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In high latitude coastal regions, benthic scavenger communities are largely composed of invertebrates that play a key role in the cycling of organic matter. Factors including temperature and depth can structure Arctic and Subarctic fjord benthic communities, but the response of scavenging communities to these factors is poorly known. To address this, we compared scavenging fauna in eight fjords with different physical characteristics in Svalbard and northern Norway using time-lapse imagery of scavengers consuming Atlantic herring (Clupea harengus) bait. Fjords influenced by relatively warm Atlantic waters, both in Norway and Svalbard, had high scavenger richness. However, Svalbard fjords with negative bottom temperatures had the lowest species richness and were dominated by lysianassoid amphipods and ophiuroids. In these cold Svalbard fjords, the mean carrion removal rates were almost 20 times higher than mean values noted elsewhere, except in the warm Norwegian fjord Kaldfjorden. Amphipods and ophiuroids quickly reduced the bait to bones (207.6–304.7 g removed per hour (g h−1); mean 290.6 ± 7.3 g h−1, n = 4) in cold Svalbard fjords. In the warmer Svalbard fjords, carrion removal rates were low (0–51.5 g h−1; mean 14.6 ± 9.0 g h−1, n = 5). Carrion removal rates in Kaldfjorden were higher than other Atlantic Water influenced fjords (132.1 and 372.5 g h−1, n = 2) owing to the scavenging activity of Atlantic cod (Gadus morhua). The results demonstrate potential ecosystem responses to warming in Arctic and Subarctic fjords, particularly effects related to range expansion of boreal species.

Fjordic systems in temperate and Arctic regions often feature extensive kelp forests at their shallow coastal margins as well as extensive terrestrial forests. Detrital export from these shallow-water and terrestrial ecosystems is an important source of carbon for deep-sea communities in the form of kelp and wood falls. Benthic landers with experimental substrates (wood blocks and kelp parcels) were deployed for 10 mo at a depth of 530 m in a deep Norwegian fjord to investigate and compare macro- and megabenthic community structure, biodiversity and ecosystem functioning on kelp and wood falls. Results revealed that while wood and kelp falls can support a similar number of species and abundance of fauna, they support significantly different faunal communities. Biomass and secondary production on both wood and kelp substrates were significantly greater than in the control samples. Secondary production estimates were similar or higher than those reported from soft-sediment ecosystems at shallower European marine sites. Biological trait analysis showed that macrofaunal assemblages were distinct between the kelp and wood, providing evidence for differences in ecosystem function between the substrates. This case study from a deep-sea fjord in Norway provides clear evidence that while wood and kelp organic falls can support similar abundances of fauna, the associated benthic biodiversity, community structure and ecosystem functioning can be dramatically different between these substrates. The work presented here aims to provide information that is useful in assessing the extent of anthropogenic impacts on deep fjord ecosystems with respect to informing future conservation and management strategies.

Most studies on the potential impacts of deep-sea mining in the Clarion Clipperton Zone (CCZ) have largely focused on benthic ecosystems but ignore the pelagic environment. To model full-scale impacts, it is important to understand how sediment discharge might affect the pelagic zone as well. This study combines in situ optics, hydrography, and remote sensing to describe particle abundance and size distribution through the entire water column in the CCZ (German sector). CCZ surface waters were characterized as productive over the year. During the winter, we observed the formation of a sharp transition zone in Chla concentration, identifying the area as a productive transitional zone toward a more depleted ocean gyre. In the German sector, median particle size was small (± 77 μm), and large particles (>300 μm) were rare. By assessing particle flux attenuation, we could show that the presence of a thick oxygen minimum zone (OMZ) plays an essential role in export and transformation of settling aggregates, with strong diel variations. We suggest that the combination of small aggregate size, bottom currents and slow seafloor consolidation may explain the extremely low sedimentation rate in the CCZ. We conclude that sediment incorporations and ballasting effect on settling particulate matter represent the most significant hazard on midwater and benthic ecosystems.

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