Historic changes in abundance, biomass and taxonomic composition of seaweed-associated fauna in Kongsfjorden, Svalbard

Abstract

The Arctic is warming rapidly. Atmospheric temperatures in the Barents Sea region are increasing 5 – 7 times faster than the global average. As a result, Arctic sea ice extent is declining by nearly 12% per decade during the summer months. The study site in Kongsfjorden, Svalbard, has been mostly ice free since 2006. These changes in the physical environment likely affect the ecology of coastal Arctic ecosystems. Increased underwater irradiance seems to improve the growth of kelp forests on rock shores. This thesis is a continuation of a time series to estimate historic developments in abundance, biomass, and taxonomic composition of seaweed-associated fauna, comparing data from 2021 with data from 2012/13 and 1996/98. At each time point, samples were collected along the same gradient from 2.5 m to 15 m water depth. There is limited evidence for a difference in taxonomic composition between 2021 and 2012/13, while taxonomic composition in 1996/98 was significantly different from both other time points. Moreover, both faunal abundance and biomass increased about two-fold between 2012/13 and 2021. These results might suggest that the seaweed-associated fauna at Hansneset reached a new stable state after initial shifts in the taxonomic composition between 1996/98 and 2012/13. Differences in taxonomic composition, based on biomass data, were largely a result of an increase in cirripedian and decrease in bryozoan biomass. These taxonomic groups possibly show different responses to some biotic and abiotic factors, such as macroalgae cover or sedimentation.