What can seabirds tell us about ecological interactions occurring beneath the sea surface? A great deal, according to a new PhD-thesis by Martina Kadin, focusing on the interaction between seabirds and fish through the lens of ecosystem services.

Actually, seabirds make important contributions to all four types of ecosystem services recognized by the UN Millennium Ecosystem Assessment; provisioning, regulating, cultural, and supporting services. Seabirds also serve an important ecological function as "mobile links" between and within marine and terrestrial ecosystems.

The common murre
A major part of Martina's work has taken place in the middle of the largest seabird colony in the Baltic Sea, on the island of Stora Karlsö. Particularly, her thesis investigates reproductive success and foraging behaviour, of the fish-eating seabird the common murre (Uria aalge).

Martina has investigated how such variables may be impacted by changes in food abundance and food quality, directly linked to fisheries targeting the same species as the murres but also indirectly when effects cascade through the food-web.

Her work has included statistical tools such as generalized linear models, additive models and mixed models, as well as combinations of them.

"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 which are top predators in marine ecosystems, can provide insights about multiple pressures and the state of the oceans", she explains.

In the Baltic Sea, the common murres raise their chicks on fish of the species sprat (Sprattus sprattus). Martina Kadin and her colleagues investigated the effects of sprat quality versus the abundance of sprat during the chick-rearing period. Their study, conducted in the period 2005-2009, was then compared to observations from the 1970s and 1990s. This comparison showed that food quality (measured as sprat weight-at-age), not quantity (sprat abundance), influenced the murre's fledging success. Parental effort showed the opposite pattern. That is, foraging trips had shorter duration when quantity was higher, but there was no relationship with food quality.

Another paper in the thesis, published 2013 in Marine Ecology Progress Series, found indications of good food availability for common murre adults at sea, in line with overall high sprat abundance. Efforts by the parents to adjust provisioning of food according to the needs of the chicks were detected in a follow-up study, but the adjustments do not seem to be enough to counteract the impact of lower food quality.

Beyond the Baltic
The focus of the last paper of her thesis goes beyond the Baltic Sea and the common murre. It is an exploration of ecosystem services obtained from seabirds over time. Together with colleagues she identified a shift in use, from provisioning (goods) to cultural services, where current cultural services are often connected.

"Seabirds have become well-known symbols of coasts and oceans and their struggles with the consequences of human actions provide an illustration of the need to properly govern marine resources," she concludes.

In summary, the findings of Martina’s thesis have the potential to be important beyond the Baltic Sea. Around the world many other marine top predators are impacted by changes in their food abundance and food quality, due to overfishing and climate change. The findings presented in her thesis can aid the selection and interpretation of indicators for ecosystem approaches to fisheries management, and be used to communicate the need for such approaches.

Reconnecting to the ocean
Martina is also interested in how seabird studies can engage people, through classic approaches like public lectures and popular science to participatory field studies and projects linking seabird ecology and art. She says that 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.

In future research she would like to focus more on the links between the cultural ecosystem services of seabirds, including scientific knowledge and communication.

"One interesting topic could be online cameras placed in breeding colonies and their influence on people’s perceptions about the marine environment, and if such cameras could be used to collect seabird data in citizen science approaches", Martina says.

"Further, the importance of food quality to breeding murres points towards a value of studying its relevance for other demographic parameters, such as survival. Combining such ecological studies with transdisciplinary work can improve our understanding of the multi-faceted interactions between humans and seabirds, and ultimately of how we influence and depend on the oceans."