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In recent years, several indicators have been proposed to assess the effect of human activities on ecosystems provisioning capacity. Some of these methods focus on the Net Primary Production (NPP) available for ecosystem functioning through the comparison between the Human Appropriated Net Primary Production (HANPP) and the ecosystem's initial NPP at a given reference year. While some approaches have been proposed for marine ecosystems, most of the HANPP studies focus on terrestrial systems. This study highlights the relation between the HANPP methods and the production of natural resources in marine ecosystems. The linkage between current overfishing and future fish provisioning (ecosystem service) is well known. However, less studied before, is the relation between seaweed aquaculture and fish provisioning through the marine food web. Seaweed growth requires nutrients and light that will consequently be no longer available for natural phytoplankton production. As seaweed is periodically harvested, a fraction of the ecosystem's NPP (HANPP) is no longer available for ecosystem production. The HANPP of aquaculture reduces the ecosystem carrying capacity and thus affects commercial fish stocks. Therefore, an integrative approach is proposed in this study to assess the potential effect of seaweed farming on fish landings in the Greater North Sea. Three indicators are proposed to assess the Lost Potential Yield (LPY) in fish landings: LPYB, LPYV and LPYE, accounting respectively for reduction in biomass, monetary value and eco-exergy. For these three aspects, the LPY results remains smaller than the seaweed production, meaning that the overall natural resources balance for seaweed farming is positive.

For rapid growth and appropriate pigmentation,Porphyra requires the constant availability of nutrients, especially in summer when temperate waters are generally nutrient depleted. Cultivation near salmon cages allows the alleviation of this seasonal depletion by using the significant loading of fishf arms, which is then valued (wastes become fertilisers) and managed (competition for nutrients between desirable algal crops and problem species associated with severe disturbances). Porphyra,being an extremely efficient nutrient pump, is an excellent candidate for integrated aquaculture for bioremediation and economic diversification. Frequent harvesting provides for constant removal of significant quantities of nutrients from coastal waters, and for production of seaweeds of commercial value. The production of P. yezoensis being limited in the Gulf of Maine, an assessment of the potential of seven native north-west Atlantic Porphyra species is presently in progress. To enable the production of conchospores for net seeding, the phenology of these species and the conditions for their vegetative conchocelis exponential growth, conchosporangium induction, and conchospore maturation were determined. The development of integrated aquaculture systems is a positive initiative for optimising the efficiency of aquaculture operations, while maintaining the health of coastal waters.

Distributions of dissolved nutrients and particulate matter downstream from a ma- rine fish farm at the Norwegian coast were examined. The samples were taken on transects from 25 m to 215 m distance to a specific fish cage. The samplings were carried out repeatedly while there was fish in that cage and once, after the fish were taken out. The outflow from a fish cage was estimated and a time series of current velocities was recorded downstream from a fish farm. The concentrations of nitrate, nitrite and phosphate were at very low levels and did not reveal any dependence on the distance to the fish cages. An influence of the fish farm on nutrient levels was only visible in the ammonia concentrations, which ranged around 15 μg NH4-N · l−1 on average and showed heavy fluctuations along the transects. Seaweed profits from higher ammonia concentrations in general, but enhanced growth in the study area would be limited by phosphate. On average, the concentrations of total particulate matter and particulate organic matter were at low levels, but showed an increase from 20.04.2005 to 02.06.2005 and a decrease after the fish were taken out of the net cage. This may have reasons other than the clearance of the fish cage, as an effect of the discharge from the cage on the concentrations of particulate matter within more than 50-60 m distance is highly unlikely. The fraction of organic matter was on high levels around 80% throughout the whole period of the study and did not show any dependence on the distance to the fish farm. Structures were found in the wake of a fish farm, that indicate the existence of eddies or swirls in the flow. It is very likely, that a vortex street develops downstream of a net cage, which would be associated with a recirculation area close to the cage. Such a wake characteristic might suppress the horizontal spreading of particles leaving the cage. A net outflow out of a fish cage was found from 3-23 m depth, which indicates the existence of some internal force. This might well be generated by fish swimming in circles. Fish behaviour, therefore, might play a role in the spreading of particles, as already small changes in the strength of the outflow might change the characteristics of the wake flow.