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Great Salt Lake—Planktonic and Benthic Habitats

Hypersaline lakes. Click for a larger picture.Hypersaline lakes are often regarded as "simple" ecosystems because they typically have fewer species than freshwater lakes. Although fewer species are capable of tolerating the stress of a salty lake, those species that are present interact on many levels to efficiently use the food and energy resources available. There is an open water (planktonic) habitat and a bottom-dwelling (benthic) habitat in Great Salt Lake.

The planktonic habitat is dominated early in the year by phytoplankton (algae) blooms. These often occur in January when the water temperature is only a few degrees Celsius (36 degrees Farenheit). In the last few years, the green alga, Dunaliella viridis, has bloomed at this time and been followed by blooms of several species of diatoms.

Brine shrimp (Artemia franciscana) hatch from cysts in early April and within a month or so intensely graze the phytoplankton crop. If sufficient nutrients are available later in the summer and enough of the brine shrimp die from lack of food, there may be fall blooms of diatoms. The phytoplankton crop provides much of the food for the shrimp to grow and reproduce during the summer. Large numbers of local and migratory birds feed on brine shrimp during the spring and summer. A small water bug known as a corixid also eats shrimp nauplii (larva) and adult shrimp in the lake. As phytoplankton become scarce, the shrimp may reprocess fecal pellets produced earlier in the year or graze on algae and blue-greens (sometimes called algae, but recognized to be a separate group) that grow on some areas of the lake bottom. The shrimp also may graze on diatoms that colonize cast-off exoskeleton parts from shrimp molts. When the shrimp are stressed by lack of food or harsh environmental conditions, they switch from producing live young to producing cysts. Some of these cysts are commercially harvested and some remain in the lake to start the shrimp population the following year. Graphic of ecosystem.

The Benthic habitat. Click for a larger picture.The Benthic habitat relies on photosynthesis by the blue-greens and other benthic algae to produce much of the food needed by benthic grazers. Additional food comes in the form of detritus that settles from the water. In the springtime, after the shrimp have grazed the phytoplankton from the water, light penetrates to the bottom of the lake in many areas and provides energy for benthic photosynthesis by algae and the blue-greens. Living in close association and feeding upon detritus and the blue-greens are two species of brine fly (genus Ephydra).These small insects spend their larval existence on the bottom of Great Salt Lake. They emerge from the lake as adults in early summer and form dense clouds that cover the beach and everything on the beach. Although they may be annoying, they do not bite.

Although the planktonic and benthic habitats seem to be separate, they are linked. Both habitats require nutrients entering from the watershed around the lake, brine shrimp feed on algae and organic material in the benthic habitat and contibute nutrients back to the benthic habitat, several kinds of bacteria and protozoa occur in both habitats and recycle nutrients between them, and brine-fly larvae and pupae released from the bottom enter the planktonic habitat prior to emerging from the lake.

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