Effect of light colour on Gracilaria edulis growth and agar

Abstract

The seaweed industry is a rapidly growing global industry. The present study aimed at empirically ascertaining the effect of different colours of visible light spectrum on morphology and growth rate of red algae (Gracilaria edulis), and agar yield and quality of the G. edulis to elucidate the most suitable depth range for culturing G. edulis commercially. Changes in colour and biomass of fresh G. edulis were recorded fortnightly, and the characteristics of agar extracted from G. edulis exposed to different colours of light (natural, red, green, and violet) were evaluated. G. edulis exposed to green light showed the highest growth rate, while the highest agar yield could be obtained from G. edulis exposed to red light. Comparatively higher gel strength, viscosity, and water holding capacity of extracted agar were reported in G. edulis exposed to red light. The growth rate & agar quality of G. edulis cultured under natural light were comparatively lower. The study confirms that G. edulis should be cultured under green light to obtain a significant growth rate and, G. edulis should be cultured under red light to obtain agar of better quality and quantity. Penetration depths of red and green light in the water column are up to 5m and 30m, respectively. Present findings unfold that culture facilities for G. edulis should be established at 1-5m water depths for obtaining a comparatively higher growth rate and high-quality agar. The study warrants empirical studies in-situ to make a robust conclusion.