Raft culture of Gracilaria edulis in open sea along the south-eastern coast of India

Culture of Gracilaria edulis was undertaken using a floating raft method to improve biomass production. Research on seasonality of growth, growth rate differences in different localities, subtidal (off-shore) and intertidal (near-shore) cultivation and seasonal occurrence of epiphytes was carried out. Lowest biomass (1.5 ± 0.1 kg fresh wt m−2) and daily growth rate (DGR) (2.6 ± 0.1%/day) were obtained during January–February which were significantly different (P < 0.001) from other maximum growth periods. The range of biomass (1.6–2.6 kg fresh wt m−2) and DGR (3.6–5.9%/day) was higher at Ervadi than Thonithurai, but not significantly different (P > 0.05). Cultivation in subtidal region gave significantly higher biomass (12.5 ± 0.9 kg fresh wt m−2) and DGR (7.4 ± 0.4%/day) than those from intertidal region (4.4 ± 0.4 kg fresh wt m−2) and DGR (5.1 ± 0.1%/day). Epiphytes are reported to cause severe problems for the growth of Gracilaria. A maximum of 15 epiphytic algae recorded in April and August and minimum of 7 in February. The findings presented here indicate that G. edulis can be cultivated successfully for 8 months each year with maximum growth rates during November–December. Cultivation in the subtidal region, harvest after 60 days of growth, periodical weeding of epiphytic algae improved the yield further.

► We cultivated G. edulis by raft method. ► Four good harvests achieved with maximum yield in November–December. ► Subtidal cultivation gave higher biomass and daily growth rate. ► Epiphytic algae affected the growth of G. edulis. ► Lowest biomass yield obtained in January–February each year.