Biogeochemical impact of seaweed cultivation in the Belgian part of the North Sea. A model approach

Abstract

There is a growing worldwide interest in algaculture, mainly in response to the increasing needs of the population, as well as because of the potential ecological services it can offer. The most widely cultivated seaweed in Europe is the sugar kelp (Saccharina latissima). Before establishing seaweed farms, it is essential to carry out an impact study aimed at assessing site-scale production in relation to the carrying capacity (CC) of the system in question. With this in mind, a S. latissima life cycle model was integrated into the ROMS-Fennel hydrobiological model, enabling environmental interactions to be taken into account in the growth of this alga. This model was applied to the Belgian coastal zone, where Saccharina latissima cultivation is currently expanding. The aim of this study was dual: firstly, to estimate the ecosystem's carrying capacity in the face of the introduction of sucrain crops, and secondly, to determine the optimum number of farms in terms of production. To this end, we have set up several scenarios representing different percentages of the Belgian EEZ covered by algae cultivation. Even if a competition between S. latissima and phytoplankton occurred in spring for nutrients (nitrate), the model results suggest that expanding the kelp farming area to ∼0.05%–50% of the BCZ weaken only slightly the spring bloom (<5%). The ecological CC was therefore not reached even when farming ∼50% of the BCZ. Although total production peaks in the last scenario, we observe that at this percentage, there is a significant reduction in total yield compared to what was expected.