A new cultivation technique for Kappaphycus alvarezii was used in the Brazilian southeastern coast (23°02′25″ S and 43°53′39″ W), the tubular netting on floating rafts. The tubular net technique (TN) was compared with the current method of tie-tie (TT). After 47 days, the daily growth rate (mean±SD of TN and TT=3.4±0.7% day −1 ), carrageenan yield (mean±SD of TN and TT=36± 1.3%), gel strength (mean±SD of TN and TT=730±114.5 g cm²), and viscosity (mean±SD of TN and TT=350±60.4 cP) did not differ between the two techniques (p>0.05). The amount of time used to plant (TT=30.2±2.3 min and TN= 13.3±3.4 min) and to harvest the seedlings (TT=36.2± 2.7 min and TN=17.8±3.7 min) were lower in TN (p< 0.001). It is concluded that TN was more effective than TT, the cultivation management (time rates used to plant and harvest the seedlings) was 53.6% faster, no seedlings were lost, the cost was lower, and an estimated return in 1 year of nearly 20% more than that of the TT technique.

Kappaphycus alvarezii commercial cultivation is increasing along Brazilian coast. After 2008, more than 30 farms were established at Rio de Janeiro state in Sepetiba and Ilha Grande bays. Each farm has about ten floating rafts corresponding to near 900 m of cultivation line. Understanding the effect of the environmental factors on the growth and carrageenan yield and quality of the target algae in commercial farms will subsidize the establishment of efficient management activities to be used in the farms. In this sense, the temporal variation of the K. alvarezii daily growth rate, productivity, carrageenan yield, and quality (viscosity and gel strength) were analyzed using the seedlings cultivated in the largest Brazilian commercial cultivation at Sepetiba Bay. The daily growth rate, productivity, and carrageenan yield and quality were within the commercial requirement desirable for commercial crops. The main factors that caused the breakage of the floating rafts and consequently diminished the productivity are the storms. Water temperature and salinity were the other factors that influenced the daily growth rate and carrageenan yield and quality.

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