The Future Arctic Biosphere : Environmental Drivers of Change in Arctic Benthic Biota

Abstract

Arctic ecosystems are facing unprecedented changes today. Annual surface temperatures increased almost twice the rate than the global average, and both sea ice thickness and extent decreased drastically, reaching a record low in summer 2012. Sea ice is the main structuring force in the Arctic environment as it modulates water column stratification and light intensities, and subsequently also pelagic and benthic production. Changes in sea ice conditions accordingly will lead to unforeseeable changes and consequences for the entire arctic ecosys-tem. This situation stresses the need for more information to enable us to predict upcoming scenarios. However, studies that link benthic production patterns to ecosystem processes on large spatial scales are still scarce, and baseline data from which change could be identified are lacking. Studies that focus on the eco-logical functioning of Arctic benthic communities are equally rare. The aim of this thesis is to fill knowledge gaps of macro- and megabenthic com-munity dynamics on the Barents Sea shelf and the adjacent Eurasian deep sea by means of an integrated approach. Benthic secondary production was estimat-ed for the first time on Arctic shelf-wide scale and in the Arctic deep sea. Envi-ronmental drivers significantly explaining the observed patterns were identified by using geostatistical modeling and multivariate statistics. A biological trait ap-proach was applied to estimate and compare the ecological functioning of Arctic benthos between shelf, slope and basin communities and between datasets from 1991 and 2012. A thorough literature review supported the discussion of our re-sults and expected future scenarios in a wider context. The results of this study showed significantly higher benthic secondary produc-tion in the northeastern, seasonally ice covered region of the Barents Sea shelf than in the permanently ice-free southwestern areas. In the deep-sea areas a significant decrease of secondary production with increasing water depth was apparent, but also with distance from the marginal ice zone. The major conclu-sion of this thesis is that food input and the tight pelagic-benthic coupling in the marginal ice zone are explaining the observed patterns. As ongoing warming drags the productive sea ice edge closer towards the North Pole, we expect shelf food webs to shift from a state favoring the benthic production towards one favor-ing the pelagic food web. Regions in the central Arctic could on the other hand benefit from increased food input associated with the approaching ice edge. The comparison of macrobenthic functioning at stations from the central Arctic sam-pled recently with stations sampled 20 years ago indicates that functional chang-es are already happening. The present thesis provides for the first time estimates of Arctic macro-and megabenthic secondary production on a shelf- and basin-wide scale and contrib-utes to a better understanding of Arctic benthic energy flow and ecosystem func-tioning. Results presented here provide a valuable input into prospective Arctic food web models and will help to improve our predictions of the future Arctic bio-sphere.