COLONIZATION OF THE LAND
Lower Plants on Surtsey
First Colonization Around Steamholes
In the beginning, favourable conditions for lower plants on land were only to be found around steamholes where emission of cold or hot steam kept pumice and lava rock continually damp. The first mosses on Surtsey, Funaria hygrometrica and Byrum argenteum, were found under such conditions in 1967, and the following year a total of six other species were discovered. These first mosses were found primarily on damp pumice near steam emissions or in crevices and drains in the lava. At this time nitrogen-binding cyanophyta (Anabaena variabilis, Nostoc spp.) were also found around steamholes. Anabaena vaiabilis seemed to grow in close association with the prothallus of the moss Funaria hygrometrica. Quite a few species of chlorophyta and diatoms were discovered at approximately the same time in the green film that formed on the damp pumice. The only lichen that was able to grow in such steam emission sites was Trapelia coarctata. It had become widely distributed near the western crater in 1970 and had undoubtedly arrived there somewhat earlier. It was restricted to rock and was unable to grow on the loose pumice.
Colonization of the Lava
In 1970 the first indicators of colonization of the extensive bare lava flows were found. This community needed more time to develop, and the species grew considerably slower than those found earlier around the steamholes. In 1970, the lichens Stereocaulon vesuvianum and Placopsis gelida and the moss Racomitrium lanuginosum were discovered. The moss Racomitrium ericoides had been found the previous year. The lichen Stereocaulon capitellatum and the moss Schistidium strictum joined this community in 1971. At this point, all the principal pioneers of new lavas in Iceland had arrived. The extensive distribution of all these species on the lava fields of Surtsey where conditions allowed shows that their dispersal to the island must have been by air currents. In comparison with the first pioneers at the steamholes, these species were able to grow on bare lava and did not need humidity from steam emission holes. On the other hand, they needed a considerably longer time to grow. The three lichen species had the service of the blue-green nitrogen-binding Nostoc-algae in addition to green algae. It had also been shown that, by this time, Nostoc muscorum had already dispersed all over the island by way of its very light endospores, which are dispersed by air currents.
In the following years, this lava vegetation progressed well, but it was clear that it developed more rapidly in humid lava basins than it did on the tops of lava mounds. It also developed considerably more rapidly in the rough aa lava on the eastern part of the island than in the smooth pahoehoe lava farther west. Despite a good start, this pioneer vegetation suffered setbacks because of prevailing stormy weather and sandstorms on the island. The western crater was the most sheltered part of the island, and it is in that area that the lichens developed most rapidly and the moss Racomitrium lanuginosum quickly formed a more continuous and dense patch. Soon this moss species dominated all other pioneering species at several sites and formed small patches of continuous moss cover similar to those found on young lava flows in southern Iceland. In 1990 the first lichens of the genus Peltigera had also developed well in the moss patches.
A milestone in the colonization of mosses and lichens was reached when the gull nesting colony was well on its way after 1985 and soil formation was progressing. Various soil lichens colonized the land, i.e. mealy pixie-cup (Cladonia chlorophaea), many-forked clad (Cladonia furcata), Cladonia rangifera and brown-grey moss-shingle (Pannaria pezizoides). At this time, mosses that are usually characteristic of grasslands and peatlands, such as Sanionia uncinata and golden ragged moss (Brachythecium salebrosum), were also found in this plant community. In this enriched soil, Agaricales fungi also developed; for example, the small Omphalina rustica, which had become widespread in small bald patches in the gull colony in 1990.
Diversity of Mosses and Lichens
By the year 2003, the growth of 53 species of mosses on Surtsey had been confirmed, their increase in number having been very rapid after 1970. A few other species have also been recorded. Mosses were quicker to colonize Surtsey than were lichens, most likely due to their ability to utilize the damp pumice around steam emission sites, among other places, and due to their more rapid growth. Only one lichen, Trapella coarctata, could compete with them, and then only on bare lava.
Lichen colonization has been slower on Surtsey than colonization by mosses. Forty-five different species of lichens have been collected on Surtsey, but the total number is undoubtedly higher, as there are samples that have not been identified yet.
All of the first lichens to colonize bare lava on Surtsey have three constituents; that is, their fungus has both a green alga and a nitrogen-binding blue-green alga in its service. Two species that arrived later, Acarospora smaragdula and Xanthoria candelaria, were especially associated with lava mounds and birds’ roosting sites. At first the latter species was limited to roosting sites of sea gulls by the cliffs, and it is almost certain that it was dispersed to the island on the birds’ feet. The growth of this species is limited to fertile places where birds roost.
The shore lichens that are plentiful on sea cliffs along Iceland’s coast have not yet been found on Surtsey. The shores of Surtsey are too exposed for these lichens to become established and develop.
Microscopic fungi colonized Surtsey immediately in places where organic material was available, as on driftwood on the shores and elsewhere. Such fungi cannot be seen under ordinary circumstances without optic aids, except as mildew, but if they are isolated from collected samples and placed in culture they can be observed more accurately. The spores of most of these fungi are airborne and thus readily dispersed to new and distant sites.
Some fungi become visible temporarily with the formation of fruiting bodies; for example, the bowl-shaped asci of Ascomycetes. Such fungi have been seen on Surtsey occasionally, on organic material such as bird corpses or fish remains carried up onto the lava by birds. In 1994, for example, a very specialized fungus was discovered, whose only essential nutrient need is keratin; i.e., animal hair, nails, horns and feathers. This fungus has been given the Icelandic common name of fjaðrasveppur which means feather fungus (Onygena cervina). It was discovered on Surtsey in feather remains.
Many of the fungi in the Basidiomycetes group form hatlike fruiting bodies. The first of the Agaricales (hat fungi) to be found on Surtsey was a fungus of the Omphalina genus, a species that forms a symbiotic life form with a green alga, a kind of lichen. The thallus of this lichen is green and grows on the bare lava, and the hat grows up out of it. The most apparent fungus on Surtsey is another fungus that belongs to the same genus but does not form a symbiotic life form. This fungus is Omphalina rustica, which grows mostly in spots of bare soil in the breeding area.