Oregon Sea Grant

Cultivation of the macrophytic red alga Palmaria mollis (Pacific dulse) on vertical arrays of mesh panels in aerated tanks

Abstract: This study assessed the productivity of the red alga Palmaria mollis (Pacific dulse) plantlets immobilized on a vertical array of mesh panels in aerated tank culture. Biomass productivity rates based on panel surface area, as well as areal productivity based on liquid surface area, were assessed at different panel spacing intervals in a greenhouse with continuous illumination (500 µmol photons m−2 s−1) and weekly f/2 nutrient enrichment, as well as outdoors with natural solar irradiance and continuous natural seawater inflow at 10 exchanges per day. The temperature of all cultivations averaged 12 °C. For greenhouse cultivation in 60-L aerated tanks (0.8 L air L−1 culture min−1), as the panel spacing decreased from 12 to 6 cm, biomass productivity per panel on the 30 × 30 cm panels decreased from to 165 to 112 g FW (fresh weight) m−2 panel day−1, due to reduced growth associated with light attenuation by fronds crowding into the space between panels. However, areal productivity was maintained at 17–18 g AFDW (ash-free dry weight) m−2 day−1, because twice as many panels were present in the same liquid surface area. Areal productivity for tumble culture was statistically higher at 21 g AFDW m−2 day−1. For outdoor cultivation in an 850-L tank with 30 × 80-cm panels, the same trends were observed, but the best panel productivity was 72 g FW m−2 panel day−1 at 25 cm spacing, and the best areal productivity was 8.0 g AFDW m−2 day−1 at 6-cm spacing. Overall, the immobilization of P. mollis on a vertical array of mesh panels offers a modular and flexible cultivation platform, but further optimization is needed to maximize productivity.