The distribution and composition of vascular plant communities on Heard Island

Summary Six major higher plant communities are defined for sub-Antarctic Heard Island: tussock grassland, meadow, herbfield, pool complex, cushion-carpet, fellfield. The communities were mapped at a scale of 1:50000, using colour aerial photographs and field observations. The floristic composition of twelve vegetation transects and of thirty sample quadrats along these is used to describe the communities and identify dominant or indicator species. The vegetation is compared with that of other sub-Antarctic islands.     

Production and nutrient dynamics of plant communities on a sub-Antarctic Island

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°54S, 37°45E). 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.     

Production and nutrient dynamics of plant communities on a sub-Antarctic Island

Summary Studies of plant standing crop and of the nutrient concentrations in precipitation, soils and plants have enabled an assessment of the inter- and intra-system nutrient flows for five plant communities at Marion Island (46°54S, 37°45E). These communities, which are representative of those occupying more than 90% of the island's lowland (below 300m above sea level) were: a fjaeldmark on a rocky plateau (dominated by the cushion plant Azorella selago), an open fernbrake and closed fernbrake (both dominated by the fern Blechnum penna-marina) and two mire-grasslands (on very wet peats and dominated by graminoid and bryophyte species). Annual net primary production (ANP) at the five communities was high and substantial quantities of nutrients were taken up annually by the vegetation. N (6.5 to 24.8 g m^-2 year^-1) was the element taken up from the soil in the largest quantities, despite the fact that instantaneous values of available N pools were exceptionally low (0.003 to 0.69 g m^-2 to 25 cm depth). Either K (3.5 to 9.9 g m^-2 year^-1) or Ca (1.7 to 9.7 g m^-2 year^-1) was taken up in the second largest amount. Net quantities of nutrients translocated into the annual aboveground growth of vascular plants were, except for K and Na, greater than the seasonal mean standing stocks in the aerial biomass. Net translocation estimates ignored leaching losses from the biomass. Nutrient turnover times in the total (living plus dead, above- and belowground) vegetation were between 1 and 4 years, lower than for most Northern Hemisphere tundra communities. The quantities of nutrients in circulation were mostly less than 3% of their total pool (plants plus soil) sizes, except for K (13 to 26%) and, in four of the communities, Mg (6 to 15%). Precipitation inputs of N, K, Ca and Mg were considerably lower than the amounts required in the ANP. No P occurred in the precipitation. Biological fixation of N was much less than the precipitation input. The vascular plant species appear to be less efficient in conserving N through back-translocation from senescing photosynthetic tissue than are most plants of similar life forms from northern hemisphere tundra and tundra-like areas. Only 11 to 30% of the N taken up into the annual aboveground growth was back0translocated before or during senescence. Back-translocations of P (39 to 71%) and K (71 to 965) were greater. However, all of these estimates ignore leaching losses. Despite the apparently poor ability of the plants to back-translocate N, the total nutrient costs of the aboveground ANP at the five sites (14 to 32 mg per g m^-2 ANP) were very much in the lower part of the range reported for a wide variety of vegetation types. Nutrient costs of the ANP for the miregrassland communities were especially low, mainly because of low requirements for Ca and Mg. In view of the small soluble and available pools of some nutrients (especially N and P) and the substantial nutrient requirement for the ANP, it is concluded that net nutrient mineralization in decomposition and nutrient absorption by the vegetation are closely coupled.     

Restricted plant species on sub-Antarctic Macquarie and Heard Islands

The recent distributional history of two Macquarie Island vascular plant species, Carex trifida, Poa litorosa, and the Heard Island vascular plant, Ranunculus crassipes is examined. C. trifida is known from only one small population on the north west coast of Macquarie Island. Four populations of P. litorosa were first recorded in the 1980s; we believe however, that it was first observed, but misidentified in the 1950s. R. crassipes was first discovered on Heard Island in the late 1980s. We argue that all three species are indigenous and arrived on their respective islands within the last 200 years by natural processes, most likely from warmer neighbouring islands, where these species have more extensive distributions. There have been small-scale changes in distribution of all species, mainly expansion. Further expansion of all three species is expected as a response to warming climate. Feral rabbit grazing is having a confounding negative influence on populations of P. litorosa.     

Ecology of Heard Island Diptera

Phenology, distribution and abundance of three Diptera species on Heard Island were investigated to provide baseline data for monitoring the effect on climate change on populations. Five vegetation types at two localities were sampled in two different years, firstly in the summer of 1987–1988 at Atlas Cove and secondly at Spit Bay over 12 months from summer 1992 to summer 1993. Pitfall traps and soil core extractions were operated in summer at both localities and pitfalls alone for 12 months from Spit Bay. The wingless Anatalanta aptera was the most abundant species in traps at Atlas Cove with most individuals collected from Poa tussock grassland, half as many from Pringlea and Azorella vegetation and fewest with a significantly higher level of asymmetry in the large katepisternal setae, from Azorella and Fellfield. Calycopteryx moseleyi was the most abundant fly in traps at Spit Bay, and A. maritima was the least abundant at both localities. Monthly pitfall catches from 1992–1993 indicated that A. aptera was active in most months of the year apart from winter, females early in the season and males active throughout the summer; teneral individuals only detected in January. C. moseleyi was more strongly seasonal with peak adult numbers occurring in January. Amalopteryx maritima was least seasonal in activity. Asymmetry in A. aptera suggests that it was at the limit of its ecological tolerance in Fellfield and Azorella on Heard Island. Changes caused by climate warming or invasive species are mooted.     

Statistical models for monitoring and predicting effects of climate change and invasion on the free-living insects and a spider from sub-Antarctic Heard Island

Terrestrial ecosystems of sub-Antarctic islands are particularly sensitive to global and local human impacts, including climate change and species invasion. Invertebrates form a central component of these ecosystems. We conducted a stratified survey of 60 sites on sub-Antarctic Heard Island and used Poisson regression models to describe the spatial distribution and abundance of five of the ten free-living species captured. Acari and Collembola were not considered. Five species were not caught in traps in sufficient numbers to model. The distributions of species were described by altitude, vegetation type and aspect. The resulting distribution models can be used to both monitor and predict the effects of climate change and species invasion on this unique and valuable ecosystem.     

The invertebrates of sub-Antarctic Bishop Island

We report on the first comprehensive collection of invertebrates made on sub-Antarctic Bishop Island, which lies 33 km south of Macquarie Island. A total of 15 species were collected, of which 14 also occur amongst the 168 species recorded from Macquarie Island. We hypothesise that the greater species richness of Macquarie Island relative to Bishop Island is largely caused by the greater habitat diversity on Macquarie Island but that other factors, including accidentally introduced species, may also be important. Received: 3 July 1996 / Accepted: 2 October 1996     

Diversity, ecology and biogeography of the freshwater diatom communities from Ulu Peninsula (James Ross Island, NE Antarctic Peninsula)

The diversity, ecology and biogeography of diatoms in lakes, seepage areas and streams on the Ulu Peninsula, a large ice-free area in the northern part of James Ross Island (Weddell Sea), were studied. A diverse diatom flora of 123 taxa was observed, dominated by several Nitzschia taxa, Psammothidium papilio, Eolimna jamesrossensis, Fragilaria capucina and Fistulifera saprophila. The results from the similarity and diversity analysis suggest James Ross Island to be biogeographically positioned within the Maritime Antarctic region, yet with some affinities with the flora of Continental Antarctica, as shown by the presence of Luticola gaussii and Achnanthes taylorensis. Based on our data, James Ross Island can thus be located close to the boundary of the two main Antarctic biogeographical regions. Diatom communities present in streams and seepage areas could be clearly distinguished from those in lakes, the latter being much more species rich. Based on the multivariate analysis, conductivity and nutrients were selected as the two main environmental factors determining the diatom composition in the Ulu Peninsula lakes. The revised taxonomy of the Antarctic diatom flora induced the construction of a transfer function for water conductivity in the studied lakes that can be applied in further palaeoecological studies.     

Metabolic rate, genetic and microclimate variation among springtail populations from sub-Antarctic Marion Island

Measurement of metabolic rates (made at 10°C) of individuals of the springtail Cryptopygus antarcticus travei from six geographically distinct populations on sub-Antarctic Marion Island were combined with mitochondrial DNA (COI) haplotype analysis to examine in parallel both physiological and genetic variation of distinct populations. We found evidence of genetic differentiation among populations and a general indication of long-term isolation with limited gene flow. While we found support for an overall pattern of metabolic rate structure among populations from different geographic locations on the island (mean rate = 0.0009–0.0029 μl O₂ μg⁻¹ h⁻¹ for populations of a mean individual mass of 8–26 μg), we were unable to demonstrate a coherent common pattern between this and genetic variation. However, spatial structure in metabolic rate variation was strongly related to the extent of variability in microclimate among sites, and also showed some indication of a phylogeographic signal. Thus, over the relatively short timescale of Marion Island’s history (<1 million years), the periodic geographic barriers that have driven population differentiation from a molecular perspective may also have resulted in some physiological differentiation of populations.     

Epiphytic diatom communities on intertidal seaweeds from Iceland

Epiphytic diatom communities on macroalgae from Iceland coastal waters were investigated during July 2005. Ten species of seaweeds have been collected belonging to brown, red and green algae. The analysis of epiphytic diatom community was carried out under scanning electron microscopy. The epiphytic diatom abundances varied from 7 ± 5 to 7524 ± 3491 cells mm⁻². Erect growth forms were the most abundant, representing on average 50% of the total diatoms (Achnanthes cf. brevipes var. parvula, Tabularia investiens, T. fasciculata, Hyalosira cf. delicatula, Gomphoseptatum aestuarii, Pseudogomphonema plinskii), followed by adnate (29%) (Cocconeis stauroneiformis, C. scutellum) and motile forms (21%) (Nitzschia cf. amphibia and Navicula perminuta). Highly branched seaweeds with articulated thallus surface, offering a number of microenvironments to be occupied by the epiphytes, showed a high level of colonization, mainly due to erect and motile diatoms. Flat thalli with smooth surface allowed for the growth of mainly erect diatoms.     

Pre-freeze mortality in three species of aphids from sub-Antarctic Marion Island

Understanding the mechanisms by which aphids survive low temperature is fundamental in forecasting the risk of pest outbreaks. Aphids are chill susceptible and die at a temperature close to that at which a small exothermal event is produced. This event, which can be identified using differential scanning calorimetry (DSC), normally occurs at a higher temperature than the supercooling point (SCP) and has been termed a pre-freeze event (PFE). However, it is not known what causes the PFE or whether it signifies the death of the aphid. These questions are addressed here by using a sensitive DSC to quantify the PFE and SCP and to relate these thermal events to the lower lethal temperature (LT₅₀) of sub-Antarctic aphids acclimated to low temperatures. PFEs were observed in each of the 3 species of aphids examined. They occurred over a narrower temperature range and at a higher temperature range than the SCP (−8.2 to −13.8 and −5.6 to −29.8 °C, respectively). Increased acclimation temperature resulted in increased SCPs in Myzus ascalonicus but not in Rhopalosiphum padi. The LT₅₀ reduced by approximately 1 °C from −9.3 to −10.5 °C with reduced acclimation temperature (10–0 °C). The LT₅₀ was close to the temperature at which the PFE occurred but statistically significantly higher than either the PFE or the SCP. In the majority of cases the PFE exotherm occurred well before the main exotherm produced by the bulk of the insect’s body water freezing (SCP). However, in a few cases it occurred at the same temperature or before the super-cooling point making the term, pre-freeze event (PFE), rather misleading. The possible origins of the PFE are discussed.     

Respiratory Metabolism of sub-Antarctic insects from different habitats on Marion Island

Oxygen uptake of the foliage-dwelling larvae ofEmbryonopsis halticella Eaton (Lepidoptera: Yponomeutidae) and adults ofEctemnorhinus marioni Jeannel (Coleoptera: Curculionidae), the litter-dwelling larvae ofPringleophaga marioni (Lepidoptera: Tineidae) and the wrack-dwellingParactora dreuxi Séguy (Diptera: Helcomyzidae) was examined over the range of temperatures experienced by these insects in their microhabitats. With the exception of the kelp fly,P. dreuxi, Q₁₀s and activation energies were generally lower than those found in temperate and Arctic insects, but were similar to values found in beetles from sub-Antarctic South Georgia Island. Q₁₀ and activation energy of each species reflected the temperature regime found in its microhabitat. Activation energies of the Marion Island species were intermediate between those found in temperate and polar arthropods, but towards the polar end of the range. The hypothesis that insects are capable of showing respiratory adaptation to temperature is supported.     

Nitrogen fixation in the sub-Antarctic Macquarie Island

Summary The N₂-fixing biota of Macquarie Island are dominated by cyanobacteria growing epiphytically or symbolically with plants or lichens. Highest rates of C₂H₂-reducing activity were found in the leafy lichen Peltigera sp. colonizing herbfields and short grasslands and in the coastal angiosperm Colobanthus muscoides. Significant rates of C₂H₂ reduction were also found to be associated with the liverwort Jamesoniella colorata, commonly occurring in coastal and plateau mires, in a mossbed of Dicranella cardotii colonizing a land-slip face on the grassland slopes at 100 m altitude and within polsters of the mosses Ditrichum strictum and Andreaea sp. found in exposed localities on the plateau at 200–300 m altitude. It was concluded that the common feature of plants supporting active N₂ fixation in dry habitats was the dense packing of stems and leaves, enabling water translocation to the cyanobacterial zone by wick action. Epiphytic cyanobacterial C₂H₂ reduction in wet habitats was widespread and not restricted to any particular plant species. Notable N₂-fixing lichens of the plateau were Pseudocyphellaria delisea and Stereocaulon sp., although both were also occasionally found in coastal herbfields. No significant N₂-fixing activity was associated with any of the dominant grasses tested. Heterotrophic N₂ fixation was also found to be insignificant in the various habitats tested, however N₂-fixing Bacillus (B. macerans or B. polymyxa) were universally present in coastal, grassland slope, or plateau samples, including moss polster samples. A N₂fixing Clostridium sp. was isolated in only one instance, from soil in the vicinity of a seal wallow on the coast.     

Habitat use, diet and body size of Heard Island weevils

Habitat use, diet and body-size variation are examined in weevils from Heard Island, with specific attention being given to the Ectemnorhinus viridis species complex. E. viridis shows marked altitudinal variation in body size and vestiture, but there are no consistent associations between body size and diet, nor are there consistent among-individual differences in conventional taxonomic characters. Thus, the status of E. viridis as a single, variable species is maintained. This species occurs from sea level to 600 m and it feeds on vascular plants and bryophytes. Canonopsis sericeus also feeds on bryophytes and vascular plants and occurs over a narrower altitudinal range. Palirhoeus eatoni is restricted to the surpralittoral zone where it feeds on marine algae and lichens. Bothrometopus brevis and B. gracilipes both feed on cryptogams, with the former species occurring from sea level to 450 m, and the latter from 50 to 550 m above sea level. In all species, males are smaller than females and there is a size cline such that populations from higher elevations are smaller than those at lower altitudes. This cline is the reverse of that found on the Prince Edward Islands which, unlike Heard Island, lie to the north of the Antarctic Polar Frontal Zone. This difference in body-size clines between weevils on the two island groups is ascribed to the shorter growing season on the colder Heard Island. The information presented here supports previous ideas regarding the evolution of the Ectemnorhinus-group of weevils on the South Indian Ocean Province Islands, although it suggests that subsequent tests of these hypotheses would profit from the inclusion of molecular systematic work.     

Food, reproduction and survival in mice on sub-Antarctic Marion Island

The house mouse Mus musculus is the most widespread introduced mammal on sub-Antarctic islands, where it may alter ecosystem function. Ambient temperature and food availability affect reproduction and survival for mice. It is unclear how these factors influence mouse demography in the sub-Antarctic, and we tested the influence of food experimentally on Marion Island. Using food supplementation trials, we did not alter reproduction or overwinter survival. Alternatively, we argue ongoing climatic change on Marion could increase mouse densities through summer, while increased winter survival may reduce population growth rates the following summer through density dependence. The overall influence of these apposing forces depends on their relative strengths but may limit changes in mouse numbers with ongoing changes in climate in the sub-Antarctic.     

Attached diatom communities from the lower Truckee River,summer and fall, 1986

The algal flora of the Truckee River below Reno, Washoe County, Nevada was examined during the summer and fall months of 1986. This reach of the lower Truckee River exhibited a substantial gradient in dissolved inorganic nitrogen associated with sources which included treated wastewater from the Reno metropolitan area. The algal communities were similar to those of other river systems of the Great Basin. Cyanophyta and Chlorophyta formed encrusting mats on the substrate, with the nitrogen fixer Calothrix atricha relatively abundant upstream from the nitrogen source. Diatoms were abundant within and upon this mat. A total of 139 diatom taxa and 11 taxa other than diatoms was identified from this flora. Several of the diatom taxa, including Achnanthes minutissima, Diatoma vulgare, Nitzschia dissipata, and Nitzschia palea, demonstrated distinct downriver patterns in relative abundance.     

Biotic zonation on rocky shores of Heard Island

Summary The zonation of rocky shore biota on Heard Island is described for the first time, related to a universal zonation scheme and compared with that recorded for other sub-Antarctic localities. The Kelp Zone of holdfasts of the giant kelp, Durvillea antarctica (Chamisso) Hariot (one of the characteristic features of these regions) is confirmed as a sublittoral fringe. The occurrence of a Bare Zone within the littoral zone on sub-Antarctic shores is discussed. The possible roles of submersion, spray, freezing and predation by gulls in influencing the extent and composition of zones are discussed.     

Thermal tolerance limits in six weevil species (Coleoptera, Curculionidae) from sub-Antarctic Marion Island

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. Received: 4 February 1997 / Accepted: 3 May 1997