Biogeochemical impacts of fish farming on coastal sediments: Insights into the functional role of cable bacteria.

Fish farming in sea cages is a growing component of the global food industry. A prominent ecosystem impact of this industry is the increase in the downward flux of organic matter, which stimulates anaerobic mineralization and sulfide production in underlying sediments. When free sulfide is released to the overlying water, this can have a toxic effect on local marine ecosystems. The microbially-mediated process of sulfide oxidation has the potential to be an important natural mitigation and prevention strategy that has not been studied in fish farm sediments. We examined the microbial community composition (DNA-based 16S rRNA gene) underneath two active fish farms on the Southwestern coast of Iceland and performed laboratory incubations of resident sediment. Field observations confirmed the strong geochemical impact of fish farming on the sediment (up to 150 m away from cages). Sulfide accumulation was evidenced under the cages congruent with a higher supply of degradable organic matter from the cages. Phylogenetically diverse microbes capable of sulfide detoxification were present in the field sediment as well as in lab incubations, including cable bacteria (Candidatus Electrothrix), which display a unique metabolism based on long-distance electron transport. Microsensor profiling revealed that the activity of cable bacteria did not exert a dominant impact on the geochemistry of fish farm sediment at the time of sampling. However, laboratory incubations that mimic the recovery process during fallowing, revealed successful enrichment of cable bacteria within weeks, with concomitant high sulfur-oxidizing activity. Overall our results give insight into the role of microbially-mediated sulfide detoxification in aquaculture impacted sediments.

Gill damage and delayed mortality of Northern shrimp (Pandalus borealis) after short time exposure to anti-parasitic veterinary medicine containing hydrogen peroxide.

Hydrogen peroxide (H2O2) is used as anti-parasitic veterinary medicine in salmon farms worldwide. In the period from 2009 to 2018 a total of 135 million kg of H2O2 was used in Norway, the world's largest producer of Atlantic salmon. Since the treatment water is discharged to the sea, concerns have been raised about effects of H2O2 on the coastal ecosystem. In the present study, Northern shrimp (Pandalus borealis) have been exposed to short pulses of H2O2 in the PARAMOVE® formulation, followed by a recovery period in clean seawater. The exposure concentrations represented 100, 1000 and 10 000 times dilutions of the prescribed treatment concentration for salmon; 15 mg/L, 1.5 mg/L and 0.15 mg/L H2O2. Significantly increased mortality was observed after 2 h exposure to 15 mg/L H2O2 (50%) and after 2 h exposure to 1.5 mg/L H2O2 on 3 consecutive days (33%), but no mortality was observed after 2 h exposure to 0.15 mg/L. The mortality occurred 2-4 days after the first pulse of exposure. The patterns of acute effects (immobility and death) could be captured with a toxicokinetic-toxicodynamic model (GUTS), which allows extrapolations to LC50s for constant exposure, or thresholds for effects given untested exposure profiles. Effects of H2O2 were also detected in shrimp that survived until the end of the recovery period. The feeding rate was 66% lower than in the control after 12 days of recovery for the three-pulse 1.5 mg/L exposure. Furthermore, dose dependent tissue damage was detected in the gills and evidence of lipid peroxidation in the hepatopancreas in shrimp exposed for 1 h to 1.5 mg/L and 15 mg/L and kept in recovery for 8 days. Fluorescence intensity in the hepatopancreas of treated shrimp increased 47% and 157% at 1.5 mg/L and 15 mg/L, respectively, compared to the control. Local hydrodynamic conditions will determine how fast the concentration of H2O2 will be diluted and how far it will be transported horizontally and vertically. Results from dispersion modelling (literature data) together with the current experiments indicate that treatment water with toxic concentrations of H2O2 (1.5 mg/L) could reach P. borealis living more than 1 km from a treated salmon farm.

First record of characterization, concentration and distribution of microplastics in coastal sediments of an urban fjord in south west Norway using a thermal degradation method.

Plastic waste is of increasing concern in the aquatic environment. A large proportion of plastic waste is generated onshore from where it eventually reaches the marine environment, which is considered the main sink of plastic debris To date there is a substantial lack of knowledge on the composition of these accumulated polymers, their environmental levels and distribution in marine and coastal areas. Current efforts are underway to develop standardized methods to characterize and quantify the occurrence of microplastic in different environmental matrices using microscopy-oriented methods using Fourier Transformed Infra-Red (FTIR) or Raman techniques. However, time-consuming sample preparation, processing and interpretation of complex data limits their use within monitoring programs. As an alternative, a thermal degradation method based on a gas chromatographic mass spectrometer coupled with pyrolysis represents a validated method for qualitative and quantitative polymer analyses. A technique has been developed that combines sample preparation and thermo-analysis for identifying microplastics in samples of marine sediment. Quantification and polymeric composition of plastic particles found in sediment samples taken from ten sites located in Boknafjorden subjected to diverse sources of pollution and anthropogenic pressure were investigated. Plastic microparticles were extracted from 8 kg of wet sediments per site, purified, size-fractionated thorough a set of stainless-steel certified sieves covering the range of 10-250 µm mesh size, pre-concentrated on fiberglass filters and whole filters analyzed by thermal desorption pyrolysis gas chromatography/mass spectrometry. Most of the detected polymers were identified as polypropylene, polyethylene, polyethylene terephthalate, polyvinylchloride, polystyrene or polyamide. In most of the sites, the largest fraction of the extracted micro debris fell in the size range 10-40 µm. Some shifts in size distribution were also observed in some sites and were likely related to the marine sea bottom currents and the influence of specific anthropogenic activities. The adopted thermal degradation method showed good sensitivity, reliability and rapidity and therefore represents a promising technique for microplastic analysis within monitoring activities.