Thermophilic Eukarya

Steam rises from a wide geyser basin with light blue pools
Unseen, microscopic eukarya live in the extreme environments of Yellowstone. Norris Geyser Basin is one of the best places in Yellowstone to see thermophilic algae.

NPS / Jim Peaco


Plants, animals, and mushrooms are the eukarya most of us know. Millions of unseen, microscopic members of this kingdom exist throughout our world, including in the extreme environments of Yellowstone.

Norris Geyser Basin is one of the best places to see thermophilic algae. Bright green Cyanidioschyzon grows on top of orange-red iron deposits around Whirligig and Echinus geysers and their runoff channels. Waving streamers of Zygogonium are especially easy to see in Porcelain Basin, where their dark colors contrast with the white surface.

From the boardwalk crossing Porcelain Basin, you can also see larger eukarya, such as ephydrid flies. They live among the thermophilic mats and streamers, and eat, among other things, algae. The species that lives in the waters of Geyser Hill, in the Upper Geyser Basin, lays its eggs in pink-orange mounds, sometimes on the firm surfaces of the mats. Part of the thermophilic food chain, ephydrid flies become prey for spiders, beetles, and birds.

A fly rests near a clump of eggs
Ephydrid flies lay eggs in pink-orange mounds, sometimes on the firm surfaces of the mats.


Dark webs stream in a shallow pool
Waving streamers of Zygogonium are easy to see in Porcelain Basin.



Some microscopic eukarya consume other thermophiles. A predatory protozoan, called Vorticella, thrives in the warm, acidic waters of Obsidian Creek, which flows north toward Mammoth Hot Springs, where it consumes thermophilic bacteria.

Thermophilic eukarya include one form that is dangerous to humans: Naegleria, a type of amoeba, that can cause disease and death in humans if inhaled through the nose.

Although they aren't visible like mushrooms, several thermophilic fungi thrive in Yellowstone. Curvularia protuberata lives in the roots of hot springs panic grass. This association helps both survive higher temperatures than when alone. In addition, researchers have recently discovered a virus inside the fungus that is also essential to the grass's ability to grow on hot ground.

Of all the thousands (if not millions) of thermophilic species thriving in Yellowstone's extreme environments, the eukarya are the group that bridges the world of thermophilic microbes with the larger life forms—such as geese, elk, and bison—that thrive in ecological communities beyond the hot springs.

Green vegetation with sharp, purple points
The fungi Curvularia proturberata lives in the roots of hot springs panic grass.

Thermal Biology Institute, Montana State University


Thermophilic Eukarya in Yellowstone National Park

Name pH and Temperature Description Location
Red algae
pH 0–4
40–55°C (104–131°F)
Color: bright green
Metabolism: photosynthetic
Form: coating on top of Formations; mats
  • Norris Geyser Basin
  • Lemonade Creek
  • Nymph Creek
Green algae
pH 0–4
32–55°C (90–131°F)
Color: appears black or dark purple in sunlight.
Metabolism: photosynthetic
Form: filaments and mats
Naegleria (amoeba)
Predator; can infect humans when ingested through nose
  • Huckleberry Hot Springs
  • Boiling River
Vorticella (ciliate)
Consumer; single-celled ciliate (feathery appendages swirl water, bringing prey)
  • Obsidian Creek
pH 1–2
<43°C (109°F)
Single-celled; photosynthetic; moves by waving one or two strands called flagella
Fungi (Curvularia protuberata) ≤65°C (149°F) with panic grass
<55°C (131°F) without
Grows in roots of hot springs panic grass (Dichanthelium lanuginosum), enabling both to survive high temperatures; the plant also produces sugars that the fungus feeds on
Ephydrid fly (Ephydra sp.) >pH 2
<43°C (109°F)
Nonbiting insect that eats microscopic algae as larvae and adult; prey for spiders, beetles, dragonflies, killdeer
  • Norris, especially Porcelain Basin
  • Upper Geyser Basin, especially Geyser Hill
  • Mammoth Hot Springs
Ross’s bentgrass (Agrostis rossiae) 38°C (100°F­) One of Yellowstone’s three endemic plant species; may bloom in winter; dries out in summer’s hot air temperatures
  • Banks of Firehole River
  • Near Shoshone Lake
Warm springs spike rush, with some Tweedy’s rush Warm
Forms thick floating mats, which also provide habitat for thermophilic algae and other thermophiles
  • Obsidian Creek


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