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Case StudiesSurtseyThe birth of the island of Surtsey, about 32 kilometres south of Iceland, began with an undersea volcanic eruption in November 1963 and island-building eruptions continued until mid-1967. At that stage the island's area was a little under 3 square kilometres but erosion had reduced the island to about half by 2002. The island has remained an uninhabited natural laboratory for the study of biological colonization of virgin land and the later succession of species. You can find out more on the website of the Surtsey Research Society (http://www.surtsey.is/index_eng.htm). Though the island was visited in 1965, 1967 and 1968 it was not until the 1970 visit that the first lichens were found: Placopsis gelida, Stereocaulon vesuvianum and Trapelia coarctata. Trapelia coarctata, the first species to be spotted, was found near two craters and was growing on steep lava rocks in areas kept moist by steam from nearby vents. In 1970 the species was already abundant in such habitats and with numerous apothecia. Given that abundance the species must have been on the island by 1969 but there had been no lichen survey that year. Placopsis gelida was found in similar habitats and Stereocaulon vesuvianum was found on lava fields influenced by warm steam. By 1973 the Placopsis and Stereocaulon were more widespread and found in areas free of steam influence whereas the Trapelia was still found only in steam-influenced habitats where it was the most successful colonizer and grew rapidly. In 1970 Placopsis gelida and Stereocaulon vesuvianum were known to be common in Iceland but by that time there had been no record of Trapelia coarctata from the country. That does not imply the species was absent since knowledge of Icelandic crustose, rock-inhabiting lichens (such as Trapelia) was still quite poor. After 1970 there were further lichen surveys in 1971, 1972, 1973, 1975, 1978, 1984, 1990, 1994, 1998, 2002, 2006 and the 2006 visit saw the discovery of Surtsey's 87th lichen species. Many, once discovered on the island, have been seen on all subsequent surveys but there are also many where that has not been the case. For example, in 2006 58 species were seen on the island and 12 species, found during or before the 2002 visit, have been seen only once. Otherwise, species that have not been seen during each visit after their initial sighting, have been seen on and off. It is possible that such species have been on the island during the other years, but in small amounts and overlooked. Of the three species found in 1970 Stereocaulon vesuvianum was not seen in 1984 but otherwise all three have been found on each of the visits listed above. By 2006 Trapelia coarctata had been found in many localities, near steam holes, in other damp areas or dry and sheltered sites. In such areas it could be abundant locally but overall it was not as abundant in 2006 as it had been in 1970. Over time there was change in the habitats available on the island. In the first years lichen colonization was in areas where steam condensed directly onto the lava. This was followed by the colonization of the cooled lava fields over the next few years and the major colonizers of those areas were Placopsis gelida, Stereocaulon capitellatum and Stereocaulon vesuvianum. All three have green algae as the main photobiont and also have nitrogen-fixing cyanobacteria in cephalodia. From the start of the lava field colonization the colonizing species were distributed fairly evenly through the lava fields, indicating that the propagules had arrived by wind. Amongst the lava fields' primary colonizers was a basidiolichen in the genus Lichenomphalia, first seen in 1971 and again in 1975 and 1978. The same period saw the colonization of the various exposed or sheltered niches created by the lava peaks and craters. The first nesting gulls were found on Surtsey in 1986 and the numbers increased in the following years resulting in dense colonies. There are various lichens which are commonly found in the excrement-rich roosting areas and the establishment of permanent bird colonies created suitable habitats on Surtsey for such lichens which are described as ornithocoprophilous (derived from Greek roots that literally mean bird-dung-loving). One such, Xanthoria candelaria, had been seen in 1972. At that time it was found only around one of the fresh water tubs that had been set up in 1967 as part of an experiment to study colonization by freshwater organisms. This tub was removed later but while present attracted gulls who used it for bathing and it was in the splash zone around the tub that small Xanthoria candelaria thalli were seen in 1972 and 1973. It is supposed that propagules had been carried to Surtsey by gulls and then washed out and splashed away from the tub when the gulls bathed. By 1975 these thalli were deteriorating and the species was not found again until 1990, after gulls had permanently colonized the island, but since then has been seen during each survey of the island. The species is coprophilous and frequently found in bird roosting sites where the supply of bird excrement is continually being replenished. Once the tub had been removed and birds no longer visited that spot, there would have been no more replenishment of excrement so presumably the Xanthoria thalli were unable to obtain the necessary nutrients and therefore disappeared from the tub site. The possibility of bird dispersal of lichen propagules is mentioned often in the literature but direct evidence of bird transport is rarely reported. In 1969 and 1970 the feet and plumage of birds trapped on Surtsey were searched for lichen propagules, but with no success, though cyanobacteria, moss fragments, fern sporangia and fragments of vascular plants were found. A thin soil layer formed on the lava blocks in some of the bird roosting areas and these were colonized by soil inhabiting lichens of the genera Baeomyces, Cladonia, Collema and Leptogium. Soil also allowed the establishment of various vascular plants, especially grasses, and competition from vascular plants has led to a decrease in some of the lichens that initially colonized soil areas, though species of Cladonia and Peltigera were still prominent in the grasslands. Soils had formed also in or near craters and such developments were accompanied by various soil-inhabiting lichens. The lava fields, craters, lava peaks and soil layers had been colonized by various bryophytes as well. Bryophyte colonies can compete with lichens but also help create habitats for some lichens. Stereocaulon alpinum is one of the most common Stereocaulon species in Icelandic heaths and was first found on Surtsey in 1984, growing on a carpet of the moss Racomitrium lanuginosum inside a crater. The lichen is rare on Surtsey and there have been no verified sightings outside that crater. In the Icelandic region various spray-tolerant lichens are found on coastal cliffs and some could have been expected on Surtsey's coastal cliffs. However, on Surtsey there is considerable coastal erosion each year so these littoral lichens would have great difficulty in becoming established. Collemopsidium halodytes, the first and thus far only species to be collected on coastal cliffs, was not found until 2002 and was seen again during the 2006 survey. Four seashore species, usually found on cliffs, have been found on Surtsey away from cliff faces but still subject to some sea spray, especially during winter storms. One of these, Caloplaca verruculifera, was first seen in 1990 within a gull colony. By 2006, in the central area where colonization had started, the rapid thickening of the soil layer and expansion of grassland had led to a deterioration of the Caloplaca verruculifera habitat. However, it was still growing at the margins where new areas were colonized by birds. Three lichenicolous fungi have been found on Surtsey: Arthonia gelidae (in 1988, on a Placopsis thallus), Pyrenidium hyalosporum (2002, on Placopsis gelidae) and Endococcus fusiger (2006, on Rhizocarpon lavatum). Occasionally there was an oddity. Scoliciosporum umbrinum is common on rocks in Iceland (though it is also found on other substrates) and the first sighting of this species on Surtsey was in 1990, when it was found growing on fish bone in a lava field. It is not known whether the fish bone had been carried up from the coast or whether it had been brought from outside the island. The species was found again in 1998 and 2002 on lava peaks or crater margins. Many species found on Surtsey are thought to be rare in or are even unknown from Iceland. Amongst those many have small thalli or are inconspicuous in colour and therefore could be overlooked easily . Another important fact is that Surtsey has been intensively studied. Hence those 'rare' or 'absent' species might well occur in Iceland and even be fairly common in areas not yet well explored for lichens. Conversely, many of the common rock-inhabiting lichens found in Iceland that might be expected on Surtsey have not been found there. For example, Aspicilia cinerea, Lecanora intricata, Lecanora polytropa, Rhizocarpon geographicum and Tremolecia atrata, described as "found on almost every piece of rock in Iceland", were still absent from Surtsey in 2006. Certainly, some time would be needed before fresh volcanic rock can be colonized but some decades have passed, during which many other species have arrived on Surtsey. Those five species were found on the Hekla lava flows in southern Iceland within 20 years of Hekla's 1947 eruption. This suggests the overseas distance to Surtsey represents an impassable barrier to a number of species, including the five just listed. References
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