The Mono Basin Ecosystem Effects of Changing Lake Level (1987) / Chapter Skim
Currently Skimming:
4. Biological System of Mono Lake
4. Biological System of Mono Lake
Pages 69-120
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 69... ...
These algae are grazed by the brine shrimp, Artemia monica, which are preyed upon mainly by eared grebes (Podiceps nigricoZlis) and California gulls (Laws californicus)
|
From page 70... ...
, primary consumers (brine shrimp and brine fly) , and secondary consumers (aquatic bird populations)
|
From page 71... ...
The presence of numerous gas seeps on the floor of Mono Lake is supported by the discovery that large areas of bottom sediments are disturbed by gas bubbles (Pelagos Corporation, 1987~. Pelagic, aerobic bacteria are often abundant in alkaline, saline lakes.
|
From page 72... ...
The seasonal dynamics of the phytoplankton in Mono Lake are unusual (Mason, 1967; Lovejoy and Dana, 1977; Melack, 1983, 1985; Jellison and Melack, in press) (Figure 4.
|
From page 73... ...
FIGURE 4.1 Mean mixolimnetic chlorophyll a for 1982, 1983, 1984, 1985, and 1986. Primary Consumers Zooplankton The Mono Lake brine shrimp, Artemia monica, is the major zooplankton species (Mason, 1967; Lenz, 1980, 1982~.
|
From page 74... ...
During the summer, brine shrimp are abundant in the oxygenated upper waters and very sparse or absent in the anoxic deeper waters. By September, the brine shrimp begin to decline in numbers and are almost absent from the plankton by December.
|
From page 75... ...
When the spring hatch is relatively low, firstgeneration adults are less abundant, algal densities remain higher later into the spring, and a large second generation can occur. The spatial distribution of brine shrimp is heterogeneous on large (square kilometers)
|
From page 76... ...
No efforts are in progress to sample zooplankton other than brine shrimp. Zoobenthos The benthic community of Mono Lake includes several species of dipteran insects, as is typical of hypersaline waters.
|
From page 77... ...
If the lake level dropped, the loss of hard-surface sediments would reduce brine fly habitat. PHYSIOLOGICAL ASPECTS AND SALINITY TOLERANCES OF AQUATIC PELAGIC AND LITTORAL ORGANISMS Primary Producers Two kinds of evidence are available to evaluate the effects of increased salinity on phytoplankton: (1)
|
From page 78... ...
(1982) studied microcosms containing Mono Lake water and microflora, some with brine shrimp and some without.
|
From page 79... ...
This physical relationship sets an absolute upper limit on the salinity of salt lakes in which a self-sustaining population of halophilic organisms such as brine shrimp and brine flies can persist. Physiological solutions within and surrounding cells are primarily dilute aqueous solutions.
|
From page 80... ...
The movement of free water is coupled with transit of monovalent ions, sodium, and potassium. The free water requirements for larval and adult stages of brine shrimp living in various environmental salinities
|
From page 81... ...
(1972, 1977~. Brine shrimp maintain an uptake of water by metabolically controlling osmotic desiccation.
|
From page 82... ...
This outward toss of water is offset by coupling the passive inward diffusion of ions carrying water with selective removal of sodium and chloride ions (Come, 1977~. Figure 4.5 compares the osmotic potential of changing environmental salinities in terms of the movement of free water molecules being translocated across a membrane along with each ion transported into the
|
From page 83... ...
Biological System of Mono Lake 83 1.2 1.0 In In 0.8 o :C 0.6 0.4 0 1 I .5 m It To l .5 J 1 _ l NONVIABLE CYST HYDRATION — is l ~Y I At/ 0~2 0.8 a 0.9 w 1.0 FIGURE 4.4 A comparison of the hydration behavior of viable (~) and nonviable (o)
|
From page 84... ...
Zooplankton Reproduction and Development. The dynamics of larval brine shrimp populations can be strongly influenced by the physiological mechanisms that control the development of
|
From page 85... ...
The Mono Lake brine shrimp species. Artemia monica.
|
From page 86... ...
Therefore, environmental conditions under which cyst development and termination occur are unlike those found in shallow saline lakes. For instance, because cysts from A
|
From page 87... ...
monica cysts can synthesize ~~ ~ ~ ~ ~~ to those found In other species of Artemia at higher temperatures and Therefore, it Would seem that the Mono Lake brine shrimp has evolved controls that act differently from those of other Artemia species in avoiding the inhibiting effects of low temperatures on preemergence mechanisms. 7 ~ .~ —- -- - - -- — - _ _ _ _ _ __ cysts organic acids and glycogen at levels similar · .
|
From page 88... ...
~~ dry weight of cells. This is the limiting value of the water of hydration that protects the viability of brine shrimp cells.
|
From page 89... ...
monica, Mono Basin brine shrimp, with unlimited food supply. Young reproductive adults were paired to assess the effect of salinity on reproduction.
|
From page 90... ...
Loss of free water by osmotic desiccation in early brine fly embryogenesis results in increased mortality of adult and juvenile life stages. Herbst (1981)
|
From page 91... ...
Adaptation of Brine Shrimp and Brine Fly to Changes in Salinity If brine flies and brine shrimp could adapt genetically to increased salinity and alkalinity, a lowered lake level would have a smaller effect on their populations. There are two lines of evidence suggesting that the probability that brine flies and brine shrimp would adapt to higher salinities (> 150 g/~)
|
From page 92... ...
Each of these three species is present in extraordinarily high numbers, and each exploits brine shrimp and brine fly populations. The grebes and phalaropes rely on Mono Lake's aquatic resources during stopovers on their fall migrations.
|
From page 93... ...
Peak numbers of grebes occur during late September, October, and November (Winkler, 1977; Jehl, 1982a; Cooper et al., 1984) , a time when grebe predation contributes to the annual decline in brine shrimp densities (Cooper et al.,
|
From page 94... ...
94 1,000,000 100,000 10,000 1000 _ coot J , J F M A M J J A TIME (month) The Mono Basin Ecosystem / l S O N D FIGURE 4.6 Estimates of the number of eared grebes on Mono Lake each month in a typical year (based on Winkler, 1977; Jehl, 1982a, Cooper et al., 1984~.
|
From page 95... ...
Although these population figures certainly leave much to be desired, the conclusion that Mono Lake is visited by one quarter to one third of the eared grebes in North America each year seems to be justified. While at Mono Lake, grebes feed on adult brine shrimp and brine fly larvae, these two food items constituting over
|
From page 96... ...
Grebes swallow minimal amounts of saltwater while ingesting their food and apparently can meet their water requirements with water obtained from their food. Eared grebes are gregarious migratory birds; they typically concentrate at a few major stopover sites, especially during the autumn migration (Palmer, 1962; Cramp and Simmons, 1977~.
|
From page 97... ...
It is not known whether or not food resources during the fall in the Salton Sea, Pacific Ocean, and Gulf of California would be able to support all of the grebes that visit Mono Lake if they visited these areas earlier in the autumn than they do now. The primary feature of Mono Lake of importance to eared grebes is the abundance of brine shrimp.
|
From page 98... ...
would not stay long at Mono Lake or molt heavily if mean lakewide brine shrimp densities were below 25,000/m2 or if similarly high local concentrations of shrimp could not be located. On the other hand, grebes arriving in poorer condition might stay for a while and attempt to slowly fatten themselves, even if brine shrimp densities were lower.
|
From page 99... ...
Grebes would then be forced to interrupt or delay their molt until they reached wintering areas, as they apparently do in eastern North America (Palmer, 1962~. If brine shrimp densities reached a level so low that it would be impossible for grebes to rapidly fatten themselves (probably somewhere below 20,000 shrimp/m2)
|
From page 100... ...
The impact on the North American population would probably be manifested in greater year-to-year variations in population size than occur now. If grebes were largely redistributed among other stopover sites when Mono Lake's food resources became comparable to those at other lakes, there might be a reduction in the North American population, but its magnitude is impossible to predict.
|
From page 101... ...
Certainly, Mono Lake is of major importance to this species in California (Winkler, 1982~. The time of arrival of phalaropes at Mono Lake coincides with the presence of immense numbers of brine shrimp and brine flies.
|
From page 102... ...
The principal prey of red-necked phalaropes at Mono Lake is the brine fly (Jehl, 1986~. The phalaropes take adult flies, as well as pupae and larvae; they will eat brine shrimp when brine flies are not available.
|
From page 103... ...
and they forage over much of the lake's surface for brine shrimp and brine flies. Given the virtual absence of any quantitative data on this species at Mono Lake, it is difficult to evaluate habitat requirements, except that it is clear that the lake provides a foraging habitat and a location for molting while staging in preparation ~ or migration to South America (Jehl, 1986~.
|
From page 104... ...
nest on several of the islands and islets in Mono Lake. In addition, California gulls nesting elsewhere in the Great Basin may visit Mono Lake during migration (J.
|
From page 105... ...
Given the lack of precision in estimates of the world population, the Mono Lake population is likely to be between 15 and 25 percent of the breeding population of California gulls. The Mono Lake colony is the second largest known California gull colony in North America (Conover, 1983~.
|
From page 106... ...
is caused by a scarcity of brine shrimp early in the season at the time of egg formation. Energy for egg production is apparently not sufficient for the female gulls to produce a clutch of three full-sized eggs.
|
From page 107... ...
California gulls at Mono Lake have three requirements of their habitat. They need predator- and disturbance-free areas on which to breed, they require a plentiful, nearby source of food; and they need access to fresh water.
|
From page 108... ...
studied habitat selection by California gulls nesting in Wyoming and found that gulls nesting in shrubbery had higher nesting success than those nesting in the open. Gull chicks can die from overheating, and in some cases vegetation or rock crevices provide protection from insola tion (Salzman, 1982; Chappell et al., 1984~.
|
From page 109... ...
The vast majority of the prey was brine shrimp, with small amounts of brine flies, fish, and freshwater insects. Garbage had been eaten as well.
|
From page 110... ...
Summarizing the information on birds, large numbers of eared grebes, red-necked phalaropes, Wilson's phalaropes, and California gulls use the lake and depend on the brine shrimp and brine flies for their food. Additionally, the gulls require safe refuges on which to nest.
|
From page 111... ...
Pp. 1154 in The Brine Shrimp Artemia.
|
From page 112... ...
1977. Development of sodium regulation and de nova synthesis of Na+K-activated ATPase in the larval brine shrimp Artemia salina.
|
From page 113... ...
1981. Comparative Population Ecology of the Brine Shrimp Artemia.
|
From page 114... ...
1981. Ecological physiology of the larval brine fly, Ephydra hians, an alkaline-salt lake inhabiting Ephydrid.
|
From page 115... ...
1983b. Breeding Success of California Gulls and Caspian Terns on the Paoha Islets, Mono Lake, California, 1983.
|
From page 116... ...
Pp. 79-96 in The Brine Shrimp Artemia.
|
From page 117... ...
1983. Large, deep salt lakes: a comparative limnological analysis.
|
From page 118... ...
1985. Population Size and Breeding Success of California Gulls at Mono
|
From page 119... ...
feet of anoxia on nucleotide metabolism embryos of the brine shrimp.
|
From page 120... ...
1983. Genetic and morphological similarity of two California gull populations with different life history traits.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.