They always say time changes things – a comparative study of epibenthic assemblage in high Arctic fjord between 2005 and 2020

Abstract Accelerated warming has been reported in the Arctic in recent years. Climate change forcing has been detected in many aspects of high-latitude ecosystem ecology. Given previous reports of shifts within the Arctic benthos, we anticipated changes when revisiting the structure of epibenthic assemblages colonising the shallow subtidal zone in Svalbard’s largest sill-less fjord, Isfjorden. To investigate that, experimental constructions holding replicate settlement plates (artificial substrata) were set up at two stations on the rocky bottom of southern Isfjorden in the summer of 2004 and were retrieved after a year of immersion. The same procedure was conducted again after 15 years, in summer 2019. The comparison of the samples from those two periods showed significant differences in assemblage structure. The most substantial change observed was a shift in species dominance suggesting a reorganisation of the assemblage. Most notable was a difference in the abundance of the typically Arctic bryozoan Harmeria scutulata (from 100 to 0 ind. per 100 cm2 between 2005 and 2020), which before 2004 was found to account for more than 50% of bryozoan individuals encrusting stones around Svalbard. The overall taxonomic composition was, however, representative of West Spitsbergen. The Arctic, particularly the Eurasia sector, has been under sustained climate change forcing long prior to the establishment of our field experiment, thus even the 2005 results may showcase an epibenthic assemblage in an already altered state. We think this emphasises how important robust baseline data are to provide crucial reference points to measure and understand change.