A Decade of Monitoring Annual Benthic Recruitment in the Arctic Shallows—A Field Experiment Using Artificial Substrate

ABSTRACT The Arctic around Svalbard has experienced among the most intense, sustained warming anywhere on Earth for multiple decades, which is projected to continue. Increasing air and sea temperatures are not the only parameters affecting the ecosystem, although to date, they have been the most noticeable. Besides overall increases in thermal conditions, arctic inhabitants also have to cope with more frequent warm anomalies. Our study focused on multiyear colonisation patterns of sessile fauna, for which established adults have no way of avoiding challenging conditions and so become strong sentinels of environmental forcing. A field experiment in the Isfjorden shallows (west Svalbard) was run between 2009 and 2020 with year‐long submersion periods for artificial substrata (settlement plates). Number of taxa, density and assemblage structure varied over the 11‐year‐long study, providing valuable insight into the state of the epibenthic assemblage. Although differences among years were statistically significant, no linear trend in response to accelerated warming was distinguished within the study time frame. Some of the variability observed within the current study could be linked to warm anomalies reported from Isfjorden. Extreme and repeated warm events could lead to negative impacts on the ecosystem adapted to more stable thermal conditions, such as the apparent loss of a typically arctic species of bryozoan— Harmeria scutulata after 2013. Nonetheless, no new arrivals of boreal origin were identified on the settlement plates. There is a possibility that exposure to repeated heatwaves leads to increased resilience within the arctic fauna. The up‐to‐date knowledge is necessary to approach the conservation of the hard‐bottom ecosystems adequately.