Photosynthetic bacteria in meromictic lakes and stratified fjords of the Vestfold Hills,Antarctica

Thirteen meromictic lakes and two permanently stratified fjords in the Vestfold Hills, Antarctica, were surveyed in 1983 for photosynthetic bacteria. Burton Lake and Ellis Fjord were sampled throughout the year to determine seasonal variations. Physical and chemical parameters were recorded and related to the species present. The dominant species in waters with salinities of 100.7 g kg^–1 were Chlorobium vibrioforme and Chlorobium limicola with populations at the O₂–H₂S interface in the range 0.3 to 6.7 × 10⁶ ml^–1. Neither of these species was found at higher salinities. Thiocapsa roseopersicina and a Chromatium sp. were found in low numbers (< 10⁵ ml^–1) in most of the same waters as the Chlorobium spp. These bacterial phototrophs developed in a narrow band below the O₂–H₂S interface where both light and H₂S were available. Very low numbers (< 10² ml^–1) of Rhodopseudomonas palustris were found in both oxic and anoxic waters having salinity 148 g kg^–1. The dominance of the Chlorobium spp. is ascribed to their more efficient maintenance metabolism during the darkness, their faster growth at low light intensities (< 1 µE m^–2 s^–1) and the lack of selective filtering of incident light. The Chlorobium spp. grew well at –2 °C, but not –5°C in hypersaline waters. The concentration of H₂S had no apparent effect on the development of the bacterial flora. Viable cells were found to depths of 100 m in Ellis Fjord indicating that viability in total darkness could have been maintained for periods of the order of 1700 days.     

The plankton community of a young, eutrophic, Antarctic saline lake

A shallow, saline lake (Rookery Lake) close to the sea and surrounded by a penguin rookery was investigated during the austral spring and summer of 1996/1997. The proximity to the sea means that the lake is likely to have been formed recently during isostatic uplift. Inputs of carbon and nutrients from the penguin rookery have rendered Rookery Lake eutrophic compared with other brackish and saline lakes in the Vestfold Hills. Chlorophyll a concentration, bacterioplankton, heterotrophic nanoflagellate and phototrophic nanoflagellate abundances were all significantly higher than in other non-enriched lakes. The high productivity created seasonal anoxia during winter and spring below ice cover. The ciliate community resembled the marine community, and was dissimilar to that seen in older saline lakes within the Vestfold Hills. Thus Rookery Lake provides valuable evidence of the impact of natural eutrophication on an Antarctic lake, as well as of the evolution of the typical microbial community which dominates the older lakes of the Vestfold Hills. Accepted: 2 May 1999     

Temporal changes in zooplankton composition in a hypersaline,Antarctic lake subject to periodic seawater incursions

Colonisation of Lake Fletcher, a hypersaline, meromictic lake in the Vestfold Hills, Antarctica, by the calanoid copepod Drepanopus bispinosus, the cyclopoid copepod Oncea curvata and an undescribed cydippid ctenophore is discussed. In 1978, salinity directly under the ice was 66‰ and repeated net hauls found no zooplankton. In 1983, adults of D. bispinosus were found, and in 1984, a reproductively active population of this species. Surface water salinity in 1984 was 56‰. During winter 1986, surface salinity was 54‰ and three zooplankton species (D. bispinosus, O. curvata and an undescribed cydippid ctenophore) had established populations in the lake. In 1986/87, high tides caused nearby Taynaya Bay to flood into the lake, and three further species (the calanoid, Paralabidocera antarctica, and two harpacticoids, Harpacticus furcatus and Idomene sp.) were found in the lake. It appears that periodic flooding after 1978 caused a salinity decrease in the lake from 66 to 54‰, and this enabled some invertebrate species to maintain year-round populations, whereas others require marine incursions to re-establish summer only populations.     

Ace Lake: three decades of research on a meromictic,Antarctic lake

Ace Lake (Vestfold Hills, Antarctica) has been investigated since the 1970s. Its close proximity to Davis Station has allowed year-long, as well as summer only, investigations. Ace Lake is a saline meromictic (permanently stratified) lake with strong physical and chemical gradients. The lake is one of the most studied lakes in continental Antarctica. Here, we review the current knowledge of the history, the physical and chemical environment, community structure and functional dynamics of the mixolimnion, littoral benthic algal mats, the lower anoxic monimolimnion and the sediment within the monimolimnion. In common with other continental meromictic Antarctic lakes, Ace Lake possesses a truncated food web dominated by prokaryote and eukaryote microorganisms in the upper aerobic mixolimnion and an anaerobic prokaryote community in the monimolimnion, where methanogenic Archaea, sulphate-reducing and sulphur-oxidizing bacteria occur. These communities are functional in winter at subzero temperatures, when mixotrophy plays an important role in survival in dominant photosynthetic eukaryotic microorganisms in the mixolimnion. The productivity of Ace Lake is comparable to other saline lakes in the Vestfold Hills, but higher than that seen in the more southerly McMurdo Dry Valley lakes. Finally, we identify gaps in the current knowledge and avenues that demand further investigation, including comparisons with analogous lakes in the north polar region.     

Late-Holocene succession of dinoflagellates in an Antarctic fjord using a multi-proxy approach: paleoenvironmental genomics, lipid biomarkers and palynomorphs

Recent work has shown that paleoenvironmental genomics, i.e. the application of genomic tools to analyze preserved DNA in sedimentary records, is a promising approach to reconstruct the diversity of past planktonic communities. This provides information about past ecological and environmental changes. A major advantage of this approach is that individual species, including those that did not leave other characteristic markers, can be identified. In this study, we determined which dinoflagellate marker (i.e. 18S rDNA, dinosterol or dinocysts) provided the most detailed information about the late-Holocene succession of dinoflagellates in an Antarctic Fjord (Ellis Fjord, Vestfold Hills). The preserved rDNA revealed two intervals in the 2750-year-old sediment record. The dinoflagellate diversity was the highest until ∼1850 cal yr bp and included phylotypes related to known dinosterol producers. A lower concentration of dinosterol in sediments <1850 cal yr bp coincided with a community shift towards a predominance of the autotrophic sea-ice dinoflagellate Polarella glacialis , which is not a source of dinosterol. Remarkably, cultures of P. glacialis are known to produce other diagnostic sterols, but these were not recovered here. In addition, conspicuous resting cysts of P. glacialis were not preserved in the analyzed sediments. Overall, dinocysts were rare and the paleoenvironmental genomics approach revealed the highest diversity of dinoflagellates in Ellis Fjord, and was the only approach that recorded a shift in dinoflagellate composition at ∼1850 cal yr bp indicative of a colder climate with more extensive ice cover – this timing coincides with a period of changing climate reported for this region.     

Denitrification in a meromictic lake and its relevance to nitrogen flows within a moderately impacted forested catchment

We analysed the spatial and temporal variability of benthic nitrogen fluxes and denitrification rates in a sub-alpine meromictic lake (Lake Idro, Italy), and compared in-lake nitrogen retention and loss with the net anthropogenic nitrogen inputs to the watershed. We hypothesized a low nitrogen retention and denitrification capacity due to meromixis. This results from nitrate supply from the epilimnion slowing down during stratification and oxygen deficiency inhibiting nitrification and promoting ammonium recycling and its accumulation. We also hypothesized a steep vertical gradient of sedimentary denitrification capacity, decreasing with depth and oxygen deficiency. These are important and understudied issues in inland waters, as climate change and direct anthropic pressures may increase the extent of meromixis. Nearshore sediments had high denitrification rates (87 mg m^?2 day^?1) and efficiency (~ 100%), while in the monimolimnion denitrification was negligible. The littoral zone, covering 10% of the lake surface, contributed ~50% of total denitrification, while the monimolimnion, which covered 70% of the sediment surface, contributed to < 13% of total denitrification. The persistent and expanding meromixis of Lake Idro is expected to further decrease its nitrogen removal capacity (31% of the incoming nitrogen load) compared to what has been measured in other temperate lakes. Values up to 60% are generally reported for other such lakes. Results of this study are relevant as the combination of anthropogenic pressures, climate change and meromixis may threaten the nitrogen processing capacity of lakes.     

Volatile fatty and dissolved free amino acids in Organic Lake,Vestfold Hills,East Antarctica

The distributions of volatile fatty acids (C1–C5) (VFAs) and dissolved free amino acids (DFAAs) in Organic Lake, a shallow hypersaline meromictic lake in the Vestfold Hills, East Antarctica, were determined during the winter and spring of 1987. The concentrations of the two VFAs detected, formic and acetic acid, were low (<10 M) in the oxic upper waters of the lake, but increased dramatically (up to 250M) beneath the oxycline. The distribution of DFAAs was similar, with a total concentration of 280M in the anoxic water early in the study. The amino acids occurring at the highest concentrations were alanine, glutamic acid, leucine and valine. Total VFA concentrations in the anoxic zone increased during the study period, but the total amino acid concentration dropped significantly to 64 M by the end of the study. The high concentrations beneath the oxycline were probably the result of bacterial utilisation of these substrates that was slow due to the high salinity and low temperature of the lake water.     

In situ determination of nitrogen fixation in Antarctica using a high sensitivity portable gas chromatograph

A portable gas chromatograph was employed in the Vestfold Hills, Antarctica, during the austral summer of 1979-80 for determining nitrogenase activity of the blue-green alga Nostoc commune Vaucher by the acetylene reduction assay. Acetylene reduction was measured in samples taken along a transect where the vegetation changed with respect to differing topography and water availability. Submerged colonies of Nostoc recorded the highest fixation rates (6.89 nmol C₂H₄. cm^-2 h^-1). Damp mosscyanophyte associations growing on shallow slopes showed moderate rates of acetylene reduction (1.99 nmol C₂H₄. cm^-2 h^-1) whilst the drier vegetation of the steeper terrain was the least active (0.19 nmol C₂H₄. cm^-2 h^-1. The employment of a high sensitivity portable gas chromatograph provided an accurate and reliable method of measuring acetylene reduction.     

Life and Times of Five Saskatchewan Saline Meromictic Lakes

Five closed saline lakes near Humboldt, Saskatchewan, were found to be meromictic. Two of these lakes (Waldsea, Deadmoose) were first discovered to be meromictic in the early 1970s and three (Arthur, Marie, Sayer) in 1985. The origin of their meromixis is ectogenic. One of the lakes, Waldsea, had surface salinities far higher in 1960–1961 than those of 1970 or later and as high as that of the monimolimnion occasionally was from 1970 to the present. During the late 1960s to 1980 the lake level of Waldsea rose four metres as a result of higher than normal snowpacks and subsequent high snowmelt runoff. Endogenic processes of freezing out of salts from the upper metre during ice formation and precipitation of sodium sulphate during autumn cooling also promote meromixis. The lakes which are located in depressions in a relatively flat topography are very exposed to periodic high velocity westerly winds. Although Deadmoose and Waldsea lakes are relatively deep, Arthur, Marie and Sayer lakes have maximum depths of only three to five metres. Meromixis has persisted until the present in three lakes but Marie and Arthur lakes became holomictic during the autumn of 1988, a severe drought year. Bacterial plates were prominent in Waldsea, Deadmoose and Sayer lakes. BChl-a and BChl-d were present in 1988 with maxima of 2652 mg · m⁻³ BChl-a and 4290 mg · m⁻³ BChl-d in Sayer Lake. BChl-a virtually disappeared in subsequent years.     

Fossil bivalves in marine sediments of Vestfold Hills in Eastern Antarctica

Bivalves collected in Vestfold Hills during the 55th Russian Antarctic Expedition (RAE, 2009?2010) are represented by five species. Four of them (Laternula elliptica, Thracia meridionalis, Adamussium colbecki, and Philobrya sublaevis) were collected in the sediments that filled the coastal lake terraces during the Holocene; these species are still abundant on the Antarctic shelf at present. Bivalves were found in eight samples, with L. elliptica shells and fragments thereof found in seven of those samples. The sample collected near Deep Lake had the most diverse species composition, as it contained all four species named above. Shells of named species widely occurring in present-day Antarctica were found high above sea level in the marine sediments of the oasis. This indicate to the similarity of the oasis habitats in the past and the recent marine conditions. Fragments of shells of the fifth (now extinct) species Ruthipecten tuftsensis were found in glacial–marine sediments of the Marine Plain dating back to the late Pleistocene. The present study of fossil bivalves from the late Cenozoic marine sediments in Vestfold Hills is the first of its kind in Russia.     

The biology and evolution of Antarctic saline lakes in relation to salinity and trophy

. Five brackish to hypersaline lakes (Highway, Ace, Pendent, Williams and Rookery) in the Vestfold Hills, eastern Antarctica were investigated during the austral summer of 1999/2000. The aims were to characterise the functional dynamics of the plankton and gain an understanding of how the different environments in the lakes have led to the evolution of different communities. The plankton was dominated by microorganisms and differed across the salinity spectrum in relation to trophy, age and the presence of meromixis. However, some elements of the plankton were common to all of the lakes, e.g. the mixtrophic ciliate, Mesodinium rubrum, which reached abundances of 2.7᎒⁵ l^-1 and spanned a salinity gradient of 4-63‰. Marine dinoflagellate species also occurred in all of the lakes, often at high abundances in Highway Lake, Pendent Lake and Lake Williams. During December (mid-summer), primary production showed an increase along the salinity gradient from Highway Lake to Lake Williams; however, it was low in hyper-nutrified Rookery Lake because of the turbidity of the waters. Bacterial production followed the same trend and was extremely high in Rookery Lake (327 µg l^-1 h^-1 in January). The lakes possessed a marine microbial plankton that has become very simplified through time, and now contains a small number of highly successful species, which were pre-adapted to surviving in extreme Antarctic lakes.     

The Origin and Evolution of Lake Vähä-Pitkusta, SW Finland – A Multi-Proxy Study of a Meromictic Lake

Lake Vähä-Pitkusta is a 35-m deep meromictic kettle-hole lake in SW Finland. The topmost 15cm of the sediment stratigraphy consists of black gyttja, representing the last ca. 600years. A sediment core from the deepest point was examined with multi-proxy methods to determine the origin and evolution of the basin, the onset of the meromictic conditions and the primary factors that initiated the meromictic processes. The results indicate that Lake Vähä-Pitkusta became isolated from the Baltic basin during the Yoldia Sea stage. After initial unstable sedimentary conditions the development continued steadily until ca. 2500–2300 cal.BP when there is indication of lake level rise and/or increased surface runoff, probably resulting from a cooler and moister climate. The diatom and cladoceran results indicate only a slight rise in the trophic state following the increased erosion. Pollen evidence suggests weak anthropogenic activity in the catchment during the last 1000 years, and this had only little effect on the trophic state, which remained rather low. Thus, it is most unlikely that the trophic state was the primary reason for the origin of meromixis, although it may have contributed to it. We tentatively suggest that the primary reason was the peculiar morphometric dimensions of Lake Vähä-Pitkusta (small, deep, sheltered from winds) which made it very sensitive and that even a very slight increase in soluble electrolytes may push it over the edge into meromixation. It is possible that this did not occur during the cold/moist period around ca. 2300 cal.BP but during the Medieval Climate Anomaly. Studies on sediment geochemistry are needed to verify this assumption.     

Physico-chemical characteristics and origin of hypersaline meromictic Lake Garrow in the Canadian high Arctic

Garrow Lake (75° 23 N; 96° 50 W), located 3 km from the southern tip of Little Cornwallis Island and 6.7 m above mean sea level, is a meromictic ecto-creno-cryogenic lake with an area of 418 ha and a maximum water depth of 49 m. The thermal stratification of this lake is mesothermic (heliothermic). Some of the solar energy that penetrates through the 2 m ice cover is stored for a long period of time in the upper level of the monimolimnion, under a greenhouse effect due the water density gradient. The energy transfer (0.06 °C m ^–1) by conduction toward the bottom sediments is very constant from one year to the next and is likely to prevent the presence of permafrost under this water body.In its chemical composition, this meromictic lake is quite comparable to the world's saltiest water bodies and is the first lake, with a salinity greater than sea water to be reported for the Canadian Arctic. Its anoxic monimolimnion is nearly three times (90) as salty as normal sea water.This hypersaline water seems to have been derived from isostatic trapped marine waters within the present lacustrine basin as well as from underground during deglaciation of the area. The subsequent freezing-out of salt from the underground waters and the migration and accumulation of these waters in the bottom of Garrow Lake through a talik within the permafrost were the main contributing factors. The speed of formation and migration of the underground brine was a function of the postglacial isostatic uplift rate as well as the permafrost growth rate.     

Viruses in the plankton of freshwater and saline Antarctic lakes

1. Virus‐like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68° S) were determined in December 1999. In the ultra‐oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 × 10⁶ mL^–1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 × 10⁶ mL^–1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter. 2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star‐like particles of about 80 nm diameter. 3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers or chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r=0.845, P < 0.01). 4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus‐like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy. 5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems.     

Nitrogen limitation and particulate elemental ratios of seston in hypersaline Mono Lake, California, U.S.A.

Particulate elemental ratios (C:N, N:P and C:Chl a) of seston in hypersaline (70–90 g kg^–1) Mono Lake, California, were examined over an 11-year period (1990–2000) which included the onset and persistence of a 5-year period of persistent chemical stratification. Following the onset of meromixis in mid-1995, phytoplankton and dissolved inorganic nitrogen were substantially reduced with the absence of a winter period of holomixis. C:N, N:P and C:Chl a ratios ranged from 5 to 18 mol mol^–1, 2 to 19 mol mol^–1 and 25 to 150 g g^–1, respectively, and had regular seasonal patterns. Deviations from those expected of nutrient-replete phytoplankton indicated strong nutrient limitation in the summer and roughly balanced growth during the winter prior to the onset of meromixis. Following the onset of meromixis, winter ratios were also indicative of modest nutrient limitation. A 3-year trend in C:N and N:P ratios toward more balanced growth beginning in 1998 suggest the impacts of meromixis weakened due to increased upward fluxes of ammonium associated with weakening stratification and entrainment of ammonium-rich monimolimnetic water. A series of nutrient enrichment experiments with natural assemblages of Mono Lake phytoplankton conducted during the onset of a previous episode of meromixis (1982–1986) confirm the nitrogen will limit phytoplankton before phosphorus or other micronutrients. Particulate ratios of a summer natural assemblage of phytoplankton collected under nitrogen-depleted conditions measured initially, following enrichment, and then after return to a nitrogen-depleted condition followed those expected based on Redfield ratios and laboratory studies.     

E-mail: J.Laybourn-Parry@nottingham.ac.ukAnnual plankton dynamics in an Antarctic saline lake

1. The plankton dynamics of Ace Lake, a saline, meromictic basin in the Vestfold Hills, eastern Antarctica was studied between December 1995 and February 1997. 2. The lake supported two distinct plankton communities; an aerobic microbial community in the upper oxygenated mixolimnion and an anaerobic microbial community in the lower anoxic monimolimnion. 3. Phytoplankton development was limited by nitrogen availability. Soluble reactive phosphorus was never limiting. Chlorophyll a concentrations in the mixolimnion ranged between 0.3 and 4.4 μg L^??1 during the study period and a deep chlorophyll maximum persisted throughout the year below the chemo/oxycline. 4. Bacterioplankton abundance showed considerable seasonal variation related to light and substrate availability. Autotrophic bacterial abundance ranged between 0.02 and 8.94 × 10⁸ L^??1 and heterotrophic bacterial abundance between 1.26 and 72.8 × 10⁸ L^??1 throughout the water column. 5. The mixolimnion phytoplankton was dominated by phytoflagellates, in particular Pyramimonas gelidicola. P. gelidicola remained active for most of the year by virtue of its mixotrophic behaviour. Photosynthetic dinoflagellates occurred during the austral summer, but the entire population encysted for the winter. 6. Two communities of heterotrophic flagellates were apparent; a community living in the upper monimolimnion and a community living in the aerobic mixolimnion. Both exhibited different seasonal dynamics. 7. The ciliate community was dominated by the autotroph Mesodinium rubrum. The abundance of M. rubrum peaked in summer. A proportion of the population encysted during winter. Only one other ciliate, Euplotes sp., occurred regularly. 8. Two species of Metazoa occurred in the mixolimnion; a calanoid copepod (Paralabidocera antarctica) and a rotifer (Notholca sp.). However, there was no evidence of grazing pressure on the microbial community. In common with most other Antarctic lakes, Ace Lake appears to be driven by ‘bottom-up’ forces.     

Widespread occurrence of populations of the unique autotrophic ciliate Metodinium rubrum (Ciliophora: Haptorida) in brackish and saline lakes of the Vestfold Hills (eastern Antarctica)

The occurrence of the unique autotrophic ciliate Mesodinium rubrum was investigated in a suite of lakes of various salinities situated in the Vestfold Hills oasis, Princess Elizabeth Land (eastern Antarctica). M. rubrum was found to occur in all but the most hypersaline lakes in the survey but was most numerous in the more brackish lakes. Salinity and water column temperature appeared to be the most important factors controlling the occurrence and abundance of this species. Nutrient levels (phosphate and nitrate) did not appear to be important controlling factors, although their influence may have been distorted by the fact that nutrient concentrations were generally higher in the more saline lakes. The widespread occurrence of this species in brackish and saline lakes of the Vestfold Hills provides opportunities to study the ecology and possible physiological and ultrastructural adaptations to living in a high-latitude environment of this ubiquitous and important species in marine microbial food webs.     

An early meromictic stage in Lobsigensee (Switzerland) as evidenced by ostracods and Chaoborus

Lobsigensee is a small kettle on the western Swiss Plateau in a tectonic depression of the tertiary Molasse. At present its maximum depth is 2.7 m. Analysis of ostracods and other organisms (Chaoborus) from a 13 m core indicates that the lake became meromictic during the Bølling and returned again to a holomictic stage during the Boreal when the lake was approximately 10 m deep. The meromictic period is characterized by the disappearance of ostracods — especially of Cytherissa lacustris and Limnocythere sanctipatricii — and the appearance of Chaoborus, whereas the onset of the second holomictic stage is marked by the recolonization of the profundal zone by ostracods not present before in the lake (Metacypris cordata, Darwinula stevensoni). A very similar case of fossil meromixis has been found in Kleinsee in Carinthia.     

Microgeographic variation and songs in the underwater vocalisation repertoire of the Weddell seal (Leptonychotes weddellii) from the Vestfold Hills,Antarctica

Recordings of underwater vocalisations of the Weddell seal (Leptonychotes weddellii) were made in fjords of the Vestfold Hills near Davis Station, Antarctica. The repertoire was examined for the presence of microgeographic variation. Recordings covered the period from the end of mating to the beginning of the moult in the 1989/1990 breeding season. The repertoire was classified into 44 vocalisation types using a classification method based on objective parameters. Unique vocalisations were identified at each site, with 48% exclusive to Long Fjord and 41% to Tryne Fjord. A small percentage (11%) of the repertoire was common to both fjords reflecting the limited, observed interchange of individuals between these populations due to their strong breeding site fidelity. Seven male songs are described in the present study and possibly function to maintain underwater territories.     

Halorhabdus tiamatea: proteogenomics and glycosidase activity measurements identify the first cultivated euryarchaeon from a deep‐sea anoxic brine lake as potential polysaccharide degrader

Euryarchaea from the genus Halorhabdus have been found in hypersaline habitats worldwide, yet are represented by only two isolates: Halorhabdus utahensis AX‐2^T from the shallow Great Salt Lake of Utah, and Halorhabdus tiamatea SARL4B^T from the Shaban deep‐sea hypersaline anoxic lake (DHAL) in the Red Sea. We sequenced the H. tiamatea genome to elucidate its niche adaptations. Among sequenced archaea, H. tiamatea features the highest number of glycoside hydrolases, the majority of which were expressed in proteome experiments. Annotations and glycosidase activity measurements suggested an adaptation towards recalcitrant algal and plant‐derived hemicelluloses. Glycosidase activities were higher at 2% than at 0% or 5% oxygen, supporting a preference for low‐oxygen conditions. Likewise, proteomics indicated quinone‐mediated electron transport at 2% oxygen, but a notable stress response at 5% oxygen. Halorhabdus tiamatea furthermore encodes proteins characteristic for thermophiles and light‐dependent enzymes (e.g. bacteriorhodopsin), suggesting that H. tiamatea evolution was mostly not governed by a cold, dark, anoxic deep‐sea habitat. Using enrichment and metagenomics, we could demonstrate presence of similar glycoside hydrolase‐rich Halorhabdus members in the Mediterranean DHAL Medee, which supports that Halorhabdus species can occupy a distinct niche as polysaccharide degraders in hypersaline environments.