Immobilized cultivation of the red macroalga Ochtodes secundiramea via fluid injection of clonal shoot tissues onto porous mesh panels

This study investigated the feasibility of cultivating clonal red macroalgae on a porous mesh support. Clonal plantlets of macrophytic red alga Ochtodes secundiramea served as the model culture system. The morphology of O. secundiramea is defined by highly-branched shoot tissues. Plantlets were mechanically blended (8000 rpm, 7 s) and allowed to recover for 7 days prior to immobilization. A 2.0 g FW L−1 slurry of 3 mm branched shoot tissues was injected onto a fiberglass mesh with 1.6 mm openings in 0.5 s bursts at pressure of 8 bar and nominal fluid velocity of 1.7 m s−1. Each burst deposited a 25 mg shoot tissue cluster onto the mesh. Clusters were placed on a rectangular pitch at decreasing intervals of 20, 12, 8, and 6 mm (contiguous layer) in order to increase the inoculation density. A parallel array of upright, plantlet-inoculated mesh panels was positioned at the base of an aerated, externally illuminated tank, and enriched artificial seawater medium flowed across both sides of each panel. Biomass growth was linear with time, and increased by a factor of 10 over the 28 day cultivation period. Increasing panel inoculation density from 49 to 114 g FW m−2 panel mesh area doubled panel biomass productivity from 14.5 to 28.6 g FW m−2 day−1. Immobilized plantlets proliferated outward across the mesh surface to form a highly branched, densified shoot tissue mass about 1.5 cm thick, and final panel biomass coverage exceeding 3.0 kg FW per m2 of active panel area was achieved. Overall, the outcomes of this study demonstrate that pressurized fluid injection of clonal plantlets onto a mesh surface, and the subsequent proliferation of the shoot tissues on the mesh to form a contiguous panel, offers potential for the future automation and intensification of red macroalgal biomass production.