Index: Why aren't there any vertebrates
that live in the lake?
What are the common invertebrates in the lake?
The life cycle of the Brine Fly
The effects of salinity on Corixid Bug populations
For further information on these aquatic insects
WHAT ARE THOSE FLIES ON
THE BEACH AND WHY DON'T WE GET RID OF THEM?
The most visibly obvious invertebrate that inhabits the lake is probably the brine fly. Visitors to the lake, whether a
first time or local, walk away with a vivid image of the huge, coal black clouds of flies that inhabit the salty shores. Many
leave without desire to return because of these "noxious insects;" However, there is a Utah State Park sign on
Antelope Island that assures visitors that the masses of sometimes annoying flies are imperative to the ecological "plan" of
the lake. Astute and sensitive observers can connect the flies to the rest of the lake's system of existence -- that is if one
does not follow the conditioned trail of imagery in history that characterizes places like saline lakes as wastelands. As Ella
Sorenson puts it in the voice of the lake itself: "Do you call my waters dead because you expected fish and found none? An
abundance of plants and animals live within and around my briny depths. If not life, what do you call brine shrimp, bacteria,
algae, brine flies?" So a shift in thinking from traditional wilderness imagery (green trees, mountains, and mammals) to one
that celebrates dryness, adaptation, and specialization is necessary and important if we are to understand and value places
like the Great Salt Lake that have been traditionally neglected due to their "non-traditional" characteristics.
AREN'T THERE ANY VERTEBRATES THAT LIVE IN THE LAKE?
The salinity of the Great Salt Lake poses extreme physiological stresses on the organisms that live in and around the
lake. Vertebrates like birds and voles inhabit areas surrounding the lake like fresh/brackish marshes, rocky outcrops, the
salt playa, and dunes. Many of the vertebrates have adapted to excessive salts in their diets. For example, California gulls
excrete excess salt from their diet of brine shrimp, brine flies, and algae through their salt secreting adapted nostrils;
However, organisms that live in the lake must regulate salt levels more efficiently and vigorously than
the part time residents like birds. Most vertebrates such as fish have not evolved mechanisms to deal with so much salt and
therefore, none inhabit the lake.
ARE THE MOST COMMON INVERTEBRATES?
There are two identified species of brine flies: Ephedra
cinerea and a larger species E. hians. E. cinerea is far
more abundant in the south arm outnumbering its larger
counterpart by 100:1 possibly due to the differences in
salinity between the North and South arms. The flies do not
prey on humans and/or other mammals and birds – instead
grow on the surface of rocks and wood on the floor of the
lake or near the shoreline. In this way, the brine fly is
important to the lake in that the flies reuse massive amounts
of organic "waste" from the lake.
The adult flies are 3-6mm in length and their average life span is 3-5 days. Egg laying is continuous through the summer
and females typically lay 75 eggs – which are laid on or near the surface of the water (females lay eggs under water by
“walking” underneath with a bubble of air surrounding her) then the eggs hatch into long cylindrical larvae that consume
large quantities of algae and decaying organic detritus in the lake. The larvae are distributed throughout
the lake at different depths and build up by drifting in to algal reefs. On these reefs of algae, the larvae
survive completely submerged and receive dissolved oxygen from the water that passes through their tracheal gills. Lab
observation shows a high mortality rate during pupation, the time when the larvae metamorphose and develop wings and
leave their pupal cases behind. When they emerge they rise to the surface enclosed in an air bubble and are then
transported to shore by
|Wind direction and velocity
have a large impact on
distribution of brine flies throughout the lake and help to
create the long, dense windrows of pupal cases and huge
clouds of flies on the shore as shown in this photo. This
whole life cycle lasts 3-4 weeks. Since the fly's complete
life cycle depends on the growing conditions of the lake, it
seems that the lack of numbers in the north arm may be
indicative of the disruption of natural salinity because of the
division of the lake by railroad in 1959.
the lake in 1926 by a scientist named Allen. Later, Woodbury (1936) reported that no other invertebrates besides brine
shrimp and brine flies existed in the lake; However, about ten years ago at the Silver Sands Marina (South arm) E. Rawley
collected adult Corixids that were identified as Tricorixia verticalis Fiber. Corixids are predatory and prey on brine shrimp,
Artemia salina, as well as the larvae of the two species of brine flies. The effect of this predation on the shrimp and the
brine fly population is under investigation by the Utah Division of Wildlife Resources in cooperation with the United States
Geological Society. For research updates on the Great Salt Lake Ecosystem Project see:
http://www.nr.state.ut.us/dwr/GSLECO.HTM#university. At one time, it was thought that the bug reproduced in the
fresher marshes and migrated in as adults. Winget, however reported collecting immature and adult Corixids from several
areas in the south arm and so it seems that these water boatmen are true inhabitants of the lake.
drawn by Nghia Ngyen, 1998
|These bugs belong to the
family Corixidae (commonly
called water boatman) and constitute the largest group of
water bugs in north America with over one hundred
species. Water boatman are free swimming bugs
and have modified scoop shaped forelegs and oar like
hind legs with swimming hairs. In a habitat like the Great
Salt Lake which is generally oxygen poor, the Corixids
surface regularly for air but also have a physical gill called
a plastron which stores air and ventilates as the bug rows
its oar like legs. In more oxygen rich environments the bug
can stay submerged for longer
periods of time.
EFFECTS OF SALINITY ON CORIXID BUGS:
When the lake water was more dilute, such as in the fall of 1998 due to an abnormally high amount of precipitation for
the year, high populations of this bug were found by students of Westminster in the Farmington Bay arm of the lake which is
South of the north Antelope Island causeway. A sample of the lake water showed that the salt concentration was 3.7%.
Similarly, A rise in water level that occurred from 1960-1989 decreased the Great Salt Lake's salinity from more than 30% in
both the northern and southern basins to 17% salinity in the northern basin and only about 6% salinity in the southern
basin. These changes in salinity and water level had profound ecological repercussions. For example, the lower salinity
level made it possible for this predacious water bug, Trichorixia verticalis, to increase their numbers in the lake. This insect
preyed extensively upon the previously dominant brine shrimp, Artemia franciscana. A marked change in the composition of
phytoplankton was also a consequence of this increased inflow of runoff. Once dominated by salt tolerant algae such as
Dunaliella salina and D. vividis, the phytoplankton gradually changed as the lake became diluted so that opportunistic
forms, such as Nodularia
spumigena, had a chance to flourish (Williams).
For Further Reading See:
The Division of Wildlife Services Great Salt Lake Ecosystem Project web site for up to date research
Salt Lake Tribune Archives article on dioxin pollution and its effects
on the lake
Gwynn, J. Wallace, ed. Great Salt Lake; a Scientific, Historical, and Economic Overview.
Utah Geological and Mineral Survey, 1980.
Mccafferty, Patrick W. Aquatic Entomology; The Fisherman's and Ecologists' Illustrated Guide
to Insects and Their Relatives. Boston: Science Books International, 1981.
Sorenson, Ella. Seductive
Beauty of Great Salt Lake; Images of a Lake Unknown. Salt
Lake City: Gibbs-Smith, 1997.
Williams, David Williams. "What Future for Saline Lakes?" Environment. Nov 1996 v38 n9