sub-Antarctic Marion Island Research Articles

Moisture, carbon and inorganic nutrient controls of soil respiration at a sub-Antarctic island

Respiration rate of soils manured by seabirds and seals on sub-Antarctic Marion Island (47°S, 38°′E) is considerably higher than that of unmanured soils, and the main objective of this study was to determine whether this is caused by an enhanced supply of inorganic nutrients (N and P) or organic C substrates, or both. The effect of soil moisture content was also investigated. Soils from five habitats were studied: Mesic fellfield, Dry mire, Closed fernbrake, Coastal herbfield and Cotula herbfield. The latter two are strongly influenced by manuring. Respiration rate increased with soil moisture content up to full water holding capacity, and the response of respiration to moisture increased strongly with temperature (especially above 10 °C). Respiration Q 10 increased with soil moisture content. Glucose addition markedly stimulated soil respiration rate in all the soils, despite the fact that they all possessed substantial concentrations of organic C, a wide range of N and P concentrations and a 2-fold variation in C:N ratio. This suggests that the primary factor limiting soil respiration on the island is the supply of labile carbon substrate. Soil N and P status is also important, since adding glucose with N and/or P to soils with low N and P concentrations resulted in a significantly greater stimulation of respiration rate than adding glucose alone. In fact, for the Mesic fellfield and Dry mire soils (especially poor in N and P) adding N and P stimulated respiration rate even without added glucose. For soils with adequate endogenous concentrations of N and P (the Coastal herbfield and Cotula herbfield soils), adding further N and P did not stimulate respiration, and adding N and P with glucose did not enhance respiration more than adding glucose alone. It is proposed that manuring results in a whole syndrome of consequences for soil respiration rate, including increased litter input and root exudation due to higher primary production, higher quality of litter and soil organic matter, larger, more active and more diverse soil microbial populations and larger numbers of microbivores that stimulate microbial activity and turnover.

On the Development of Autochthonous Blockfields in the Grey Basalts of Sub-Antarctic Marion Island

Sub-Antarctic Marion Island has experienced a periglacial climate since the Last Glacial Maximum. Post-glacial allochthonous openwork accumulations appear to be well developed below 750 m a.s.l., although basalt surfaces exhibit only poorly developed autochthonous blockfields. Bedrock disintegration appears to be confined to a single layer of detritus, probably formed by pressure release on deglaciation. Holocene environmental conditions have not produced chemical weathering products and have preserved the layer of mechanically derived residuals. At altitudes above 750 m a.s.l., blockfield formation appears to be limited by former permanent snow cover. Given the ideal conditions for frost action throughout the Holocene, the absence of well-developed mechanically derived detritus supports the argument for longer time intervals of formation and the non-periglacial origins of autochthonous blockfields.

Rock Weathering Rates on Subantarctic Marion Island

Subantarctic Marion island (46°S) is a shield volcano of basal “gray” lavas and younger “black” lava outflows. Rock weathering rates, as determined by annual mass loss from small clasts (<400 g), was measured over a 3-yr period at 4 sites on the island on an altitudinal transect from the coast toward the interior. Mass loss from gray lava clasts was found to be 0.02% near sea level, increasing to 0.10% yr−1 at 730 m a.s.l. Black lava clasts yielded mean losses of up to 0.72% at the sites, although no altitudinal trend in mass loss was evident. In the sea-spray zone, gray and black lava clasts monitored over 1 yr had mean losses of 0.30% and 0.41%, respectively. Weathering rates are marginally inflated by the annual weighing procedure, which has been determined to contribute approximately 0.01% to the measured gray lava clast mass losses, and 0.07% to the black lavas. Since none of the clasts showed visual signs of fracturing or flaking, mass loss appears to be on a granular scale at most, and material removal is probably assisted by rainwash. Extrapolated values suggest that black lava clasts can weather completely within 200 yr and gray lava clasts within approximately 1000 yr at high altitudes. These data have implications for the lifespan of periglacial landforms constituting small clasts, particularly those formed in the early Holocene.

Seasonal changes in age class structure and reproductive status of house mice on Marion Island (sub-Antarctic)

Feral house mice on sub-Antarctic Marion Island become reproductively active (males scrotal, females with perforate vaginas or pregnant) at an age >60 days and breed until death, which may occur at more than 13 months. Breeding is strongly seasonal; pregnant or lactating females were found only from October to May. A substantial proportion of mice old enough to breed in one summer overwinters to form a significant component of the breeding population the following summer but it is unlikely that any survive a second winter. The onset of breeding is closely synchronized with increasing day length but occurs about 2 months before mean temperature at the ground surface starts to increase significantly. Cessation of breeding is more closely associated with declining temperatures in late summer. For both males and females, the best correlation between reproductive activity and any of the temperature parameters measured was with average maximum temperature 1 cm above the ground. Competition for macroinvertebrate prey increases sharply in early winter due to high mouse numbers. The breeding season in 1991/1992 and 1992/1993 was at least 2 months longer than in 1979/1980, because the mice started breeding earlier, and stopped breeding later, in 1991/1993. The later cessation of breeding in 1991/1993 was despite the fact that there was a greater competition for macroinvertebrate prey, and that mean air temperatures during the early winter months were lower, than in 1979/1980.

Impact of Trampling on the Vegetation of Subantarctic Marion Island

We assessed the impact of human trampling in three different habitats on Marion Island (46°50′S, 37°50′E). The habitats were (1) mires with wet, peaty soils and grass- and bryophyte-dominated vegetation; (2) slopes with relatively dry mineral soils, dominated by small ferns and dwarf shrub; and (3) feldmark on dry mineral soils with an open vegetation of cushion dicots and bryophytes. We examined existing walking tracks on the island. Track width (25 to 800 cm) increased with soil moisture content. Trampling reduced vegetation height, total cover, and species richness in mires and feldmark and vegetation height and herb layer cover (but not bryophyte cover or species richness) in slopes. In mires, most species were negatively affected by trampling, but in slopes trampling increased the cover of 6 out of 9 significantly affected species. The total number of species in all trampled plots in mire and feldmark communities was ∼10% lower, but in slopes 28% higher, than in control plots. The impact of trampling differed between growth forms. Cushion dicot, shrub, and fern covers were reduced, whereas graminoid and pleurocarpous moss covers were unaffected or increased with trampling. Trampling reduced the cover of most bryophyte species, but it did increase the cover of some. In the slope habitat, destruction by trampling of the closed herb canopy allows increased light penetration and makes the habitat more favorable for small plants such as bryophytes. We attribute the differences in how the vegetation of different habitats responds to trampling to differences in the structure of the original vegetation as well as differences in soil characteristics, especially the soil’s structural stability under pressure.

Morphometric measurement selection: an invertebrate case study based on weevils from sub-Antarctic Marion Island

A character-selection procedure initially applied in vertebrates (viverrid carnivores and murid rodents), but with a potential, more general application, was used to select appropriate characters for a morphometric investigation of weevils on Marion Island. An initial set of 23 linear measurements, adopted from a previous morphometric study, was subjected to cluster and ordination procedures to summarize patterns of correlations between measurements. Criteria were developed for the selection of representative measurements within cluster analysis-generated sub-clusters, after the exclusion of redundant measurements. This reduced the 23 initial variables to a final set of 15 measurements. The general grouping of variables was broadly consistent across all weevil species examined. Apart from economizing, by reducing the number of characters that have to be measured for subsequent analyses, the procedure also provides a way to adequately represent the phenotype, and to investigate morphological integration.

Absence of Haematozoa in Breeding Macaroni Eudyptes Chrysolophus and Rockhopper E. Chrysocome Penguins at Marion Island

Haematozoan infections cause the death of penguins in captivity, but seldom in the wild. No haematozoa were found in 89 blood smears taken from macaroni penguins Eudyptes chrysolophus or 80 smears from eastern rockhopper penguins E. chrysocome filholi at subantarctic Marion Island between October and November 2001. Discussion centres on the possibility of vector introduction and establishment under conditions of climatic and/or anthropogenic change.

Unusual Breeding by Seabirds at Marion Island During 1997/98

In 1997/98, breeding at subantarctic Marion Island was exceptionally good for five species of seabirds capable of foraging over wide areas and for a tern. The number of king penguin Aptenodytes patagonicus chicks surviving to the start of spring in 1997 was considerably more than previously recorded. Greater numbers of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses, northern giant petrels Macronectes halli and Kerguelen terns Sterna virgata bred than previously recorded, and more southern giant petrels M. giganteus did so than in any other year since 1994. For southern giant petrels, reproductive success was higher than in any other year, as was survival of chicks of northern giant petrels. Conversely, for two seabirds that feed close to the island, gentoo penguin Pygoscelis papua and Crozet shag Phalacrocorax [atriceps] melanogenis, 1997/98 was a particularly poor breeding season. Gentoo penguins initiated breeding later than usual and fledged few chicks. The number of Crozet shags that bred decreased; probably about 25% of the adult population did not breed. For two species with an intermediate foraging range that eat mainly crustaceans, macaroni Eudyptes chrysolophus and eastern rockhopper E. chrysocome filholi penguins, breeding was not noticeably different from normal except that chicks of rockhopper penguins fledged with a slightly heavier mass than in other years. However, for both these penguins, the mass of adults on arrival at colonies decreased substantially in the following (1998/99) breeding season. The unusual breeding by most of the seabirds coincided with the El Niño Southern Oscillation (ENSO) event of 1997/98. This synchrony contrasts with lagged responses to ENSO events of seabirds that breed farther south in the Southern Ocean. Continued monitoring of seabirds over well-separated sites in the Southern Ocean may elucidate how climatic perturbations operating at a global scale impact seabirds in the region.

Population, Breeding, Diet and Conservation of the Crozet Shag Phalacrocorax [atriceps] Melanogenis at Marion Island, 1994/95–2002/03

The number of Crozet shags or cormorants Phalacrocorax [atriceps] melanogenis breeding at subantarctic Marion Island decreased by 68% from 841 pairs in 1994/95 to 272 pairs in 2002/03. The mean number of pairs at colonies also decreased and was significantly related to the overall number of birds breeding in any given season. The decreases coincided with a period of warming and reduced precipitation at Marion Island and with a decrease in the number of gentoo penguins Pygoscelis papua breeding there. Both these seabird species forage inshore and there is considerable overlap in their diets. Nototheniid fish and the decapod Nauticaris marionis continued to be important in the diet of Crozet shags, but a change in dominance among nototheniid prey suggests availability of prey to shags changed after the mid 1980s. Crozet shags breed for the first time when aged three years. It is probable that about 25% of the mature population did not breed in 1997/98, coincident with a strong El Niño Southern Oscillation event. In four seasons, breeding pairs on average fledged 0.30 chicks from first clutches, an amount thought inadequate to sustain the population. Crozet shags at the Prince Edward Islands should now be regarded as Endangered. Placing breeding colonies in the most highly protected zone on Marion Island, considering the establishment of an ex situ population and undertaking a genetic study of the specific status of the Crozet shag are recommended conservation measures.

Decrease in Numbers of the Eastern Rockhopper Penguin Eudyptes Chrysocome Filholi at Marion Island, 1994/95–2002/03

The number of eastern rockhopper penguins Eudyptes chrysocome filholi breeding at subantarctic Marion Island decreased from about 173 000 pairs in 1994/95 to about 67 000 pairs in 2001/02. During 1994/95 – 2002/03 pairs fledged on average 0.40 chicks per year, an amount thought insufficient to balance mortality of breeding adults, and there was a decrease in the mass at arrival at breeding colonies of both males and females. Except in 1997/98, the mass of chicks at fledging was less than that recorded at two other localities. These factors suggest an inadequate supply of food for rockhopper penguins at Marion Island. Decreases of rockhopper penguins at several other localities also have been attributed to inadequate food. Rockhopper penguins at Marion Island continued to feed mainly on crustaceans during chick rearing. There was a marked increase in the contribution of fish to the diet in 1999/00 that coincided with an increase in mass at arrival at colonies of both males and females. Trends in numbers of pairs breeding in different sections of Marion Island were not always consistent, indicating the need for island-wide monitoring to establish the overall trend.

Population and Breeding of the Gentoo Penguin Pygoscelis Papua at Marion Island, 1994/95 – 2002/03

The numbers of gentoo penguins Pygoscelis papua breeding at subantarctic Marion Island fell by 40% from 1994/95 to 2002/03, from 1 352 pairs to 806 pairs. Apart from a slight increase in 1998/99, there was a steady decrease in numbers breeding between 1995/96 and 2000/01, when the population stabilized. There is indication that in some years not all breeders nested and that some birds relocated to another colony after disturbance. From first clutches, pairs on average fledged between 0.01 chicks in 1997/98 and 0.58 chicks in 2002/03 (mean 0.38 ± 0.21). In 1994/95, replacement clutches increased the overall production of fledged chicks by 11%. Based on demographic parameters measured at other localities, the production of chicks at Marion Island was inadequate to maintain the population during the period 1995/96 – 2000/01. Consistency in trends in breeding success at five colonies suggests that factors operating at a mesoscale, rather than those specific to particular colonies, often influenced breeding success. Laying was later than normal in 1997/98, when there was almost total breeding failure with large losses of eggs and small chicks to returning Subantarctic skuas Catharacta antarctica. Future research on this Near Threatened species at Marion Island must take full account of its susceptibility to human disturbance.

Soil respiration and its determinants on a sub-Antarctic island

The effect of temperature on soil respiration at field moisture holding capacity was assessed for 100 sites representing 21 habitats on sub-Antarctic Marion Island (47°S, 38 °E). Respiration rates were compared across habitats and related to soil chemistry, soil microrganism counts and botanical characteristics. Median Q 10 across the 100 sites was 2.0, in the lower part of the range reported for soils elsewhere. Q 10 did not differ with temperature between 5 and 20 °C, indicating a mixed community of soil microorganisms having different responses to temperature. Respiration rates are about an order of magnitude higher than those reported at the same temperature for surface soils from Northern Hemisphere tundra. Edaphic richness (high concentrations of available P, inorganic N and total N), associated with large soil microbial populations and substantial relative covers of nitrophilous or coprophilous plants and caused by manuring by seals and seabirds, is the main determinant of soil respiration rate. The island's habitats were originally defined on the basis of canonical correspondence analysis of structural (vegetation and soil chemistry) variables. Since habitat-mean soil respiration rate correlated highly positively with the mean positions of the habitats on a canonical axis interpreted as representing a gradient in the intensity of animal influence, it is concluded that the habitat classification reflects differences in at least one ecosystem functional attribute, soil respiration.

Haemolymph osmolality and thermal hysteresis activity in 17 species of arthropods from sub-Antarctic Marion Island

In this paper, we present measurements of haemolymph osmolality for individuals from 17 species of arthropods on Marion Island, including a mite, a spider, Collembola, Psocoptera, Coleoptera, Diptera and Lepidoptera. This is the largest such survey for a Southern Hemisphere habitat. We also screened these species for thermal hysteresis activity, and show that the lepidopteran Embryonopsis halticella has a haemolymph thermal hysteresis agent that imparts approximately 0.2°C of thermal hysteresis. This low level leads us to conclude that, in this mild habitat, it may have a role in preventing nucleation, rather than directly acting to depress the freezing point of whole caterpillars. Haemolymph osmolalities were generally concordant with published values for the groups examined. With the exception of Isotomurus cd. palustris acclimated at 5 and 10 °C, we found no statistical evidence of acclimation altering the haemolymph osmolality for any of the arthropods investigated.

The first record of a terrestrial crustacean, Porcellio scaber (Isopoda, Porcellionidae), from sub-Antarctic Marion Island

Here we present the first record of Porcellio scaber Latreille, 1804 (Isopoda, Porcellionidae) from sub-Antarctic Marion Island. Because surveys for new species introductions are undertaken on a regular basis (at least annually) on the island, it seems likely that the species arrived in April 2001. The present distribution of P. scaber at the station suggests that it probably arrived with building supplies from Cape Town, although it may have been introduced from Gough Island from where it is also known. The species feeds on detritus as it does elsewhere, and appears to be reproductively most active over the summer months from October until March. The introduced house mouse and indigenous lesser sheathbill, the main vertebrate predators of invertebrates at the island, would not take individuals of P. scaber. The introduction of this highly successful invasive species at Marion Island highlights the ongoing conflict between use and conservation on the Southern Ocean islands.

Habitat Specificity of Mites on Sub-Antarctic Marion Island

Studies on sub-Antarctic insects have suggested that species inhabiting the epilithic biotope (cryptogam-dominated habitats) exhibit higher habitat specificity than those species of the vegetated biotope (habitats dominated by vascular plants), and that this is partially the consequence of recolonization of the latter by migration from the former, which acted as glacial refugia during the Neogene. Here, the Acari is used to independently test this idea. To do so, 17 different habitats belonging to both the epilithic and vegetated biotopes were quantitatively sampled on sub-Antarctic Marion Island. These habitats included those on a rocky shore zone, in lowland vegetation, and in a mid-altitude fellfield. Thirty-nine morphospecies/taxa from 27 families were recorded, with a maximum abundance exceeding 300,000 individuals/m−2. Mite assemblages differed significantly between all habitats, although the most pronounced differences were between the rocky shore, fellfield epilithic, and vegetated biotope habitats. Major differences between the rocky shore and fellfield habitats indicated that a clear distinction must be drawn between these two groups of habitats, although both were previously considered part of the epilithic biotope. It seems likely that the mite fauna of the vegetated biotope was derived mostly from fellfield habitats following deglaciation. Habitat specificity was also more pronounced in the epilithic (rocky shore and fellfield epilithic) species than in those from the vegetated biotope. Thus, the Acari provide support for the hypothesis of reduced habitat specificity in vegetated biotopes, possibly as a consequence of recent recolonization.

Population trends of albatrosses and petrels at sub-Antarctic Marion Island

We report on the population changes of five species of Procellariiform seabirds breeding at Marion Island: wandering albatross (Diomedea exulans), grey-headed albatross (Thalassarche chrysostoma), northern giant petrel (Macronectes halli), southern giant petrel (M. giganteus), and white-chinned petrel (Procellaria aequinoctalis). The four large surface-nesting species (wandering albatross, grey-headed albatross and the northern and southern giant petrel) show similar population trends over the last 16–18 years. All were stable or decreasing during the 1980s, followed by a recovery period during the early to mid-1990s. Recently, all species have once again stabilized or decreased in numbers. Population trends of wandering albatross at Marion Island were strongly correlated with other Indian Ocean populations, but were different from the Atlantic Ocean population. These similarities suggest a common cause and can be explained by changes in tuna (Thunnus spp.) longline fishing effort in the southern Indian Ocean. A recent increase in tuna longlining, as well as recent large-scale Illegal, Unregulated and Unreported (IUU) longline fishing for Patagonian toothfish (Dissostichus eleginoides) close to Marion Island, could be contributing to the recent decreases in some of these species. Adoption of mitigation measures and an effective means of dealing with IUU longline fishing seem necessary to reduce the potential impacts of longline fishing on populations of albatross and petrel.

Terrestrial habitats on sub-Antarctic Marion Island: their vegetation, edaphic attributes, distribution and response to climate change

The vegetation, soil chemistry characteristics and altitudinal distributions of 23 habitats in 7 habitat complexes on sub-Antarctic Marion Island (47°S, 38°E) are described. The habitat complexes (number of habitats in complex) are; Coastal Salt-spray Complex (2); Fellfield Complex (2); Slope Complex (6); Biotic Grassland Complex (3); Biotic Herbfield Complex (3); Mire Complex (6); Polar Desert Complex (1). The habitat classification closely reflects the between-habitat variation in the relative magnitudes of the main forcing variables that determine ecological succession on the island (moisture, exposure, parent soil material, saltspray and manuring and trampling by seals and seabirds). Hence, it can serve as a framework against which to detect and evaluate ecological responses to the marked climatic change currently occurring in the sub-Antarctic. Suggestions are made on how the habitats might respond to climatic change (warming, drying) and other perturbations (increasing or decreasing influences of salt-spray and manuring).

The animal species-body size distribution of Marion Island.

Body size is one of the most significant features of animals. Not only is it correlated with many life history and ecological traits, but it also may influence the abundance of species within, and their membership of, assemblages. Understanding of the latter processes is frequently based on a comparison of model outcomes with the frequency of species of different body mass within natural assemblages. Consequently, the form of these frequency distributions has been much debated. Empirical data usually concern taxonomically delineated groups, such as classes or orders, whereas the processes ultimately apply to whole assemblages. Here, we report the most complete animal species-body size distribution to date for those free-living species breeding on sub-Antarctic Marion Island and using the terrestrial environment. Extending over 15 orders of magnitude of variation in body mass, this distribution is bimodal, with separate peaks for invertebrates and vertebrates. Under logarithmic transformation, the distribution for vertebrates is not significantly skewed, whereas that for invertebrates is right-skewed. Contrary to expectation based on a fractal or pseudofractal environmental structure, the decline in the richness of species at the smallest body sizes is a real effect and not a consequence of unrecorded species or of species introductions to the island. The scarcity of small species might well be a consequence of their large geographic ranges.

Biological invasions of Southern Ocean islands: the Collembola of Marion Island as a test of generalities

It has been suggested previously that the presence and abundance of indigenous species have a marked influence on the likelihood of invasion of a community. It has also been suggested that such biotic resistance has a negligible influence on the outcome of an invasion, but that the abiotic characteristics of the environment being invaded are more important. The latter has been claimed to be especially important on the islands of the Southern Ocean. In order to test these competing hypotheses we examined the distribution and abundance of indigenous and introduced springtails across 13 habitats, which differ considerably in the properties of their soils, and soil temperature, on the eastern quarter of sub‐Antarctic Marion Island. There was no evidence of negative abundance covariation or species associations within habitats, nor were there significant relationships between species richness or abundance of the indigenous as opposed to the introduced collembolans across habitats. Interspecific interactions thus seem to have played no readily identifiable role in the outcome of invasions by Collembola on Marion island. In contrast, the indigenous and introduced species responded very differently to abiotic variables. The indigenous Collembola prefer drier, more mineral soils with a low organic carbon content, and species richness tends to be highest in cold, fellfield areas. On the other hand, the introduced springtails prefer moist, warm sites, with organically enriched soils, introduced species richness was negligible in cold, fellfield areas. Disturbance also appeared to influence positively the species richness and abundance of introduced species at a site. These results provide independent support for the idea that abiotic factors, especially temperature, significantly influence the likelihood of biological invasions on Southern Ocean islands. They also suggest that predicting the outcome of climate change on community structure in this region is likely to be problematic, especially in the case of the Collembola.

Turgidosculum complicatulum on sub-Antarctic Marion Island: carbon acquisition response to climate change

The lichen Turgidosculum complicatulum (formerly Mastodia tesselata) occurs in the shore-zone of Marion Island (sub-Antarctic: 47°S,38°E). Net CO2 exchange in the lichen is dominated by a strong temperature-dependence of respiration rate. The light/temperature response of photosynthesis is such that under the prevailing climatic regime on the island the lichen, if sufficiently hydrated, would exhibit near-maximal photosynthesis rates for 75% of the photoperiod over the year. A photosynthetic response model predicts that the lichen's net annual carbon acquisition is 3.1 g C g–1 year–1 under the current solar radiation and temperature regime at the island. The model predicts that changes in temperature and radiation by the amounts known to have occurred in the past few decades, and even greater changes (temperature increase by up to 2°C, radiation by up to 10%), would negligibly affect the annual amount of carbon acquired provided the thalli remain hydrated. Incorporating hydration/desiccation cycles into the model resulted in a substantial lowering of annual net C exchange. However, attempts to include the increase in aridity known to have occurred at the island since 1971 gave conflicting scenarios for the effect on annual C acquisition, depending on whether atmospheric drying or thallus drying was considered.