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4 Biological System of Mono Lake INTRODUCTION Mono Lake is a productive aquatic ecosystem but with very few species. The lake has two major habitats--an open water pelagic region and a nearshore littoral region. Trophic structure, the linkages within the food web, is different in these two habitats. In the pelagic waters, phytoplankton are the primary producers, using sunlight to reduce inorganic carbon to organic matter. 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). No fish live in Mono Lake. The cur- rent combination of high salinity and alkalinity makes it impossible for fish to survive. Inputs of organic material to the profundal sediments, those sediments under the pelagic zone, consist largely of fecal pellets and cysts of brine shrimp and detritus. No zoobenthos has been record- ed in the profundal sediments, which are anoxic much or all of the year. The role of protozoans and bacteria as food for brine shrimp or as decomposers of organic matter remains undetermined, but is likely to be of importance. In the littoral region, the overlying waters have the same planktonic organisms as the pelagic zone and an intermittent complement of organisms associated with the bottom. The benthic habitat is highly variable as a func- tion of depth and substrate (Herbs", 1986; Pelagos Corpora- tion, 1987~. The principal constituents are a microbial 69

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70 The Mono Basin Ecosystem community, an algal flora, and a brine fly, Ephydra hians, which feeds upon the benthic algae and probably bacteria and detritus derived from a number of sources, some likely to be terrestrial. The brine fly is prey to a variety of birds including phalaropes, and to a lesser extent eared grebes and gulls. Although the trophic structure of Mono Lake is simple in comparison with that in many aquatic ecosystems, the lack of sufficient information on key components such as bacteria and protozoans precludes the formulation of a complete, quantitative description of carbon or nitrogen _~ ~ ~ . Two trophic links that have received some quantitative attention are the algae- brine shrimp and brine shrimp-bird links. Grazing by brine shrimp contributes to a decline in phytoplankton during the spring and maintains a low algal abundance during the summer (Lenz, 1982, Jellison, 1985~. The regeneration of ammonium by the brine shrimp, in turn, sustains the growth of the phytoplankton (Jellison and Melack, 1986~. The decline in brine shrimp in the autumn can be, in part, attributed to predation by the grebes (Cooper et al., 1984~. The remainder of this chapter discusses the ecological and physiological aspects of the components of the food web--and primary producers and decomposers (bacteria, phytoplankton, and phytobenthos), primary consumers (brine shrimp and brine fly), and secondary consumers (aquatic bird populations). flow through the whole food web ECOLOGICAL ASPECTS OF AQUATIC PELAGIC AND LITTORAL ORGANISMS Primary Producers and Decomposers Bacteria The abundance and significance of bacteria in alkaline, saline lakes are not well-known. Bacteria probably func- tion as both decomposers and primary producers in the food web of Mono Lake. Recent research by R. S. Oremland and his associates indicates that the same major processes that are carried

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Biological System of Mono Lake 71 out by anaerobic bacteria in fresh water and marine habi- tats also occur in alkaline, saline lakes. They have exam- ined, for example, methanogenesis, sulfate reduction, and other anaerobic processes in Big Soda Lake, Nevada (Orem- land et al., 1982, 1985; Iversen et al., in press). In Mono Lake, R. S. Oremland (U.S. Geological Survey, Menlo Park, personal communication) has discovered that large quanti- ties of methane are leaving the sediments even though relatively small amounts of methane are produced at the sediment-water interface. He argues that most of the methane-rich gas seeps in the lake produce biogenic meth- ane that is derived from the anaerobic decomposition of fossil organic matter by bacteria. However, the methane from one seep associated with a hot spring had a more thermogenic character, indicating a chemical process that does not involve bacteria. The presence of numerous gas seeps on the floor of Mono Lake is supported by the dis- covery that large areas of bottom sediments are disturbed by gas bubbles (Pelagos Corporation, 1987~. Pelagic, aerobic bacteria are often abundant in alkaline, saline lakes. In freshwater lakes and in the ocean, con- centrations of pelagic bacteria between 105 and 1 o6 bac- teria/ml are commonly observed. . . . , . ~ . . . .. However, alkaline, saline lakes In east At~r~ca contain from 107 to 108 bacteria/ml (Kilham, 1981~. These large concentrations presumably rep- resent a balance between the availability of organic sub- strates in these highly productive lakes and the abundance of heterotrophic organisms that consume bacteria (e.g., ciliates). Pyramid Lake in Nevada is the only alkaline, saline lake in the Great Basin in which a detailed study of bacteria has been carried out. Hamilton-Galat and Galat (1983) found from 5.1 x 105 to 2.5 x 107 bacteria/ml in Pyramid Lake. Bacterial numbers more or less tracked periods of algal production. One reason that bacterial numbers are not higher in Pyramid Lake is that the lake is only moderately productive (i.e., mesotrophic). For Mono Lake, R. S. Oremland (personal communication) and R. W. Harvey (U.S. Geological Survey, Menlo Park, personal com- munication) have observed bacterial concentrations of between 1.4 and 2.0 x 107 bacteria/ml. On average, these concentrations are considerably higher than most found in

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72 The Mono Basin Ecosystem Pyramid Lake and generally similar to those observed in the lakes in east Africa. Phyto plank ton and Phyto b e nthos The algal community of Mono Lake includes few species, as is typical of hypersaline waters. The phytoplankton is dominated by a coccoid green alga, NannochZoris sp., cyan- obacteria, and diatoms (Mason, 1967; Lovejoy and Dana, 1977; Melack, 1983~. The benthic algae are composed of Nitzschia frustum, other less common diatoms, filamentous cyanobacteria, and the green alga, Ctenocladus circinnatus (Herbs", 1986~. 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. 1~. During the winter, the phytoplankton are abundant throughout the lake, and after the onset of the seasonal thermocline in early spring, the algae increase in the upper water. This increase was reduced during 1984, 1985, and 1986 after the initiation of meromixis. As described in chapter 3, the chemical stratification reduced vertical mix- ~ -- ~ ~ ~ ~~ ~~ nutrient, nitrogen, to the euphotic zone. A rapid decrease in algal abundance occurs in late May and June above the thermo- cline. During the summer, the phytoplankton are sparse in the upper waters and abundant in the deeper, cold and dim or dark waters. In midsummer, higher chlorophyll concen- trations occur in a layer coinciding with the chemocline. In autumn, algal concentrations increase in the upper waters as thermal stratification weakens and brine shrimr, sing, wn~cn reoucecl the supply of the limiting numbers decline (Figure 4.1~. Primary productivity measurements spanning the period from 1983 to 1985 vary from 340 to 540 g carbon/m2/yr (Jellison and Melack, in press). Mono Lake would thus be classified as eutrophic. Production was higher during the spring of 1983 than in 1984 and 1985; the difference may be at least partially attributed to meromixis.

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Biological System of Mono Lake 60~ - CL O 30 o I O 82 /~` 86 73 , i, . , i, I `, , I 1 1 1 _ 'v' WN I~ - I I~ at/ 1 J F M A M J J A S O N D TIME (months) 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~. A. monica, a member of the A. franciscana superspecies, is now considered a sibling species (Bowen et al., 1985~. The zooplankton also includes protozoans and has included roti- fers (Mason, 1967~. The abundance of brine shrimp in Mono Lake varies seasonally (Lenz, 1982, 1984; Figure 4.2~. The brine shrimp hatch from overwintering cysts from January through May. By mid-May, the first adult brine shrimp are present. For

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74 The Mono Basin Ecosystem 50 45 40 35 - Standard Enora 55 ~ Naupill ~ ~ ~ I I I~Adults O~ in J F M A M J J A S O N MONTH . , D FIGURE 4.2 Seasonal abundance of brine shrimp at Mono Lake in 1985. Lakewide mean of 10 stations (three vertical net tows per station). approximately one month females bear live young, which mature rapidly in the warm upper mixed layer. In June females switch to oviparous reproduction. The diapause eggs lie dormant on the bottom of the lake until the fol- lowing winter. During the summer, brine shrimp are abun- dant 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. Studies conducted with similar methods since 1978 per- mit interannual comparisons of brine shrimp abundances and reproductive characteristics (Lenz, 1984; G. Dana, R. Jellison, and J. M. Melack, University of California, Santa Barbara, unpublished). Statistically significant interannual

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Biological System of Mono Lake 75 differences in abundances of first-generation adults (late May to June populations) occurred. In 1979, 1984, and 1986 brine shrimp numbered between 19,000 and 31,000 ani- mals/m2. whereas from 1980 to 1983 numbers were only . . ~ . . 2,400 to 5,700 an~ma~s/m~. dances (first- and second-generation adults) were much higher in 1981 and 1982 than in other years. A number of factors are associated with these variations. First- generation adult abundances denend on the number of cysts Maximum midsummer aoun- . available for hatching, hatching success, and survival to adulthood. In laboratory experiments, Dana and Lenz (1986) determined that salinities in the period from 1979 to 1986 are not indicated as a cause for changes in hatching success. Emergence trap trials in spring 1985 showed that ~ ~ . ~ . ~ . ~ . . ~7 ~ J very low hatching occurred In sediments In anoxlc water below the chemocline (Dana et al., in press). In contrast, large numbers of cysts lying in sediments under the oxy- genated mixolimnion hatched. The number of cysts available depends on the production of cysts during the previous year and possibly past years and on the viability of the cysts. Cyst production is related to brood size, numbers of ovigerous females, the percentage of those females producing cysts, and the time interval between broods. Brood size varied from 30 to 140 eggs per brood from 1983 to 1986 and is explained primarily by differences in female length and algal abundance. Second-generation abundances depend on the abundance, percent ovoviviparity, and fecundity of the first-generation females. Recruitment to adults depends on survival of naupliar and juvenile stages. Differences in all these factors occurred from 1982 to 1986. The switch from ovoviviparity (live bearing) to oviparity (cyst production) occurred at the time of dec- reasing phytoplankton in all years studied. In years with a substantial spring hatch, the first generation dominates the population. When the spring hatch is relatively low, first- generation 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) and small (square meters) spa- tial scales and varies on time scales from hours to days to seasons (Lenz, 1982; Melack, 1985; Lenz et al., 1986; Conte

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76 The Mono Basin Ecosystem et al., in press). These differences in concentrations of brine shrimp result in variable profitability of foraging for Small- spr~ngs where upwelling varies widely in strength and hence in the entrainment of brine shrimp. Mason ( 1966) hypothesized that the very dense plumes that formed near shore, but not in association with springs, result from thermal currents and behavioral responses of the animals. Foam lines con- tain concentrations of living ant! dead brine shrimp as well as other debris and can stretch for hundreds of meters. These features seem to delimit water masses. Large-scale patchiness has been documented by sampling transects and lakewide grids. Abundance differences between the eastern and western halves of the lake are common. The degree of variability differs seasonally and appears greater during transition periods such as spring and autumn. the birds (see section on bird populations below). scale patches are associated with sublacustrine . . . ~ . - - ., Current sampling programs are designed to assess the lakewide abundance of brine shrimp and include biweekly or monthly samples from 10 pelagic stations. Regular sampling is not performed in water overlying the littoral region or at sites of aggregation such as springs. Therefore, while providing statistically sound estimates of the overall abun- dance of brine shrimp, the sampling does not include sites that may be of particular importance to some birds some of the time. 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. The predominant dipteran is the brine fly, Ephydra hians, but other species are present, such as the deer fly (Chrysops spy and the long-legged fly (Hydrophorus plum- beus). The biting midge (Culicoides occidentalis) is also found among the macroinvertebrates (Herbs", 1986~. The seasonal dynamics of the macroinvertebrates are not well-known. However, recent research on brine flies by Herbst (1986) using the third instar and pupae as popula- tion~ indices showed a phase of rapid population growth

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Biological System of Mono Lake 77 occurring in the spring (May and June), a summer maximum (July through September), a gradual decline in the autumn, _ _ : ~1 ~ ~ late winter through early spring. Since seasonal dynamics of the phytobenthic bac- terial and algal populations (diatoms and filamentous algae) are unknown, one cannot determine if the zoobenthic com- munity, as reflected by numbers of brine flies, is tracking periods of algal production. The spatial distribution of brine flies is heterogeneous on large (square kilometers) and small scales (Herbs", in press). . ~ ~ and minimal abundance ~ rom , (square meters) Small-scale patches are associ- ated with tufa pinnacles and nearshore grasses, which are excellent substrates for larval and pupal attachment. Large-scale patchiness has recently been documented by video and lakewide bathymetric transects (Pelagos Corpora- tion, 1987~. Large mats of pupae have been found on dead submerged grasses along the eastern shore and on under- water tufa and hard-surface sediments at depths sometimes greater than 10 m in the central and eastern provinces, as shown in Figure 4.3. Abundance differences observed be- tween tufa-hard rock shoal regions and soft mud-sand lake bottom sediments common to the eastern and central prov- inces are probably due to the larvae's inability to attach to smooth surfaces. The placement of eggs by brine fly females at depths greater than a few meters has been ob- served (Pelagos Corporation, 1987~. This observation raises questions about the typical mechanism of oviposition re- ported for other ephydran flies, including whether females utilize respiratory mechanisms other than gas bubble entrapment for vertical descent. 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) algal responses to experimental increases in the salinity of Mono

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78 The Mono Basin Ecosystem /~ EphydrahiansMats ' 1 Paoha _\ z / \ \` Island I / \~ \\ ~/O~,N OCR for page 69
Biological System of Mono Lake 79 arsenic, and fluoride contribute to these reductions in growth. Overall, Chapman's results indicate that a salinity of about 175 g/1 results in fairly large decreases in growth of the two currently dominant algae. A number of species of phytoplankton, not currently extant or dominant in Mono Lake, are known to grow well at salinities reaching 200 g/1 (Hammer, 1986; Melack, in press). In particular, a green alga, DunalieZ/a sp., now occurs in low numbers in Mono Lake, and a related species, D. parka, grew best in Mono Lake concentrated to 150 g/1 . . and still grew slowly at 235 g/1 (Chapman, 1982). Herbst (1986) isolated a clone of Ctenocladus circinnatus from Mono Lake and determined its growth rate and yield at salinities of 25, 50, 75, 100, and 150 g/1. The solutions were obtained by dilution or low-temperature evaporation of Mono Lake water. The experiments indicated decreased growth and yield at 75 and 100 g/1 and no growth at 150 g/l. Primary Consumers A fundamental requirement for aquatic organisms living in saline lakes is to have sufficient "free water," or water that is available to sustain vital cellular activities. (In aquatic organisms, water molecules forming hydration shells are termed "bound water"; water molecules not associated with these shells are termed "free water.") This biological axiom is most evident in the osmotic effects of salinity upon the growth and larval development of brine shrimp and brine flies. If the salinity of the medium in which the organisms reside is sufficiently high, the thermodynamic forces responsible for the osmotic gradient will not allow sufficient free water to remain inside the organism. The loss of free water will in turn cause an inhibition or ces- sation of metabolic processes. 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. These solutions contain a large amount of free water and behave in a manner

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110 The Mono Basin Ecosystem major refuse dump within 15 km of the colonies and exten- sive agricultural fields nearby, Mono Lake has only a few small refuse dumps nearby and has no nearby agricultural activity that would sustain a large gull population twinkler, 1 983b). There is a lack of information on the types and availability of prey taken by gulls early in the breeding season, and additional sampling is required to determine the importance of foods other than brine shrimp throughout the season. 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. Present cen- sus techniques are statistically inadequate to detect small but possibly biologically significant changes in avian num- bers or temporal patterns of use of Mono Lake. Likewise, we do not know critical food densities below which the invertebrates taken by birds are not sufficient to provide needed body weight, or how the density of available prey will change with overall prey densities. These data are needed if we are to quantitatively predict how bird popula- tions will respond to changing food supplies with changing lake salinity. Clearly, however, if the invertebrate popula- tions are drastically reduced, there will be reductions in the number of birds visiting and using Mono Lake. REFERENCES Them, C. R. 1980. The energetics of migration. Pp. 175- 224 in Animal Migration, Orientation, and Navigation, S. Gauthreaux, Jr., ed. New York: Academic Press. Bowen, S. T. 1962. The genetics of Artemia satina. I. The reproductive cycle. Biol. Bull. 122:25-32. Bowen, S. T., E. A. Fogarino, K. N. Hitchner, G. L. Dana, V. H. S. Chow, M. R. Buoncristiani, and I. R. Carl. 1985. Ecological isolation in Artemia: population differ- ences in tolerance of anion concentrations. J. Crusta- cean Biol. 5:106-129.

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Biological System of Mono Lake 111 Busa, W. B., and J. H. Crowe. 1983. Intracellular pH regulates the dormancy and development of brine shrimp (Artemia salina) embryos. Science 221:366-368. Busa, W. B., J. H. Crowe, and G. B. Matson. ~ 982. Intracellular pH and the metabolic status of dormant and developing Artemia embryos. Arch. Biochem. Bio- phys. 216:711-718. Chapman, D. J. 1982. Investigations on the salinity toler- ance of a diatom and green algae isolated from Mono Lake. Abstract from Mono Lake Symposium, Santa Barbara, Calif., May 5-7, 1982. Chappell, M. A., D. L. Goldstein, and D. W. Winkler. 1984. Oxygen consumption, evaporative water loss, and tem- perature regulation of California gull chicks (Laws cali- fornicus) in a desert rookery. Physiol. Zool. 57:204-214. Clegg, J. S. 1964. The control of emergence and metabo- lism by external osmotic pressure and the role of free glycerol in developing cysts of Artemia salina. J. Exp. Biol. 41:879-892. Clegg, J. S. 1974. Interrelationships between water and metabolism in Artemia salina cysts: hydration-dehydra- tion from the liquid and vapour phases. J. Exp. Biol. 61:291-308. Clegg, J. S. 1976a. Hydration measurements on individual Artemia cysts. J. Exp. Zool. 198:267-272. Clegg, J. S. 1976b. Interrelationships between water and cellular metabolism in Artemia cysts. II. Carbohydrates. Comp. Biochem. Physiol. 53A:83-87. Clegg, I. S. 1976c. Interrelationships between water and cellular metabolism in Artemia cysts. III. Respiration. Comp. Biochem. Physiol. 53A:89-93. Clegg, I. S. 1978. Interrelationships between water and cellular metabolism in Artemia cysts. VIII. Sorption iso- therms and derived thermodynamic quantities. J. Cell. Physiol. 94:123- 137. Clegg, J. S., and F. P. Conte. 1980. A review of the cellular and developmental biology in Artemia. Pp. 11- 54 in The Brine Shrimp Artemia. Vol. 2. Physiology, Biochemistry, Molecular Biology. G. Persoone, P. Sorgeloos, O. A. Roels, and E. Jaspers, eds. Wetteren, Belgium: Universa Press.

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112 The Mono Basin Ecosystem Collins, N. C. 1975. Population biology of a brine fly (Diptera: Ephydridae) in the presence of abundant algal food. Ecology 56:1139- 1148. Collins, N. C. 1980a. Population ecology of Ephydra cinerea Jones (Diptera Ephydridae), the only benthic metazoan of the Great Salt Lake, USA. Hydrobiologia 68:99- 112. Collins, N. C. 1980b. Developmental responses to food limitation as indicators of environmental conditions for Ephydra cinerea Jones (Diptera). Ecology 61:650-661. Conover, M. R. 1983. Recent changes in ring-billed and California gull populations in the western United States. Wilson Bull. 95:362-383. Conover, M. R., and D. O. Conover. 1981. A documented history of ring-billed and California gull colonies in the western United States. Colonial Waterbirds 4:37-43. Conte, F. P. 1977. Molecular mechanisms in the bran- chiopod larval salt gland (Crustacea). Pp. 143- 1 59 in Water Relations in Membrane Transport in Plants and Animals, A. M. Jungreis, T. K. Hodges, A. Kleinzeller, and S. G. Schultz, eds. New York: Academic Press. Conte, F. P. 1984. Structure and function of the crus- tacean larval salt gland. Pp. 45-106 in Membranes, J. F. Danielli, ed. International Review of Cytology, Vol. 91. Orlando, Fla.: Academic Press. Conte, F. P., S. R. Hootman, and P. I. Harris. 1972. Neck organ of Artemia salina nauplii: a larval salt gland. J. Comp. Physiol. 80:239-246. Conte, F. P., P. C. Droukas, and R. D. Ewing. 1977. Development of sodium regulation and de nova synthesis of Na+K-activated ATPase in the larval brine shrimp Artemia salina. I. Exp. Zool. 202:339-361. Conte, F. P., J. Lowy, J. Carpenter, A. Edwards, R. Smith, and R. D. Ewing. 1980. Aerobic and anaerobic metabo- lism of Artemia nauplii as a function of salinity. Pp. 126- 136 in The Brine Shrimp Artemia. Vol. 2. Physiol- ogy, Biochemistry, Molecular Biology. G. Persoone, P. Sorgeloos, O. A. Roels, and E. Jaspers, eds. Wetteren, Belgium: Universa Press. Conte, F. P., R. S. Jellison, and G. L. Starrett. In press. Nearshore and pelagic abundances of Artemia monica in Mono Lake, Calif. In Saline Lakes, J. M. Melack, ed.

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Biological System of Mono Lake Developments in Hydrobiology. Dr W. Junk Publishers. 113 Dordrecht, Netherlands: Cooper, S. D., D. W. Winkler, and P. H. Lenz. 1984. The effect of grebe predation on a brine shrimp population. I. Anim. Ecol. 53~1~:51-64. Cramp, S., and K. E. L. Simmons, eds. 1977. Handbook of the Birds of Europe, the Middle East and North Africa, Vol. 1. Oxford, England: Oxford University Press. 722 PP. Croghan, P. C. 1958. The osmotic and ionic regulation of Artemia salina. I. Exp. Biol. 35:219-233. Dana, G. L. 1981. Comparative Population Ecology of the Brine Shrimp Artemia. Master's thesis, San Francisco State University. 125 pp. Dana, G. L., and P. H. Lenz. 1986. Effects of increasing salinity on an Artemia population from Mono Lake, Cali- fornia. Oecologia 68:428-436. Dana, G. L., C. Foley, G. Starret, W. Perry, and J. M. Melack. In press. In situ hatching rates of Artemia monica cysts in hypersaline Mono Lake. In Saline Lakes, J. M. Melack, ed. Developments in Hydrobiology. Dordrecht, Netherlands: Dr W. Junk Publishers. Dick, W. J. A., and M. W. Pienkowski. 1978. Autumn and early winter weights of waders in north-west Africa. Ornis Scand. 10: 117- 123. 1986. Physiological , Effects of Salinity on Dormancy and Hatching in Mono Lake Artemia Cysts. Los Angeles, Calif.: Los Angeles Department of Water and Power. Drinkwater. L. E.~ and J. H. Crowe. Drinkwater, L. E., and ]. H. Crowe. 1987. Regulation of embryonic diapause in Artemia: env~ronmental and phys- iological signals. I. Exp. Zool. 241:297-307. Evans, P. R., and D. J. Townshend. In press. Site faith- fuIness of waders away from the breeding grounds: how individual migration patterns are established. In Proceedings of the Congress, Ottawa. Hamilton-Galat, K., and D. L. Galat. 1983. Seasonal variation of nutrients, organic carbon, ATP, and micro- crops in a vertical profile of Pyramid Lake, Nevada. Hydrobiologia 105:27-43. 19th International Ornithological bial standing .

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114 The Mono Basin Ecosystem Hammer, U. T. 1986. Saline Lake Ecosystems of the World. Monographiae Biologicae 59. Dordrecht, Netherlands: Dr W. Junk Publishers. 616 pp. Herbst, D. B. 1981. Ecological physiology of the larval brine fly, Ephydra hians, an alkaline-salt lake inhabiting Ephydrid. Master's thesis, Oregon State University, Corvallis. 65 pp. Herbst, D. B. 1986. Comparative Studies of the Population Ecology and Life History Patterns of an Alkaline Salt Lake Insect: Ephydra (Hyd~ropyrus) hians Say (Diptera: Ephydridae). Ph.D. dissertation, Oregon State Univer- sity, Corvallis. 222 pp. Herbst, D. B. In press. Comparative population ecology of Ephydra hians Say (Diptera: Ephydridae) at Mono Lake (California) and Abert Lake (Oregon). In Saline Lakes, J. M. Melack, ed. Developments in Hydrobiology. Dor- drecht, Netherlands: Dr W. Junk Publishers. Iversen, N., R. S. Oremland, and M. J. Kulg. In press. Big Soda Lake (Nevada). 3. Pelagic methanogenesis and anaerobic methane oxidation. Limnol. Oceanogr. Jehl, I. R., Jr. 1981a. Mono Lake: A vital way station for the Wilson's phalarope. Natl. Geogr. 160:520-525. Jehl, J. R., Jr. 1981 b. Mortality of Waterbirds at Mono Lake, California. Technical Report 81-133. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, J. R., Jr. 1981 c. The Biology of Northern Phalaropes at Mono Lake, California, 1981. Technical Report 81- 134. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, J. R., Jr. 1 982a. Biology of Eared Grebes at Mono Lake. California. Technical Report 82-136. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, J. R., Jr. 1982b. The Biology of Northern Phalaropes at Mono Lake, California, 1982. Technical Report 82- 146. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, J. R., Jr. California Gull Chicks at Special Reference to Populations on Technical Report 83-156. San Diego, Calif.: Hubbs-Sea World Research Institute. 6 pp. 1 983a. Comments on the Annual Census of Mono Lake, California with the Paoha Islets.

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Biological System of Mono Lake 115 Jehl, J. R., Ir. 1983b. Breeding Success of California Gulls and Caspian Terns on the Paoha Islets, Mono Lake, California, 1983. Technical Report 83-157. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, J. R., Jr. 1983c. The Biology of Eared Grebes at Mono Lake, California. Technical Report 83- 136. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, J. R., Jr. 1984. Comments on the Cooperative Gull Census of 1984, with Special Reference to the Paoha Islets. Technical Report 84- 167. Hubbs-Sea World Research Institute. lehl, I. R., Jr. 1985. The Cooperative Gull Census of 1985: Comments and Recommendations. Technical Report. 85- 183. San Diego, Calif.: Hubbs-Sea World Research Institute. 5 pp. Jehl, I. R., Jr. 1986. Biology of red-necked phalaropes (Phalaropus Zobatus) at the western edge of the Great Basin in fall migration. Great Basin Nat. 46:185-197. Jehl, I. R., Jr., and S. I. Bond. 1983. Mortality of eared grebes in winter of 1982-83. Am. Birds 37:832-835. Jehl, J. R., Jr., and C. Chase, III. In press. Foraging pat- terns and prey selection in avian predators: a compara- tive study in two colonies of California gull. Stud. Avian Biol. Jehl, I. R., Jr., and D. R. Jehl. 1981. Post-Fledging Mor- talitv of California Gulls. San Diego, Calif.: Technical Report ~ 1 - 135. San Diego, Calif.: Hubbs-Sea World Research Institute. Jehl, I. R., Ir., and D. R. Jehl. 1982. Post-Fledging Mor- tality of California Gulls, 1982. Technical Report 82- 147. ~ *, T Institute. Jehl, I. R., Ir., and S. A. Mahoney. 1983. Possible sexual differences in foraging patterns in California gulls and their implications for studies of feeding ecology. Colo- nial Waterbirds 6:2 ~ 8-220. Jehl, J. R., Jr., and S. A. Mahoney. In press. The roles of thermal environment and predation in habitat choice in the California gull (Laws californicus). Condor. Jehl, J. R., Jr., and P. K. Yochem. 1986. Movements of eared grebes indicated by banding recoveries. J. Field Ornithol. 57:208-212. San forego, cant.: nunos-~ea worm Research

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