General 2 — Mary Anne Karren

A microbialite powered food chain

Great Salt Lake owes its fecundity to the unusual collection of microbialites on its lakebed. These structures are veritable bird food factories. Microbialites are akin to a reef, grown over centuries by the metabolic activities of the lake’s salt-loving microbes. Through photosynthesis, they generate a tremendous amount of biomass that feeds dense concentrations of the lake’s only two invertebrates - brine flies and brine shrimp - which in turn feed the birds. Record low water allows a closer look at these ancient “living rocks” of the lakebed and how they underpin the entire Great Salt Lake ecosystem.

An American Avocet plucks at insects on the exposed microbialite reef of the drying Great Salt Lake. In recent years, Great Salt Lake has lost over eleven feet of elevation and more than half its surface area. Much of the lake's microbialite reef is — An American Avocet plucks at insects on the exposed microbialite reef of the drying Great Salt Lake. In recent years, Great Salt Lake has lost over eleven feet of elevation and more than half its surface area. Much of the lake's microbialite reef is now exposed and bleaching as seen here.

Adult brine flies massing on the Great Salt Lake shoreline. Brine flies spend much of their lives underwater in larval form, attached to microbialites, where they are eaten year-round by millions of diving ducks and grebes. In summer, the adult flies — Adult brine flies massing on the Great Salt Lake shoreline. Brine flies spend much of their lives underwater in larval form, attached to microbialites, where they are eaten year-round by millions of diving ducks and grebes. In summer, the adult flies hatch and float to shore in large rafts, where they are eaten by millions of gulls and shorebirds.

Partially submerged microbialite showing the desiccated and bleached part above, and the dark microbial mat at the waterline where the microbialites are still hydrated The black material is a dense mat of photosynthetic microbes that the brine shrim — Partially submerged microbialite showing the desiccated and bleached part above, and the dark microbial mat at the waterline where the microbialites are still hydrated The black material is a dense mat of photosynthetic microbes that the brine shrimp and brine fly larvae feed on. The metabolic activities of the microbes in this dense mat cause mineral deposition that forms the rounded mounds and reef like structures of microbialites over centuries.

Partially submerged microbialites showing the desiccated and bleached parts above. The black material is a dense mat of photosynthetic microbes that the brine shrimp and brine fly larvae anchor to and feed on, creating a reliable year-round food sour — Partially submerged microbialites showing the desiccated and bleached parts above. The black material is a dense mat of photosynthetic microbes that the brine shrimp and brine fly larvae anchor to and feed on, creating a reliable year-round food source for birds.

The density of brine fly larvae and brine shrimp is ten times higher on microbialites than elsewhere in Great Salt Lake, making the microbialites literal food factories for birds. This image shows a partially submerged microbialite with brine shrimp — The density of brine fly larvae and brine shrimp is ten times higher on microbialites than elsewhere in Great Salt Lake, making the microbialites literal food factories for birds. This image shows a partially submerged microbialite with brine shrimp attached below the water, brine fly larvae both above and below water, a few adult brine flies above the waterline, and salt crystals forming on old brine fly casings at the top.

Submerged microbialite "bird food factory" showing brine shrimp and brine fly larvae attached. The black material is the photosynthetic microbes that the brine shrimp and brine fly larvae feed on.

California gulls feed by running along the shore of the Great Salt Lake, raising up clouds of brine flies and snapping them up. Brine flies are one of only two invertebrates that thrive in the salty waters of the Great Salt Lake, reaching enormous p — California gulls feed by running along the shore of the Great Salt Lake, raising up clouds of brine flies and snapping them up. Brine flies are one of only two invertebrates that thrive in the salty waters of the Great Salt Lake, reaching enormous population densities and providing food for millions of shorebirds, waterfowl, and gulls.

A young California gull feeds by running along the shore of the Great Salt Lake, raising up clouds of brine flies and snapping them up.

A Wilson's Phalarope plucks brine flies from the surface of Great Salt Lake during a smoky sunset. Great Salt Lake and its brine fly buffet attracts the largest staging concentration of Wilson's Phalaropes in the world, with as many as 500,000 birds — A Wilson's Phalarope plucks brine flies from the surface of Great Salt Lake during a smoky sunset. Great Salt Lake and its brine fly buffet attracts the largest staging concentration of Wilson's Phalaropes in the world, with as many as 500,000 birds visiting at peak migration.

A Franklin's gull feeds by running along the shore of the Great Salt Lake, raising up clouds of brine flies and snapping them up.

An American Avocet guards a nest near a puddle trapped in the contours of the exposed microbialtes of Great Salt Lake. The nesting birds were all gone, apparently failed, the following week.

Great Salt Lake hosts the world's largest concentration of threatened Western Snowy Plovers. The birds nest on the beaches and playas of the lake, feeding on plentiful insects. Here a Western Snowy Plover stands among pickleweed growing in last yea — Great Salt Lake hosts the world's largest concentration of threatened Western Snowy Plovers. The birds nest on the beaches and playas of the lake, feeding on plentiful insects. Here a Western Snowy Plover stands among pickleweed growing in last year's exposed and eroded microbialites.

Great Salt Lake hosts the world's largest concentration of threatened Western Snowy Plovers. The birds nest on the beaches and playas of the lake, feeding on plentiful insects. Here a Western Snowy Plover stands among exposed microbialite mounds.

A pool of water from the receding Great Salt Lake is trapped in the contours of the microbialite reef. As Great Salt Lake dries up, salinity increases, favoring a population of extreme halophilic microbes that are orange to pink in color. At these e — A pool of water from the receding Great Salt Lake is trapped in the contours of the microbialite reef. As Great Salt Lake dries up, salinity increases, favoring a population of extreme halophilic microbes that are orange to pink in color. At these extreme high salt concentrations, the lake's two invertebrate species, brine flies and brine shrimp, do not survive for long.

Pools of water from the receding Great Salt Lake are trapped in the contours of the microbialite reef. As the pools dry up, salt concentration increases, favoring a population of extreme halophilic microbes that are orange to pink in color. At thes — Pools of water from the receding Great Salt Lake are trapped in the contours of the microbialite reef. As the pools dry up, salt concentration increases, favoring a population of extreme halophilic microbes that are orange to pink in color. At these extreme high salt concentrations, the lake's two invertebrate species, brine flies and brine shrimp, no longer thrive.

Sunset at Great Salt Lake with Fremont Island in the distance and exposed microbialites in the foreground.

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