Effects of seagulls on ecosystem respiration, soil nitrogen and vegetation cover on a pristine volcanic island, Surtsey, Iceland

Abstract

Abstract. When Surtsey rose from the North Atlantic Ocean south of Iceland in 1963, it became a unique natural laboratory on how organisms colonize volcanic islands and form ecosystems with contrasting structures and functions. In July, 2004, ecosystem respiration rate (R e ), soil properties and surface cover of vascular plants were measured in 21 permanent research plots distributed among the juvenile communities of the island. The plots were divided into two main groups, inside and outside a seagull (Larus spp.) colony established on the island. Vegetation cover of the plots was strongly related to the density of gull nests. Occurrence of nests and increased vegetation cover also coincided with significant increases in R e , soil carbon, nitrogen and C:N ratio, and with significant reductions in soil pH and soil temperatures. Temperature sensitivity (Q10 value) of R e was determined as 5.3. When compared at constant temperature the R e was found to be 59 times higher within the seagull colony, similar to the highest fluxes measured in drained wetlands or agricultural fields in Iceland. The amount of soil nitrogen, mainly brought onto the island by the seagulls, was the critical factor that most influenced ecosystem fluxes and vegetation development on Surtsey. The present study shows how ecosystem activity can be enhanced by colonization of animals that transfer resources from a nearby ecosystem.

Accumulation of nitrogen and organic matter during primary succession of <i>Leymus arenarius</i> dunes on the volcanic island Surtsey, Iceland

“…This further supports such indications found for vascular plant cover and species composition in different habitats on the island (Magnússon and Magnússon, 2000;Magnússon et al, 2009Magnússon et al, , 2014del Moral and Magnússon, 2014) and for process rates, such as ecosystem respiration (Sigurdsson and Magnusson, 2010). Therefore the "nitrogen use efficiency" for ecosystem C stocks estimated by Eq.…”

“…The vegetation cover of these tephra sands is generally below 20 % (Magnússon and Magnússon, 2000) and was only 2.3 % on the average in 2012 at the site of the present study . The tephra sands are also extremely nutrient-poor, with SON concentrations < 0.01 % and SOC of < 0.05 %, with relatively high pH of 7.6 (Sigurdsson and Magnusson, 2010).…”

Microbial colonization in diverse surface soil types in Surtsey and diversity analysis of its subsurface microbiota

“…The SR samples were soil that were totally or partly vegetated or pure pumice. They were all collected inside of a defined area used for activity measurements of soil (Magnús-son et al, 2014;Sigurdsson and Magnússon, 2010). Ecosystem respiration (Re) was measured inside these zones in order to investigate soil properties and surface cover of vascular plants.…”

“…The measurement of net ecosystem exchange (NEE, µmol CO 2 m −2 s −1 ) and ecosystem respiration (Re, µmol CO 2 m −2 s −1 ) were performed as described by Sigurdsson and Magnússon (2010) on top of microbial samples marked as SR samples that were collected from permanent vegetation survey plots, which are 10 × 10 m in area (Magnússon et al, 2014;Sigurdsson and Magnússon, 2010). Briefly, an EGM-4 infrared gas analyser and a CPY-2 transparent respiration chamber (PP Systems, UK) were first used to measure NEE in light, which was measured as photosynthetically active radiation (PAR) inside the chamber.…”

Spatial genetic structure of the sea sandwort (&lt;i&gt;Honckenya peploides&lt;/i&gt;) on Surtsey: an immigrant's journey

“…Philipp and Adsersen (2014) describe how ecological conditions for H. peploides have changed during its colonization on Surtsey, and how the changes may affect selective forces. Facilitated by the species long-distance dispersal capabilities, in this case seed dispersal by sea currents, the colonization of H. peploides on Surtsey started with a few individuals but increased rather quickly to cover most of the empty niches on the island (Sigurdsson and Magnusson, 2010). This development fits the general dynamic model (GDM) of oceanic island biogeography relatively well regarding young and small islands (Whittaker et al, 2008).…”