Terrestrial biology

Ecosystem comparisons of oasislakes and soils

G. M. SIMMONS, JR., B. C. PARKER, F. C. T.ALLNUTT, D. P. BROWN, D. D. CATHEY, and K. G.

SEABURG

Virginia Polytechnic Institute and State UniversityBlacksburg, Virginia 24061

During the 1978-79 field season, the ecosystem com-parisons of oasis lakes and soils (EcoLs) project followedup on last season's preliminary studies of ten lakesamong the unusual and highly diverse lake ecosystemslocated within a relatively small area of about 3,000 km2in southern Victoria Land. Focusing on Lakes Fryxelland Hoare, we used the wide variety of limnologicalmethods described earlier (Parker and Simmons, 1978)and also used a team of research divers to make the firstdirect underwater observations and sampling of benthicalgal mats.

The general objectives of the ECOLS project are to un-derstand the interactions between dry valley (or oasis)lakes and their associated soil and glacial meltstream in -puts and to assess the mechanisms by which the bioticcommunities have evolved in these arheic (i.e., nonout-flowing) antarctic lakes.

The first ECOLS season indicated that the planktoncommunity of Lake Fryxell was the most productive andthat of Lake Vanda the least productive in terms of car-bon-14 measured photosynthesis, extractable chloro-phyll a, adenosine triphosphate, and community diver-sity. Lakes Bonney, Joyce, Miers, and Hoare, in thatorder, fell between Lakes Fryxell and Vanda. The sec-ond field season has confirmed that, while seasonal anddepth variability in numerous measurements occurs,Lake Fryxell consistently remains more productive thanLake Hoare. The list of selected measurements fromthese two lakes in the accompanying table documentsthis point. Much more data are now being interpreted.

The maximum depth of attached blue-green algal matcommunities in highly oxygenated Lake Hoare remainsobscure, but we do know that the anaerobic, sulfide-richlayer below 10-11 meters is the limit for blue-green algalmats in Lake Fryxell. Of considerable interest is the ob-servation that well-developed mat communities in LakeHoare occur at the peizometric depth of about 8 meters,where the light intensity is equal to or less than 1 percentof the photosynthetically available surface radiation.

This presence of well-developed algal mats at low lightlevels is even more unusual when one recognizes thatthis lake receives no light for at least 4 months duringthe antarctic winter and very little or no light duringmost of the remaining months of the year. Thus, thechromatic adaptive capability of these deep benthic at-tached algae may reach a maximum in this type of lake.

Two years of data on orthophosphate concentrationlevels and phosphorus-33 uptake experiments havedemonstrated that phosphorus is a major limiting nu-trient to the plankton of these southern Victoria Landlakes. This degree of limitation appears to follow theorder:

Lake Vanda = Joyce > Hoare > Bonney (west lobe)> Fryxell > Miers.

Only in the monimolimnia of Lakes Fryxell and Bon-ney were phosphorus levels detectable by direct wetchemical analysis. In every lake studied, the Km + P0data greatly exceeded the ambient concentrations of dis-solved phosphorus, which means that phosphorus wouldbe taken up at greater velocities whenever it becameavailable. The mathematical model for Lake Bonney alsopredicted that phosphorus was limiting.

Acetylene reduction was significant in shallow andmoat water blue-green algal mats of Lakes Chad andFryxell and the blue-green algal communities in periph-eral waters of Lakes Hoare and Fryxell. The dominantblue-green algae in those shallow and peripheral watermats are heterocystous species (figure 1). In contrast, noconclusive acetylene reduction was detected in matstaken from deeper waters beneath the ice of these lakes.The deeper water mats also lacked heterocystous blue-green algae, consisting primarily of Oscillatoria, Phormi-dium, and/or Schizothrix spp.

Although there is limited ammonium and nitrate ionconcentration data, it is clear that nitrogen fixation and

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HFigure 1. Anabaena sp. with heterocysts and developing ak-metes, while actively fixing nitrogen In Lake Hoare, southern

Victoria Land (approximately 188 x).

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sc:-A.

Table 1. Data for select measurements during 1978-79 austral summer for Lakes Fryxell and Hoare *

Measurement Lake FryxellLake Hoare

Water Column Adenosine Tnphosphate (Extractable, ng 11)

Overall Range Detected 3 -435 1 -69Season's Range for Means of All Water Samples for Given Sample Dates 29 -123 3 -49

Chlorophyll a(Extractable, 1Lg 11)Overall Range Detected 0.3 -18 0.02-5Season's Range for Means of All Water Samples for Given Sample Dates 4 -7 0.2 -4

Ammonium Nitrogen(AM, as NH4-N)Range with Depth and from Habitat-to-Habitat 0.26-0.51 0.31-6.1

Nitrate Nitrogen(SM, as NO3-N)Range with Depth and from Habitat-to-Habitat 0 -0.320.34-2.5

Detectable Significant Nitrogen(C21-12)-flxing ActivityShallow Moat or Peripheral Water Mats (Anabaena in Hoare; Nostoc + +Deep Water Mats Beneath Permanent Ice (No Heterocystous Blue-green Algae; only

Oscillatonaceae) ± -Dissolved Silicate Range

(SM, as Si(OH)4) 11 -69 10 -1300 0

Orthophosphate-P (except 1-2(LM, as PO4-P) in monimolimnion)* Lake Chad, which has extensively developed, attached heterocystous blue-green algal mats, also showed significant acetylene

reduction.

the presence of heterocystous species occurred in everycase where there was little available fixed nitrogen (<0.6SM-N). We hypothesize that light and temperature maybe important variables for nitrogen-fixing blue-greenalgal communities. That is, the shallow pool and moatwaters would receive significantly more light and per-haps enable slightly higher temperatures to develop inthe mats. It has been suggested that these features areimportant for nitrogen fixation on Signy Island (Foggand Home, 1970). We shall test this hypothesis nextseason.

Considering the ecological roles of the attached deepwater benthic blue-green algal mats, Wilson (1965)pointed out that attached mats become filled with gas,

tear away from their substrate, rise through the waterto the ice water interface, and then gradually melt orthrough ablation reach the upper ice surface. They thendry up and blow away. Holm-Hansen (1963) found thatmany of these antarctic algae were viable after lyophi-lization or desiccation. Since plankton productivity is lowand the water is supersaturated with oxygen, it may bethat the gas in these mats is oxygen. This unique eco-logical phenomenon will be studied more intensivelynext season.

Besides being a mechanism for distribution of the al-gae, loss of mats from lakes is a major mechanism bywhich nutrients and organic matter are removed.Through the first scuba diving reconnaissance of Lakes

Figure 2. Floating blue-green algal mat In Lake Bonney,southern Victoria Land (approximately 49x).

Figure 3. First underwater photographs of attached blue-green algal mat communities, Lake Hoare, southern Victoria

Land (approximately 0.5x).

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Fryxell and Hoare during the early season, extensiveblue-green algal mat community appeared relatively flat.By January, mats were lifting off in large pieces (figures2 and 3). This biological phenomenon is significant notonly to the present geochemistry of the dry valley lakesbut also because the accumulation of mat pieces frozenin the ice may reduce light penetration in the water col-umn and thus phytoplankton production. This signifi-cance has not been previously recognized.

An artificial substrate system (Cairns et al., 1969) wasused to study colonization rates and composition ofplanktonic and benthic microfaunal communities. Thelength of times required to reach 99-percent speciesequilibrium in both lakes was considerably shorter in thebenthic mats than in the limnetic zone. In addition, LakeHoare had fewer species at equilibrium than did LakeFryxell and took longer to reach equilibrium than LakeFryxell. In comparable temperate studies (Cairns, Kuhn,and Plaflin, 1979), colonization was found to takelonger in oligotrophic systems than in eutrophic lakes.This also emphasizes the greater productivity of LakeFryxell. The protozoan colonization rate of the artificialsubstrates fits the hypothetical model for island coloni-zation proposed by McArthur and Wilson (1963). Smallparticle feeders dominated the microfaunal communi-ties indicating an organically rich substrate. Studies ofchlorophyll a levels from the artificial substrates alsoshowed increases during the season as a result of an

increase in phytoflagellate density. The increase in thesedensities may have been related to increased solar ra-diation and nutrient inputs from surrounding melt-streams.

We are grateful for support of this research throughNational Science Foundation grant DPP 76-23996. Also,we would like to acknowledge the other members of ourfield research team: Dale Andersen, John Baggerly,Debbie Biesemeyer, Jim Gilicrist, Lita Proctor, Mike VanBrunt, and Martha Wolfe.

ReferencesCairns, J . , Jr., M. L. Dahlberg, K. L. Dickson, N. Smith, and

W. T. Wailer. 1969. The relationship of freshwater proto-zoan communities to the MacArthur-Wilson equilibriummodel. The American Naturalist, 103: 439-54.

Cairns, J., Jr., D. L. Kuhn, and J. L. Plafkin. In prep. Protozoancolonization of artificial substrates.

Fogg, G. E., and A. J . Home. 1970. Algal physiology. In Ant-arctic Ecology, ed. M. W. Holdgate, 2: 639-50. London: Ac-ademic Press.

Holm-Hansen, 0. 1963. Viability of blue-green and green algaeafter freezing. Physiologia Plantarum, 16: 531-40.

MacArthur, R. H. and E. 0. Wilson. 1963. An equilibrium the-ory of insular zoogeography. Evolution, 17: 373-87.

Parker, B. C. and G. M. Simmons, Jr. 1978. Ecosystem com-parisons of oasis lakes and soils. Antarctic Journal of the UnitedStates, 13(4): 168-69.

Wilson, A. T. 1965. Escape of algae from frozen lakes andponds. Ecology, 46(3): 376.

Sex ratio in Belgica antarctica

JOHN S. EDWARDS

Department of ZoologyUniversity of Washington

Seattle, Washington 98195

JOHN G. BAUST

Department of BiologyUniversity of Houston

Houston, Texas 77004

PATRICK SUGG

Department of ZoologyUniversity of Washington

Seattle, Washington 98195

During the austral summer of 1978-79, we continuedour 1977-78 studies on sex ratio in populations of thewingless chironomid fly Belgica antarctica in the vicinityof Palmer Station, Anvers Island, in conjunction with

studies of low-temperature tolerance (Baust, Edwards,.and Brown, 1979; Baust and Edwards, 1979).

It is a basic tenet of population genetics that, as shownby Fisher (1930), the sex ratio of bisexually reproducinganimals should approximate 1:1. Departures fromequality, as in facultatively parthenogenetic insects (e.g.,Chironomidae, Lindberg, 1971), favor females. There-fore, reports of male predominance in populations of B.antarctica (Strong, 1967; Peckham, 1971) are of excep-tional evolutionary interest.

In our fieldwork, to eliminate the possibility that pre-vious reports of male-biased sex ratio reflected merelytemporary deviations, we made collections of adult ag-gregations on moss rock and water surfaces throughoutthe emergence seasons. The sex ratio in samples takenduring the 1977-78 season are shown in the accompa-nying chart. Similar results were obtained during 1978-79. The overall ratio of about 6 males (d) to 1 female('i ) confirms earlier reports and further shows that thebias persists throughout the emergence season. The ac-centuated male bias early in the season may be an ex-ample of the protandry known in other chironomids(Danks and Oliver, 1972).

To eliminate possible sampling artefacts, a measure ofsex ratio at adult emergence is essential. We obtainedsuch a measure during the 1978-79 season by samplingcast pupal cuticles (exuviae). The pronounced sexualdimorphism of the exuviae allows unequivocal deter-mination of sex. During warm periods groups of adults,which probably were cohorts derived from single egg

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