COLONIZATION OF THE LAND

The Arrival of Organisms

Dispersal by Sea

In the first spring after the formation of Surtsey, seeds and other plant parts were found washed up on the newly formed shore. Some of the seeds were collected and germinated in the laboratory. This was an early indication that seeds carried by ocean currents to the island would be candidates as the first pioneers. In the spring of 1965 the first higher plant was discovered at the shoreline. This pioneer was the sea rocket (Cakile arctica). Other coastal species that followed the sea rocket were the sea sandwort (Hokenya peploides), sea lyme grass (Leymus arenarius) and oyster plant (Martensia maritima). The seeds of these species washed up on the shore in the first years after the eruption and germinated in the uppermost part of the sandy shore. The seeds of these pioneer coastal species are rather large, and they float easily and can tolerate the salty sea water. It is most likely that they originated from sandy shores of Heimaey or the south coast of Iceland, where they are abundant. The distance from Surtsey to Heimaey is 18 km, while 32 km separate Surtsey from the Landeyjasandur sand flats on the south coast.

Seeds were also dispersed to Surtsey attached to drifting material. For example, a number of skate eggs were found washed up on the shore, and attached to them were large quantities of seeds. Living plant parts and small animals have also been dispersed to the island in floating clumps of grass turf and root tangles from nearby islands.

Dispersal by Wind

Seeds and fruits with tufts of hairs (pappus) and adapted to wind dispersal have frequently been found in Surtsey during the latter part of summer when the wind blows off the mainland to the island. The fruits of cottongrass (Eriophorum species) and the common groundsel (Senecio vulgaris) were brought to the island by these means, although these species have not become established. Dwarf willow (Salix herbacea), woolly willow (Salix lanata) and tea-leaved willow (Salix phylicifolia) have on the other hand become established on Surtsey, as have the common dandelion (Taraxacum spp.) and the autumn hawkbit (Leontodon autumnalis). The seeds of these species can be dispersed long distances by the wind, and it is most likely that they were brought to the island in this manner.

Pteridophyta (ferns and horsetails) mosses, lichens, fungi and algae all reproduce by tiny spores and fruiting bodies that are spun up by air currents and dispersed by winds. It is most probable that the majority of species in these groups that have been found in Surtsey have been dispersed by the wind. Among these species are the field horsetail (Equisetum arvense), the common bladder fern (Crystopteris fragilis), the moss Racomitrium ericoides, and the lichen Stereocaulon vesuvianum.

Dispersal by Birds

It is a well known fact that birds are seed carriers. Some species of birds eat berries or fruits that contain seeds, which they then carry with them and expel as waste in new locations. In addition, seeds can stick to birds or end up in their digestive tract when they eat their prey. Furthermore, birds carry materials for nest building, and these materials are most often plant materials. This is another way that birds may transport seeds to new areas.

There are numerous indications that birds have carried seeds to Surtsey. In the first years of the island’s history, research was carried out on the contents of the digestive tracts of migrating birds. Some migratory birds stop to rest on Surtsey on their way over the Atlantic from the European continent. It was of interest that seeds were found in the digestive tracts of snow buntings (Plectrophenax nivalis), which indicated that these birds distributed seeds long distances. Scurvy grass (Cochlearia officinalis) colonized Surtsey early and was first found in a place where seagulls rested. Likewise the lichen Xanthoria candelaria was first discovered in 1972 near a water container frequented by birds. This lichen is a nitrophile and is commonly found wherever birds rest and leave their droppings.

Once a dense seagull population had begun to form in Surtsey in 1986, numerous new plant species colonized the island in the following years. It is likely that most of these were carried by the gulls or other birds that dwelled in the gull breeding areas. Among these species are crowberry (Empetrum nigrum), meadow buttercup (Ranunculus acris), smooth meadow grass (Poa pratensis), bering’s tufted hairgrass (Deschampsia beringensis) and northern dock (Rumex longifolius).