Macrofauna and meiofauna food-web structure from Arctic fjords to deep Arctic Ocean during spring: A stable isotope approach

The knowledge on benthic trophic relations is particularly important for understanding the functioning of still pristine and less studied Arctic Ocean ecosystems. This study examines the benthic food-web structure in the European sector of the Arctic Ocean and assesses if and how it differs along depth gradients in the marginal sea-ice zone during spring. Samples of the sediment organic matter were collected in May/June 2015 and May 2016 at stations representing different sedimentary habitats (fjord, shelf, slope/basin), and stable isotopes of δ13C and δ15N were used to determine macro- and meiofauna food-web structure. Our results show that the food-web structure differed both among the three studied habitat types and between macro- and meiofauna components of benthic communities, and that these differences were related to the quality and quantity of organic matter. Meiofauna in fjords and on the shelf mainly relied on the reworked sediment organic matter while macrofauna utilized more fresh organic matter, sedimenting to the sea floor. In fjords and on the shelf, benthos displayed a high degree of omnivory and non-selective feeding while on the slope and in deep basins feeding on higher trophic levels dominated. In the latter, benthos seemed also to have utilized highly reworked organic matter. As the organic matter quantity and quality were major drivers of trophic relations in all studied areas, the benthic food webs will likely face cascading effects following the modification of pelagic food webs due to climatic changes.