Subarctic Freshwater Research Articles

The effect of habitat on benthic diatoms in subarctic ponds – differences between rock and sediment

Subarctic ecosystems represent a vulnerable environment for their biota and studying their habitats provides a better understanding of ongoing and accelerated environmental change. Literature suggests that habitat and environmental variables such as water chemistry jointly influence benthic algal species richness and assemblage composition. However, the combined effects of habitat and water chemistry on benthic algal communities are poorly understood especially in subarctic freshwaters. This study compared benthic diatom assemblages on rocks and on sediment and examined if environmental variables affect diatoms similarly in these habitats. A total of 20 subarctic ponds were sampled for diatoms on sediment and rock in summer 2022 in northern Fennoscandia. Differences in species richness and Pielou evenness between habitats were analysed by a paired Wilcoxon signed-rank test. The most significant environmental variables influencing diatom species richness were determined by generalized linear models. Differences in diatom assemblage compositions were analysed using non-metric multidimensional scaling, analysis of similarities, and Jaccard similarity index. Finally, to study how environmental variables shape diatom compositions on rock and sediment, a redundancy analysis was performed. According to our results species richness and evenness were significantly higher on sediment than on rock, and water pH was the major determinant for diatom richness in both habitats. Diatom assemblage composition did not differ between rocks and sediment, and composition was shaped by the same environmental variables such as pond surface area and water pH in both habitats. Our results support the prevailing conception that sediment habitat contains higher diatom species richness than rocks, while assemblage composition does not differ between these habitats. This study highlights the role of water pH on benthic diatoms regardless of their habitat. Given that global warming is expected to affect water pH levels, such a change will probably have a notable influence also on subarctic diatom communities in the future decades.

Patterns and drivers for benthic algal biomass in sub-Arctic mountain ponds

This study investigated the spatial variation in total benthic algal biomass and within cyanobacteria, green algae, and diatoms in sub-Arctic ponds. Additionally to more widely used explanatory variables, snowmelt and ice duration were considered as their importance on algal communities is poorly understood. The data comprised algal biomasses from 45 sub-Arctic ponds in the Finnish Lapland. A generalized linear model and hierarchical partitioning were used to identify the significantly influential variables. Cyanobacteria were the most abundant algal group. Trace elements (e.g. Fe, Al, and Mn) were the most significant explanatory variable group in explaining algal biomasses. Macronutrients apart from K were found insignificant in all models. There were positive relationships between some algal biomasses indicating no strong competition between them. Snow and ice variables were found insignificant for all models, but they could have an important secondary role on algal communities. The results highlight the importance of trace elements in shaping algal biomasses in sub-Arctic ponds and thus their wider use in research can be advocated to better understand the productivity of nutrient poor and acidic waters in sub-Arctic regions. Focussing on benthic algal biomasses and the chemical composition of sub-Arctic freshwaters provides important information on the aquatic primary production.

Elevational microbial β diversity and community assembly processes in subarctic ponds

Abstract Knowledge about elevational β diversity patterns and processes is limited for microorganisms, especially in sensitive aquatic ecosystems at high latitudes. Our aim is to investigate elevational β diversity patterns and underlying assembly processes for three biofilm microbial groups in subarctic freshwater ponds. We sampled 89 ponds covering an elevational gradient from 10 to 1038 m above sea level in subarctic Finland and Norway. The microbial groups studied included benthic diatoms, cyanobacteria, and bacteria (i.e., bacteria other than cyanobacteria). We expected to find elevational distance decay in community similarity, driven primarily by variation in the local environment. We further tested whether the level of β diversity decreased towards higher elevations, and whether the relative influence of deterministic and stochastic processes on community assembly changed along the elevational gradient, with increasing effect of deterministic processes at higher elevations under more extreme environmental conditions. As statistical methods, we used generalised dissimilarity modelling, Mantel tests, and a null model with Raup–Crick dissimilarities. For all microbial groups, community dissimilarities increased with increasing environmental or elevational distances. The pure effects of environment were significant for all groups, and pH was the most important variable affecting community dissimilarities. Mean community dissimilarities generally decreased with elevation for all microbial groups. The communities were influenced by both deterministic and stochastic processes, the former of which was stronger towards higher elevations. The influence of deterministic processes was strongest for bacteria. Generally, the communities under deterministic control were more similar to each other than expected by chance. Elevational β diversity patterns of subarctic pond microorganisms primarily reflected environmental effects, showing decreasing β diversity towards high elevations owing to stronger environmental filtering. The relative effects of deterministic or stochastic assembly processes varied among microbial groups, highlighting the need for including multiple groups when studying biodiversity patterns and underlying ecological processes.

Microeukaryotic Communities of the Long-Term Ice-Covered Freshwater Lakes in the Subarctic Region of Yakutia, Russia

Currently, microeukaryotic communities of the freshwater arctic and subarctic ecosystems are poorly studied. Still, these are of considerable interest due to the species biogeography and autecology as well as global climate change. Here, we used high-throughput 18S rRNA amplicon sequencing to study the microeukaryotic communities of the large subarctic freshwater lakes Labynkyr and Vorota in Yakutia, Russia, during the end of the ice cover period, from April to June. By applying the statistical methods, we coupled the microeukaryotic community structure profiles with available discrete factor variables and hydrophysical, hydrochemical, and environmental parameters. The sub-ice layer and the water column communities were differentiated due to the temporal change in environmental conditions, particularly temperature regime and electric conductivity. Additionally, the community composition of unicellular eukaryotes in lakes Labynkyr and Vorota was changing due to seasonal environmental factors, with these alterations having similar patterns in both sites. We suggest the community developed in the sub-ice layer in April serves as a primer for summer freshwater microeukaryotes. Our results extend the current knowledge on the community composition and seasonal succession of unicellular eukaryotes within subarctic freshwater ecosystems.

Photooxidation of arsenic in pristine and mine-impacted Canadian subarctic freshwater systems

The redox transformations of arsenic (As) in lakes are thought to be mainly controlled by algal/microbial processes. We tested if photochemical oxidation could also be a significant redox process in northern freshwater systems. We exposed filtered natural water samples from four northern mine-impacted lakes (Northwest Territories, Canada) and three unimpacted ponds (Nunavik, Canada) to simulated solar radiation, and followed As(III) oxidation. During short-term incubation experiments (less than 8 h), all samples amended with As(III) displayed a rapid photooxidation (ca. 0.06-0.27 h−1) whereas no significant oxidation was observed in the dark. This photooxidation process was controlled by UV radiation, was influenced by short-lived oxidants and was partly driven by the concentrations of organic matter. Natural As complexes in unamended water samples were more rapidly photooxidized than in samples with As(III) amendments. Addition of goethite or simulation of snowmelt did not alter photooxidation rates significantly. Overall, these results imply that photooxidation of As should be considered as a potentially significant mechanism controlling inorganic As speciation in aquatic systems. This is particularly true for northern systems affected by mining activities and by changes of inputs of organic matter related to climate change.

Arsenic bioaccumulation in subarctic fishes of a mine-impacted bay on Great Slave Lake, Northwest Territories, Canada.

A subarctic fish community in mine-impacted Yellowknife Bay (Great Slave Lake, Northwest Territories, Canada) was investigated for biological and ecological processes controlling arsenic bioaccumulation. Total concentrations of arsenic, antimony, and metals were measured in over 400 fishes representing 13 species, and primary producers and consumers were included to characterize food web transfer. Yellowknife Bay had slightly more arsenic in surface waters (~3 μg/L) relative to the main body of Great Slave Lake (<1 μg/L), resulting in two-fold higher total arsenic concentrations in muscle of burbot (Lota lota), lake whitefish (Coregonus clupeaformis), and northern pike (Esox lucius). Other mining-associated contaminants, specifically antimony, lead, and silver, were typically below analytical detection in those fish species. No evidence was found for enhanced bioaccumulation of arsenic in long-lived, slow-growing subarctic fishes. Food web biodilution of total arsenic occurred between primary producers, aquatic invertebrates, and fish, although trophic position did not explain arsenic concentrations among fishes. Pelagic-feeding species had higher total arsenic concentrations compared to littoral fishes. Arsenic accumulated in subarctic fishes to comparable levels as fishes from lakes around the world with similar water arsenic concentrations. This first comprehensive study for a subarctic freshwater food web identified the importance of water exposure, biodilution, and habitat-specific feeding on arsenic bioaccumulation.

Conceptualising the interactive effects of climate change and biological invasions on subarctic freshwater fish.

Climate change and species invasions represent key threats to global biodiversity. Subarctic freshwaters are sentinels for understanding both stressors because the effects of climate change are disproportionately strong at high latitudes and invasion of temperate species is prevalent. Here, we summarize the environmental effects of climate change and illustrate the ecological responses of freshwater fishes to these effects, spanning individual, population, community and ecosystem levels. Climate change is modifying hydrological cycles across atmospheric, terrestrial and aquatic components of subarctic ecosystems, causing increases in ambient water temperature and nutrient availability. These changes affect the individual behavior, habitat use, growth and metabolism, alter population spawning and recruitment dynamics, leading to changes in species abundance and distribution, modify food web structure, trophic interactions and energy flow within communities and change the sources, quantity and quality of energy and nutrients in ecosystems. Increases in temperature and its variability in aquatic environments underpin many ecological responses; however, altered hydrological regimes, increasing nutrient inputs and shortened ice cover are also important drivers of climate change effects and likely contribute to context‐dependent responses. Species invasions are a complex aspect of the ecology of climate change because the phenomena of invasion are both an effect and a driver of the ecological consequences of climate change. Using subarctic freshwaters as an example, we illustrate how climate change can alter three distinct aspects of species invasions: (1) the vulnerability of ecosystems to be invaded, (2) the potential for species to spread and invade new habitats, and (3) the subsequent ecological effects of invaders. We identify three fundamental knowledge gaps focused on the need to determine (1) how environmental and landscape characteristics influence the ecological impact of climate change, (2) the separate and combined effects of climate and non‐native invading species and (3) the underlying ecological processes or mechanisms responsible for changes in patterns of biodiversity.

Climate and productivity shape fish and invertebrate community structure in subarctic lakes

Summary Climate change and land‐use intensification are increasing productivity in subarctic lakes. Simultaneously, fish and invertebrate species adapted to temperate conditions are expanding their range northwards into subarctic habitats. Community level studies are required to predict long‐term effects of these dual stressors on subarctic freshwater ecosystems. We conducted a space‐for‐time study examining the fish, benthic invertebrate and pelagic zooplankton communities in littoral, profundal and pelagic habitats in 19 subarctic lakes situated on a temperature, land‐use and productivity gradient in northern Europe. Fish density (ranging between 0.5 and 150.5 fish per net series h−1) and biomass (range between 92 and 5,147 g per net series h−1) increased significantly with increasing lake temperature and productivity. This was associated with significantly decreasing body size (26 to 12 cm total length; 174 to 19 g body mass) and a shift in fish community structure from salmonid (Arctic charr Salvelinus alpinus, whitefish Coregonus lavaretus), to percid (ruffe Gymnocephalus cernua, perch Perca fluviatilis) and ultimately cyprinid (roach Rutilus rutilus, bleak Alburnus alburnus) dominance. Changes in fish community composition were most apparent in littoral and pelagic zones. Benthic macroinvertebrate density peaked in mesotrophic lakes, zooplankton density was highest at either end of the gradient, indicating habitat specific differences in predation pressure and top‐down control. Body size of zooplankton and benthic macroinvertebrates was negatively related to temperature and productivity. These results suggest that climate change and intensification of land‐use practices are gradually turning subarctic lakes into warmer, less transparent and more productive systems harbouring abundant, small‐sized and warmer adapted communities.

Unexpected differences in the population genetics of phasmavirids (Bunyavirales) from subarctic ponds.

Little is known of the evolution of RNA viruses in aquatic systems. Here, we assess the genetic connectivity of two bunyaviruses (Kigluaik phantom orthophasmavirus or KIGV and Nome phantom orthophasmavirus or NOMV) with zooplanktonic hosts from subarctic ponds. We expected weak genetic structure among populations as the hosts (phantom midges) have a terrestrial winged dispersal stage. To test whether their respective viruses mirror this structure, we collected and analyzed population datasets from 21 subarctic freshwater ponds and obtained sequences from all four genes in the viral genomes. Prevalence averaged 66 per cent for 514 host specimens and was not significantly different between recently formed thaw ponds and glacial ponds. Unexpectedly, KIGV from older ponds showed pronounced haplotype divergence with little evidence of genetic connectivity. However, KIGV populations from recent thaw ponds appeared to be represented by a closely related haplotype group, perhaps indicating a genotypic dispersal bias. Unlike KIGV, NOMV had modest structure and diversity in recently formed thaw ponds. For each virus, we found elevated genetic diversity relative to the host, but similar population structures to the host. Our results suggest that non-random processes such as virus–host interactions, genotypic bias, and habitat effects differ among polar aquatic RNA viruses.

Additive impacts of experimental climate change increase risk to an ectotherm at the Arctic's edge.

Globally, Arctic and Subarctic regions have experienced the greatest temperature increases during the last 30years. These extreme changes have amplified threats to the freshwater ecosystems that dominate the landscape in many areas by altering water budgets. Several studies in temperate environments have examined the adaptive capacity of organisms to enhance our understanding of the potential repercussions of warming and associated accelerated drying for freshwater ecosystems. However, few experiments have examined these impacts in Arctic or Subarctic freshwater ecosystems, where the climate is changing most rapidly. To evaluate the capacity of a widespread ectotherm to anticipated environmental changes, we conducted a mesocosm experiment with wood frogs (Rana sylvatica) in the Canadian Subarctic. Three warming treatments were fully crossed with three drying treatments to simulate a range of predicted changes in wetland environments. We predicted wetland warming and drying would act synergistically, with water temperature partially compensating for some of the negative effects of accelerated drying. Across all drying regimes, a 1°C increase in water temperature increased the odds of survival by 1.79, and tadpoles in 52-day and 64-day hydroperiod mesocosms were 4.1-4.3 times more likely to survive to metamorphosis than tadpoles in 45-day mesocosms. For individuals who survived to metamorphosis, there was only a weak negative effect of temperature on size. As expected, increased temperatures accelerated tadpole growth through day 30 of the experiment. Our results reveal that one of the dominant herbivores in Subarctic wetlands, wood frog tadpoles, are capable of increasing their developmental rates in response to increased temperature and accelerated drying, but only in an additive manner. The strong negative effects of drying on survival, combined with lack of compensation between these two environmental drivers, suggest changes in the aquatic environment that are expected in this ecosystem will reduce mean fitness of populations across the landscape.

Allochthonous carbon is a major regulator to bacterial growth and community composition in subarctic freshwaters.

In the subarctic region, climate warming and permafrost thaw are leading to emergence of ponds and to an increase in mobility of catchment carbon. As carbon of terrestrial origin is increasing in subarctic freshwaters the resource pool supporting their microbial communities and metabolism is changing, with consequences to overall aquatic productivity. By sampling different subarctic water bodies for a one complete year we show how terrestrial and algal carbon compounds vary in a range of freshwaters and how differential organic carbon quality is linked to bacterial metabolism and community composition. We show that terrestrial drainage and associated nutrients supported higher bacterial growth in ponds and river mouths that were influenced by fresh terrestrial carbon than in large lakes with carbon from algal production. Bacterial diversity, however, was lower at sites influenced by terrestrial carbon inputs. Bacterial community composition was highly variable among different water bodies and especially influenced by concentrations of dissolved organic carbon (DOC), fulvic acids, proteins and nutrients. Furthermore, a distinct preference was found for terrestrial vs. algal carbon among certain bacterial tribes. The results highlight the contribution of the numerous ponds to cycling of terrestrial carbon in the changing subarctic and arctic regions.

Methylovulum psychrotolerans sp. nov., a cold-adapted methanotroph from low-temperature terrestrial environments, and emended description of the genus Methylovulum.

Two isolates of aerobic methanotrophic bacteria, strains Sph1T and Sph2, were obtained from cold methane seeps in a floodplain of the river Mukhrinskaya, Irtysh basin, West Siberia. Another morphologically and phenotypically similar methanotroph, strain OZ2, was isolated from a sediment of a subarctic freshwater lake, Archangelsk region, northern Russia. Cells of these three strains were Gram-stain-negative, light-pink-pigmented, non-motile, encapsulated, large cocci that contained an intracytoplasmic membrane system typical of type I methanotrophs. They possessed a particulate methane monooxygenase enzyme and utilized only methane and methanol. Strains Sph1T, Sph2 and OZ2 were able to grow at a pH range of 4.0-8.9 (optimum at pH 6.0-7.0) and at temperatures between 2 and 36 °C. Although their temperature optimum was at 20-25 °C, these methanotrophs grew well at lower temperatures, down to 4 °C. The major cellular fatty acids were C16 : 1ω5c, C16 : 1ω6c, C16 : 1ω7c, C16 : 1ω8c, C16 : 0 and C14 : 0; the DNA G+C content was 51.4-51.9 mol%. Strains Sph1T, Sph2 and OZ2 displayed nearly identical (99.1-99.7 % similarity) 16S rRNA gene sequences and belonged to the family Methylococcaceae of the class Gammaproteobacteria. The most closely related organism was Methylovulum miyakonense HT12T (96.0-96.5 % 16S rRNA gene sequence similarity and 90 % pmoA sequence similarity). The novel isolates, however, differed from Methylovulum miyakonense HT12T by cell morphology, pigmentation, absence of soluble methane monooxygenase, more active growth at low temperatures, growth over a broader pH range and higher DNA G+C content. On the basis of these differences, we propose a novel species, Methylovulum psychrotolerans sp. nov., to accommodate these methanotrophs. Strain Sph1T (=LMG 29227T=VKM B-3018T) is the type strain.

Seasonal depletion of resources intensifies trophic interactions in subarctic freshwater fish communities

Summary Climate change in recent decades has resulted in an increase in both the density and diversity of consumers in subarctic freshwater ecosystems. Despite this, harsh winter conditions in the region limit productivity and may serve as a bottleneck driving trophic interactions within the fish community, potentially determining the outcome of climate change for resident biota. However, due to the difficulties in sampling during winter months, few studies have assessed seasonal variation in the ecological interactions between native and range‐expanding species in subarctic regions. We examined seasonal variation in activity, diet (stomach content) and resource use (δ13C and δ15N stable isotope ratios) of two fishes: the resident cold‐water‐adapted European whitefish (Coregonus lavaretus L.) and the range‐expanding cool‐water‐adapted ruffe (Gymnocephalus cernua L.) in lakes with low and high consumer density. Results were contrasted with seasonal availability of benthic and pelagic resources and indirect measures of individual fitness, that is condition, growth and estimated lipid content (muscle elemental C : N ratio) of both species. The effects of fish density were apparent in both the diet and resource use of whitefish, which altered their diet and displayed reduced stomach fullness during winter in high‐density lakes. This was associated with an overall reduction in whitefish growth, condition and estimated lipid content in high‐density lakes, which was especially pronounced during winter. Ruffe utilised a greater proportion of profundal resources than whitefish in both summer and winter, potentially exploiting a vacant niche. Ruffe maintained condition and lipid reserves throughout the winter, highlighting the potential for further northward range expansion of the species. Winter acts as a seasonal bottleneck in subarctic lakes, but assumptions that this bottleneck primarily selects against warmer‐water‐adapted invasive species such as ruffe may be too restrictive. The effects of seasonal resource depletion on fish condition and invertebrate density were most severe in lakes with a high density of fish, and in these conditions, the cold‐water‐adapted resident whitefish was most adversely affected.

Fish pathogens near the Arctic Circle: molecular, morphological and ecological evidence for unexpected diversity of Diplostomum (Digenea: diplostomidae) in Iceland

Host–parasite systems at high latitudes are promising model systems for detecting and predicting the impact of accelerated environmental change. A major challenge is the lack of baselines for the diversity and distribution of parasites in Arctic wildlife, especially in the freshwater environment. Here we present the first known estimates of the species diversity and host associations of Diplostomum spp. in sub-Arctic freshwater ecosystems of the Palaearctic. Our analyses integrating different analytical approaches, phylogenies based on mitochondrial and nuclear DNA, estimates of genetic divergence, character-based barcoding, morphological examination, precise detection of microhabitat specialisation and host use, led to the discovery of one described and five putative new species that complete their life-cycles within a fairly narrow geographic area in Iceland. This increases the species richness of Diplostomum in Iceland by 200% and raises the number of molecularly characterised species from the Palaearctic to 17 species. Our results suggest that the diversity of Diplostomum spp. is underestimated globally in the high latitude ecosystems and call for a cautionary approach to pathogen identification in developing the much needed baselines of pathogen diversity that may help detect effects of climate change in the freshwater environment of the sub-Arctic.

Spurious AMOC trends in global ocean sea-ice models related to subarctic freshwater forcing

Global ocean sea-ice models with an atmospheric forcing based on bulk formulations of the air-sea fluxes exhibit spurious trends in key flow indices like the Atlantic Meridional Overturning Circulation (AMOC), constraining their use in investigations of multi-decadal ocean variability. To identify the critical model factors affecting the temporal evolution of the AMOC on time scales of up to 60years, a series of experiments with both eddy-permitting (0.25°) and non-eddying (0.5°) ocean-ice models has been performed, focusing on the influence of artificial choices for the freshwater forcing, in particular the restoring of sea surface salinity towards climatological values. The atmospheric forcing builds on the proposal for Coordinated Ocean-ice Reference Experiments (CORE), utilizing the refined atmospheric reanalysis products for 1948–2006 compiled by Large and Yeager. Sensitivity experiments with small variations in precipitation (within the observational uncertainty) and sea surface salinity restoring in the subarctic Atlantic produce a wide range of AMOC transports, between upward drifts to more than 22Sv and nearly-collapsed states with less than 7Sv, reflecting the excessive role of the salinity feedback in such simulations. In all cases the AMOC is tightly related to the density of the Denmark Strait overflow; changes in that density are governed by the salinity in the Nordic Seas; and in turn, that salinity is strongly affected by the properties of the inflowing North Atlantic water.

Trajectory Shifts in the Arctic and Subarctic Freshwater Cycle

Manifold changes in the freshwater cycle of high-latitude lands and oceans have been reported in the past few years. A synthesis of these changes in freshwater sources and in ocean freshwater storage illustrates the complementary and synoptic temporal pattern and magnitude of these changes over the past 50 years. Increasing river discharge anomalies and excess net precipitation on the ocean contributed approximately 20,000 cubic kilometers of fresh water to the Arctic and high-latitude North Atlantic oceans from lows in the 1960s to highs in the 1990s. Sea ice attrition provided another approximately 15,000 cubic kilometers, and glacial melt added approximately 2000 cubic kilometers. The sum of anomalous inputs from these freshwater sources matched the amount and rate at which fresh water accumulated in the North Atlantic during much of the period from 1965 through 1995. The changes in freshwater inputs and ocean storage occurred in conjunction with the amplifying North Atlantic Oscillation and rising air temperatures. Fresh water may now be accumulating in the Arctic Ocean and will likely be exported southward if and when the North Atlantic Oscillation enters into a new high phase.

Effects of temperature and ultraviolet radiation on microbial foodweb structure: potential responses to global change

Summary1. A series of growth experiments were conducted with natural plankton communities from a lake and river in northern Quebec, to evaluate the response of microbial foodweb structure to changes in ambient temperature and solar ultraviolet radiation (UVR).2. Bioassays were incubated for 6 days at two temperatures (10 and 20 °C) and three near‐surface irradiance conditions [photosynthetically active radiation (PAR) + UVA + UVB, PAR + UVA, and PAR only).3. The concentration of total bacteria showed no net response to temperature, but the percentage of actively respiring bacteria, as measured with the cellular redox probe5‐cyano‐2,3‐ditolyl tetrazolium chloride (CTC), was up to 57% higher at 20 °C relative to 10 °C. Chlorophyll a concentrations in the &lt; 2 μm size fraction also reacted strongly to temperature, with a net increase of up to 61% over the temperature range of 10–20 °C.4. The UVR effects were small or undetectable for most of the measured variables; however, the percentage of actively respiring bacteria was significantly inhibited in the presence of UVR at 20 °C, decreasing by 29–48% on day 6 in the lake experiments and by 59% on day 2 in one river experiment.5. The results show differential sensitivity to temperature among organisms of microbial communities in subarctic freshwaters, and a resilience by the majority of micro‐organisms to their present UVR conditions. Microbial foodwebs in northern freshwaters appear to be relatively unresponsive to short‐term (days) changes in UVR. However, the observed responses to temperature suggest that climate change could influence community structure, with warmer temperatures favouring picoplanktonic phototrophs and heterotrophs, and a shift in nanoplankton species composition and size structure.

Studies on the Alaskan Blackfish Dallia pectoralis I. Habitat, Size and Stomach Analyses

The end-product of evolution via mutation and natural selection frequently results in the establishment of a species well adapted to a limited environment. The distribution of the Alaskan blackfish, Dallia pectoralis Bean, limited to arctic and sub-arctic fresh waters, (Jordan and Everman, 1896; Wilimovsky, 1954), suggests that because of modifications necessary for survival in the cold, this species may have become over-specialized, resulting in an organism suitably adapted to the cold. We successfully maintained 50 live blackfish under refrigeration in the laboratory at Catholic University during 1953 and 1954. A second group of 30 animals was kept at room temperature (250C). The members of this group died within a few weeks even though we attempted to gradually acclimatize them to room temperature. Other factors suggest that this species is well adapted for survival in the cold. For example, Turner (1886) reports that the Alaskan blackfish was frequently collected by natives, stored in grass baskets, frozen, and fed to dogs. Upon being rewarmed, it is reported, the fish was regurgitated alive by the dogs. Such reports are part of Alaskan folk-lore. Scholander et. al. (1953) in an attempt to verify such reports performed critical metabolic and survival studies on the blackfish, the results of which indicated that the fish is, indeed, coldadapted but it cannot survive freezing. The above studies suggested to us that an ecological and physiological investigation of the blackfish was warranted. The physiological study will be published separately. The ecological study included determinations of the total alkalinity, pH, dissolved oxygen and temperature of the environment, and of the total length, weight, and stomach contents of the fish. All these factors are interrelated; the physical environment influences the occurrence of food as well as the distribution of the blackfish.