The WelFin LTER-site is located at the Hanko peninsula, at the entrance to the Gulf of Finland. The activities are largely focused to the coastal areas surrounding Tvärminne Zoological Station (University of Helsinki); a marine station established in 1902. The site is well equipped to meet the research demands, offering differently sized research vessels, field equipment, a range of climate chambers, and modern analytical instrumentation. A large part of the surrounding area is a nature reserve, to be used only for science and education. Many of the partners of this site have a long history of scientific collaboration. Although high-quality basic research continues to be at the heart of the site’s activities, many of the research questions nowadays include aspects of human induced long-term change.