The importance of the benefits that humans obtain from the oceans is increasingly recognized, along with the rapid decline in marine resources that threatens these benefits. Studying seabirds – top predators in marine ecosystems, can provide insights about multiple pressures and the state of the oceans. The thesis links studies of seabirds through the lens of ecosystem services with an ecological case study. Paper I reviews ecosystem services, finding that seabirds contribute to provisioning, regulating, supporting and cultural services. Seabirds serve as mobile links in marine and terrestrial ecosystems, through regulating and supporting services. Further, scientific knowledge and indicators based on seabirds can be seen as an ecosystem service as they facilitate management. Papers II-IV proceed to build such knowledge about the importance of food quality and quantity for breeding seabirds, in particular common murres Uria aalge in the Baltic Sea. Here, there is a negative relationship between quantity (sprat Sprattus sprattus abundance) and quality (sprat weight-at-age). Quality, but not quantity, was positively related to common murre fledging success while parental foraging trips had shorter duration when quantity was higher, but showed no relationship with food quality (paper II). Paper III describes foraging behaviour of adults and found indications of good foraging conditions at sea. Parents made efforts to adjust provisioning of food according to the needs of the chicks (paper IV), but the adjustments did not seem to be enough to counteract the impact of lower food quality. Paper V explores ecosystem services obtained from seabirds over time identifying a shift from provisioning to cultural services, where current cultural services are often connected. The integration of ecosystem services with seabird ecology shows that seabirds are illustrative of changes in marine resources and provide ways to help people reconnect with the health of marine systems.

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Martina Kadin, Stockholm Resilience Centre, martina.kadin(at)su.se