Aim of the project

In continental Antarctica macroscopic life is restricted to a few categories of organisms. The most numerous are lichens, numbering up to perhaps around 100 identified species, followed by mosses, birds and arthropods. Apart from birds migrating across peripheral areas, all of these exclusively inhabit nunataks that constitute the only solid ground available for colonization. Normally, the distance between peaks and ranges is considerable. Dispersal is most certainly a rather haphazard process, whether propagules are dispersed by wind or by birds. The colonization process is probably equally random and, in combination with the differing living conditions offered by various kinds of substrate, the distribution of species becomes very patchy. Although poorly known in general, one can easily imagine that the presence of living specimen is erratic even within nunataks.

A previous study monitored the lichens at the nunatak Basen in the Vestfjella mountain range (73°03’S, 13°25’W, 200–600 m.a.s.l, 120 km from the coast), and at the Svea station in Scharffenbergbotnen, Sivorgfjella in central Heimefrontfjella massif (74°34’S, 11°13’W, 1 200–2 000 m.a.s.l., 300 km from the coast) (Thor, in preparation). This inventory lists 52 species, and some exceptionally species-rich spots were identified. In the present investigation the distribution of lichen vegetation, in particular concerning the most common and conspicuous, Xanthoria elegans, was quantitatively investigated all over Basen, and Thor’s results were merged with my own. In addition, a series of experiments were carried out in order to quantify the flow of propagules in and out of, and within Basen and Scharffenbergbotnen respectively.

Method

The investigation consists of several parts, as listed below:

1. A ”vegetation” map was con-structed by providing a 1:5 000 scale map of the Basen with a grid, producing 482 100 x 100 m squares containing predominantly bare ground. During the field survey, each square was assigned various levels of four different categorizing values representing:

• the particle size of the dominating ground cover,
• the incidence of fluid water,
• the angle and
• the bearing of the slope.

Each such square was extensively scanned while walking across, and a single representative 1 x 1 m plot in the centre of each 1 ha square scrutinized with regard to the presence and the amount of visible and identifiable lichens, notably Xanthoria elegans. Precipices and scree slopes that were inaccessible without special gear were judged from a distance using binoculars. Four levels of vegetation cover were identified.

2. A dispersal experiment was carried out using 14 series of 6 x 4 sticky glass slides, aimed at collecting wind-dispersed propagules; eight at Basen, and six at Svea. Slides were placed in lines running perpendicular to the prevailing wind direction (i.e. north-east) at the windward and lee ends of the nunatak or mountain sides. Each series consisted of six plastic cones (height: 30 cm) fitted at the top end with four glass slides (mounted using two-sided tape) onto which a sticky surface of vaseline (20 x 50 mm) had been applied. The glass slides were vertically oriented and placed one in each of the four points of the compass, projecting the sticky surfaces at 45o, 135o, 225o, and 315o angle to the prevailing wind. A final series of 9 x 4 slides was placed in an aerial at the Wasa station. The slides in the aerial were equally placed at 45o to the four points of the compass. Altogether, 372 glass slides were thus exposed for 35–40 days between 15 December 2001 and 25 January 2002. When collecting the samples, covering glasses were put on top of the vaseline, and the slides placed in boxes for storing microscope slides during transportation. Each slide will subsequently be carefully scanned (the entire sticky surface) under a microscope, any occurring spores or fragments of lichen noted and – as far as possible – identified by type (spores simple or septate, spores coloured or colourless, soredia, thalloconidia, fragments etc.). The number and size of other particles were also noted, as was the degree of abrasion reducing the vaseline coating of the slides. The lichen flora in each area surrounding the cones was superficially determined prior to the positioning of the cones (Johansson, in preparation). The result of the scanning of slides will finally be matched to the result of the vegetation mapping and to the earlier inventory.

3. The number of spores that might be caught out of a known amount dispersed was examined in another experiment. In 12 replicate dispersal events Lycopodium spores were used as dummy propagules. Again plastic cones were used as fundaments for sticky glass slides as earlier described. This time each series consisted of one cone placed 0.5 m from the point of release in the direction of the prevailing wind at the time, a second one 5 m away and a third cone and a 1.5 m high iron rod 50 m away. 144 slides were used in this experiment. During each replicate the wind direction was noted and when necessary the cones were moved in order to make them always stand in a line as the wind blew. The average wind speed over one minute was noted on every release. Spores were released approx. 0.15 m above ground by opening the lid and emptying a test tube containing the spores, into the wind. The tests were carried out at three different wind speeds: 2 m/s, 5 m/s and 10 m/s. Each of the 12 portions of spores released consisted of 1.5 ml Lycopodium spores (approximately 200,000,000 spores/portion, as calculated by counting the number of known – weighed – fractions of spores in a microscope). Lycopodium spores are the only available substitute of roughly similar size and appearance to lichen spores (rounded, diameter approx. 20 μm). They are easy to identify and would not mistakenly be counted as lichen spores. Before brought to Antarctica, the spore samples were exposed for four weeks to UV-light (235 nm) emitted 0.15 m above a tray with spores spread out evenly over it. Lycopodium sp. does not grow naturally in Antarctica, nor can it establish in this continent. This experiment was approved by the Swedish Polar Research Secretariat and it conforms to the Protocol on Environmental Protection to the Antarctic Treaty.

4. The dispersal in the immediate neighbourhood of lichen thalli producing apothecia was investigated by placing 200 vaseline-sticky glass slides in five sets of two concentric circles on the rock immediately around isolated Xanthoria elegans thalli found in an area with an otherwise comparatively dense cover of this species, plus another five sets used as control where no lichens were found. An inner circle consisting of four slides was placed approx. 0.1 m from the centre of the thallus and an outer circle with 16 slides posted 0.3 m from the centre. The thalli used all grew on more or less vertical rocks. In the analysis the glass slides a separated into groups consisting of those positioned above and below the surrounded thalli.

5. The pattern of primary dispersal by wind of spores and thallus fragments close to the source of dispersal was analyzed experimentally by emitting portions of Lycopodium spores and ground, dried thalli of Umbilicaria aprina (collected in situ). Each of eight replicate series consisted of 20 sticky slides, 5 placed at 0.2 m distance from the point of release of diaspores, 6 placed 0.5 m away and another 9 placed 0.75 m in the direction of the prevailing wind. The wind speed during this experiment was 5 m/s.

6. An approximation of the number of apothecia per mm2 Xanthoria elegans thallus was made by Johansson (in prepraration). Together with data from the vegetation mapping and counts of mature spores in a number of apothecia, this figure produces a very rough estimate of the number of spores produced at Basen. The number and size of fragments being dispersed is of course very difficult to calculate.

7. Finally, a number of representative samples of Xanthoria elegans thalli were collected for future analysis in the lab with regard to the genetic composition of Antarctic specimens (to be compared with samples from elsewhere in the world.

Results

The vegetation is unevenly distributed at Basen and surrounding Svea. Large areas are almost completely barren, whereas at a few places a comparatively rich community of lichens and mosses is found. A few lichen species occur scattered across the nunataks, but the total ground cover of lichens never exceeds more than one or a few per cent of the ground, except around cracks in vertical rocks in precipices, where the dominating, crustose Xanthoria elegans may occasionally form an almost coherent cover over several square metres. However, many species are easily overlooked due to their less distinctive colouring and general appearance, and the diversity is actually higher than expected at first sight.

Only preliminary results are available from the analysis of microscope slides, but a distinct difference between localities is noted in the degree of exposure (as shown by the amount of vaseline left upon collection), and the amount of particles trapped at different sites. Substantial amounts of Lycopodium spores were trapped in the vaseline following release, indicating that this release-recapturing method is adequate. Microscopic thallus fragments have been identified among the catch, and larger fragments were observed once or twice drifting across minor snow-fields within nunataks, but they were never seen during traverses.

The major preliminary conclusion is that dispersal and subsequent establishment are extraordinary events, and that the pattern of distribution of the investigated lichen vegetation in Antarctic nunataks results from a very slow and irregular process.