Seasonal and individual variability of lipid reserves in <Emphasis Type="Italic">Oithona similis</Emphasis> (Cyclopoida) in an Arctic fjord

The lipid storage of the cyclopoid copepod Oithona similis was investigated from spring to late summer 2007 in Kongsfjorden (Svalbard, Norway). The volume of lipid droplets in each individual reflected the amount of stored wax esters. Seasonal changes of lipid storage coupled with informative inter-individual variability were thus obtained. The seasonal pattern showed an increase in lipid store during the spring bloom, starting before the chlorophyll a maximum for both copepodids stage V and females. Those reserves were used during the main reproductive event in June. Individual variability was very high, with a significant proportion of copepods having no droplet, while others were lipid rich. Because of the overlap of generation, females could have different age and feeding history, particularly in September. Consideration of intra-population variability in lipid storage using an optical approach has been shown to be important to understand O. similis’s ecology and life cycle.     

Variation in Serripes groenlandicus (Bivalvia) growth in a Norwegian high-Arctic fjord: evidence for local- and large-scale climatic forcing

We examined the growth rate of the circumpolar Greenland Cockle ( Serripes groenlandicus ) over a period of 20 years (1983–2002) from Rijpfjord, a high-Arctic fjord in northeast Svalbard (80°10'N, 22°15'E). This period encompassed different phases of large-scale climatic oscillations with accompanying variations in local physical variables (temperature, atmospheric pressure, precipitation, sea ice cover), allowing us to analyze the linkage between growth rate, climatic oscillations, and their local physical and biological manifestations. Standard growth index (SGI), an ontogenetically adjusted measure of annual growth, ranged from a low of 0.27 in 2002 up to 2.46 in 1996. Interannual variation in growth corresponded to the Arctic climate regime index (ACRI), with high growth rates during the positive ACRI phase characterized by cyclonic ocean circulation and a warmer and wetter climate. Growth rates were influenced by local manifestations of the ACRI: positively correlated with precipitation and to a lesser extent negatively correlated with atmospheric pressure. A multiple regression model explains 65% of the variability in growth rate by the ACRI and precipitation at the nearest meteorological station. There were, however, complexities in the relationship between growth and physical variables, including an apparent 1 year lag between physical forcing changes and biological response. Also, when the last 4 years of poor growth are excluded, there is a very strong negative correlation with ice cover on a pan-arctic scale. Our results suggest that bivalves, as sentinels of climate change on multi-decadal scales, are sensitive to environmental variations associated with large-scale changes in climate, but that the effects will be determined by changes in environmental parameters regulating marine production and food availability on a local scale.     

Trading forage quality for quantity? Plant phenology and patch choice by Svalbard reindeer

Plant phenology of Luzula heathland plots in Spitsbergen (78°N) was manipulated by adding or removing snow, which altered the time for plots (2 m×2 m; n=10) to become snow-free. A 2-week difference in snowmelt, equivalent to approximately one-sixth of the growing season, was achieved between advanced (first to be snow-free) and delayed (last to be snow-free) treatments, which influenced plant biomass and plant quality. Nitrogen content of the forage species decreased with time after snowmelt, whereas C:N ratio increased. Manipulation of snowmelt led to a shift in ”phenological time”, without altering these plant quality parameters as such. Early in the growing season, Svalbard reindeer (Rangifer tarandus platyrhynchus) selected the advanced plots which had been snow-free for longest, presumably because of the greater biomass of both Luzula confusa and Salix polaris, major components of reindeer diet at that time of the year. Moreover, the proportion of live Luzula leaves was highest in advanced plots, relative to both unmanipulated control and delayed plots. In contrast, plant quality, measured as nitrogen content and C:N ratio of leaves, was lowest in the preferred plots. Phenolic content did not differ among treatments, and is therefore unlikely to play a role in reindeer selection for plots with early snowmelt. Unlike in temperate regions, where selection for plant quality seems to be of major importance, selection for plant quantity might be an outcome of generally low levels of plant biomass and high forage quality during the growing season in the high Arctic. Reindeer selection for high plant biomass is likely to lead to a more favourable nitrogen and energy return than selection for high plant quality. Received: 25 May 1999 / Accepted: 15 November 1999     

Climate change in the Arctic: Testing the poleward expansion of ticks and tick-borne diseases

Climate change is most strongly felt in the polar regions of the world, with significant impacts on the species that live there. The arrival of parasites and pathogens from more temperate areas may become a significant problem for these populations, but current observations of parasite presence often lack a historical reference of prior absence. Observations in the high Arctic of the seabird tick Ixodes uriae suggested that this species expanded poleward in the last two decades in relation to climate change. As this tick can have a direct impact on the breeding success of its seabird hosts and vectors several pathogens, including Lyme disease spirochaetes, understanding its invasion dynamics is essential for predicting its impact on polar seabird populations. Here, we use population genetic data and host serology to test the hypothesis that I. uriae recently expanded into Svalbard. Both black-legged kittiwakes (Rissa tridactyla) and thick-billed murres (Uria lomvia) were sampled for ticks and blood in Kongsfjorden, Spitsbergen. Ticks were genotyped using microsatellite markers and population genetic analyses were performed using data from 14 reference populations from across the tick's northern distribution. In contrast to predictions, the Spitsbergen population showed high genetic diversity and significant differentiation from reference populations, suggesting long-term isolation. Host serology also demonstrated a high exposure rate to Lyme disease spirochaetes (Bbsl). Targeted PCR and sequencing confirmed the presence of Borrelia garinii in a Spitsbergen tick, demonstrating the presence of Lyme disease bacteria in the high Arctic for the first time. Taken together, results contradict the notion that I. uriae has recently expanded into the high Arctic. Rather, this tick has likely been present for some time, maintaining relatively high population sizes and an endemic transmission cycle of Bbsl. Close future observations of population infestation/infection rates will now be necessary to relate epidemiological changes to ongoing climate modifications.     

Changes in trophic state and aquatic communities in high Arctic ponds in response to increasing goose populations

相似文献   

Snow cover and extreme winter warming events control flower abundance of some,but not all species in high arctic Svalbard

The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes.     

The dynamic bacterial communities of a melting High Arctic glacier snowpack

Snow environments can occupy over a third of land surface area, but little is known about the dynamics of snowpack bacteria. The effect of snow melt on bacterial community structure and diversity of surface environments of a Svalbard glacier was examined using analyses of 16S rRNA genes via T-RFLP, qPCR and 454 pyrosequencing. Distinct community structures were found in different habitat types, with changes over 1 week apparent, in particular for the dominant bacterial class present, Betaproteobacteria. The differences observed were consistent with influences from depositional mode (snowfall vs aeolian dusts), contrasting snow with dust-rich snow layers and near-surface ice. Contrary to that, slush as the decompositional product of snow harboured distinct lineages of bacteria, further implying post-depositional changes in community structure. Taxa affiliated to the betaproteobacterial genus Polaromonas were particularly dynamic, and evidence for the presence of betaproteobacterial ammonia-oxidizing bacteria was uncovered, inviting the prospect that the dynamic bacterial communities associated with snowpacks may be active in supraglacial nitrogen cycling and capable of rapid responses to changes induced by snowmelt. Furthermore the potential of supraglacial snowpack ecosystems to respond to transient yet spatially extensive melting episodes such as that observed across most of Greenland''s ice sheet in 2012 merits further investigation.     

Can soil temperature direct the composition of high arctic plant communities?

Abstract. Low temperatures exert a primary constraint on the growth of high arctic vascular plants. However, investigations into the impact of temperature on high arctic plants rarely separate out the role of air and soil temperatures, and few data exist to indicate whether soil temperatures alone can significantly influence the growth of high arctic vascular plants in a manner that might direct community composition. We examined the response of high arctic plants of three functional types (grasses, sedges/rushes and non‐graminoids) to manipulated soil temperature under common air temperature conditions. Target plants, within intact soil cores, were placed in water baths at a range of temperatures between 4.9 and 15.3 °C for one growing season. Grasses responded most rapidly to increased soil temperature, with increased total live plant mass, above‐ground live mass and total below‐ground live mass, with non‐graminoids having the lowest, and sedges/rushes an intermediate degree of response. The ratio of above‐ground live mass to total live mass increased in all growth forms. Grasses, in particular, responded to enhanced soil temperatures by increasing shoot size rather than shoot number. In all growth forms the mass of root tissue beneath the moss layer increased significantly and to a similar extent with increasing soil temperature. These results clearly indicate that different growth forms, although collected from the same plant community, respond differently to changes in soil temperature. As a consequence, factors influencing soil temperature in high arctic ecosystems, such as global climate change or herbivory (which leads to reduced moss depth and increased soil temperatures), may also direct changes in vascular plant community composition.     

Assessing species richness of macrofauna associated with macroalgae in Arctic kelp forests (Hornsund,Svalbard)

Kelp beds support diverse and productive benthic coastal ecosystems and are often perceived as cold water analogs of tropical coral reefs, yet the levels of species richness in polar regions have remained largely unexplored. The present study aims to assess the magnitude of macrozoobenthic species richness associated with the macroalgae in an Arctic kelp forest. The study was conducted in Hornsund, a high latitude Arctic fjord off west Spitsbergen (76–77°N). A total of 403 samples (i.e., individual algae) were collected by scuba divers at three sites located along the fjord axis at varying depths (5–10 m). The most common invertebrate species and the sample species richness (mean 11.5 species per sample) were consistent among the most common algal species (Laminaria digitata, Saccharina latissima, Alaria esculenta, Desmarestia aculeta, Odonthalia dentata, Phycodrys rubens). Fauna associated with overstory kelps was concentrated on the holdfasts. A total of 208 species were identified; Bryozoa, Polychaeta and Hydrozoa yielded the highest numbers of species (70, 52 and 37, respectively). The non-parametric Chao2 estimator of true species richness gave an estimate of 259 species (with 95% confidence intervals from 234 to 308). Despite the high sampling effort, the total species richness was not captured. This may stem from the high level of rarity within the fauna associated with kelps; 38% of the species occurred only in one or two samples. The studied fauna was much less diverse than similar assemblages surveyed at lower latitudes. The high numbers of species and the common occurrence of colonial forms (Bryozoa, Hydrozoa) in the current study show that these taxa cannot be omitted in macrobenthic diversity surveys performed within kelp habitats.