Seabirds bring substantial amounts of nitrogen (N) and phosphorous (P) from sea to their breeding colonies. On Svalbard, previous research has focused on the ornithogenic fluxes from sea to land, but little is known of the effects of seabird colonies on nearby marine environments. External nutrient input has potential to increase primary production during summer, when nutrient availability is the limiting factor. Seabirds can also function as biovectors for transport of contaminants, such as mercury (Hg), from their foraging areas to the colony, but there are uncertainties on how the presence of these colonies could affect contaminant accumulation in affected coastal food webs. The objective of this thesis is therefore twofold: (i) characterising the nutrient and Hg flux from a seabird colony, and (ii) investigating the response in a nearby coastal ecosystem. To study these seabird driven fluxes, a mixed colony of Black-legged kittiwakes (Rissa tridactyla) and Brünnich’s guillemots (Uria lomvia) at Alkhornet, west coast of Spitsbergen, was visited on five occasions from June to September 2018. Water was collected for chemical analysis from three streams influenced by the seabird colony and in three control streams, with little seabird presence. In the adjacent coastal ecosystem, stable carbon and nitrogen isotope analysis (δ15N and δ13C) was used to assess the ornithogenic nutrient uptake by primary producers (Acrosiphonia sp.) and its propagation to higher trophic levels (amphipods). Concentrations of methyl-mercury (MeHg) were also determined in a primary consumer (amphipods). The seabird influenced streams had much higher (5-100 fold) concentrations of organic carbon and dissolved N and P than control streams. Aqueous Hg was positively related to organic matter in colony-influenced streams, while turbidity was a better predictor for aqueous Hg for control streams. An ornithogenic signal (higher 15N) was found in all biota collected from the seabird influenced sites. Acrosiphonia close to the colony had lower C:N ratios than specimens collected from control sites, indicating higher N-availability. Low MeHg concentrations were observed in amphipods close to the colony, possibly due to availability of high-quality food, which could lead to high trophic efficiency and therefore lower bioaccumulation of MeHg. In light of ongoing climate change and declining seabird populations, effort should also be put on understanding potential future changes in ornithogenic fluxes from land to sea, and the implications for adjacent coastal ecosystems.