Bryophytes of Surtsey, Iceland: Latest developments and a glimpse of the future

Abstract

Surtsey island was formed in a volcanic eruption south of Iceland in 1963 – 1967 and has since then been protected and monitored by scientists. It is the youngest island in the Vestmannaeyjar archipelago. The archipelago is of volcanic origin, but the other islands are ca. 5 000 to 40 000 yrs old. The first two moss species were found on Surtsey as early as 1967 and several new bryophyte species were discovered every year until 1973 when regular sampling ended. Systematic bryophyte inventories in a grid of 100 m × 100 m quadrats were made in 1970 – 1972 and 2008. Here we report results from an inventory in 2018, when the same quadrats of the grid system as in 2008 were searched for bryophytes. In addition, we surveyed the bryophyte flora of Elliðaey – a ca. 5 000 yrs old island at the more sheltered north-eastern end of the archipelago. On Surtsey, distributional expansion and contraction of earlier colonists was revealed as well as presence of new colonists. Total number of taxa increased from 43 to 59 between 2008 and 2018. The average species richness increased from 4.5 taxa/quadrat in 2008 to 6.6 taxa/quadrat in 2018 (empty quadrats omitted): 32 quadrats showed an increase in species richness; three quadrats showed no change; ten quadrats showed a slight decrease of 1 – 2 taxa, while one quadrat showed a considerable decrease of 7 taxa – that quadrat was within the lush grassland of the gull colony where bryophytes were outcompeted by the graminoids. Quadrats with the strongest increase in species richness were also within areas affected by seabirds but had not been as overgrown with grassland. On Elliðaey, the predominant habitat was grassland, like the one at the centre of the gull colony on Surtsey. On the island, we registered 22 taxa; 13 were also found on Surtsey in 2018, 4 have been found on Surtsey in earlier surveys and 4 species have never been found on Surtsey. We predict the species richness on Surtsey will continue to grow but level off before starting to decrease as the lava fields disappear and grassland becomes more dominant. Continued monitoring, without long breaks, is essential to evaluate how fast the bryophyte vegetation develops in the years to come.