Immobilization and growth of clonal tissue fragments from the macrophytic red alga Gracilaria vermiculophylla on porous mesh panels

Abstract

New approaches are needed to automate and intensify the cultivation of commercially important red macroalgae. For example, cultivation of Gracilaria vermiculophylla on vertically stacked panels, deployed in raceway circulation tanks or in the open ocean, may enable process intensification. A scalable process for panel inoculation is a first step toward this end. Clonal plantlets of G. vermiculophylla were mechanically blended (1000 rpm, 5 s) into tissue fragments of 2 cm nominal size, deposited on a 3-mm polypropylene mesh sheet, and then sprayed with a pressurized water jet at 4.5 bar in 0.1 s bursts with average velocity of 13 m s−1. The force of the water jet pushed the 1 mm diameter thallus tissue fragments into the mesh openings, securing the plantlet to the mesh support. Gracilaria vermiculophylla test panels (7 cm per side) were placed in an upright orientation, with rising air bubbles providing fluid motion over the panel surface. During cultivation at saturation light intensity in nutrient-replete medium, near-exponential growth was sustained over 42 days at a specific growth rate of 8–9% per day, identical to the freely suspended thallus tissues. The tissue fragments proliferated over the panel surface and extended outward from the panel surface, ultimately creating a loose mat of tissue nearly 8–10 cm in thickness and biomass loadings exceeding 3000 g FW per m2 of panel surface. The steps used to prepare the G. vermiculophylla panels can be automated, and dense arrays of stationary G. vermiculophylla panels cultivated under defined current flow offer future potential for process intensification.