| dc.description.abstract | Norwegian fjords, with their complex bathymetry and deep basins, are easily accessible study areas for deep sea communities. Impacts of climate change and increasing pressure from anthropogenic activities on fjord ecosystems, especially the aquaculture industry , reinforce the need to assess the state of the often poorly studied ecosystems. Less frequent basin water renewal linked to ocean warming can result in deoxygenation and hypoxic conditions, with unknown implications on the fjord communities. This study aimed to identify environmental drivers of benthopelagic and hyperbenthic community structures in West-Norwegian fjords, with a particular focus on fish and crustacean species composition, diversity and catch rates. Catch rates and distributions of P. periphylla were also investigated. The datasets consisted of 88 bottom trawl stations paired with CTDs, sampled from 2011 to 2022. The data was analyzed with generalized regression models, hierarchical clustering together with Indicator Species (IndVal) analysis to determine community clusters with associated key species, and NMDS ordination with fitted environmental variables over the clusters. The results show that diversity (H) decreases with bottom depth and is highest for stations located in fjords with intermediately deep sills (150 to 250 m). Fish and crustacean catch rates decreased with distance to the coastline, whereas catch rates of P. periphylla were linked to lower temperatures. Catch rates of P. periphylla were also lower in basins with intermediately deep sills, where diversity was highest. Four community clusters were identified, in which bottom depth and geographic distributions had the strongest differentiation effects: 1) fjord stations at intermediate depths (H ̅ = 1.91) linked to higher temperatures and salinity, 2) mostly coastal stations at shallower depths (H ̅ = 1.85) linked to higher oxygenation, 3) deeper fjord stations (H ̅ = 1.26) with inverse relationships to oxygen, and 4) both coastal and fjord stations with high prevalence of P. periphylla (H ̅ = 0.87) linked to lower temperatures. Fjord communities were dominated by vulnerable key species with complex life history traits and lacked gadoid species in contrast to the coastal communities. These results illustrate how deep-sea fjord community composition, diversity and density responses are complex, with a multitude of interacting environmental variables shaping the observed communities. Long-term monitoring over a larger scale might be necessary to assess community responses to changing environments, which will be key for sustainable management of vulnerable fjord ecosystems. The present study provides a first thorough analysis of species communities in West-Norwegian fjords in relation to environment and, thus, an important baseline for future research. | |
