Taxonomic and functional diversity of soft-bottom benthic communities in Tysfjord Introduction The increasing use of coastal areass as locations for aquaculture aquaculture demands biggerbigger knowledge about the ecological functioning of the fjords in order to monitor and manage future impacts of these activities. Fjords are generally dynamic and resilient systems subject to extreme gradients of environmental parameters.param It is then of vital importance to provide an accurate description of ththee system if anthropogenicanthropogenic effects on biologicalbiological communities are to be discerned from natural drivers. Only few fjords in Nordland have been investigated. The presentpresent study investigates the sosoft-bottomft-bottom benthic communities of the deepest fjord of northern Norway: Tysfjorden. The main objective of the study is to identify patterns in community composition and functional diversity of soft-bottom benthic communities together with the prevailing environmental drivers along the Tysfjord system. Preliminar results Study area Phylum abundances, sediment properties and diversity indices Tysfjord is a subarctic fjordfjoord withwwith 3 basins anda 3 main sills (Korsnes(Koorsnes sill: 280 m, HellandHellandll d sill: ill 330330 m and Musken sill: 60 m) from mouth to head. The deepest basin has a maximum depth of 725 m. MuskenMusken sillsill Korsnes HellandHelland sill sillsill BasinBasin 2 BasinBasin 3 36 Van Veenn grab samplessamples of 0.1 m² BasinBasin 1 were collected in May 2017 alonalongg a "mouth"-"head" transect. MouthMouth HeadHead The clusterincclusteringg analysis Community structure (data sqrt. transformed) At least 220 taxa were identified to the lowest possible taxonomic level. The highest showedshowwedwed significantsignificant groups abundances were found around the Helland sill and in the inner-most station. differentiatingrentiating the 3 main Molluscs and polychaetes dominated in all stations, but the first increased towards the basins,ns, especiallyespecially the inner- "mouth" while the second increased towards the inner parts. Echinoderms were almostmost most basin (salmon). absent in the deepest stations but were quite abundant around the Helland sill. The shallowesthallowest stations The shallowest stations showed higher diversity (H') and higher evenness (J'). constitutedtituted single units. The stationstations close to the Helland sill also formed a CTD profile showing the dissolved oxygen in the water column consistent group (green). The dierent colours show the dierent signicant groups The physico-chemical Sediment properties driving the properties of the sediments together with depth were community data submitted to forward selection prior to construct the CCA model. The properties of the sediment selected seem to DDatat interpolatedi t l t d fromf 23 CTDCTD castst alongl theththe ordd not fully explain the The CTD profile showed oxygen deficiency ([4 mg/L]) in the patterns observed in the inner-most basin probably due to deep water stagnation. This clustering of the could be an explanation for the difference in community community data. composition. The diierent colours show the diierent signiicant groups Conclusions The community composition revealed different groups according to the 3 main basins, the inner-most ProportionProportion exexplained:plained: basin being more different than the others. The sediment properties did not completely explain the CCA1: 0.1490.14999 community patterns. The oxygen deficiency in the inner-most basin could be a cause for this pattern. CCA2: 0.07020.0702 The measurements from bottom water together with the TOC content on the sediments will be added in future analysis. To identify difference in ecological functioning along the fjord, biological trait analysis (BTA) will be carried out. Acknowledgments: A big thank you to Morten Korgstad and Roald Jakobsen for assisting in the fieldwork and to Corinna Steffensen for her help on the processing of samples for sediment grain size analysis. Èric Jordà Molina Master student at Nord University Follow us on Facebook: E-mail: [email protected] Benthos Ecology Arctos Member at Nord University.