‘Proof of concept’ of how tube-net diameter affects growth and agar content in industrially important farmed red seaweed Gracilaria dura

Abstract

Several emerging therapeutic applications of agar and its derivatives make it one of the sought-after hydrocolloids, commanding the highest price in global markets. In India farming of local agarophyte species is commercially successful supporting domestic demand coupled with natural harvesting. Several investigations have addressed issues with cultivar development and biological attributes, but technology improvements in farming are seldom attempted. The aim of the present investigation was to study the effect of tube-net diameter on growth and agar obtained from the industrially important red alga Gracilaria dura. CFD modelling also was used to predict the water velocity distribution in tube-nets. Daily growth rate (DGR) in 10-cm diameter (10 cm-DN) tube-nets was 2.5 ± 0.15% day−1 and 3.39 ± 0.10% day−1 in 8 cm diameter (8 cm-DN) tube-nets. In the 8 cm-DN, the biomass outside the tube was 51.83 ± 2.69% higher than biomass inside the tube and in 10 cm-DN, biomass inside the tube was 53.53 ± 2.16% higher. Two-dimensional CFD simulations confirmed that the velocity distribution in and around the tube-net was higher in 8 cm-DN than 10 cm-DN leading to better growth in the former. The agar yield after tissue segregation showed a 14.06% increase for the biomass harvested from inside the tube than outside in the 10 cm-DN, while it was 17.75% in the 8 cm-DN. Similarly, agar gel strength recorded a 38.47% increase in the biomass harvested from outside the tube compared with the inside biomass in the 10 cm-DN, and the increase was 11.96% in the 8 cm-DN. Further studies using various tube-net diameters are necessary to select the optimal diameter for undertaking commercial farming of G. dura in the open sea.