Effects of outplanting time on growth, shedding and quality of Saccharina latissima (Phaeophyceae) in its northern distribution range

To reach the goal of large-scale seaweed cultivation in Norway and the rest of Europe, new knowledge about the commercially important kelp species Saccharina latissima is needed. Efforts to maximise biomass by outplanting the seaweed in different seasons can affect seaweed quality. Here, we investigate the effects of outplanting time (February, April, and May) when cultivating S. latissima in the northern range of the species' distribution. We studied the quantity and quality of the seaweed biomass produced in the autumn following outplanting. Effects on quantity were evaluated as seaweed frond area, relative daily growth rate (DGR) and relative daily shedding rate (DSR). Quality was evaluated by tissue content of carbon and nitrogen compounds and number of fouling epizoans. Cultivation was successful when seedlings were outplanted in both February and April, but not in May. An earlier outplanting, in February, gave a prolonged time for grow-out at sea prior to the main recruitment event of epizoans that occurred in September, thereby earlier outplanting resulted in larger frond areas. The frond area reached in September was doubled when seedlings were outplanted in February compared to April, whereas a later outplanting in April gave a higher DGR and DSR, higher carbon content, and lower amount of fouling epizoans. The outplanting season did not affect tissue nitrate concentration or internally stored nitrate. These results show that outplanting time is an important factor to consider especially for biomass yield, but also for seaweed quality, including epibiosis of the seaweed biomass.

Automated summary

The study investigated the effects of outplanting time on the cultivation of the commercially important kelp species Saccharina latissima in Norway. Early outplanting in February resulted in larger frond areas, while later outplanting in April led to higher growth and shedding rates, higher carbon content, and fewer fouling epizoans. Outplanting time is an important factor affecting biomass yield and seaweed quality.