Nitrogen and Carbon Isotope Ratios in Seabird Rookeries and their Ecological Implications

Abstract

Various samples around gull and penguin rookeries were examined for nitrogen and carbon isotope ratios. The results showed that input of organic nitrogen from avain breeding activity, followed by its aerobic decomposition in soil and by volatilization of the resultant ammonia, strongly dominated nitrogen flow in both rookeries. Plants, animals, and soils in the rookeries appeared dependent on the nitrogen thus provided. In the penguin rookery, soil organic carbon was also derived from breeding activity. A large input of organic carbon by gulls, however, appeared to have quickly escape from the gull rookery through respiration. It had little effect on the soil organic carbon; the main source of organic carbon there seemed to have come from higher plants. Major pathways of material flow in the seabird rookeries were deduced from the isotopic data. Study of stable isotopes should enable us to draw similar pictures for other ecosystems; it is particularly useful in places where frequent visits are impractical.