Patterns and processes of biofouling on salmon farms
Occurrence of biofouling and common management strategies
Through interviews with managers of fish farms situated along the Norwegian coast, the occurrence of common biofouling organisms throughout the year and the related biofouling management strategies employed were investigated. The resulting data allows an overview over the distribution of biofouling species and the variation in antifouling strategies along a geographic cline.
Spatial variation in biofouling on salmon farm cages
A 1-year field study was conducted at a commercial salmon farm to provide background knowledge about how natural and farm operational factors influence the biomass, species richness and community composition of biofouling on cage nets. The effects of immersion period, sampling time, mesh size and variability between three individual cages were investigated.
Depth distribution of biofouling on salmon farm cages
The depth distribution of biofouling biomass, net aperture occlusion and community composition was investigated through image analysis and the sampling of net panels in depths between 1 - 15m at various times of year and for different fish farms.
Water quality and biofouling
Biofouling development on nylon nets of a stocked salmon cage was monitored and related to simultaneous measurements of water quality parameters and plankton composition.
Physical effects of biofouling- drag increase and water blockage on salmon farm cages
The accumulation of fouling organisms obstructs net openings, thus reducing the water exchange across nets and increasing hydrodynamic forces acting on net cages. The effects of different amounts of several important fouling organisms on the drag force on nylon nets were tested and compared to clean nets. The tests allow a description of the effects of fouling on the forces on nets and the parameterization of fouling.
Net cleaning technologies and practices
Effectiveness of current net cleaning technologies
The rate of removal of various biofouling organisms from net panels using in-situ high-pressure cleaning was assessed in a field experiment with net panels. This involved examinations of different combinations of volume flow and water pressure and the use of both nylon and monofilament plastic nets.
Effects of net cleaning on larval release and localised recruitment
Two experiments were carried out to examine effects of high-pressure underwater net cleaning on the recruitment of biofouling within salmon farms. In an initial experiment, biofouling larvae and other material released before, during and after net cleaning operations were sampled within a salmon farm. In a follow-up study, the 'recruitment pressure' of biofouling organisms (numbers of organisms per unit area) was quantified in farm and control sites both before and after net cleaning.
Effects of net cleaning on biofouling development
In a field experiment the growth rate of hydroids after cleaning (recolonisation) was compared to growth rates of hydroids on undisturbed net surfaces
Effects of recurring net cleaning on the tensile strength of nets and on renewed biofouling development
The effects of in-situ washing on the structure of nets were investigated in laboratory test where the tensile strength of frequently washed nets was measured and compared to unwashed nets. Both coated and uncoated nets were tested. In a separate field experiment, biofouling development was documented on nets that had undergone repeated cleaning.
The effects of copper coatings on hydroid settlement
The settlement preferences of hydroids with regards to substrate colour and the presence of copper in antifouling coatings were determined in laboratory and field test.
The effects of copper and binding agents in coatings
The efficacy of different combinations of binding agents and concentrations of copper in antifouling coatings for nylon nets to suppress or reduce the accumulations of fouling organisms were tested in field experiments.
Heat and acid treatment against hydroids
To contribute to the development of novel cleaning methods, laboratory and field studies determined the effects of heat and acetic acid on the settlement of hydroid larvae and the survival of juveniles and adults. Furthermore, the effect of hot water treatment alone or in combination with high pressure cleaning on the community composition and biofouling development over time was investigated in preliminary field trials.
Prototype for underwater heat treatment
Heat treatment has been shown to be efficient against hydroids in laboratory and field trials. A prototype for under water heat treatment of fouling on aquaculture nets was developed and tested.
Biology of hydroids
The hydroid Ectopleura larynx is one of the main biofouling organisms in Norwegian salmon aquaculture and has therefore been chosen as a model organism in many of the experiments. The species is not only known from Norway but causes problems on salmon farms in Scotland, Ireland and North America, while hydroids of the same genus trouble fin fish farmers in Australia, New Zealand and Japan. Excessive hydroid growth on fish nets reduce water flow through the cage and distract the cleaner fish used for lice control. Hydroid biofouling may also impact on fish health and welfare.
The ability of hydroids to recovery from physical damage
The ability of hydroids to recover from damage sustained during net cleaning operations was examined in a laboratory experiment. Net cleaning is often not 100% effective and removes the "stem" and "head" of polyps while other parts remain on the net. In laboratory experiments hydroids were repeatedly 'maimed' and left to recover for comparison to an undisturbed control group.
The copper resistance of hydroids
To investigate if previous exposure to copper used in antifouling coatings has led to an increased copper tolerance in the biofouling hydroid Ectopleura larynx, the copper tolerance of animals growing at a conventional (regular copper use) and an ecological (no copper use) salmon farm was compared in a field experiment.
The oxygen consumption of hydroids
Hydroid biofouling can affect the oxygen levels in a cage through the reduction of the water exchange across the net. To determine if the oxygen consumption of the hydroid population can further affect the oxygen budget of a cage, hydroid respiration was measured in a laboratory experiment.
Analysis of food sources of hydroids
To identify the main food sources of hydroids living on salmon cages and to evaluate if their high abundances may be facilitated by ingestion of farm-derived nutrients, a stable isotope and fatty acid analyses of hydroids and their potential food sources was conducted.
Attachment strategies of hydroids
The attachment strategies of hydroids were identified via laboratory experiments to support the development of improved antifouling technologies and net cleaning methods.
Analysis of settlement preferences
In order to find a non-toxic alternative to copper-based antifouling coatings, the effects of the physical surface properties wettability and microtopography on the settlement of the hydroid Ectopleura larynx were analysed in laboratory bioassays and field tests.
Practical and analytical tools for biofouling characterisation and quantification
Physical models of hydroid fouling
In order to assess the effect of hydroid fouling on drag on nets, physical models of nets with artificial hydroid growth were constructed and subsequently tested in the laboratory.
Image analysis of biofouling
Biofouling on aquaculture nets can be quantified via digital image analysis. An algorithm was developed that allows the calculation of the amount of biofouling on nets and other porous structures. To assure consistent results of the analysis for different types of nets and varying environmental conditions, a protocol was established for the acquisition of high-quality under water images of aquaculture nets.
Biofouling in other industries
We are engaged in a range of other R&D activities that range from biofouling prevention and management in the Oil and Gas industry to the evaluation of artificial reef prototypes for impact mitigation projects.