ALBERT

Description: In Arctic macroalgal belt ecosystems, macrozoobenthic production is thought to be an important link between primary production and higher trophic levels. Macrozoobenthic biomass and secondary production were studied along transects (2.5-15 m depth) in the macroalgal belt at Hansneset in Kongsfjorden, Svalbard, from 2012 to 2013. At 2.5m, the standing stock reached its maxima of 174.8 ± 54.4 g ash free dry weight per 1 m2, while density (4341 ind. m-2± 1127 95% CI) and production (7.0 g C m-2 y-1 ± 2.8 95% CI) were highest at 5 m water depth in 2012/13. Compared to a study from 1996/98, this re-sampling indicated a drastic change in the depth-distribution of macrozoobenthic biomass and secondary production at Hansneset. While both biomass and secondary production increased with water depth in 1996/98, this pattern was inversed in 2012/13 owing to a tenfold increase of biomass and secondary production in the upper most sublittoral (2.5-5 m). Variability of macrozoobenthic biomass and secondary production corresponded to differences in the physical environment and macroalgal vegetation along the depth gradient. In the last decade, the number of ice free days per year increased probably due to Arctic warming. As a result, shallow rocky habitats (2.5-5 m) are less affected by ice scouring, thereby opening new space for colonization by benthic fauna. However, faunal secondary production was low compared to macroalgal primary production, indicating a considerable export of most of the algal production from the shallow habitats to the adjacent areas.

Description: Arctic West Spitsbergen in Svalbard is currently experiencing gradual warming due to climate change showing decreased landfast sea-ice and increased sedimentation. In order to document possible changes in 2012–2014, we partially repeated a quantitative diving study from 1996 to 1998 in the kelp forest at Hansneset, Kongsfjorden, along a depth gradient between 0 and 15 m. The seaweed biomass increased between 1996/1998 and 2012/2013 with peak in kelp biomass shifted to shallower depth, from 5 to 2.5 m. The kelp biomass at 2.5 m was 8.2-fold higher in 2012/2013 (14 kg fresh biomass m-2) than in 1996/1998 and mostly due to an increase in the kelp Laminaria digitata. This resulted in a very high density of 2- to 8-year-old kelp (70 ind. m-2) and a high leaf area index of nearly 10 at 2.5 m. The entire zonation seemed to have shifted upwards to shallower depth, since also the lower depth limit of most dominant brown algae was shallower as well as the biomass maximum of several taxa. The cumulated annual photosynthetic active radiation at 15 m depth (42 mol m-2 year-1) determined the current depth limit of kelps. Changes also resulted in an altered seaweed community pattern. The complex pattern of change was probably driven by opposing effects of coacting environmental drivers, namely lack of ice-scouring, elongation of the open-water period and deterioration of the underwater irradiance climate. The results are interpreted as a consequence of Arctic warming probably reflecting a typical scenario for change along other Arctic shores in near future.