Effect of different growth periods on agar properties of Gracilaria dura (Gracilariaceae, Rhodophyta) cultivated using hanging long-line method along the northwest coast of India

Gracilaria dura (C. Agardh) J. Agardh is a promising red alga for agar and agarose production, with significant potential for commercial farming in India. The present study investigated the effect of the different growth periods (15, 25, 35, 45, and 55) on the daily growth rate (DGR), biomass yield, and agar quality of G. dura cultivated using the floating long-line method. The cultivation trials were conducted from January to February 2018 along the Rajpara coast of Saurashtra, India. Results revealed a progressive decline in both DGR and biomass yield with increasing growth period. The 15-day growth period exhibited the highest average DGR (8.52 ± 0.92% day−1) and biomass yield (382.66 ± 30.95 g fr.wt. m−1) that varied significantly (p < 0.05) with other growth periods tested throughout the study period. A maximum agar yield (34.33 ± 0.58%) was recorded during the 35-day growth period, while the highest gel strength (1606.33 ± 19.65 g cm−2) was noted during the 25-day growth period. Statistical analysis showed that both agar yield and gel strength varied significantly across the different growth periods (p < 0.05). However, the post hoc Tukey’s test indicated no significant difference in agar yield and gel strength between 25, 35, and 45-day growth periods (p > 0.05). Based on these findings, a 25-day growth period was identified as optimal, balancing high biomass yield with superior agar properties. This shorter growth period allows for more frequent harvests annually, potentially enhancing total yearly biomass production and the availability of raw material for agar processing.