Cultivation of Gracilaria dura in the open sea along the southeast coast of India

Gracilaria dura is an important red alga having the potential for commercial farming. To cultivate this alga, the floating bamboo raft method was employed. The study was carried out during October 2010 to September 2012 at the southeastern coast of India. The impacts of seasonal variation, initial seed density, harvest period, depth, and epiphyte and epifauna attachment on the raft were analyzed. A clear seasonal trend was observed in the biomass yield in G. dura in this 2-year study. The highest biomass yield (2.01 ± 0.68 kg FW m −2 ) and daily growth rate (DGR; 3.17 ± 1.71 % day −1 ) were observed in winter (January to March). ANOVA results also showed no significant variations between DGR and biomass yield between the first and second year ( p > 0.05). The algal biomass decreased during summer (April to June) due to high surface seawater temperature and tissue bleaching. Maximum biomass yield and DGR were observed at a low initial seed density of 50 propagules m −2 (2 kg raft −1 ) with 45 days of culture period. The rafts cultivated in submerged condition showed a high growth rate (2.31 ± 1.35 % day −1 ); however, it did not vary significantly with cultivation at the surface level. Grazing was observed to be most severe during the months of April to August by selective fishes like Pteroscirtes mitratus , Siganus canaliculatus , Pelates quadrilineatus , and Monodactylus kottelati ; the crab Portunus pelagicus ; and the isopod Cymodoce truncata . From the 2-year study, it was found that October to March is the ideal period for the large-scale cultivation of this alga.