Weber State University
Department of Botany
Antelope Island Field Trip
Life in the Great Salt Lake
How often have you heard people say........ "There is no life in the Great Salt Lake!"? This is even said by people who KNOW about the harvesting of the brine shrimp from the lake itself! It is always a mystery how animals are supposed to survive without a primary producer to provide them with food and oxygen. Well, it is now safe to say that wherever there is natural water, no matter the quality, there will be life in it. In recent years we have discovered life in places we assumed it was impossible. When we did discover life in extreme environments we still resisted the fact that they were active and not passive (ie. simply washed into)in such settings. Now we have evidence that living organisms can not only tolerate but prefer extreme environments. Bacteria, and sometimes algae, have been found in extremely: cold water (psychrophiles), hot water (thermophiles), high acid environments (acidophiles), high hydrostatic pressures such as on the ocean floor (barophiles), and in high salt concentrations like the Great Salt Lake (halophiles). Actually, the salt concentration of the Great Salt Lake is too low to support high populations of certain algae as we shall see later.
Lakes such as the Great Salt Lake that are hypersaline are considered to be rather simple ecosystems with a simple food web because they contain fewer species than freshwater lakes. There is a very efficient system of energy exchange between the few levels of life in this environment, however.
Primary Producers (Algae and Photosynthetic Bacteria):
The primary producers in the lake are found in one of two habitats: planktonic (water column) or the benthic (bottom). The planktonic primary producers are referred to as phytoplankton and dominated by algae and a few bacterial species. Over the years of studies on the lake, roughly a dozen species of algae and a similar number of bacteria have been recorded. The lists compiled by some investigators is longer than that of others, however, few efforts have been carried out to culture the algae to determine if they are truly active or are simply tolerating the brine for a while after having been washed into the lake.
The planktonic algae are dominated by a variety of pennate diatoms in early spring and late autumn when they are apt to reach bloom proportions in numbers. In summer and occasionally in winter two species of Dunaliella (green algae) dominate. In the less saline south arm of the lake, Dunaliella viridis dominates, imparting a green cast to the water, whereas in the more saline north arm of the lake, Dunaliella salina dominates and this species produces beta-carotene in such large quantity that the water Qbecomes quite red in color. However, even the north arm is not saline enough for this species to reach maximum populations. This they do in the solar evaporation ponds of various companies that extract salts from the lake by concentrating brines. You may have noticed the brilliant red color of the solar evaporation ponds of GSL-Minerals & Chemicals as you fly over the lake in summer. Even the entire north arm develops a reddish color in summer due to this alga. Contributing somewhat to the red color of the north arm is the presence of Halobacterium, a bacterial species that accumulates a rhodopsin-type of pigment.
Two genera of blue-green algae or cyanobacteria are commonly found in the plankton. These are
Aphanothece and Coccochloris. These two genera along with the Dunaliella spp. along with the dozen or so bacterial species found in the south arm, provide the food for the grazing brine shrimp (Artemia franciscana). Diatoms, though valuable, are tougher for the brine shrimp to digest because of their thick silica cell walls.
Some of the bacteria found in the south arm belong to the following genera: Micrococcus, Bacillus, Achromobacter, Flavobacterium, Bacterioides, Serratia and Cellulomus.
The benthic habitat is dominated by blue-green algae (cyanobacteria) and some diatoms with the occasional green alga. These collectively cause the precipitation of calcium-carbonate (limestone) which accumulates as reefs on the bottom of the lake. These primary producers are especially active when the phytoplankton and brine shrimp numbers above decline and the resulting clear water allows light to penetrate to the bottom. The algal mats that develop are important as the food for two species of brine fly (genus Ephydra). These small insects spend their larval developmental stage grazing on this benthic community, later form pupae and emerge as adults in early summer. They form dense clouds that hover over the beaches and everything on the beach, including people. Many people are annoyed by the brine fly but they do not bite and are unique to brine environments. You may have noticed large wind-rows of pupae cases from these brine flies on the shore of the lake.
a) Brine Shrimp
In the late 19th century, various investigators identified the brine shrimp as Artemia salina or Artemia gracilis, however, more recently they have been named Artemia franciscana (the same as the one in San Francisco Bay). Brine shrimp (also called "Sea Monkeys" by aquarium enthusiasts and aquaculturists) are Crustaceans that have about 15 larval molting stages ( their larvae are called nauplii) before they become full adults of about 10 mm. The eggs are very thick-walled, can survive for very long periods of time if kept dry, and are called cysts. While some species of Artemia can produce live young parthenogenically, Artemia franciscana has both male and females present. Large numbers of these small cysts are produced which float on the brine and provide the basis of a multi-million dollar industry where these cysts are harvested for use in the aquaculture industry and by aquarium enthusiasts. Adult shrimp feed on the phytoplankton suspended in the water but can also "graze" on the benthic algae (both blue-greens and diatoms) that grow on the limestone reefs. During times of plentiful algal biomass, even fecal pellets contain enough undigested food to make ingestion profitable from an energy budget standpoint. These fecal pellets also provide the nuclei for the precipitation of calcium carbonate that grows into "oolites" which forms the majority of the sand grains on the shore of the lake.
b) Brine Flies
Due to our terrestrial nature we notice the huge, coal black clouds of flies on the lake shore. We are often annoyed by their presence and fail to realize just how important they are to the aquatic ecosystem of the Great Salt Lake. These flies and their larvae & pupae support an enormous number of shorebirds. As mentioned above, there are two species of brine flies present. Ephydra cinerea and a larger species, Ephydra hians. The former is more abundant in the south arm outnumbering its larger counterpart by 100:1.
The adult flies have an average life span of 3-5 days. Eggs are laid continuously through the summer at the surface of the water. The eggs hatch quickly into larvae which graze on the algal and bacterial community on the bottom, on rocks, or on logs. The larvae receive all their oxygen from algal photosynthesis. When the larvae develop into pupae the adult features develop rapidly and the pupae trap air bubbles which cause them to float and be transported to the shore by the wind, hence the enormous windrows of pupae on shore.
Corixids are predatory aquatic insects referred to as "water boatmen" that are common in freshwater. It was first believed that the corixids found in the Great Salt Lake were simply transported to the lake from nearby freshwater marshes but the consensus now seems to be that they are indeed true inhabitants of the lake. The one identified in the lake is Tricorixia verticalis. This corixid preys on the brine shrimp as well as the larvae of the two species of brine flies. The ecological impact of this predation is currently being investigated by the Utah Division of Wildlife Resources.
The Great Salt Lake supports between 2 and 5 million shorebirds, mostly migratory. The lake and its associated marshes provide a resting and staging area for the birds, as well as an abundance of food in the form of brine shrimp and brine flies. The importance of the lake ecosystem to migratory birds has been recognized in the last decade and the lake was designated as part of the Western Hemisphere Shorebird Reserve Network in 1992. As an example of the value of the lake to birds the lake serves as: the largest staging concentration of the Wilson’s Phalarope (500,000); largest number of American Avocets and Black-Necked Stilts in the Pacific Flyway; and the world’s largest assemblage of Snowy Plovers, representing 55% of the entire breeding population west of the Rocky Mts.
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