An assessment of the biological feasibility of an offshore macroalgal aquaculture system in the North Sea.

Abstract

An ever expanding global population has lead to increased pressure on available land for food production. Thoughts are turning to the large expanses of space and resources available in the sea, in particular offshore areas. Macroalgae are an ideal solution due to their productivity, high nutritional value and use as a dietary protein substitute. This research has been conducted with Deltares and as a component of the MERMAID European Union initiative which aims to incorporate aquaculture into their designs for multi functional offshore platforms. This research aimed to determine the biological feasibility of an offshore macroalgal farm in the North Sea. To do so, we therefore assumed that macroalgae cultivated offshore would respond in a similar manner as when cultivated nearshore. Two species, Laminaria digitata and Saccharina latissima were studied in nine selected sites in the North Sea in monoculture and polyculture scenarios. These sites represented characteristic offshore areas of the North Sea and aquaculture sites in planning. The suitability of sites and the controlling factors to growth were studied with the generic integrated ecosystem model Delft3D. Results indicate offshore aquaculture systems to be biologically feasible based on macroalgal farming in the North Sea. L. digitata produced the largest biomass when grown in a monoculture and in a polyculture with an increase in total biomass production being observed in the polyculture scenario. The site that produced the largest biomass was Borssele which had one of the highest current velocities observed. A positive trend was found between current velocity, seawater temperature and maximum biomass produced. A relationship was found between the concentration of dissolved inorganic nitrogen (DIN) and phosphorous (DIP) throughout the year and the biomass produced at each site. The sites which produced the most biomass had a simultaneous increase in DIN, DIP and biomass between July and October. Therefore this research recommends that in order to achieve maximum biomass production, L. digitata and S. latissima should be grown in a polyculture. The current velocity, DIN and DIP concentrations and seawater temperature were found to be the main controlling factors to biomass production and should be considered when selecting a suitable offshore macroalgal site. This model can be used as a starting point to which additional modifications and data from test sites when available can be implemented into in order to bridge the gap between model output and reality. Despite this research concluding that it is biologically feasible for an offshore macroalgal farm, the feasibility of other aspects such as economic and social must also be accessed.