Digestibility of ice algae and phytoplankton: The potential impacts of changing food supply to the arctic benthos

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0222500LopezSea ice is a dominant feature of marine ecosystems in the Arctic. Its presence impacts Arctic marine ecosystems, especially on the shelves where benthic and pelagic systems are extensively coupled. If the extent and thickness of sea ice continue to decline, a shift is predicted in the type of algal material reaching the benthos (from ice algae to phytoplankton), which will potentially impact the food requirements of the benthos. Several pieces of evidence show that both types of ice algae (below-ice ice algae dominated by Melosira arctica and within-ice ice algae dominated by Nitzchia frigida) presently reach the benthos in significant quantities. This research effort will investigate the digestibility of ice algae and phytoplankton-derived organic matter by the Arctic macrobenthos. From the perspective of a macrofaunal organism, digestibility includes three separate components: 1) selection (is encountered organic material ingested or rejected?); 2) absorption (is ingested organic material absorbed during passage through the gut, or does it get egested in the feces?); and 3) assimilation (is absorbed organic material assimilated into biomass?). Assessment of long-term assimilation of the various types of algae (within-ice ice algae; below-ice ice algae; and phytoplankton) will be conducted by determining lipid biomarkers and their isotopic ratios, and by determining CHN and protein signatures of organisms collected during all aspects of the work in both Norway and Kotzebue, Alaska. Assessment of short-term absorption will first use the ash-ratio method in a whole-core delivery experiment. Following the whole-core experiments, dominant taxa from each trophic group will be identified and used in a comparison of absorption efficiencies as calculated by the ash-ratio method, and carbon retention efficiencies as calculated using a pulse-chase radiotracer approach. Finally, the group plans to repeat the dominant taxa absorption efficiency experiments in both Svalbard, Norway at the Ny Aalesund lab and in Kotzebue Sound, Alaska. This proposed project compliments, and will derive synergistic benefits from two projects funded by the Norwegian Research Council in Norway.