ALBERT

Notes: Abstract A survey was made of the distribution of introduced vascular plants on Marion and Prince Edward Islands. The results of this survey were compared to results of previous surveys (1965/66, 1975, 1981, 1989). Four new introductions to Marion Island have taken place, three of which involved species that had been introduced in the past, but had disappeared or were eradicated. Eighteen species of alien vascular plants are now known from Marion Island. Of these, three were not observed during the present survey, and another three have been eradicated. Many of the naturalised aliens are still increasing markedly in area and/or in numbers. Rates of spread of up to 300 m year−1 occur. Three alien vascular species occur on Prince Edward Island. Two are recent introductions, presumably transported to this island from neighbouring Marion Island by wind or birds.

Notes: Summary Studies of plant standing crop and nutrient concentrations have enabled an assessment of the seasonal changes in nutrient standing stocks (the mass of nutrients per m2) in a fjaeldmark and two fernbrake communities on Marion Island (46°54′S, 37°45′E). These communities are an important component of the island's vegetation on rocky plateaux and slopes. For most species the aboveground accumulations of N, P and K early in the season were more rapid than increases in the aerial biomass. Rates of Ca, Mg or Na accrual were either similar to, or lower than, rates of aboveground growth. Nutrient (N+P+K+Ca+Mg+Na) standing stocks at the three communities were high; 71 g m-2 at fjaeldmark, 116 g m-2 at open fernbrake and 154 g m-2 at closed fernbrake. The aboveground component accounted for 47% to 65% of these values. N was the most abundant element in the vegetation, followed by K (closed fernbrake) or Ca (open fernbrake and fjaeldmark). Nutrient standing stocks at the two fernbrakes were mostly higher than for most sub-Arctic and alpine dwarf-shrub tundras. Nutrient pool sizes (i.e. the total quantities of nutrients contained in the soil/plant system to a depth of 25 cm) were lower than those reported for arctic tundra meadows but were similar to, and often greater than, those found at heath communities, sub-Arctic dry meadows and dwarf-shrub tundras and some boreal forests. Annual net primary productions of the fernbrake vegetations were high and substantial quantities of nutrients are aquired annually from the soils by the vegetations. Depending on plant species, either N or K was the element taken up in the largest quantity, whereas P was mostly taken up in the lowest amount. A large proportion (mostly all) of the Ca and Mg and a substantial proportion of the N taken up aboveground was lost in the litterfall but little of K taken up was lost in this way.

Notes: Summary Climatic, edaphic, and vegetation parameters are compared among three Subantarctic islands and one Maritime Antarctic island, and Northern Hemisphere tundras and tundra-like ecosystems (ranging from higharctic to cool-temperate oceanic and temperate alpine), mainly by Principal Component Analyses (PCA). All analyses of abiotic variables emphasized the extreme oceanicity of the Southern Hemisphere sites and showed the strong influence of seaspray on soil nutrient ratios in the southern sites. Analyses of climate classified all the southern sites as “Cold Oceanic” within a series of very oceanic climates that were distinct from the continental/subalpine climates more typical of the northern sites. Four factorial groups were derived from the vectors in PCA of soils and climate combined. Each was a grouping of several variables that was essentially independent of the other groups. They were: general climatic severity, soil base status, supply of “labile” nutrients, and a combined index of oceanicity with organic/mineral balance and drainage. The ecological significance of these is discussed. The range of soil nutrient levels in the southern sites is approximately equal to that of the northern sites; however, in the southern sites soil nutrient levels are inversely related to climatic severity while in the north the reverse is true. The two most important causes of these opposed trends are the relative ages of the sites and the much greater effects of sea-based vertebrates (e.g. seals and seabirds) in the southern islands. Cluster analyses of component scores derived from climatic and soil data linked the southern sites with northern sites at higher latitudes, indicating the effect of the Antarctic continent on the Southern Ocean (hence on the overall climate of the southern islands) and of wind-chill on the aerial and soil climates of the southern sites. Vegetation patterns (derived from PCA of life form data) were more complex because of the serial replacement of one lifeform by onother along continuous environmental gradients. Wind exposure was an important element in the first two vectors derived from the PCA of the botanical data. The Southern Hemisphere sites exhibited almost the full range of vegetation types found in the Northern Hemisphere, despite their floristic poverty. Variation within individual islands was comparable with that found at considerably higher (up to 30° more) northern latitudes and reflects the overriding importance of wind exposure in the southern islands. Subarctic ecosystems are generally less severe forms of Arctic ones, and decreasing latitude leads to increasingly milder environments with no great changes overall in continentality. In contrast, the Subantarctic combines elements from the extremes of the range of northen tundras (i.e. high-Arctic and cool-temperate oceanic) with its own peculiar features (e.g. animal influences) to produce ecosystems that are qualitatively different both from Subarctic systems and from the continental Antarctic regions to which they are geographically closest.

Notes: Summary Investigations of the seasonal changes in vegetation standing crop have enabled and assessment of annual net primary production (ANP) for two miregrasslands at Marion Island (sub-Antarctic; 46°54′S, 37°45′E). Mire-grasslands are a conspicuous part of the island's vegetation, occurring on waterlogged peats, and being dominated by graminoid and bryophyte species. Aboveground ANP's were 883 g m-2y-1 and 570 g m-2 y-1 for the two study sites and a substantial proportion of these values was due to bryophyte production. Total (above- plus belowground) ANP's were 2178 g m-2 y-1 and 1117 g m-2y-1, greater than values reported for most graminoid and bryophyte-dominated tundra and tundra-like communities of the northern hemisphere and also greater than the ANP at many grasslands from more temperate areas. Concise descriptions are provided of the island's climate and vegetation and the sub-Antarctic is compared with the sub-Arctic based on parameters most likely to influence primary production.

Notes: Summary Bacteria were counted (direct counts using acridine orange) in soil samples from 12 sites on Marion Island (subantarctic). Numbers, cell types and cell volumes all varied widely between sites; numbers from 7 to 151×108 cm-3 and from 5 to 1300 g-1 oven-dry soil (o.d.s.), volumes from 63 to 825 μ3 cm-3 and from 61 to 6570 μm3 g-1 o.d.s. Five main cell shapes were distinguished, and each divided into up to 4 size-classes. Numbers were related negatively to climatic severity and positively to soil nutrient concentrations, vertebrate manuring, and availability of organic substrates. Volumes were not markedly related to climate; the main division was simply between edaphically rich and poor sites. Manured sites and high-altitude sites both had characteristic cell-types, and there was a strong altitudinal sequence of cell sizes among fjaeldmarks. Among the manured sites, seal wallows and albatross nest differed from gull- or penguin-manured sites under Cotula plumosa, especially in the proportions of different cell types and sizes. One sample, from a high-altitude fjaeldmark, was totally unlike all others. It was excluded from all general comparisons but it is suggested that this site deserves further study. The combination of numbers, volumes, cell types and sizes, and fluorescence characteristics are interpreted as indicators of contrasting strategies for growth and reproduction, especially high or low “standing crop” vs high or low turnover, and these strategies related to site conditions.

Notes: Summary Investigations of the seasonal changes in vegetation standing crop have enabled an assessment of annual net primary production (ANP) at a fjaeldmark, open fernbrake and closed fernbrake at Marion Island (46°54′S, 37°45′E). These communities represent a successional sequence on relatively dry ridges and slopes on the island. Together, they are representative of a large proportion of the island's lowland (c. 300 m above sea level) vegetation. Aboveground ANP's were 728 g m-2 y-1 at closed fernbrake, 502 g m-2 y-1 at open fernbrake and 226 g m-2 y-1 at fjaeldmark. Total (above-plus below) ANP's were 1958 g m-2 y-1, 1578 g m-2 y-1 and 685 g m-2 y-1, respectively. These values are greater than those found for most tundra and tundra-like shrub and dwarf shrub-dominated communities of the northern hemisphere. The island's oceanic climate ensures a long growing season (c. 300 days for vascular plants, 365 days for bryophytes) and aboveground productivities for the island communities (including two mire-grasslands reported on previously), based on the length of the growing season, were 0.9 to 2.9 g m-2 d-1, lower than for most comparable shrub and dwarf shrub sub-Arctic or alpine communities and more similar to low Artic and low alpine sedge-moss and grass-herb communities. Production efficiencies (0.7% to 2.1% of photosynthetically active radiation) were in the range reported for northern hemisphere subpolar vegetations.

Notes: Summary Nineteen bryophyte species containing epiphytic cyanobacteria on Marion Island (46°54′ S, 37°45′ E) were investigated for their capacity to reduce acetylene in the field. Fourteen species exhibited reduction, varying from 0.36 to 310.57 nmol C2H2 g-1 dry weight h-1. These values are within the range of those reported from northern hemisphere subpolar sites. The highest reduction rate occurred at a highly minerotrophic mire receiving nutrient-rich run-off from an adjacent bird-occupied slope. The lowest non-zero values occurred in moss-balls growing on exposed, wind-swept rocky ridges. Multiple regression analysis indicated a strong correlation between acetylene reduction rate and sample water content, with cyanobacteria abundance the next most important variable. Under the incubation conditions employed neither temperature nor radiation were related to reduction rate. In view of the predominance of bryophyte-dominated communities in the island vegetation it is likely that fixation of N by bryophyte-cyanobacteria associations forms an important contribution of reduced N to the ecosystem.

Notes: Abstract Supercooling points, lower lethal temperatures, and the effect of short-term exposures to low temperatures were examined during both winter and summer in the adults of six weevil species from three different habitats on Marion Island. Upper lethal limits and the effects of short-term exposure to high temperatures were also examined in summer-acclimatized adult individuals of these species. Bothrometopus elongatus, B. parvulus, B. randi, Ectemnorhinus marioni, and E. similis were freeze tolerant, but had high lower lethal temperatures (−7 to −10°C). Seasonal variation in these parameters was not pronounced. Physical conditions of the habitat appeared to have little effect on cold hardiness parameters because the Ectemnorhinus species occur in very wet habitats, whereas the Bothrometopus species inhabit drier areas. The adults of these weevil species are similar to other high southern latitude insects in that they are freeze tolerant, but with high lower lethal temperatures. In contrast, Palirhoeus eatoni, a supra-littoral species, avoided freezing and had a mean supercooling point of −15.5 ± 0.94°C (SE) in winter and −11.8 ± 0.98°C in summer. Survival of a constant low temperature of −8°C also increased in this species from 6 h in summer to 27 h in winter. It is suggested that this strategy may be a consequence of the osmoregulatory requirements imposed on this species by its supra-littoral habitat. Upper lethal temperatures (31–34°C) corresponded closely with maximum microclimate temperatures in all of the species. This indicates that the pronounced warming, accompanied by the increased insolation that has been recorded at Marion Island, may reduce survival of these species. These effects may be compounded as a consequence of predation by feral house mice on the weevils.

Notes: Summary Little is known regarding the role of arthropods as herbivores on subantarctic islands. In grassland and drainage line communities on Marion Island maximum densities (up to 220/m2) of Ectemnorrhinus similis adults occur in March to April, representing a maximum biomass of ca. 1 g m-2. Captured beetles ingest approximately 14% of body weight per day of Acaena magellanica leaf material and 37% of body weight per day of Brachythecium rutabulum fronds. No significant feeding on Poa cookii leaves was observed. It is proposed that E. similis be regarded as a significant primary consumer on the island.