Hanging gardens - do floating kelp farm communities resemble natural kelp forests?

The interest in seaweed cultivation is increasing globally, which requires knowledge of the potential effect of seaweed production on the marine environment, both negative and positive. We therefore wanted to study the fauna communities found in a kelp farm and compare these with what is found in natural kelp forests with the aim of finding out if a kelp farm ecosystem resembles that of natural kelp forests. The field work was conducted in north-western Norway, just before the kelp was harvested in the spring. Fauna traps were deployed and kelp plants scraped in the kelp farm (both in the sugar kelp, Saccharina latissima, and the winged kelp, Alaria esculenta, part), in natural sugar kelp, winged kelp and tangle kelp (Laminaria hyperborea) forests and in the water masses. The potential effect of the duration of the growth period of the farmed sugar kelp on the associated community was also analysed. The study shows that a kelp farm has lower taxa richness and fewer individuals than natural kelp forests, but indicates that the farm still has an ecological function as a habitat. However, the communities in the farm are more similar to the natural kelp forest surrounding the farm than with the natural kelp forest of similar species. The result from this study contributes with important knowledge of kelp farms ecological role in the marine environment, which is important both for today’s management and for the planned growth of the industry.