Effects of sea birds and soil development on plant and soil nutritional parameters after 50 years of succession on Surtsey

Surtsey, the island that rose from the sea in a submarine eruption during 1963 to 1967, has been the subjectof many studies on primary succession. These studies have intensified after the establishment of a seagullcolony on the island in 1986. This paper reports on the results of a short sampling expedition in 2013 thatintended to characterize the interactive effects of the seagull colony and of soil development on soil nutritionalcharacteristics in the tephra sands that cover the underlying lava, as well as in plants growing inside and outsidethe seagull colony. Feces and pellets of the gulls were extremely rich in both nitrogen (N) and phosphorus (P)and δ15N analyses showed that N was transferred from pellets and feces to the tephra soils and subsequentlytaken up by the plants. The tephra soils not affected by the birds showed a high concentration of P compared toN. The concentration of both nutrients was much lower than in the soils of the bird colony. In general, variationin tephra soil depth had little effect on nutritional characteristics, except for the very low N concentrationin deep soils. Thus, our results confirm the overriding effect of the seagull colony on Surtsey on nutritionalcharacteristics of the developing soils and vegetation. Due to the very high P availability of the volcanic soils incombination with the high P input by the birds, vegetation productivity is N limited, despite the extremely highN input of 47 kg N ha-1 yr-1 that the birds add to the system. Our findings emphasize the extreme importance ofbird colonies on the nutritional ecology of young, N-poor ecosystems.