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With the expansion of macroalgae aquaculture in oceanic waters, especially of order Laminariales , a need exists to have optimized cultivation systems suitable for exposed conditions. To enable the design of such systems with a quantifiable level of confidence, in this paper, we developed a high-fidelity hydrodynamic modeling technique for kelp farms by introducing equivalent kelp elements for kelp aggregates with Reynolds number-based drag coefficients. After validating the model with towing tests for model kelp aggregates, it was then compared with comprehensive field datasets for a single line cultivation system with two mooring connections, in Saco Bay, Maine. The model yielded a larger tension than the measured tension by 23.3% on the west mooring line but a smaller tension by 23.2% on the east mooring line. The discrepancies may be caused by the uncertainties in the model configuration and input due to difficulties quantifying exact longline orientation, anchor-anchor distance, current reduction along the kelp longline, kelp mass density, and rope axial stiffness. Sensitivity analysis indicates that addressing these uncertainties may improve the model technique. Even though, the developed model is still reliable with a safety factor in the application for the design, installation and management of kelp aquaculture farms. [Display omitted] • Reynolds number-based formulas for the drag area/coefficient of an aggregate of kelp are proposed. • Equivalent kelp element is validated with lab measurements for an aggregate of kelp. • Equivalent kelp element is validated with field measurements for a single line system. • Uncertainties in modeling the kelp farm are discussed in the context of both numerical modeling and field measurements. [ABSTRACT FROM AUTHOR]

A growing need for food is causing increased interest for seaweed farming globally. This requires the knowledge of the industry’s effects on the marine environment. We therefore aimed to explore the communities hosted by a kelp farm compared to that of wild kelp forests. The study was performed in mid-western Norway. Kelp associated fauna were collected from farmed kelp (Saccharina latissima and Alaria esculenta), in wild kelp forests (S. latissima, A. esculenta, and Laminaria hyperborea), and from fauna traps in the water column. The study showed that the kelp farm had lower taxa abundance and richness and a lower biodiversity than the wild kelp forests. Nonetheless, the farmed kelp hosted many associated species, with communities different from what was found on ropes without kelp (i.e., in the water column). The fauna communities among the farmed kelp were more similar to what was found in the wild L. hyperborea kelp forest than to its wild counterparts. The difference between the fauna communities of ‘old’ and ‘young’ farmed kelp (grown for 3 and 7 months, respectively) was not significant, but the fauna was dominated by the isopod species Idotea pelagica in the young forest and by amphipods, mainly belonging to the genus Caprella, in the older. The study contributes to our knowledge of kelp farms’ ecological role in the marine environment, which is of importance for today’s management as well as for ensuring a sustainable future development of the kelp farming industry.

The continued development of the aquaculture industry is contributing to the proliferation of artificial structures in the marine environment. Observations of seaweed farms (infrastructure and biomass) suggest they act as a habitat for associated species. Seaweed farms differ from other forms of artificial infrastructure as the material deployed already has marine organisms (i.e. culture species) growing on it. This 'priming' of ropes with juvenile sporophytes may affect future development of communities by facilitating colonizing species or suppressing competitors. We call this process 'ecological priming': the provision of a biological platform that influences the successional development of specific communities. The communities that developed on ropes primed with Alaria esculenta individuals were compared with unprimed ropes to assess the ecological priming effect, at a commercial kelp farm in south-west Ireland. Species richness increased over two cultivation seasons and species composition was consistent between years, with distinct communities developing on primed and unprimed treatments. Timing of species occurrence on primed ropes was predictable with no predictable pattern occurring on unprimed ropes. Multivariate tests indicated distinct communities between treatments, with suppression of other algal species and potential facilitation of some species that have a particular association with A. esculenta on primed ropes. Communities from primed holdfasts contained a lower diversity of algal species compared with unprimed communities. Cultivated kelp holdfasts represent a habitat for distinct assemblages that reflect ecological priming of the substratum. [ABSTRACT FROM AUTHOR]