Factors shaping epibionts recruitment in the high Arctic (Isfjorden, Spitsbergen): A year-round investigation using experimental plates

Although studies of the Arctic region have a long history there are still many aspects that require research. Benthic species are important in the studies of environmental impact. However, there is currently very little understanding of what factors drive the process of benthic larval recruitment and assemblage development. This field study, conducted in Isfjorden (Svalbard) from summer 2016 to summer 2017, investigated the seasonal trends in the development of benthic assemblages through the use of settlement plates fixed at different depths (6 and 12 m) and in different orientations. Replicate plates were additionally installed with and without cages to account for the potential impact of predation. Species richness displayed clear seasonal changes, with the highest number of species colonizing the plates was observed in the autumn. The abundance of recruits (particularly Cirripedia) peaked in the summer months. In contrast, both species abundance and richness were much lower over winter and spring, although evidence of recruitment over winter was found. The winter plates were dominated by Lithothamnion sp., red encrusting alga which is very low-light adapted and may have started to already settle in February. Organisms abundance was influenced by the interaction of season and cage treatment, demonstrating a degree of predation, whereas plate orientation was the key driver of assemblage structure. Depth, on the other hand, had a very limited impact on both recruits' abundance and species richness. This study highlights the importance of seasonality in the context of larval recruitment and is one of the first to provide insights into the process of early benthic species colonization of rocky substrates, which are common in Arctic coastal habitats.