Effects of organic effluents from a salmon farm on a fjord system. II. Temporal and spatial patterns in infauna community composition

This study examined spatial and temporal variations in infaunal community composition in a gradient away from a large salmon farm (producing 2910 tonnes during each production cycle) in Uggdalsfjorden, western Norway. The farm is located at a water depth of 230 m, is moored at a single point and moves with prevailing currents and winds. The study showed that the large-scale effects on the benthos were restricted to the nearest 250 m of the farm. This zone was dominated by the polychaetes Paramphinome jeffreysii, Prionospio steenstrupi, Capitella capitata and Heteromastus filiformis, the bivalves Thyasira sarsii and Abra nitida and the echinoderm Brissopsis lyrifera for the duration of the two-year study. Highest abundance and biomass were recorded at peak production at the farm, with 30 000 individuals m− 2 and 60 g ash-free dry weight (AFDW) m− 2. At this time abundance was 10 and biomass was 35 times higher within 250 m from the farm than 3 km away. Highest species richness was found 550–900 m from the farm, where, at peak production, the number of species doubled from 20 to 40 species per 0.1 m− 2. The study showed that at deep sites organic waste affects benthos on a spatial scale much larger than at shallow water sites, and although the infauna community composition varied over time, the consistency in the spatial pattern in the relationship between species richness, abundance and biomass in the course of the study indicates that the observed patterns were temporally stable. The loadings of organic matter from the farm did not exceed the capacity of the benthic community for decomposition, as indicated by the low and stable content of organic matter in the sediment around the farm.