoring the physical characteristics of Jellyfish Lake, such as water temperature, salinity, and oxygen, and estimating the number and sizes of golden jellyfish, to understand how the physical conditions can affect changes in the jellyfish population. Tide gauges, temperature sensors and instruments that measure water movement have also been deployed in the lake to try to understand how the lake heats up and cools down. Because atmospheric conditions can also affect physical conditions of the lake, weather stations have been installed.  With 9 years of funding from the David and Lucile Packard Foundation (2006-2015), and the approval of the Koror State Government, CRRF installed a temporary weather station on the surface of the lake to compare the lake’s weather with lagoon conditions recorded on nearby Ngeanges Island. These two stations, complementing several run by other groups archipelago-wide, allow us to understand how climate influences regional weather patterns and how these influence the lake. This ‘longitudinal’ study of Jellyfish Lake is complemented by biotic surveys of Jellyfish Lake and other marine lakes in Palau that allow a glimpse of how lake communities differ from one another, and what physical characteristics contribute to these differences.

CRRF’s lake research is carried out by Gerda Ucharm, Kaylee Giramur and Sharon Patris, with 20 years of assistance of Emilio Basilius (deceased), Mathew Mesubed and Lori Colin in collaboration with Dr Mike Dawson at University of California, Merced. The broad program looks at the ecology and evolution of marine lakes and their organisms, and how this relates to important issues such as invasive species and climate change. The overall marine lakes program is multifaceted with many collaborators working in Palau’s lakes, encompassing food web dynamics and nutrient cycling (Drs. Herwig Stibor and Philippe Pondaven), microbial diversity and community structure (Dr. Mike Beman), and using lakes to reconstruct and understand the influences of 10,000 years of climate change (Dr. Julian Sachs, Dr. Jessica Blois).

Together, we are all looking at the impacts of the 2015-2016 El Niño, the disappearance of the Mastigias jellies in 2016, and their recovery, with the goal of determining indicators for future climate aberrations applicable to the lake’s management. As we have started to understand the factors influencing the physical and biological dynamics of Jellyfish Lake, this work has also enabled CRRF to record other important observations, such as the invasion by the sea anemone Exaiptasia pallida and its zooxanthella (Patris et al., 2019), to respond to concerns about sunscreen pollution (see report), and to contribute to efforts to protect this unique natural heritage of Palau.

How many jellies are in the lake?

The graph shows the estimated population size of Mastigias papua etpisoni  in Jellyfish Lake from when they disappeared in 1999, through their disappearance in 2016 and into their present recovery. Our monthly measurements estimate the population size of the jellyfish. The same methods are used every month to maintain consistency. We use 0.5 m diameter weighted nets with a fine mesh, so that even the smallest ~1-2 mm jellyfish (ephyra) are caught. The bottom of the net is closed and dropped to 15 m (the depth of zero oxygen so we know the jellyfish are not found deeper) at 15 different, regularly-spaced stations in the lake. The top of the net opens by design as we pull it up, capturing all medusae in that column of water. All jellies caught in the net are emptied into a plastic bin. These jellyfish are counted, measured, and returned to the water, giving us the number and sizes of jellyfish caught in the area of our net at each of the 15 stations. This total is then extrapolated to the entire area of the lake, which from satellite photos measures 61,000 m². We then repeat the collections at all 15 stations twice more, so that we have a total of three estimated values. The final reported population size is the average of the three measurements.

Jellyfish Lake weather station

The weather station moored in Jellyfish Lake measures air temperature and relative humidity, rainfall, wind speed and direction, total solar radiation (visible and non-visible light including heat), photosynthetically active radiation (light that plants need to grow), and the net radiant energy that stays in the lake (and is not reflected back off the water’s surface). These data are used to help understand how different weather parameters affect the lake as it heats up and cools down.


Every month we attach a Go Pro camera to our profiling instrument that measures the physical properties of the lake from the surface to the bottom.  These horizontal and upward-looking views give a glimpse of what it looks like descending underwater.  The pink bacterial plate above the anoxic layer looks red as the camera passes through.  This layer blocks all light below, so it looks black, but if we had a light you would see crystal clear water!  (check out the IMAX movie ‘The LIving Sea’, 1995)

Marine Lakes Literature

Doug Faulkner was the first to publish commentary and his classic images from the Palau marine lakes in ‘This Living Reef’ in 1974. Bill Hamner and Ivan Hauri published the first scientific paper based on work in the lakes- about the Mastigias jellyfish migration, in 1981. Since then numerous popular and scientific articles have been published in a wide variety of magazines and journals. We present here a fairly comprehensive, though not exhaustive, list of publications on Palau’s marine lakes.

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Abromeit, L and C. Gerigk.  2009.  Der Schwarm von Palau.  GEO (5 May 2009): 24-52.

Bates, A.L., E,C. Spiker, and W.H. Orem.  1993.  Speciation and isotopic composition of sulfur in sediments from Jellyfish Lake, Palau.  Chem. Geol. 106:63-76.

Bergquist, P.R. and M. Kelly.  2004.  Taxonomy of some Halisarcida and Homoscleromorphida (Porifera:Demospongiae) from the Indo-Pacific.  N.Z. J. Mar. Freshwater Res. 38:51-66.

Burnett, W.C., W.M. Landing, Lyons, W.B., and W. Orem.  1989.  Jellyfish Lake, Palau: A model anoxic environment for geochemical studies.  Eos. 15 Aug. 1989: 777-783.

Cimino, M.A., Patris, S., Ucharm, G., Bell, L.J. and Terrill, E., 2018. Jellyfish distribution and abundance in relation to the physical habitat of Jellyfish Lake, Palau. Journal of Tropical Ecology34(1), pp.17-31.

Dawson, M.N. 2000.  Variegated mesocosms as alternativies to shore-based planktonkreisels: notes on the husbandry of jellyfish from marine lakes.  J Plankton Res. 22(9):1673-1682.

Dawson, M.N.  2003.  Macro-morphological variation among cryptic species of the moon jellyfish Aurelia (Cnidaria: Scyphozoa).  Mar. Bio. 143:369-379.  Erratum Mar. Bio. 144:203.

Dawson, M.N  2005a.  Morphological variation and systematics in the Scyphozoa: Mastigias (Rhizostomeae, Mastigiidae) – a golden unstandard?  Hydrobiologia 537:185-206.

Dawson, M.N  2005b.  Five new subspecies of Mastigias (Scyphozoa: Rhizostomeae: Mastigiidae) from marine lakes, Palau, Micronesia.  J. Mar. Biol. Ass. U.K.  85:679-694.

Dawson, M.N 2006.  Island Evolution in Marine Lakes.  JMBA Global Marine Environment 3:26-29.

Dawson, M.N 2016. Islands and island-like marine environments. Global Ecology & Biogeography 25:831–846. doi: 10.1111/geb.12314.

Dawson, M.N, A.C. Algar, L.R. Heaney, & Y.E. Stuart. 2016. The evolutionary biogeography of islands, lakes, and mountaintops. Pp. 203–210 in The Encyclopedia of Evolutionary Biology v.I (R.M. Kliman, ed). Academic Press, Oxford.

Dawson, M.N. and W.M. Hamner.  2003.  Geographic variation and behavioral evolution in marine plankton: the case of Mastigias (Scyphozoa, Rhizostomeae).  143:1161-1173.

Dawson, M.N and W.M. Hamner.  2005.  Rapid evolutionary radiation of marine zooplankton in peripheral environments.  Proc. Natl. Acad. Sci.  102:9235-9240.

Dawson, M.N. and D.K. Jacobs.  2001.  Molecular evidence for cryptic species of Aurelia aurita (Cnidaria, Scyphozoa).  Biol. Bull. 200:92-96.

Dawson, M.N. and L.E. Martin.  2001.  Geographic variation and ecological adaptation in Aurelia (Scyphozoa, Semaeostomeae): some implications from molecular phylogenetics.  Hydrobiologia 451:259-273.

Dawson, M.N., L.E. Martin and L.K. Penland.  2001.  Jellyfish swarms, tourists, and the Christ-child.  2001.  Hydrobiologia 451:131-144.

Dierssen, H., W. Balzer and W.M. Landing. 2001.  Simplified synthesis of an 8-hydroxyquinoline chelating resin and a study of trace metal profiles from Jellyfish Lake, Palau.  Mar. Chem. 73:173-192.

Fabricius, K.E., J.C. Mieog, P.L. Colin, D. Idip and M.J.H. Van Oppen.  2004.  Identity and diversity of coral endosymbionts (zooxanthellae) from three Palauan reefs with contrasting bleaching, temperature and shading histories.  Mol. Ecol. 13:2445-2458.

Faulkner, Douglas.  1974.  This Living Reef. Quadrangle/The New York Times Book Co., New York. 183pp.

Fautin, D.G. and W.K. Fitt.  1991.  A jellyfish-eating sea anemone (Cnidaria, Actiniaria) from Palau: Entacmaea medusivora sp. nov.  Hydrobiologia 216/217:453-461.

Ghiselin, M.T. and J.H. Lipps.  2019.  The sea slug Phanerophthalmus luteus (Gastropoda: Opistobranchia) and its habitat and ecology at the marine Jellyfish Lake (Ongeim’l Tketau), Palau, western Pacific ocean. Proc. Cal. Acad. Sci. 64(8):181-194.

Gotoh, R.O., H. Sekimoto, S.N. Chiba and N. Hanzawa.  2009.  Peripatric differentiation among adjacent marine lake and lagoon populations of a coastal fish, Sphaeramia orbicularis (Apogonidae, Perciformes, Teleostei).  Genes Genet. Syst. 84:287-295.

Hamner, W.M.  1982.  Strange world of Palau’s salt lakes.  Nat. Geogr. 161(2):264-282.

Hamner, W.M., R.W. Gilmer and P.P. Hamner. 1982.  The physical, chemical and biological characteristics of a stratified, saline, sulfide lake in Palau.  Limnol. Oceanogr., 27(5):896-909.

Hamner, W.M. and P.P. Hamner. 1998.  Stratified marine lakes of Palau (Western Caroline Islands).  Physical Geogr. 19(3):175-220.

Hamner, W.M. and I.R. Hauri. 1981.  Long-distance horizontal migrations of zooplankton (Scyphomedusae: Mastigias). Limnol. Oceanogr. 26(3):414-423.

Hanzawa, N., R.O. Gotoh, H. Sekimoto, T.V. Goto, S.N. Chiba, K. Kuriiwa and H.B. Tamate.  2012.  Genetic Diversity and Evolution of Marine Animals Isolated in Marine Lakes. Pp. 121-150 in Analysis of Genetic Variation in Animals (M. Caliskan, ed.) InTech,

Katija, K. and J.O. Dabiri. 2009.  A viscosity-enhanced mechanism for biogenic ocean mixing.  Nature 460:624-626.

Kawagata, S., M. Yamasaki and R.W. Jordan.  2005a.  Acarotrochus lobulatus, a new genus and species of shallow-water benthic foraminifera from Mecherchar Jellyfish Lake, Palau, NW equatorial Pacific ocean.  J. Foram. Res. 35(1):44-49.

Kawagata, S., M. Yamasaki, R. Genka and R.W. Jordan.  2005b.  Shallow-water benthic foraminifers from Mecherchar Jellyfish Lake (Ongerul Tketau Uet), Palau.  Micronesica 37(2):215–233.

Kelly, M. and L.J. Bell.  2016.  Splendid Sponges of Palau with additional design by Blayne Herr.  NIWA/Coral Reef Research Foundation, 70 pp.

Ladd, S.N. and J.P. Sachs. 2015.  Influence of salinity on hydrogen isotope fractionation in Rhizophora mangroves from Micronesia.” Geochimica et Cosmochimica Acta 168, 206-221 DOI:10.1016/j.gca.2015.07.004

Ladd, S.N. and J.P. Sachs. 2017. 2H/1H fractionation in lipids of the mangrove Bruguiera gymnorhiza increases with salinity in the marine lakes of Palau. Geochimica et Cosmochimica Acta. doi:10.1016/j.gca.2017.01.046

Landing, W.M., W.C. Burnett, B. Lyons, and W.H. Orem,  1991.  Nutrient cycling and the biogeochemistry of manganese, iron, and zinc in Jellyfish Lake, Palau.  Limnol. Oceanogr. 36(3):515-525.

Lipps, J.H. and M.R. Langer.  1999.  Benthic foraminifera from the meromictic Mecherchar Jellyfish Lake, Palau (western Pacific).  Micropaleontology 45(3):278-284.

Lobban, C.S. and M. Schefter.  1997.  Tropical Pacific Island Environments.  University of Guam Press, Mangilao, Guam.  399pp.

Lobban, C.S., M. Schefter, F. Camacho and J. Jocson.  2014.  Tropical Pacific Island Environments. 2nd Ed.  Bess Press, Honolulu.  530pp.

Lyons, W.B., R.M. Lent, W.C. Burnett, P. Chin, W.M. Landing, W.H. Orem, and J.M. McArthur.  1996.  Jellyfish Lake, Palau: regeneration of C, N, Si, and P in anoxic marine sediments.  Limnol. Oceanogr. 41(7): 1394-1403.

Martin, L.E. 1999.  Population Biology and Ecology Aurelia sp.(Scyphozoa: Semaeostomeae) in a Tropical Meromictic Marine Lake in Palau, Micronesia, PhD disssertation, UCLA, 250pp.

Martin, L.E.  2001.  Limitations on the use of impermeable mesocosms for ecological experiments involving Aurelia sp. (Scyphozoa: Seamaeostomeae).  J. Plankton Res. 23:1-10.

Martin, L.E., M.N Dawson, L.J. Bell and P.L. Colin.  2005.  Marine lake ecosystem dynamics illustrate ENSO variation in the tropical western Pacific.  Biol. Lett. doi:10.1098/rsbl.2005.0382.

McCloskey, L. Muscatine and F.P. Wilkerson.  1994.  Daily photosynthesis, respiration and carbon budgets in a tropical marine jellyfish (Mastigias sp.) Mar. Bio. 119:13-22.

McGee, T.  2017.  Palau Rainfall Changes over the Last 9,000 Years.  MSc Thesis, Univ of Washington, School of Oceanography,  pp. 33.

Meyerhof, M.S., K.M. Henry, J.M. Wilson, M.N Dawson & J.M. Beman. 2016. Microbial community diversity, structure, diversity, and assembly across oxygen gradients in meromictic marine lakes, Palau. Environmental Microbiology     doi: 10.1111/1462-2920.13416

Monniot, F. and C. Monniot. 1996.  New collections of ascidians from the eastern Pacific and southeastern Asia.  Micronesica 9(2): 133-279.

Monniot, F. and C. Monniot.  2001.  Ascidians from the tropical western Pacific.  Zoosystema 23(2):201-383.

Monniot, F. and C. Monniot.  2008.  Complements sur la diversite des ascidies (Ascidiaces, Tunicata) de l’ouest Pacifique tropical.  Zoosystema 30(4):799-872.

Muscatine, L. and R.E. Marian.  1982.  Dissolved inorganic nitrogen flux in symbiotic and nonsymbiotic medusae.  Limnol. Oceanogr. 27(5):910-917.

Muscatine, L., F.P. Wilkerson and I.R. McCloskey.  1986.  Regulaton of population density of symbiotic algae in a tropical marine jellyfish (Mastigias sp.).  Mar. Ecol. Prog. Ser. 32:279-290.

Meyerhof, M.S., Wilson, J.M., Dawson, M.N. and Michael Beman, J., 2016. Microbial community diversity, structure and assembly across oxygen gradients in meromictic marine lakes, Palau. Environmental microbiology18(12), pp.4907-4919.

Orem, W.H., W.C. Burnett, W.M. Landing, W.B. Lyons, and W. Showers.  1991.  Jellyfish Lake, Palau: Early diagenisis of organic matter in sediments of an anoxic marine lake. Limnol. Oceanogr. 36(3): 526-543.

Patris, S. 2015. The expansion and impact on native species of a sea anemone introduced into a tropical marine lake (Jellyfish Lake, Palau). MSc Thesis, Univ. Calif. Merced, Quantitative and Systems Biology, pp. 1-23.

Patris, S.W., L.E. Martin, L.J. Bell & M.N Dawson. 2019. Expansion of an introduced sea anemone population, and its associations with native species in a tropical marine lake (Jellyfish Lake, Palau). Frontiers of Biogeog. DOI:10.21425/F5FBG41048.

Patris, S, M.N Dawson, L.J. Bell, L.E. Martin and P.L. Colin.  2010.  Jellyfish Lake (Ongeim’l Tketau).  Coral Reef Research Foundation.  14 pp.

Patris, S.W., M.N Dawson, L.J. Bell, L.E. Martin, P.L. Colin, & G. Ucharm, with additional design & images by M. Etpison, 2012. Ongeim’l Tketau. Coral Reef Research Foundation/Etpison Museum, 44 pp.

Richey, J.N. & J.P. Sachs.  2016.  Precipitation changes over the western tropical Pacific over the past millennium. Geology 44:617–674. doi:10.1130/G37822.1.

Rocha de Souza, M. and M.N Dawson. 2018.  Redescription of Mastigias papua (Scyphozoa, Rhizosotomeae) with designation of a neotype and recognition of two additional species.  Zootaxa. 4457 (4): 520–536.

Sachs, J.P., D. Sachse, R.H. Smittenberg, Z. Zhang, D.S. Battisti and S. Golubic.  2009.  Southward movement of the Pacific intertropical convergence zone AD 1400-1850.  Nature Geoscience 2:519-525.

Saitoh, S., H. Suzuki, N. Hanazawa and H. Tamate.  2011.  Species diversity and community structure of pelagic copepods in the marine lakes of Palau.  Hydrobiologia  666:85-97.

Smittenberg, R.H., C. Saenger, M.N Dawson and J.P. Sachs.  2011.  Compound-specific D/H ratios of the marine lakes of Palau as proxies for West Pacific Warm Pool hydrologic variability.  Quaternary Sci. Reviews 30:921-933.

Swift, H.F.  2016.  The ecological and evolutionary effects of environmental perturbations on populations and communities. PhD Thesis, Univ. Calif. Merced, Quantitative and Systems Biology, pp. 1-142.

Swift, H.F., L.E. Gómez Daglio, & M.N Dawson. 2016. Three routes to crypsis: stasis, convergence, and parallelism in the Mastigias species complex (Scyphozoa, Rhizostomeae). Molecular Phylogenetics and Evolution 99:103–115. doi:10.1016/j.ympev.2016.02.013

Turner, P.S. 2006.  Darwin’s Jellyfishes.  National Wildlife 44(5):32R-32X.

Wilson, J.M. 2017.  Controls on Marine Community Respiration.  PhD Thesis, Univ. Calif. Merced, Environmental Systems, pp. 1-110.

Wilson, J., S. Abboud and J.M. Beman.  2017.  Primary Production, Community Respiration, and Net Community Production along Oxygen and Nutrient Gradients: Environmental Controls and Biogeochemical Feedbacks within and across “Marine Lakes,” Front. Mar. Sci.,

Venkateswaran, K., A. Shimada, A Maruyama, T. Higashihara and T. Maruyama.  1993.  Microbial characteristics of Palau Jellyfish Lake.  Can. J. Microbiol. 39:5506-512.

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