Growth and population dynamics of the moss Polytrichum alpestre. in the Maritime Antarctip. Strategies of growth and population dynamics of tundra Plants 2

first_imgThe pattern of growth of Polytrichum alpestre Hoppe, a common moss in the maritime Antarctic, is described. It may form extensive communities, sometimes growing with another moss, Chorisodontium aciphyllum (Hook. f. & Wils.) Broth. Underlying the basic stability of such communities there is a persistent change in shoot composition from season to season. These changes have been followed both photographically and stratigraphically, since a complete record of past changes exists within the slowly decomposing turf. Considerable instability in the total population of shoots of P. alpestre occurs during the first few years of its establishment but as time proceeds and conditions more favourable to the growth of P. alpestre develop, the mean life expectancy of shoots increases. Variation in spatial density of shoots is discussed in relation to size and weight of the annual increments in P. alpestre. The relationship between weight of the annual increment and the spatial density approximates to the density effect law applied to higher plants, in which yield per unit area is little affected by variation in densitylast_img read more

The rate of peat accumulation in Antarctic moss banks

first_img(1) Three Antarctic moss banks were studied in detail: two dominated by Polytrichum alpestre Hoppe and one by Chorisodontium aciphyllum (Hook. f. et Wils.) Broth. (2) The rate of upward growth of the moss banks, 0.9-1.3 mm yr-1, is approximately half the annual shoot growth. (3) The amount of decomposition which has occurred at different depths of the peat in these banks was calculated from measurements of bulk density and compression. The decomposition rate appears to be $< 1% mathrm{yr}^{-1}$. Peat 20-30 cm below the surface is permanently frozen, and about half the original material has decomposed by the time it becomes incorporated into this permafrost. Evidence is presented that a slow decomposition rate is an intrinsic characteristic of Polytrichum alpestre. (4) The rate of peat accumulation, 89-158 g m-2 yr-1, is about half the rate of production, 162-350 g m-2 yr-1. The former is similar to accumulation rates of peat elsewhere in the world.last_img read more

The effects of temperature and moisture on dark respiration in the foliose lichen Umbilicaria antarctica

first_imgThe dark respiration of field‐fresh thalli of Umbilicaria antarctica Frey et Lamb is reported for temperatures from −5.5 to 19°C, and water contents from saturation to dryness. Detailed analysis of the respiratory response with changing water content has suggested that Michaelis‐Menten kinetics appear to provide a useful model. Q10 values are used to indicate possible ice formation in the thallus and water loss characteristics are explained in terms of thallus anatomy. The ecological implications of this approach are discussed.last_img read more

A model study of ocean circulation beneath Filchner-Ronne Ice Shelf, Antarctica: Implications for bottom water formation

first_img[1] An isopycnic coordinate ocean circulation model has been applied to the southern Weddell Sea, including the cavity beneath Filchner-Ronne Ice Shelf, with the aim of investigating the buoyancy-forced circulation on the continental shelf. Buoyancy forcing is associated with both the annual growth and decay of sea ice and the interaction between ice shelf and ocean. In the model a generally anti-cyclonic circulation develops beneath the ice shelf, so that new shelf waters entering the cavity in the west emerge colder and fresher in the east. The outflow contributes to a dense current that spills off the continental shelf and descends the slope. Oceanographic observations from the region are consistent with this picture and highlight the overflow as a major source of Weddell Sea Bottom Water.last_img read more

Ecology of subtropical hermit crabs in SW Madagascar: short-range migrations

first_imgMany mobile animals migrate because of the different benefits provided by different localities in time and space. For hermit crabs, such benefits include resource (shell, water, food) acquisition and gamete release. One of the more successful crustacean land-invaders, Coenobita hermit crabs, undertake complex short-range migrations in SW Madagascar. Number of active hermit crabs was inversely related to wind strength and positively related to tidal range, emphasising that movement would conserve water. A circadian component was also recorded in the locomotory activity of Coenobita pseudorugosus and C. rugosus. Path linearity varied with many of the same parameters, but also with beach slope. Movement was primarily perpendicular to shore in small individuals, but the parallel proportion increased with hermit crab size and tidal range, probably driven mostly by shell and food searching. Despite the costs of movement and shell carriage in the terrestrial environment, C. pseudorugosus and C. rugosus were as fast as their marine counterparts. Their speeds varied principally with individual size and were approximately 20% faster without shells and about 20% slower when climbing up a 20° slope, compared to horizontal or downhill travel. Hermit crabs, which are highly numerous and speciose in SW Madagascar, do not seem to partition niches by differential movement patterns. Aside from provision of shells in middens and capturing large adults for bait or pets, human activity may have a profound effect on hermit crab movement: observations at rare uninhabited marine reserves like Nosy Ve show that considerable diurnal activity may take place despite the apparent hostility of the environment to an essentially marine animal.last_img read more

Assessment of Calanus finmarchicus growth and dormancy using the aminoacyl-tRNA synthetases method

first_imgWe obtained growth rates of the copepod Calanus finmarchicus at different locations across the North Atlantic between May 1998 and June 2004. Animals were incubated for 2–9 days and fed either with natural food assemblages or with cultured algae. During this period, we measured both somatic weight-specific growth rates (measured as protein change) and aminoacyl-tRNA synthetases (AARS) activity. We found a highly significant relationship between AARS activity and growth in protein content (R2 = 0.55, P < 0.001). Significant AARS activity also occurred when growth was negative, the relationship predicting an AARS activity level of 8.33 nmPPi·mg protein–1·h–1 when somatic growth is zero. This is because AARS activity is expected even when growth is negative, owing to the continued protein turnover in the cells. The AARS method allowed for the first time the study of protein metabolism in overwintering C. finmarchicus. Our study results showed that overwintering copepods had significantly lower values of AARS activity than non-diapausing animals (t = –3.51, P < 0.002). The AARS method opens the possibility to better understand physiology dynamics of deep-water organisms (e.g. the beginning and end of diapause).last_img read more

Climatically driven fluctuations in Southern Ocean ecosystems

first_imgDetermining how climate fluctuations affect ocean ecosystems requires an understanding of how biologicaland physical processes interact across a wide range of scales. Here we examine the role of physical andbiological processes in generating fluctuations in the ecosystem around South Georgia in the SouthAtlantic sector of the Southern Ocean. Anomalies in sea surface temperature (SST) in the South Pacificsector of the Southern Ocean have previously been shown to be generated through atmosphericteleconnections with El Nin˜o Southern Oscillation (ENSO)-related processes. These SST anomalies arepropagated via the Antarctic Circumpolar Current into the South Atlantic (on time scales of more than1 year), where ENSO and Southern Annular Mode-related atmospheric processes have a direct influenceon short (less than six months) time scales.We find that across the South Atlantic sector, these changes inSST, and related fluctuations in winter sea ice extent, affect the recruitment and dispersal of Antarctic krill.This oceanographically driven variation in krill population dynamics and abundance in turn affects thebreeding success of seabird and marine mammal predators that depend on krill as food. Such propagatinganomalies, mediated through physical and trophic interactions, are likely to be an important component ofvariation in ocean ecosystems and affect responses to longer term change. Population models derived onthe basis of these oceanic fluctuations indicate that plausible rates of regional warming of 1oC over the next100 years could lead to more than a 95% reduction in the biomass and abundance of krill across the ScotiaSea by the end of the century.last_img read more

Responses of plants in polar regions to UVB exposure: a meta-analysis

first_imgWe report a meta-analysis of data from 34 field studies into the effects of ultraviolet B (UVB) radiation on Arctic and Antarctic bryophytes and angiosperms. The studies measured plant responses to decreases in UVB radiation under screens, natural fluctuations in UVB irradiance or increases in UVB radiation applied from fluorescent UV lamps. Exposure to UVB radiation was found to increase the concentrations of UVB absorbing compounds in leaves or thalli by 7% and 25% ( expressed on a mass or area basis, respectively). UVB exposure also reduced aboveground biomass and plant height by 15% and 10%, respectively, and increased DNA damage by 90%. No effects of UVB exposure were found on carotenoid or chlorophyll concentrations, net photosynthesis, F-v/F-m or Phi(PSII), belowground or total biomass, leaf mass, leaf area or specific leaf area (SLA). The methodology adopted influenced the concentration of UVB absorbing compounds, with screens and natural fluctuations promoting significant changes in the concentrations of these pigments, but lamps failing to elicit a response. Greater reductions in leaf area and SLA, and greater increases in concentrations of carotenoids, were found in experiments based in Antarctica than in those in the Arctic. Bryophytes typically responded in the same way as angiosperms to UVB exposure. Regression analyses indicated that the percentage difference in UVB dose between treatment and control plots was positively associated with concentrations of UVB absorbing compounds and carotenoids, and negatively so with aboveground biomass and leaf area. We conclude that, despite being dominated by bryophytes, the vegetation of polar regions responds to UVB exposure in a similar way to higher plant-dominated vegetation at lower latitudes. In broad terms, the exposure of plants in these regions to UVB radiation elicits the synthesis of UVB absorbing compounds, reduces aboveground biomass and height, and increases DNA damage.last_img read more

Variability among individuals is generated at the gene expression level

first_imgSelection acts on individuals, specifically on their differences. To understand adaptation and responses to change therefore requires knowledge of how variation is generated and distributed across traits. Variation occurs on different biological scales, from genetic through physiological to morphological, yet it is unclear which of these carries the most variability. For example, if individual variation is mainly generated by differences in gene expression, variability should decrease progressively from coding genes to morphological traits, whereas if post translational and epigenetic effects increase variation, the opposite should occur. To test these predictions, we compared levels of variation among individuals in various measures of gene expression, physiology (including activity) and morphology in two abundant and geographically widespread Antarctic molluscs, the clam Laternula elliptica and the limpet Nacella concinna. Direct comparisons among traits as diverse as heat shock protein QPCR assays, whole transcription profiles, respiration rates, burying rate, shell length and ash-free dry mass were made possible through the novel application of an established metric, the Wentworth Scale. In principle, this approach could be extended to analyses of populations, communities or even entire ecosystems. We found consistently greater variation in gene expression than morphology, with physiological measures falling in between. This suggests that variability is generated at the gene expression level. These findings have important implications for refining current biological models and predictions of how biodiversity may respond to climate change.last_img read more

Demonstration of “substantial research activity” to acquire consultative status under the Antarctic Treaty

first_imgAntarctic Treaty Consultative Parties are entitled to participate in consensus-based governance of the continent through the annual Antarctic Treaty Consultative Meetings. To acquire consultative status, an interested Party must demonstrate “substantial research activity,” but no agreed mechanism exists to determine whether a Party has fulfilled this criterion. Parties have generally demonstrated substantial research activity with the construction of a research station, as suggested within the Treaty itself. However, this largely demonstrates logistical capacity, rather than research activity, and often results in major and persistent impacts on Antarctic terrestrial environments. Our study found that national investment in Antarctic infrastructure, estimated by the number of bed spaces at stations, was not a reliable indicator of scientific output. Therefore, we investigated metrics to evaluate research activity directly, and identified both the overall number of Antarctic papers and the proportion of national scientific output these represented as meaningful metrics. Such metrics could (1) demonstrate a nation’s level of research activity in Antarctica or (2) help Consultative Parties assess the level of research activity undertaken by a Party seeking to acquire consultative status. Our data showed that, even without land-based Antarctic infrastructure, Canada, Denmark and Switzerland may have reasonable grounds to demonstrate “substantial research activity” on a level comparable with existing Consultative Parties. The use of these metrics may help dispel any perceived requirement for the establishment of a research station to reach consultative status, by putting a greater emphasis on generation of scientific research outputs rather than construction of Antarctic infrastructure.last_img read more