PARENT SESSION
Oral Session # 61: Biogeochemistry IV: Al, Ca, P, and DOC.
Presiding: R Fitzhugh
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 205.
Gulls and cormorants exerting nutrient exchanges between marine and terrestrial ecosystems at the Isles of Shoals (Maine-USA).
Farina, Jose*,1, 2, Ellis, Julie1, Witman, Jon1, 1 Brown University, Providence, Rhode Island, USA2 CASEB-Pontificia Universidad Catolica de Chile, Santiago, RM, CHILE
ABSTRACT- Guano accumulation in seabird colonies often alters soils chemistry and, through it, can change plant species composition and productivity. Because the magnitude and extent of these alterations depend on nesting behavior, major differences are expected between seabird species. We compared soil nutrient concentrations and plant species composition and performance from gull (Larus marinus) and cormorant (Phalacrocorax auritus) colonies in the Isles of Shoals (Maine). Additionally, we assessed the contribution of marine nutrients to terrestrial ecosystem (using stable isotopic analysis) and tested plant responses (germination and growth) to soil nutrient concentrations recorded in the colonies. In the colonies, soils have significantly higher concentrations of nutrients (ammonia, nitrate and phosphate) and plant species assemblages were dominated by nitrophilic species. These features were extreme in the cormorant colonies, which had the highest concentrations of nutrients and where practically no plants occurred. A greenhouse experiment showed that germination and growth could be inhibited at the highest soil nutrient concentrations (cormorant colonies). The different effects of gulls and cormorants on terrestrial island ecosystems were related to nesting densities. We discuss our results in reference other examples of nutrient exchanges between marine and terrestrial ecosystems.
Key words: nitrogen, sea-land interface, guano, marine birds