Effect of Growing Environment on the Quality and Quantity of <em>Kappaphycus alvarezii</em> (Doty) Doty Yield

Kappaphycus alvarezii Doty (Doty) is a commercially important red algae known for carrageenan, a cell wall polysaccharide and thickening agent. It is also a source of major and minor nutrients and secondary metabolites with antioxidant, antibacterial, anti-diabetic, and anticancer properties. However, comprehensive studies are limited to answer the scientific questions in relation to morphotypes and their influence on quantity and quality of carrageenan. This study aimed at analyzing the growth rate, carrageenan yield, water holding capacity of carrageenan, antimicrobial properties, antioxidant properties, and total phenols of green and brown morphotypes of K. alvarezii cultivated in Pesalai and Valaippadu of Sri Lanka. The seaweed was harvested after 45 days of cultivation (n=12) and analyzed using standard methods. The antibacterial properties of ethanol extracts were evaluated by disc diffusion assay against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Antioxidant properties and total phenolic contents (TPC) were determined using DPPH radical scavenging assay and Folin-Ciocalteu method, respectively. There were no significant (P>0.05) location effect and morphotype effect in terms of growth rate, carrageenan yield, and water holding capacity. Irrespective of the cultivation location, the green morphotype showed significantly high (P<0.05) antibacterial and antioxidant properties and significantly high (P<0.05) TPC. This study suggests that the green morphotype of K. alvarezii performs better as a natural source of antibacterial and antioxidant compounds, while both morphotypes of K. alvarezii are suitable for carrageenan production. The Mannar sea area of Sri Lanka has conditions for commercial farming of K. alvarezii with an average 4.21±0.03 % growth rate.